Basics of Biogas Production

#### **Chapter 1**

## Introductory Chapter: From Biogas Lab-Scale towards Industrialization

*El-Sayed Salama and Abd El-Fatah Abomohra*

#### **1. Introduction**

Production and consumption of food and the exploitation of fossils in the past several decades due to globalization resulted in the depletion of fossil fuels and severe environmental pollution [1, 2]. The emission of greenhouse gases (GHGs) in such an increasing trend causes global warming that devastates aquatic and terrestrial ecosystems. Around 88% of energy worldwide is provided by fossil fuels despite their damage to the environment [3, 4]. In 2019, oil production reached 4484.5 Mt, with natural gas reaching 3989.3 billion cubic meters [5]. Total global coal reserves at the end of 2019 were 1,069,636 million tons (Mt). Being an ancient energy source; coal production showed a slight increase (142.89–167.58 Mt) in the last decade. Carbon emissions in the last ten years increased by 1.1% yearly. According to the British petroleum survey, carbon emissions increased from 29,745.2 Mt to 34,169 Mt in a single decade.

Worldwide energy consumption has increased 17-fold in the last century, and emissions of CO×, SO×, and NO× from fossil-fuel combustion are the primary cause of atmospheric pollution [6] and increased the GHGs [7]. Around 2 Mt of soot and dark particles are released annually only from the world's largest populations, which is responsible for heating the air and melting the glaciers. Therefore, the glaciers that provide water to south Asian nations are decreasing rapidly due to global warming resulting in catastrophic floods in the region. The fossil fuels beneath the earth's surface are not evenly distributed, promoting the search for alternative energy sources available globally [8]. Moreover, due to drastic climate changes and energy shortages, approaches to reduce environmental pollution and alternative energy resources are being explored [9–11].

Renewable energy production and consumption have been increased over time. Among the global renewable energy giants, China contributed 7.9% to the total renewable energy consumption in 2010, while in 2020, this share increased to 24.5% [12]. Besides the depletion of fossil fuels and environmental threats associated with their consumption, modern civilization has produced a tremendous amount of solid organic and inorganic wastes. The global solid waste generation rate was 0.3 Mt per day in 1900, which increased to 3 Mt per day in 2000, and it is supposed to be doubled by 2025. The world's largest landfills such as Laogang (China), Sudokwon (Seoul), the now-full Jardim Gramacho (Brazil), and Bordo Poniente (Mexico City) receive around 10,000 tons of waste daily [13]. In developed countries, the municipal solid waste generation was reported to be 1.43–2.08 kg/person/day; however, it was 0.3–1.44 kg/person/day for developing countries [14]. Solid waste (municipal solid waste) refers to any garbage, trash, or refuse material, which represents a potential cause of pollution.

The risk of waste production is getting higher day by day, even in developing countries due to the increase in the world's population and urbanization [15]. Thus, it can be said that waste generation is directly proportional to the rate of population growth. Further, waste organic and inorganic components are equally important as they hold a potential threat to living organisms and the environment [16]. According to Environmental Protection Agency (EPA), solid waste could be hazardous or nonhazardous depending upon its source. It usually consists of everyday items that people throw away. Generally, it is characterized into two major types: trash and garbage/ rubbish. Garbage can also refer to food waste or kitchen waste, comprising organic waste, clothing, and food containers. In contrast, trash consists of daily household or other items no longer needed, including furniture, leaves, grass clippings, and junk [17]. Other major waste classes include agricultural waste, bio-medical waste, chemical waste, radioactive waste, construction waste, and e-waste. Waste management is of prime focus worldwide as improper waste disposal has caused severe environmental issues such as air and water pollution, loss of endangered wildlife habitat, disease outbreaks, and climate change. All these have a direct impact on society as well as the world's economy. To treat waste properly, it is of utmost importance that waste is characterized and collected accordingly. In terms of municipal waste generation, the United States and Canada were the two of the largest per capita waste producers, generating almost 2.58 kg and 2.33 kg daily, respectively [18].

Organic waste has received great attention as it is biodegradable and can be broken down into methane, carbon dioxide, water, and other organic compounds. It could be in the form of food, green waste, or feces. Since the byproducts of organic waste are usually harmless, they can be used on an industrial scale to produce biofuels. Therefore, many countries are consuming waste to generate energy [19]. Organic waste could be the byproduct of various industries such as agriculture, meat, poultry, sugar refineries, and oil industries. The composition of organic waste constantly varies as it is a combination of a variety of compounds. It all depends upon the properties and amount of each component present in organic waste. Therefore, its characterization and segregation are equally crucial in extracting maximum nutrients cost-effectively [20, 21]. Studies have shown the importance of agricultural and livestock waste among organic wastes. With the increase in agro-based industrialization, waste production has been increased up to three folds. These residues are a rich source of biocompounds that can be used for biogas production and manufacturing enzymes, vitamins, antibiotics, and animal feed [22]. Agricultural and livestock waste is always preferred among the various types of organic waste [23, 24]. The waste of slaughterhouses and fallen stocks are also rich in organic compounds that can be converted into valuable biofuels [25]. Each year, more than 2 billion tons of agro-waste are piled up, comprising straw and husk of wheat, rice, and barley. Adding up to this is forest waste (0.2 billion cubic meters), municipal solid waste (1.7 billion tons), industrial waste (approximately 9 billion tons), and animal waste (1.3 billion tons) [26]. If the necessary measurements for waste treatment are not appropriately followed, society, humans, flora, and fauna will face many challenges. With the advancement in science and technology, scientists are focusing on the gross value of waste as the products of these waste treatments are aimed to be environmentally friendly. Organic wastes are considered a potential resource for several applications, including animal feed, raw material in different industries, and feedstocks for biofuel. The R&D for the utilization of various organic waste for biofuels including biodiesel [27], crude bio-oil [28], bioethanol [28], and biogas production [29] developed fast in the past decades due to its lower carbon and GHGs emissions and the reduction of toxic waste from the environment [30]. Among the various methods of using organic waste as an energy source, anaerobic digestion (AD) has gained the most attention.

#### **2. Biogas production**

Due to biogas production from organic waste in the last years, there is a relative decrease in greenhouse gas emissions and fossil fuel consumption. Biogas consists of 50–75% methane, 25–50% of carbon-dioxide, 1–2% ammonia, and traces of hydrogen sulfide, oxygen, nitrogen hydrogen, and fermented organic fertilizer [29]. Biogas generation is an economical method since the raw material primarily used is agricultural and food waste. It could also be termed green energy and can be used in boilers for heat generation [31]. The basic phenomenon of biogas is the conversion of solar energy stored in the organic waste into gaseous energy by anaerobic digestion. Therefore, biogas is generated by microorganisms as a byproduct of their metabolism. The total energy level could be calculated by methane quantity [32].

Various process variables affecting biogas production, like the nature of the feedstock and carbon-to-nitrogen ratio, and reactors setup, have been evaluated. Different agricultural residues (wheat stalk, soybean straw, and black gram stalk), food wastes, and animal wastes are suitable for biogas production [31, 33, 34]. In recent years, it has been observed that landfills for waste management had specific side effects on the environment. Previously, biogas plants were established for waste disposals. Nevertheless, this practice has been changed ever since. These plants are now used for energy generation from biomass. For this purpose, many studies have been conducted to evaluate the optimal capacity of waste being converted into energy with greater yields and cost-effective mechanisms [19]. Biogas is used as fuel on the domestic and commercial levels. The production capacity from the installed biogas plants across the globe has been increasing every year.

As a renewable energy, biomethane can be derived from various substrates under anaerobic conditions, including sewage and waste activated sludge, food wastes and vegetable, wastes from forestry, manure from living stocks, agriculture wastes, and wastewater [35]. Biogas derived from organic wastes through AD is suitable to clean energy to fulfill energy demand [36]. AD is commonly considered a reliable and cheap approach for energy recovery and wastes management [37], which minimizes the waste quantity and uncontrolled emissions. Besides, the AD digestates contain nutrients and can serve as a biofertilizer for crops. Biogas might substitute fossil fuels and lower the GHGs emission at households and commercial scale [38]. AD of different feedstocks may have a different biomethane production and obtain more bioenergy to compensate for the net energy utilized during the process.

#### **3. Feedstocks for biogas generation**

Most of the biowaste is landfilled, burned, or only reused after composting. However, it can be utilized as a potential source of bioenergy through different practices [10]. A variety of biowaste can be used as substrate in AD to generate clean and renewable energy in the form of biogas and biomethane [39, 40]. Biowaste is mainly composed of 3 major biocomponents, i.e., lipids, proteins, and carbohydrates. Agricultural waste, forest waste, wood residues, fruit and vegetable waste, and municipal sludge contains high content of carbohydrates-based compounds. Protein biowaste is mainly originated from animal sources such as slaughterhouse waste, meat processing industries, and dairy industries. The lipids-based feedstocks are derived from waste oil, oil mills, animal fats from the slaughterhouse, FOG, grease trap waste from sanitation, and wastewater from restaurants. Most of this waste has been applied in AD to generate biogas [7, 41]. Among carbohydrates, lipids, and proteins, the maximum biogas production potential has been reported

#### *Biogas - Basics, Integrated Approaches, and Case Studies*

for lipids. The energy potential of organic wastes and biomass mostly depends on their physiochemical and elemental commotions [42]. Among which volatile solids (VS) and the ratio of carbon to nitrogen (C/N ratio) are the most important as only the organic portion in any waste is attributed as VS, and the carbon is used as food during the microbial process to produce bioenergy [43]. Moisture is another essential aspect for improved degradability of biomasses, especially in agriculture, fruits, and vegetable waste [44]. The COD (chemical oxygen demand) of organic waste material corresponds to the amount of organic substrate available to the microbial community for biogas production [45].

The present book aims to discuss biogas production from different resources and the impact and changes of microbial community during the digestion process. In addition, the possible utilization of biogas byproducts as biofertilizers will be evaluated. Moreover, case studies on biogas production from municipal solid wastes will be presented.

### **Author details**

El-Sayed Salama1 and Abd El-Fatah Abomohra2 \*

1 Department of Occupational and Environmental Health, School of Public Health, Lanzhou University, Lanzhou, China

2 Department of Environmental Engineering, School of Architecture and Civil Engineering, Chengdu University, Chengdu, China

\*Address all correspondence to: abomohra@cdu.edu.cn

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Introductory Chapter: From Biogas Lab-Scale towards Industrialization DOI: http://dx.doi.org/10.5772/intechopen.104500*

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#### **Chapter 2**

## Biogas Production: Evaluation and Possible Applications

*Venko Beschkov*

#### **Abstract**

Biogas is an excellent example of renewable feedstock for energy production enabling closure of the carbon cycle by photosynthesis of the existing vegetation, without charging the atmosphere with excessive carbon dioxide. The present review contains traditional as well as new methods for the preparation of raw materials for biogas production. These methods are compared by the biogas yield and biogas content with the possible applications. Various fields of biogas utilization are discussed. They are listed from simple heating, electricity production by cogeneration, fuel cell applications to catalytic conversions for light fuel production by the Fischer-Tropsch process. The aspects of carbon dioxide recycling reaching methane production are considered too.

**Keywords:** biogas, raw materials, pre-treatment, production, utilization

#### **1. Introduction**

The extensive economic growth in the developed countries imposed a severe impact on the air and water quality. The impact on the air quality consists in the enormous emissions of greenhouse gases from many sources: energy production, burning fossil fuels, transport and household. The emission rate of resulting carbon dioxide in the atmosphere is too high to enable its assimilation by the present vegetation. Therefore, the concept of the use of renewable energy sources became so important during the last decades. Besides wind and solar energy, an important place occupies the biomass, namely biogas, bioethanol, biodiesel. The main reason is the replacement of fossil fuels by carbon-containing biomass that can be easily assimilated by the present vegetation. Hence, the carbon cycle is closed. Another option of use of biomass is its application as raw material for chemical productions thus replacing, at least partially the oil as the main feedstock for organic synthetic products [1–3].

Biogas is the simplest renewable fuel in comparison with bioethanol and biodiesel. Besides its use as a fuel, it can be converted into other products, like light fuels and chemical products after dry reforming and consequent catalytic conversions, like the Fischer-Tropsch process [4]. Many countries adopted programs for biogas applications in energy production [5, 6]. The comparison between the biofuels produced by different biomass as the substrate is shown below.

Biogas is produced by anaerobic digestion of organic materials from the natural origin [7–9]. Normally it contains methane (50–75% vol.). The rest is carbon dioxide with small amounts of nitrogen, hydrogen, ethane and traces of sulfur

compounds (hydrogen sulfide and mecaptanes). The calorific value of biogas is between 20 and 32 MJ/m<sup>3</sup> . Its production became popular in the first half of the twentieth century. It became more important after the growth of the oil and gas prices in the 1970s. On the other hand, its importance is steadily maintained in the developing countries in Asia and Africa where a lot of low-scale anaerobic digesters are developed and used in the household [10, 11]. Currently, biogas production is popular in Europe and North America as a tool for simultaneous treatment of waste in agriculture and food industry and energy production at the same time to maintain these activities [10, 12, 13]. Landfill gases containing methane are also the reason for concern, since the emitted methane has a 25 times stronger greenhouse effect than carbon dioxide. There are also practical applications for the utilization of these gases for energy production thus reducing their harmful greenhouse effect.

The global energy production from biogas in the year 2000 was about 280,000 TJ, growing to almost 1.3 million TJ by 2014. As a volume, the annual world production of biogas was about 59 billion cubic meters in 2013. Almost half of this amount was produced in the European Union [10, 12, 14, 15] and it is growing considerably during the last decade [13].

The classical substrate for biogas production is manure (cattle, pig), poultry litter and activated sludge. However, there are other carbon sources to be treated by anaerobic digestion, like lingo-cellulosic residues, waste from the food industry, like stillage from ethanol distilleries, vegetable and meat industries, etc. In some cases, these substrates must be pre-treated to be converted into digestible form [14–16].

In the present chapter different substrates for biogas production will be considered along with their pre-treatment and mode of operation. Different applications of biogas will be outlined below.

#### **2. Substrates and biogas yields**

The traditional substrate for biogas production is manure, poultry litter, lingocellulose, activated sludge, as well as residues from the food industry (stillage from alcohol beverage production, vegetable waste, etc.). The gas yield per unit mass of substrate is an important indicator for further decisions for process development and plant construction. There are various data for this indicator but here we shall present some of them as average figures, cf. **Table 1** [17].

The best methane yield per unit of total solids can be attained by grass as a substrate. In general, the choice of substrate depends on various factors: its availability and the problems it may cause; the economic issues, as the price of energy and waste treatment; the equipment for anaerobic digestion, etc. For example, the


#### **Table 1.**

*Experimentally estimated biogas yields per unit total solids (TS) from different agricultural waste.*

use of grass gives the best results but requires additional pre-treatment to facilitate the conversion of non-soluble lignocellulose into soluble and biodegradable oligosaccharides. More detailed survey on the waste potential for biogas production is given in [17–20].

#### **3. Pretreatment of substrates**

The pretreatment methods of biomass for biogas production depend on the type of substrate and it is associated with the main scheme of consecutive steps of AD. [21].

The pretreatment method is related closely to the first step in the technology, i.e., the hydrolysis of insoluble organics. As a result, the macromolecules, i.e., carbohydrates, proteins, lipids are converted into soluble and digestible compounds of lower molecular mass.

The main groups of pretreatment methods of organic substrates for biogas production are mechanical, chemical methods [22] and microbial ones [8].

Milling is an inevitable step in substrate pretreatment reducing the size of the material particles. It can improve susceptibility to enzymatic hydrolysis of lignocelluloses [23].

#### **3.1 Chemical methods**

The chemical methods are based on acid or alkaline hydrolysis of the natural polymers.

The biggest problems are met with the pre-treatment of lingo-cellulosic substrates. The main problem is the removal of lignin. Alkaline hydrolysis is used for this purpose. Sodium hydroxide, lime or ammonia are applied with a substantial increase of biogas production, up to 16% vol. [24, 25].

Another chemical method is the treatment of substrates by calcium hypochlorite, combining chemical oxidation with alkaline action. There are new data for the treatment of waste-activated sludge by Ca(ClO)2 thus increasing the methane yield up to 60% [26].

The acid hydrolysis of ligno-cellulose substrates consists of the treatment of the substrate by sulfuric acid [27], but hydrochloric acid and nitric acid also have been used [22]. The acid hydrolysis is usually accomplished at higher temperatures (120-180°C) and pressure. Under these conditions hemicellulose is completely degraded, cellulose to a higher extent. However, lignin is only partially degraded.

A serious disadvantage of these two kinds of chemical treatment is the necessity of pH adjustment because of the sensitivity of the methanogenics toward pH. It is known they can successfully produce methane in the pH range of 6–8.

Best results of chemical treatment are obtained by H2O2 in alkaline media combined with microwave treatment [28]. However, the price of H2O2 makes this method unpractical.

There are also some efforts for pretreatment by ozonolysis [29, 30], ionic liquids [31–33]. But they are too costly for large-scale practical application.

#### **3.2 Thermal methods and steam explosion**

#### *3.2.1 Thermal pretreatment*

Besides the thermochemical methods (acid and alkaline hydrolysis) thermal pretreatment consist of purely thermal treatment. First, it is treatment by hot water at elevated pressure so keep water at liquid state [34].

This kind of pretreatment facilitates the further enzymatic digestibility of cellulose with better sugar yield and almost no fermentation inhibitor [35]. An advantage of this method is the lack of chemicals and additional waste streams and it is eco-friendly because it does not need neutralization of liquid streams and conditioning chemicals saving time and energy for it.

A number of chemical reactions takes place during hot water pretreatment. The thermal destruction of hemicellulose results in the production of organic acids. They act as catalysts to promote the hydrolysis of carbohydrate polysaccharides into oligosaccharides and monosaccharides. These processes resemble dilute acid hydrolysis.

#### *3.2.2 Steam explosion*

The method of steam explosion consists of the action of saturated steam at high pressure on the biomass for some time. Afterwards the pressure is released abruptly causing the explosive breakdown of the macromolecules in the biomass and the bonds between them [36]. It is a widely used method of biomass pretreatment for various purposes (ethanol fermentation, biogas production, etc.). It is considered a catalyzed and uncatalyzed steam explosion. In the first case, some acidic chemicals (SO2, H2SO4, CO2) are used as catalysts to mix with biomass before steamexplosion. The commonly used temperature range is 160–260°C for short period of time at pressures up to 4.8 MPa [37].

During uncatalyzed steam, explosion hemicellulose is degraded and lignin structure is altered. The cellulose digestibility during steam explosion followed by enzymatic hydrolysis is enhanced [38, 39]. However, the catalyzed steam explosion is considered more efficient because of the deeper transformation of the biomass into mode digestible intermediates but in some cases neutralization of the mixture is required, e.g., when sulfuric acid is applied.

Certain limitations associated with the steam explosion method are: (1) incomplete disruption of fibers, (2) generation of inhibitory components to microbial growth, enzymatic hydrolysis and fermentation [40]. Because inhibitory degradation products are formed pretreated biomass needs to be washed with water to remove the inhibitory materials along with water-soluble hemicelluloses [41]. The apparent increase of lignin content during heat treatment has been observed due to hemicelluloses degradation product, furfural and lignin polymerization [41].

The more profound removal of lignin is a key-step in biomass pre-treatment before anaerobic digestion and therefore special attention is paid to it, cf. Timilsena [42].

#### *3.2.3 Enzyme methods*

This group of methods is essential for biomass pre-treatment. It can be applied in combination with other ones, as mentioned above or separately. Usually, it is relied on enzymes existing in the very biomass, for example in cattle manure [43]. Otherwise, isolation and application of certain hydrolases for the aims of biogas production are not economically acceptable.

The main microbial species, capable to convert the insoluble substrates into soluble ones are from the genera *Pseudomonas, Cellulomonas, Streptomyces, Bacillus*, etc. and white-rot fungi (like *Trichoderma, Aspergillus, Penicillium*) as well [9].

There are data about the capability of certain fungi to degrade lignin, thus enabling further cellulose hydrolysis, see Lee et al. [44].

Anyway, the enzyme methods are naturally incorporated into the overall hydrolytic process of biomass preparation for further acidogenesis, cf. **Figure 1**.

#### *Biogas Production: Evaluation and Possible Applications DOI: http://dx.doi.org/10.5772/intechopen.101544*

#### **Figure 1.**

*Scheme of the consecutive processes of biogas formation in anaerobic process, according to Garcia-Heras [21].*

#### *3.2.4 Other methods*

There are also some physical methods, including pretreatment by γ-irradiation [45], by ultrasonication [46], pulsed electric field [47] with electric field intensity of up to 20 kV/cm. The main disadvantage of these methods is that they are high energy-consuming and therefore very costly.

Microwave treatment has been also considered [48–50]. Our experience with microwave treatment of corn stalks and grass hey did not give better results for biogas yield compared to the treatment by acid hydrolysis or simple enzyme treatment.

Recently a constant electric field was applied after the steam explosion of activated sludge to remove or destroy the inhibitors formed during the steam explosion. A very high methane yield was observed. The same approach was also applied to other substrates, like cattle manure, coniferous needles, glycerol and their mixtures [51]. Some results are shown below, cf. **Figure 2**.

In the conducted experiments, we have found out that, the treatment of the waste material with electric current leads to improvement in the ingredients of produced biogas, expressed mainly in higher methane content (reaching 95–98% (vol.) in experiment E4 in a comparison with most commonly observed 50–75%).

#### **Figure 2.**

*Cumulative biogas yield for ca. 110 days under different pre-treatment conditions at different amounts of added glycerol, manure and sulfuric acid at different anode potential. Mesophilic process..E1–16 g coniferous material +200 ml 1% H2SO4 + 8 g glycerol +600 g manure. Treated by constant anode potential 0.77 V/S.H.E. for 30 minutes. E2–32 g coniferous material +400 ml 1% H2SO4 + 16 g glycerol +1200 g manure. Treated by constant anode potential 0.77 V/S.H.E. for 30 minutes. E3–16 g coniferous material +100 ml 1% H2SO4 +8g glycerol +300 g manure. Treated by constant anode potential 0.25 V/ S.H.E. for 30 minutes. E4–16 g coniferous material + + 100 ml 1% H2SO4 + 8 g glycerol +300 g manure. Treated by constant anode potential 0.5 V/ S.H. E. for 30 minutes. Original data reported in [51].*

One can see that moderate amounts of glycerol and manure with the low amount of sulfuric acid are preferable (experiment E4). We have observed that applying electrical current to cattle manure leads to the intensification of the digesting process, more biogas and higher methane content. The importance of the anode potential is visible after a comparison of the results from experiments E3 and E4. Under similar initial components of the reactive mixtures, the anode potential of 0.5 V/S.H.E. is superior to the one at E3, namely 0.25 V/S.H.E.

Generally, the decision for selection of the certain method of pretreatment has its technological and economic backgrounds and the cheapest one must be chosen depending on the very conditions. For example, simple microbial hydrolysis by cellulases contained in the cattle manure could be sufficiently effective compared to the sophisticated physical and thermochemical processes.

#### **4. Biogas production**

The mesophilic anaerobic digestion with biogas production follows the steps described in **Figure 1**.

The operation conditions for the production of biogas are associated with the selected substrate. Generally, the first choice is to decide whether the process will be mesophilic (30-40°C) or thermophilic one (50–60°C) [9].

The thermophilic process seems to be preferable because of the higher biogas production rate. Another reason is the sterilization of the sludge destroying pathogenes and parasite microbial cultures. Next, undesirable seeds of various weeds contained in the manure are also destroyed thus protecting the soil from weeds at further fertilization by the residual sludge and wastewater. However, the thermal balance of the produced energy and the energy input to maintain a higher temperature must be made carefully. Another unexpected obstacle is the higher sensitivity of the thermophilic microbes to pH variation than the mesophilic ones. From this point of view, the mesophilic process seems to be more promising.

*Biogas Production: Evaluation and Possible Applications DOI: http://dx.doi.org/10.5772/intechopen.101544*

The effectiveness of microbes involved in anaerobic digestion determines the rate of substrate decomposition and biogas production [52]. The naturally formed microbial consortia are quite sensitive to pH variations and unbalanced operation may lead to strong inhibition and process failure. At mesophilic processes, the hydrolysis is usually performed by bacteria from the genera *Bacillus, Streptococcus, Klebsiella*, etc. After hydrolysis, the following acidogenesis, acetogenesis and methanization take place, performed by different specific bacteria and archae.

Acidification is usually performed by bacteria from the genera *Acetobacterium, Clostridium, Desulfobulbus, Eubacterium,* etc. [52]. At a higher feeding rate of the substrate in the acidification phase, an excessive production of volatile fatty acids (formic, acetic, propionic, butyric ones) may occur thus decreasing pH below the optimum value for methanogens (i.e., between 7 and 8). It usually provokes stopping the process of biogas production. High volatile fatty acid (VFA) concentrations inhibit the growth of acid-producing bacteria thus reducing also rate of acidogensis. Fermentation of sugar is inhibited by total concentrations of volatile fatty acids above 4 g/l [15, 53]. The long-chain fatty acid concentration of about 30–300 mg/l was found as appropriate for anaerobic decomposition [9]. Some of the possible acidogenic reactions are listed below.

$$\text{C}\_6\text{H}\_{12}\text{O}\_6 + 2\text{H}\_2 = 2\text{CH}\_3\text{CH}\_2\text{COOH} + 2\text{H}\_2\text{O} \tag{1}$$

$$\rm{C\_6H\_{12}O\_6 + 2H\_2O = 2CH\_3COOH + 2CO\_2 + 4H\_2} \tag{2}$$

The last one is an acetogenic one too. Formic acid is formed by acetogenesis and it is carried out by bacteria from the genera *Syntrophomonas, Syntrophobacter, Clostridium, Syntrophospora, Acetobacter* [9]. Acetate is formed from propionate, bicarbonate too:

$$\mathrm{CH\_3CH\_2COO^- + 3H\_2O = CH\_3COOH + HCO\_3^- + 3H\_2} \tag{3}$$

$$\mathrm{2HCO\_3^-} + \mathrm{4H\_2} + \mathrm{H^+} = \mathrm{CH\_3COO^-} + \mathrm{4H\_2O} \tag{4}$$

Further VFA is decomposed to methane and carbon dioxide following the reactions (5):

$$\text{4HCOOH} = \text{CH}\_4 + \text{3CO}\_2 + 2\text{H}\_2\text{O} \quad (Methanebreivbater, \text{ Me}hanococus)$$

$$\text{CH}\_3\text{COOH} = \text{CH}\_4 + \text{CO}\_2 \quad (Methaneascraina) \tag{5}$$

$$\text{C}\_2\text{H}\_5\text{COOH} + 2\text{H}\_2\text{O} = \text{CH}\_4 + 2\text{CO}\_2 + 3\text{H}\_2$$

Оther schemes for methane formation from carbon dioxide and hydrogen is accomplished by *Methanobacterium, Methanobrevibacter, Methanothermus* [54]:

$$\text{CO}\_2 + 4\text{H}\_2 = \text{CH}\_4 + 2\text{H}\_2\text{O} \tag{6}$$

In this case the content of methane in the biogas is much higher. A molar (or volumetric yield) of biogas, richer of methane more than 50% is a clear indication for the pathway, shown in Eq. (6).

The method of carbon isotopes was extensively used to establish the pathway of methane production, as summarized by Conrad [55].

#### **4.1 Single stage and multi-stage systems**

It is well, in any case, to manage biogas production in a continuous or fed-batch mode. The latter is preferable because of the low process rate and the menace of washout (at high dilution rates) or accumulation of inhibitors (at high substrate dosage).

The anaerobic digestion systems are classified as single stage and multi-stage systems based on the different steps of digestion, cf. **Figure 1**. The simple single stage systems are used for many decades. They are available in the simplest design. The most used type of anaerobic digestion is the UASB (upflow anaerobic sludge blanket) digester used extensively for wastewater treatment and biogas production [56].

The substrate is introduced in the lower end of the bioreactor and passed through a layer of sludge, where granules of microbes are formed. The treated water leaves the digester from the upper side where the produced biogas is also released.

All phases of anaerobic digestion are carried out in a single apparatus with batch or continuous mode. In a single digester, all steps of anaerobic digestion take place in one space and as a result process fluctuations or low biogas production occurs because of the accumulation of inhibitors (volatile fatty acids or ammonia in some cases) at hydrolysis and acidogenesis. As a result, the pH in the digester goes out of the optimum limits for successful methanogenesis. Better and more stable operation is possible when the steps in **Figure 1** are carried out simultaneously, but separated in consecutively situated reactors. Multi-stage cascades of bioreactors with the separated acidogenesis and methanogenesis show better gas production. The main advantage of the consecutive scheme consists in the higher stability of each unit in the cascade at the undesired fluctuation of feed, substrate content, pH, temperature, etc. That is why the separation of each of the four stages of biogas production will improve substrate degradation as well as biogas/methane production. This approach was proposed by Grobicki & Stuckey [57] and later applied in a series of studies on stillage conversion to biogas [58] and glycerol utilization [59]. Microbial analysis showed that different microbial cultures were developed in the different steps, corresponding to the content of volatile fatty acids in the step [58, 60].

#### **4.2 Biogas production with glycerol addition**

Crude glycerol is the main waste product from biodiesel manufacturing. It is released in the amount equivalent to the methanol used and exceeds the market demands. This waste product contains water and it is contaminated by the catalyst and residual methanol. The demand for pure glycerol and its price makes the purification of this waste product not economically feasible. That is why the use of this glycerol for the production of value-added chemicals was sought [61–63]. Such products are propylene glycol, 1,3-propanediol, epichlorohydrin. Some of its derivatives are suitable as additives to gasoline and diesel.

There are some efforts for waste glycerol utilization as a substrate for biogas production [64–66]. There is also a study on glycerol addition to enhance the mutual production of biohydrogen and methane by crude glycerol addition [67]. It was established that glycerol and microalgal biomass as co-substrates had an antagonistic effect on hydrogen production and a synergistic effect on methane fermentation.

A hinder for this application is the rapid accumulation of VFA leading to strong inhibition of the methanogenesis and shift to production of gas with very low methane content [64, 65]. It is because in comparison to the traditional substrates glycerol has a very simple molecule and therefore it quickly yields intermediates and final products as organic acids and alcohols. If the initial amount of glycerol is high, the resulting pH drop leads to inhibition of methanogenesis. However, that small amounts of glycerol can boost biogas production based on traditional substrates, see Wohlgemut [68] and Fountoulakis & Manios [69].

When the digestate of bioethanol production was supplemented with 15% and 25% g/L of glycerol (as COD), the cumulative methane and biogas yield was increased to 318 Nml/gCOD and 196 Nml/gCOD which was approximately 6 times higher compared to digestion of the single substrate [66].

In our studies, we have shown that besides the biogas production some other valuable chemical products are obtained (2,3-butanediol, 1,3-propanediol) [60].

A multi-stage cascade bioreactor of eight consecutive compartments was used for anaerobic digestion of stillage with small controlled amounts of glycerol. The latter has been added in a fed-batch mode.

A specific microbial profile is formed along with the compartments, cf. **Table 2**. The bacteria of the strain *Klebsiella* are capable to digest glycerol to 1,3-propane diol and 2,3-butanediol. They can also produce formic acid to yield carbon dioxide and hydrogen. The microbial analysis showed that methane was produced mostly by the pathway of CO2 reduction by hydrogen, cf. Eq. (7). It is also seen that the methanogens prevail in the second compartment and further.

In the next **Figure 3** the VFA profile, the pH profile and the concentrations of 2,3-butanediol along the bioreactor compartments are shown, see [60]. The VFA


#### **Table 2.**

*Microbial profile in a multistage bioreactor with glycerol as a supplement. Microbial identification is taken from [60]*.

#### **Figure 3.**

*Profiles of the substrate, intermediate products and pH on the 12th day after a feed with glycerol; (blue) – Glycerol; (red) – Acetic acid; (white) – Propionic acid; (black) – 2,3-butanediol; (yellow) – pH. Feed 1 kg crude glycerol, cf. ref. [60].*

concentrations reach maximum values in compartments 2 and 3 and decrease along the bioreactor to zero in compartments 7 and 8. Obviously, acetic acid is converted more rapidly than the propionic one. The pH profile along the compartments correlates reasonably with the VFA variations.

The target product, i.e., 2,3-butanediol is accumulated in practically interesting concentrations, up to 12 g/l.

#### **4.3 Biogas applications**

The first and the simplest mode of application of biogas is direct combustion for heating and lighting, as it was adopted in developing countries. The next more sophisticated application is its use for power generation, so-called co-generation. Co-generation is the simultaneous production of electricity and heat by the combustion of biogas. This is the so-called "combined heat and power" process (CHP). Such applications are well spread, using municipal solid waste [70], activated sludge from wastewater treatment plants. The co-generation unit is composed of an engine that actuates as an alternator. The electricity efficiency of the co-generation units reaches 35%. The heat recovery makes it possible to reach a total output of 85% of all produced heat is utilized [71].

The flexibility of biogas systems can support electricity production to follow the temporal local electricity demand, thus facilitating grid stability. It is a decentralized component of the overall energy system and it can serve as a distribution hub in rural areas [72].

Besides CHP, another approach is the "power to gas" (PtG) where the surplus renewable electricity is used for the production of hydrogen by electrolysis [72]. It was proposed for utilization of energy surplus produced by traditional power stations when the electricity demand is low. There are proposals for carbon dioxide recycling by using the released hydrogen for the reduction of carbon dioxide to methane.

Biogas has already broad applications in transport. After upgrading, i.e., separation of carbon dioxide and the sulfur-containing impurities, it competes for natural gas in transport and it is also injected in the gas distribution grids [72].

#### **4.4 Fuel cell applications**

A very attractive application of biogas for electricity production is its use in fuel cells [73]. Before gas feed, biogas must be upgraded after the removal of carbon dioxide and sulfur compounds. The classic methane-driven fuel cells convert catalytically methane into a mixture of carbon monoxide and hydrogen. Hydrogen is separated and used as a fuel in a traditional hydrogen/oxygen fuel cell to generate electricity.

The advantages of fuel cell applications with methane consist in their higher efficiency compared to combustion and co-generation [74]. Next, the released heat can be utilized for maintaining the temperature regime in the fuel cell. A disadvantage of this method is the necessity of carbon monoxide removal and the subsequent charging of the atmosphere by carbon dioxide. More attractive is to convert methane (or biogas) into electricity in one step [74–76] in solid oxide fuel cells. However, the power density is still low for practical use.

Besides these applications biogas can be used also for chemical production using dry reforming to produce synthesis gas (a mixture of carbon monoxide and hydrogen) which is further used for light hydrocarbon production by the Fischer-Tropsch process [77].

#### **4.5 Biogas upgrading**

Biogas upgrading means the removal of carbon dioxide, partially or completely, and the traces of sulfur compounds. The produced gas is reach of methane and it is competitive to the natural gas in the gas distribution grid. It is suitable for domestic purposes and for transport as well.

Once separated, the resulting methane can be mixed at a desired ration of produce other chemicals via synthesis gas.

The most direct method for biogas upgrading is the membrane separation [78–80]. There is information about commercial equipment for biogas upgrading. Some of them is based on membrane separation [81], or by pressure-swing adsorption to reach capacity from about 500 to 5000 Nm<sup>3</sup> /h methane [82].

There are also proposals to recycle CO2 into methane using bioelectrochemical systems [83]. Although, it seems attractive, energy input is required with the release of carbon dioxide. That is why the use of the PtG approach as mentioned above based on energy surpluses, or other renewable energies, like solar or wind ones are recommended.

#### **4.6 Feasibility of biogas production and use**

The feasibility of a biogas equipment depends on different factors. First, it is the amount and generation rate of feedstock (manure, straw, activated sludge, etc.) and its threat to the environment. Next, it is the need of heat or electricity for the considered location. Then, it could be assumed to use biogas as alternative fuel for transport purposes, to be injected in the gas distribution grid or electricity production by co-generation. Biogas upgrade is required if is supposed for transport purposes or for mixing with natural gas in the grid.

It is apparent that different substrates require different approaches. Heating is beneficial because it used to maintain temperature even at mesophilic process. It is possible to maintain it using the heat from a cogeneration (CHP) system after combustion of biogas.

An innovative method is the Power to Gas method integrating the electricity grid with the gas [72].

After selection of biogas as appropriate option for waste treatment with energy recovery, there is necessity to try to select the best method of application for the present community. There are various factors that can affect the rate and amount of produced, namely.


At times of surplus of variable renewable electricity production, hydrogen may be produced via electrolysis, thus storing energy.

### **5. Conclusions**

The biogas has various applications, starting with the simple combustion. Important applications are electricity production by co-generation, by fuel cell applications, as a fuel for transport purposes and as a feedstock for production of chemicals like light hydrocarbons. Prior to its use as a fuel or for chemical purposes, upgrading of biogas with removal of carbon dioxide is desirable. A promising approach is "power to gas" process after electricity production for recycling of carbon dioxide into methane. The biogas yield and quality depend either by the pretreatment, or the operation mode (substrate dosage, choice of anaerobic digester, etc.). It seems that simple enzyme pre-treatment is good enough compared with more sophisticated methods, like ultrasonic or microwave treatment, even steam explosion. The choice of methods and scale of application depends on the regional raw material access, the energy demands and climate peculiarities.

#### **Acknowledgements**

The author kindly acknowledges for financial support to project № BG05M2OP001-1.002-0014 "Center of competence HITMOBIL - Technologies and systems for generation, storage and consumption of clean energy", funded by Operational Programme "Science аnd Education For Smart Growth" 2014-2020, cofunded by the EU from European Regional Development Fund.

### **Author details**

Venko Beschkov Institute of Chemical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria

\*Address all correspondence to: vbeschkov@iche.bas.bg

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Biogas Production: Evaluation and Possible Applications DOI: http://dx.doi.org/10.5772/intechopen.101544*

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### **Chapter 3**

## Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural Wastes

*Donald Kukwa, Maggie Chetty, Zikhona Tshemese, Denzil Estrice and Ndumiso Duma*

### **Abstract**

The chapter's goal is to highlight how the reclamation of household and agricultural wastes can be used to generate biogas, biochar, and other energy resources. Leftover food, tainted food and vegetables, kitchen greywater, worn-out clothes, textiles and paper are all targets for household waste in this area. Agricultural waste includes both annual and perennial crops. Annual crops are those that complete their life cycle in a year or less and are comparable to bi-annual crops, although bi-annuals can live for up to two years before dying. The majority of vegetable crops are annuals, which can be harvested within two to three months of seeding. Perennials crops are known to last two or more seasons. Wastes from these sources are revalued in various shapes and forms, with the Green Engineering template being used to infuse cost-effectiveness into the process to entice investors. The economic impact of resource reclamation is used to determine the process's feasibility, while the life cycle analysis looks at the process's long-term viability. This is in line with the United Nations' Sustainable Development Goals (SDGs), whose roadmap was created to manage access to and transition to clean renewable energy by 2030, with a target of net zero emissions by 2050.

**Keywords:** food waste, clothes and textiles, annual and perennial crops, post-harvest waste, green engineering, biogas and biochar, economic impact, life cycle analysis

#### **1. Introduction**

The population growth rate is an important factor to consider when examining the past, present, and future resource base for sustainability. The increase in global population, combined with increased agricultural productivity and medical advancements, has resulted in resource consumption exceeding the environment's carrying capacity [1]. As the human population expands, so does the potential for tremendous, irreversible changes. Increased biodiversity loss, greenhouse gas emissions, worldwide deforestation, stratospheric ozone depletion, acid rain,

topsoil loss, and water, food, and forest resource shortages are all signs of severe environmental stress in many parts of the world [2]. This human impact on the environment informs the current biotic and abiotic resource depletion.

Biotic resources are resources that come from the biosphere, which are living or once-living beings and forests, as well as the materials that come from them in the ecosystem [3]. Biotic resources include forests and forest products, crops, birds, wildlife, fish, and other marine life. These resources rejuvenate and duplicate themselves, making them renewable. Fossil fuels like coal, natural gas, petroleum, etc. are biotic resources as well, but they are non-renewable; as non-renewable resources get depleted, human society will increasingly rely on the self-renewing capacity of biotic resources [4]. Abiotic resources, on the other hand, are usually obtained from the lithosphere, atmosphere, and hydrosphere. Examples of abiotic resources are water, air, soil, sunlight, radiation, temperature, atmosphere, humidity, acidity and mineral raw materials [5].

Household waste is defined by Reddy [6] and Viljoen et al. [7] as waste generated by household activities such as cooking, sweeping, cleaning, fuel burning, repairs, and gardening. Old clothing, old furnishings, retired equipment, glass, paper, metal packaging, and old books and newspapers are all examples of used products or materials.

Over the last few years, the reuse of home garbage, harvest, post-harvest, and forest leftovers has gained popularity. This is to close the energy gap that has been formed as a result of rising demand from the rural-urban migration and the general improvement in the human population's lifestyle. The demand for high-quality, high-value items has put a strain on scientific research and the manufacturing sector of the economy, threatening to deplete fossil resources. Resource reclamation for benefit employs labour and generates income [8].

The strategic approach of the National Waste Management Strategy (NWMS) of South Africa 2020 to waste management adopted the circular economy approach, in which there is no waste. In a circular economy, any material whose value has degraded for a given application becomes a raw material for another process [7]. This chapter highlights the reclamation of waste resources from agricultural harvest and post-harvest operations for energy resources such as biogas and biohydrogen. Also, the flue gas from the production of biochar was harnessed. Household wastes were also harnessed for biogas generation. The chapter also streamlined the economic benefits of waste resources reclamation and the advantages of a circular economy. The life cycle analysis looked at the composition of household and farm wastes, and the volumetric flow characteristics of the waste materials.

#### **2. The characteristics and types of wastes**

#### **2.1 The characteristics of wastes**

Wastes are often characterized by professionals depending on the sources from which they are created. Household rubbish, hospitals, agricultural waste, industrial waste, mining activities, public spaces, and other sources all contribute to waste production. Wastes are toxic by nature and can harm the environment as well as animal health.

#### *2.1.1 Household waste*

Household waste is any waste that is generated from running a domestic facility, accounting for more than two-thirds of the municipal solid waste (MSW) stream [9]. *Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

It can include food materials, plastics, cardboard, rubber, metal, paper, wood, fabric, chemicals etc. Hazardous substances in household waste, unlike waste streams from industrial sources, are not strictly regulated under hazardous waste regulations. As a result, household hazardous waste (HHW) is dumped in landfills alongside general household waste (HW). Cleaning products, self-care products, pharmaceuticals, home-care products, automotive maintenance products, electronic equipment, and general maintenance products for machinery are examples of items that are frequently used in places of residence, commercial centres, corporate organizations, and institutions. These products contain substances that, on their own or when combined with others, produce secondary compounds capable of causing severe environmental and public health damage [10].

#### *2.1.2 Healthcare waste*

Surgical trash, blood, body parts, medications, wound dressing materials, syringes, and needles are all examples of hospital waste. Hospitals, clinics, veterinary hospitals, and medical laboratories all produce this form of trash. Contamination and illness are common outcomes of hospital waste [4].

#### *2.1.3 Agricultural waste*

Agricultural waste is produced by farming, animal husbandry, and market gardens, among other activities. Pesticide containers, expired medications and wormers, extra milk, corn husks, corn cubs, corn silage, rice husks, rice straw, and other agricultural wastes are the most prevalent [1].

#### *2.1.4 Industrial waste*

Industries generate a wide range of trash. Petroleum refineries, chemical plants, cement factories, power plants, textile mills, and food processing and beverage facilities are all industrial waste generators. These industries produce a considerable amount of waste, which impairs the environment's esthetics and may have an influence on the chemistry of the atmosphere [1, 2].

#### *2.1.5 Commercial waste*

The volume of items purchased and sold, as well as technical improvements in industry and transportation, all contribute to commercial waste [4]. Food, textiles, discarded household and medical supplies, and a range of other objects might be included.

#### *2.1.6 Electronic waste*

Discarded old electronic equipment such as televisions, microwaves, vacuum cleaners, and music players are examples of electronic waste sources. E-scrap, or waste electrical and equipment, is another name for it. These wastes are high in cadmium, lead, and mercury, all of which are toxic to persons and the environment [7].

#### *2.1.7 Mining and quarrying wastes*

Mine wastes are coarse wastes generated during the mining stages of rock blasting and tunnel preparation, as well as tailings from ore processing. Overburden materials that must be removed and disposed of to get access to ore or precious rock are known as quarrying wastes [10]. Two examples are toxic gases created during

blasting and other mining contaminants. The impact of mining waste on the local environment and surroundings is significant.

#### *2.1.8 Demolition and construction wastes*

Depending on the project, bricks and masonry, concrete, wood, metal (including plumbing), plaster and drywall, glass and windows, demolition debris, and other demolition and building materials may be employed. Garbage like asphalt, rubble, tile., etc., from huge projects, as well as construction and building materials trash such as packing boxes, concrete debris, plastics, and wood [8].

#### *2.1.9 Radioactive waste*

Gamma rays, alpha particles, beta particles, and neutron radiation are all forms of radiation produced by radioactive waste. Radioactive waste is produced by nuclear reactors or atomic explosions, and it is particularly harmful to animals. High-level waste, low-level waste, and transuranic waste are the three categories of radioactive waste. This technology is used in the power generating sector of the economy as well as the radiological unit in hospitals for imaging diagnosis [10, 11].

#### **2.2 Types of waste**

Professionals also have characterized waste according to (i) the physical states of materials namely solid, liquid and gas; and (ii) the potential of microbial attack namely biodegradable and nonbiodegradable materials.

#### *2.2.1 Solid wastes*

Solid wastes account for the majority of the trash produced by human civilisation. Agricultural wastes, domestic wastes, radioactive wastes, industrial wastes, and biomedical wastes are examples of solid wastes that can be categorized based on their source or nature [1, 4].

#### *2.2.2 Liquid wastes*

Liquid wastes are wastes that are formed in a liquid state as a result of industrial production, washing, flushing, or other industrial activities. Liquid waste is also produced in significant amounts by households. Used vegetable oil and kitchen wastewater are two examples [1].

#### *2.2.3 Gaseous wastes*

The principal sources of gaseous wastes include internal combustion engines, incinerators, coal-fired power plants, and industrial processes. Depending on their qualities, gaseous wastes might be odiferous or toxic. Smog and acid precipitation develop when they mix with other gases [10].

#### *2.2.4 Biodegradable wastes*

These are wastes that originate from the kitchen, such as food scraps, garden trash, and so on. Moist trash, green waste, recyclable waste, food waste, and organic waste are all terms used to describe biodegradable garbage. This may be composted to produce manure, also known as humus. Biodegradable wastes break down over

#### *Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

time, depending on the substance and can be destroyed by biotic and abiotic factors such as microorganisms (e.g. bacteria, fungus), temperature, ultraviolet radiation, oxygen, and others. They are digested anaerobically to provide energy in the form of heat, electricity, and fuel [1, 6, 11].

#### *2.2.5 Non-biodegradable wastes*

Non-biodegradable wastes are those that are not easily degraded by natural agents or dissolved by them. They stay undamaged for many years and are the primary sources of pollution in the air, water, and soil, as well as illnesses such as cancer [6, 11]. Dry waste refers to non-biodegradable waste. Newspapers, shattered glass shards, and plastics, which are employed in practically every sector, are all good examples. Cans, metals, and agricultural and industrial chemicals are further examples. Dry wastes are recyclable and reusable. Non-biodegradable trash is bad for the environment, thus there's a rising demand for alternatives. In response, biodegradable polymers (also known as biocomposites) have evolved, although they remain prohibitively costly [12]. Polymers are the backbones of plastic materials, and they are used in an ever-growing number of applications.

#### **3. Household and agricultural waste resources**

Household garbage has become one of the most prominent sources of serious impairment to the rural environment due to huge amounts of rubbish discharged and improper disposal. The amount of rubbish created rises in lockstep with the world's population. Household garbage production will have grown by about 70% per year by 2050, suggesting that waste production will have surpassed population growth by more than twice [1, 4, 7]. Household trash management is a tough task due to the rising volume of rubbish produced throughout the world and the vast variety of different components included in this waste stream. Sorting rubbish at the source is crucial for recycling and the circular economy to thrive [9]. Agricultural waste consists crop remnants, weeds, leaf litter, sawdust, forest detritus, and animal manure. Waste from agro-based industries such as palm oil, rubber, and wood processing factories has increased by several times as a result of increased agric mechanization and automation. Significant quantities of phosphate and nitrogen, as well as biodegradable organic carbon, pesticide residues, and fecal coliform bacteria, are found in agricultural wastes that run straight into surface waters [6].

#### **3.1 Household waste resources**

Household wastes can be solid, and liquid. The different categories of household waste are addressed in the following sub-sections:

#### *3.1.1 Household solid waste resources*

Many cities in developing countries have a challenge of improper management of solid household waste which is a constituent of municipal solid waste [11, 12]. Improper management is because there is usually a lack of understanding of the waste generation and its composition which leads to municipal authorities being unable to establish and execute efficient management plans [13]. This lack of understanding means that authorities most often use equipment and management plans that are not tailored for some communities/cities [14, 15]. Solid household waste is a broad term for solid waste materials found in a home which can be characterized into different

classes such as organics, plastic, paper, glass and ceramics, metals and tins, and other types of wastes. Some of these categories can be sub-divided into more specific products such as food waste, garden waste, magazine, newspaper, office paper, miscellaneous paper all being organic waste [16]. Plastic waste includes bottles, containers, jars and bags while paper waste contains cardboard, packaging material, newspapers. Other waste material includes disposable diapers and sanitation waste [17].

Solid household waste composition and quantities produced are influenced by socio-economic dynamics such as family size, income, car ownership, age, education etc. [18]. This evidence has been shown in studies where overall waste generation and generation of individual components of waste streams have differed between the less and more prosperous sectors of a city [19, 20]. Research has also shown that lower-middle-class communities generate waste with a high potential of recyclability [21]. Solid household waste has been identified as a huge contributor (82%) of the total solid waste compared to waste from commercial, institutions and industrial locations [22]. Different strategies have been developed for resolving the challenges of waste including solid household waste. It is well known for example that plastic and its related materials, glass and ceramics are non-degradable, however can be recycled into new products instead of being thrown into dumping sites as they have incredibly negative impacts on the environment [23, 24].

The organic part of solid household waste (about 68%) is biodegradable and therefore presents a great opportunity to be further used as a resource. This organic-rich waste is a good medium for microbial growth, consequently, it can be used to produce energy (in the form of biogas) which is an excellent provision for positive contribution to the environmental, energy and economic needs [25, 26]. Energy derived from household waste becomes very significant since sufficient energy access is one of the crucial factors of improvement in any country in the world. In this way of economic development, the fight against poverty, education and adequate healthcare is facilitated [27]. Biogas is a result of a four-step (hydrolysis, acidogenesis, acetogenesis and methanogenesis) microbially aided anaerobic digestion process with approximately 50–70% methane, 30–45% carbon dioxide and some trivial amount of other trace elements [28, 29]. Biogas is produced from organic substrates and therefore the resulting waste is rich in nutrients that are used as bio fertilizer [30].

Liu et al. [31] have produced hydrogen and methane from solid household waste using a two-stage fermentation process. In another study, solid household waste consisting of 80.4% organic matter has been used to produce biogas through an anaerobic batch reactor [32].

#### *3.1.2 Household liquid waste resources*

Liquid products are used in common rooms of a household such as a kitchen, bathroom, garages as well as basements. These products have the potential of causing serious environmental and health problems both during their time of use as well as after they have been discarded [33]. Often the consumer of these products is not aware of how to properly dispose of them after usage. The need for identifying appropriate ways of discarding liquid household waste has been realized when serious health problems and damage to areas of disposal started to manifest [34].

Liquid household waste incorporates any liquid waste from places such as the kitchen (cooking oil, dish detergents, floor cleaning products, microwave/oven cleaners, furniture and metal polishes, drain cleaners, etc.), bathroom (health and beauty products, disinfectants, basin and tub detergents and toilet bowl cleaners), laundry room (bleaches, fabric softeners, detergents, spot removers, etc.) as well as

#### *Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

the garages and/basements (paints, pesticides and herbicides, lawn and garden care products, fuel, oils, glues and adhesives, etc.) [34, 35]. Most of these are made from hazardous chemicals although they can be paid for over the counter by any person from supermarkets, automotive centres and hardware stores.

The negative impacts to surface water, groundwater and the soil caused by improper disposal of liquid household waste have brought about the need to look for solutions to the challenge of waste management [36]. Consequently, research has been done across the globe and solutions are slowly being realized and embraced. These include strict prevention, reduction at source, treatment of liquid waste before disposal, recycling the waste into other useful products, valorisation of waste as a form of meeting other demands (energy demands) in societies [37, 38]. For example, liquid waste is used to produce biogas, electrical energy and heat through the following processes; anaerobic fermentation, pyrolysis, biothermal composting, hydrothermal destruction,etc. [39, 40]. The realization that household liquid waste is a renewable energy source is the beginning of solving socio-economic issues because the whole technology employs people in the production of both the technology gear as well as energy thus addressing environmental issues while benefiting the economy [41].

Kitchen wastewater has been used as a substrate for the production of biogas by Kumar et al. [42] where the Up Flow—Anaerobic Sludge Blanket (USAB) reactor was employed. Another study that employed kitchen wastewater co-digested it with several other substrates such as water hyacinth, cow manure and sewage sludge for biogas production which had 60–65% methane, 14–18% carbon dioxide as well as 20–21% other gases [43]. Domestic liquid waste has been used as a constituent of the municipal liquid waste for the production of electricity in sufficient volumes to lessen the electrical load of the water treatment plant while producing surplus power to feed into the grid [44].

#### **3.2 Agricultural waste resources**

Modern agriculture depends primarily on annual crops, which are crops that can be harvested within two to three months of seeding. Annual crops live their whole life cycle in a year or less. These crops are typically classified as summer crops (warm-season) and winter crops (cool-season crops). Warm-season crops develop faster during warmer times of the year and are typically seed and fruit crops. Cool-season crops develop faster during cooler times of the year and are typically root, leaf, flower bud, and stem crops. Examples of annual crops include onions, tomatoes, popcorn, carrots, peas, kale, and corn [45]. These crops have a lower water requirement and tend to generate more crops produced per drop of water [46]. Bi-annual crops are comparable to annual crops, but they can live up to two years before dying [45]. The first year of bi-annuals results in a short stem and leaves which eventually bloom in the second year.

A more sustainable alternative to annual crops that have been advocated for is perennial crops. Examples of perennial crops include sugarcane [47], coconuts, pineapple, peppermint, spearmint [48], apples, and peaches or apricot [49]. These crops last two or more seasons and are planted once and harvested every year. They lower the chances of soil erosion and limit losses of water and nutrient due to the greater root mass nature of perennials. Perennial crops are preferred for both the quality of the product harvested and their total production [49]. Shifting to perennial crops may enhance many ecosystems services but this will come at a cost as perennial crops have higher water requirements. Furthermore, lower yields that are more stable than those of annual crops can be expected [46].

#### *3.2.1 Farm produce waste*

Farm waste is classified under the agricultural waste stream. Agricultural waste refers to the residues produced from growing and processing crops. They are the nonproducts of production [50]. Agricultural waste includes natural (biodegradable) and non-natural wastes (inorganic) which are produced from agricultural activities such as horticulture, dairy farming, livestock breeding, seed germination, nursery plots, market gardens, grazing land, and forestry. This waste comes as either liquids, solids, and slurries, or sludge. Agricultural waste can be classified according to the activity undertaken [51]. For example, crop production and harvest, sugar processing, fruit and vegetable processing, animal production, rice production, dairy product processing, and coconut production. Each of these activities generates its unique wastes.

The global agricultural waste production has been estimated to be approximately 998 million tonnes yearly. This estimate is likely to increase if farming systems are intensified in developing countries. The total solid wastes produced in any farm includes up to 80% of organic waste and the generation of manure can amount to 5.27/kg/day/1000 kg live weight, on a wet weight basis [50]. Agricultural waste tends to pose serious problems to the environment and humans due to it being toxic, especially the waste that includes pesticides, insecticides, etc. It also has a high pollution potential over extended periods, threatening surface water, underground water, and soil resources [51].

Agricultural waste can be used in various applications. These include fertilizer application (employing animal manures), anaerobic digestion (generating methane gas from manures), pyrolysis (generating bio-oil, char, and gas), animal feed, adsorbents to eliminate heavy metals (used in the adsorption process), and direct combustion [50]. The utilization of waste must either happen rapidly or the waste must be stored under controlled conditions to avoid spoilage of the residues.

#### *3.2.2 Post-harvest wastes*

In a world that is ever-growing in population which results in an increasing demand for food, postharvest waste is a critical phenomenon worth addressing. At the forefront of the bio-economy sector are plans to minimize the quantity of waste produced, advance the inescapable waste produced as a resource, and attain noteworthy levels of safe disposal and recycling [52]. Postharvest waste is defined as the amount of food wasted or lost throughout the food chain, after harvesting till consumption. Roughly a third of the food produced on a global scale for human consumption gets wasted or lost, which is about 1.3 billion tonnes of the harvest lost annually [53, 54]. Postharvest waste is intentional. Generated products can be rejected and discarded by growers, distributors, retailers, and consumers if they fail to meet established preferences [55].

Post-harvest wastes are a major contributor to agricultural biomass loss. This is true for the whole world but postharvest losses and waste are more prevalent in developing countries because of low levels of technology, poor infrastructure, low investment in the food production systems, and poor temperature management [56]. Postharvest waste is estimated to be approximately 60% depending on the production region, the season, and the crop [57]. In Brazil, for example, the postharvest losses and waste of vegetables and fruits is approximately 30% [53]. It can lead to soil fertility challenges, especially where agriculture is predominant. Soil fertility problems occur as a result of inadequate amounts of residues which through direct application, as manure, or as compost find their way back to the land [52]. Examples of agricultural residues include straw from wheat, stover, cobs and corn from maize, husks and shells from coconuts, and stalks from cotton.

#### *Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

Stages of an entire postharvest system include harvesting, threshing, drying, storing, processing, and use. Harvesting operations account for 5–8% losses, storage 15–20% and transport 10–12% [58]. The key sources of postharvest waste in economically developing and economically developed nations are uncontrolled handling, substandard planning of the amount to purchase, and defective packaging [53].

In a study, [52] assessed the residues that are generated on a farm at the time of harvest and also considered the by-products that are generated when crops are processed, for example, sugarcane bagasse produced from sugarcane. The investigation found the total post-harvest losses to be about 92 Mton/year, where 32 Mton/year is attributed to sugarcane losses, 16 Mton/year to wheat losses, and 9 Mton/year to rice.

Studies have pointed out that the reduction of postharvest waste can contribute to increasing the availability of food in the food system, thereby reducing food insecurity, improving farmers' income, bettering nutrition, and reducing the wasting of critical resources such as water, land, energy [57]. Additionally, postharvest waste can be used to generate valuable products such as bioenergy and biochar when technologies such as gasification and anaerobic digestion are employed.

#### **4. Energy resource reclamation**

Paper, cardboard, food waste, grass clippings, leaves, wood, and leather goods are examples of biogenic (plant or animal-based) materials. Non-biogenic combustible materials include plastics and other petroleum-based synthetic materials, as well as non-combustible materials like glass and metals. Many nations employ waste-to-energy plants to harness the energy contained in solid waste. Waste-toenergy facilities are widely used in various European nations and Japan, owing to a scarcity of open landfill areas in such countries. Solid waste is often burnt in waste-to-energy facilities, which use the heat from the fire to produce steam, which is then used to generate electricity or heat buildings. **Figure 1** shows the worldwide composition of solid waste from homes, towns, and farms as follows: paper (18%), plastics (12%), organic materials (43%), glass (5%), metal (4%), rubber, leather, and textile (9%), and miscellaneous materials (9%). (9%) [58].

Different types of biofuels may be recovered and purified from organic waste fractions for usage at home or in the workplace. The energy content of garbage determines the quantity of energy that can be retrieved (calorific value). **Figure 2** shows the average energy content of solid waste from houses, towns, and farms, with paper having a potential of 16 MJ/kg, plastics 35 MJ/kg, organics 4 MJ/kg, glass and metal 0 MJ/kg, and other 11 MJ/kg [59].

**Figure 1.** *Typical composition of solid waste from households, municipalities and farms.*

**Figure 2.** *The average energy content of home/municipal/farm solid waste.*

Most biogenic and non-biogenic components may be found in household, municipal, and farm solid waste (HMFSW) used to produce power. Newsprint, paper, cartons/packaging, textiles, wood, food waste, yard trimmings, and leather are biogenic components, while rubber, PET, HDPE, PVC, LDPE/LLDPE, PP, PS, and other (plastic) and metals are non-biogenic [60]. The biogenic fraction of solid waste declines when consumers reuse or recover more biogenic waste (such as paper, packaging, food waste, and yard trimmings) while discarding more non-biogenic trash (such as plastics and metals). Because non-biogenic material has a larger heat content than biogenic material, as shown in **Figure 2**, the average heat content of HMFSW as a whole is rising, making it a more efficient fuel for generating power [59].

Because of a rise in the consumption (and discarding) of non-biogenic materials, as well as enhanced recovery of biogenic materials before they reach the waste stream as discards, the biogenic proportion of HMFSW continues to decline due to more recycling activities. As a result, as the consumption of plastics rises, renewable energy provided by solid garbage decreases, and biogenic waste is more collected and/or repurposed [61].

The technologies that emphasize the biochemical processes leading to the production of biogas in **Figure 3** are discussed in depth in this chapter. The anaerobic generation of biogas, which is a combination of methane and carbon dioxide, was described in detail by Angelidaki et al. [62]. They found three major physiological groups of microorganisms that drive the bio-methanation process: (1) primary fermenting bacteria, (2) anaerobic oxidizing bacteria, and (3) methanogenic archaea, a phylogenetically varied group of strictly anaerobic *Euryarchaeota* whose energy metabolism is limited to the production of methane from carbon dioxide and hydrogen, formate, methanol, methylamines, and/or acetate.

#### **4.1 Bio-hydrogen production**

Bio-hydrogen can be produced through different thermochemical, electrochemical and biological processes. By 2020, steam reforming of natural gas, partial oxidation of methane, and coal gasification had produced around 95% of hydrogen from fossil fuels [63]. Other techniques of hydrogen synthesis include biomass gasification, methane pyrolysis with no CO2 emissions, and water electrolysis. The later processes, such as methane pyrolysis and water electrolysis, may be carried out using any form of electricity, including solar power [64].

*Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

**Figure 3.** *The technologies that drive the conversion of waste to energy.*

Anaerobic and photosynthetic bacteria can produce bio-hydrogen from carbohydrate-rich and non-toxic basic materials. Hydrogen is obtained as a by-product during the conversion of organic wastes into organic acids, which are subsequently utilized to generate methane under anaerobic conditions [63, 64]. The availability, affordability, carbohydrate content, and biodegradability of waste materials

utilized in bio-hydrogen generation are the most important factors to consider. Simple sugars like glucose, sucrose, and lactose are easily biodegradable and are excellent hydrogen generation substrates.

Ginkel investigated hydrogen synthesis from industrial effluents from confectioners, apple and potato processors, as well as greywater. From potato processing wastewater, the maximum production yield was 0.21 L H2/g COD [65, 66].

Bio-hydrogen may be produced in a variety of techniques, including dark fermentation (DF), microbial fuel cells (MFC), and microbial electrolysis cells (MEC). DF and MFC are more effective for bio-hydrogen synthesis from carbohydraterich effluents than photo-process (CRE). To enhance the optimum bio-hydrogen generation, either hydrothermal preparation of the inoculum or a high dilution rate can be utilized to minimize the activity of inhibiting bacteria and lower the pH of the medium. For an optimum bio-hydrogen generation, a mixed microbial culture is more trustworthy than a pure microbial source because pure cultures take more care to maintain, but mixed cultures include a wider range of bacteria for the biological conversion of organic materials into useful products. Some of the technologies that produce bio-hydrogen are given in **Table 1**.

Among the various renewable energy sources, bio-hydrogen is gaining a lot of traction as it has very high efficiency of conversion to usable power with less pollutant generation. During fermentation, bacteria release enzymes that hydrolyse biopolymers, resulting in depolymerization of lipids, proteins, nucleic acids, and carbohydrates to intermediate soluble monomers such as fatty acids, glycerol, amino acids, purines, pyrimidines, Mono sugars, and others, which are then converted to short-chain fatty acids, alcohols, hydrogen, and carbon dioxide. **Table 1** shows that different technologies use different fermentation methodologies to transform organic substrates into hydrogen in the absence or presence of light, such as dark fermentation and photofermentation. Bio-hydrogen is a valuable and potential source of energy [71].

#### **4.2 Biogas**

Agricultural leftovers, such as manure and straw, are among the many potential substrates for AD [72]. However, because of their high percentage of lignocellulose, which is difficult to decompose due to its complicated structure, with cellulose


#### **Table 1.**

*Technologies that produce bio-hydrogen from waste resources.*

*Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

fibers securely connected to hemicellulose and lignin, their utility for biogas production is still limited. As a result, lignocellulosic materials have a sluggish decomposition rate and a poor biogas output [72, 73].

#### *4.2.1 Production of biogas from agricultural waste*

Around half of the world's habitable land is dedicated to agriculture [74] and is the largest ecosystem managed by humans [75]. Due to continual development and intensification in response to the important dietary needs of the growing populace and bioenergy demand, agriculture has become the most anthropic activity with the largest impact on the environment, especially in the developing countries (ES) [76].

While agricultural landscapes have a lot of potential for reaching renewable energy objectives and supporting local economies, bioenergies are frequently seen as a contentious solution for long-term development due to the rivalry for agricultural land. In recent years, a lot of effort has gone into resolving such food-energy conflicts. A promising source of renewable energy is the use of residual biomass for energy production. It has gained significant economic and environmental importance in recent decades, and it has the potential to close material and energy cycles, protect the environment, recover resources, and reduce the impact and quantity of wastage [77].

Biogas is a versatile biofuel that can be produced from a variety of feedstocks [78]. The anaerobic digestion (AD) process facilitates the transformation of biomass into energy and digestate using biogas technology. The energy generated by (AD) has been utilized to generate heat, electricity, and biomethane, the digestate has also been used as a biofertilizer to restore soil nutrient levels and so boost feedstock productivity [79]. Biogas will account for 25% of all bioenergy in Europe (shortly) due to its many benefits for energy supply, security, and economic benefits [80].

Many agricultural residues have the potential to be valuable resources if they are managed properly. Stalks, straw, leaves, roots, husks, seed shells, and farm and animal farming waste make up the raw material base. These sources of biomass have a diverse set of properties. The most noteworthy difference is between dry residues (such as straw) and those that are more suited to thermo-chemical conversion routes such as combustion, gasification, and pyrolysis, while wet residues (such as animal slurries) which are more suited to biological conversion routes, like biogas production as depicted in **Figure 4** [80].

**Figure 4.** *Classification of agricultural residues.*

Various studies into the South African wine industry have looked at grape pomace as a potential biogas feedstock, notably in the Western Cape, which has a concentrated wine sector [77]. The study found that because the wine and grape industry is reliant on seasonal production, the use of grape pomace for energy generation is not feasible for a sole. However, the study found that 1 tonne of grape pomace could produce approximately 230 m3 of biogas and 828 kWh of renewable electricity. According to the study, communal digesters serving neighboring wineries would increase their viability as a long-term remedy to winery waste [81].

#### *4.2.2 Production of biogas from food waste*

A report published by the Food and Agriculture Organization of the United Nations (FAO) in 2019, Globally, over 33% of human food is wasted, equivalent to approximately 1.3 billion tonnes each year. Food waste per capita in West Asia and North Africa amounts to 6–11 kg per annum, compared to 95–115 kg in Western countries. Food waste occurs throughout the food supply chain, including agricultural processing, sorting, storage, transportation, distribution, selling, preparation, cooking, and serving [82]. Food waste costs the world economy over \$ 750 billion (US) annually [83].

Compared to other technologies such as incineration and landfilling, AD of food wastes has a lower environmental impact [82, 84]. As a result, multiple efforts to enhance biogas production from food waste have been made in recent years [85]. Despite the high potential for valorising waste food into biogas in nearly any city on the planet, not many industrial-scale plants, especially in industrialized countries, have been put into service [82].

#### **4.3 Biochar**

Crop residues, non-commercial wood and wood waste, manure, solid waste, non-food energy crops, construction scraps, yard trimmings, methane digester residues, or grasses are used in the production of sustainable biochar. Biomass for biofuels or biochar must be surplus that is, more than what should be left on-site to maintain forest and agricultural cropland health [86].

Biochar is created when biomass is pyrolyzed or gasified. These are thermal conversion methods that involve superheating and thermally converting biomass at high temperatures (350–700°C) in a specially designed furnace that captures all of the emissions produced [87].

Biochar is just one of the many valuable bioenergy and bioproducts produced during pyrolysis. Volatile gases (methane, carbon monoxide, and other combustible gases), hydrocarbons, and the majority of the oxygen in the biomass are burned or driven off, resulting in carbon-enriched biochar. All of the emissions (also known as air pollution and greenhouse gases) produced by burning biomass are captured and condensed into liquid fuels such as bio-oil, industrial chemicals, or syngas (synthetic gas). These products can be containerized for sale, stored for future use at the manufacturing facility, or used on-site as part of the energy production process.

#### *4.3.1 Production of biochar from agricultural waste*

Biochar is a unique carbonaceous porous material generated by pyrolysis or thermochemical conversion of biomass with little or no oxygen [88]. Due to its distinct characteristics such as large surface area, porous structure, oxygenated functional groups, and cation exchange capacity, biochar has recently attracted increased attention in several engineering applications [89].

*Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

Biochar can be made from a variety of different feedstocks, wood chips and pellets, tree bark, crop residues (corn stover, nutshells and rice hulls), and other feedstocks that are used commercially, internationally and in research studies. Organic wastes such as grain, sugarcane bagasse, chicken and dairy manure, and sewage sludge have been studied as potential feedstocks [90–96].

As a result, BC has a huge diversity of composition. Xie et al. [97] compiled a list of biochar conversion technologies, detailing product yields and operating conditions, finding that the biochar yield ranged from 15 to 35% with long residence periods of up to 4 h at a moderate temperature of not more than 500°C, and the bio-oil yield ranged from 30 to 50%. More bio-oil (50–70%) was discovered with a shorter residence time (up to 2 s). The thermochemical processes of pyrolysis and carbonization are used to convert biomass into biofuels and other bioenergy products. Biochar is produced by pyrolysis, thermochemically converts biomass in the absence of oxygen at a temperature greater than 400°C. The main components of biochar are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and ash. Pyrolysis is divided into three categories: slow, intermediate, and rapid. Kung et al. [98] found a slow pyrolysis process produced more biochar than other processes. Steiner et al. [99] used a top-lit updraft gasifier to make biochar from rice husk and discovered farmers produce biochar in the field with a 15–33% efficiency. Each year, biochar made from on-farm crop residues can contribute 6.3–11.8% of the total production area [100]. Carbonization (a slow pyrolysis process) produces biochar as a by-product and has been around for thousands of years. Slow pyrolysis is a technique for heating biomass to a low temperature (400°C) in the absence of oxygen over a long period [99].

#### *4.3.2 Energy recovery from the production of biochar*

Two aspects of biochar production's energy recovery have been identified. The first is that the energy value of the steam, gas, and oil by-products of biochar production can be recovered, resulting in a secondary revenue stream and a reduction in greenhouse gas (GHG) emissions [100, 101]. The volatiles in the feedstock burned during pyrolysis, releasing energy as heat, which can be used to generate steam or for combustion in electricity generation plants [102]. Bio-oils can be refined into transportation fuels or burned to provide energy for heating if adequate quantities are available [103]. The syngas and bio-oils can be used to generate steam, which can then be used to power turbines in centralized power plants [103]. However, the ability to use bio-oil is limited by the size of the operation and the volume of oils produced.

Secondly, biochar can be burned directly as a carbon-neutral or low-carbon energy source when. Worldwide, 41 million tonnes of char are produced annually for cooking and industrial purposes [104].

Biochar production and use consume less energy than burning wood for cooking or heating directly [105]. Because it expands the feedstock base to include crop residues and other by-products of agricultural-related activities. These feedstocks are already being used to meet a large portion of the world's household energy needs [106]. When opposed to conventional cooking fuels (e.g. paraffin) which pose indoor fire risks and health problems linked with poor indoor air quality due to its combustion, using char for energy provides several social benefits [107].

#### **4.4 Charcoal**

In 2018, coal combustion accounted for about 38% of global electricity production [108]. According to the International Energy Agency (IEA), the world's


#### **Table 2.**

*The potential of energy resource extraction from household and agricultural wastes.*

recoverable coal reserves are roughly 888.9 billion tonnes, with the majority of them situated in China, Australia, India, Russia, South Africa, and The United States of America [108]. The IEA's energy supply statistics for coal in 2003 and 2017 were 2,619,947 kilo tonnes and 3,789,934 kilo tonnes, respectively. Annual global combustion was estimated to be around 2.5 billion tons [109].

Charcoal is a carbon-rich solid that is derived from biomass in the same way. Charcoal is typically used for heating or cooking and is associated with barbecuing. The temperature at which charcoal and biochar are produced is a significant difference. Charcoal is produced at temperatures ranging from 400 to 1000°C, whereas biochar is produced at temperatures ranging from 600 to 1000°C. When biochar is made at lower temperatures, volatiles (smokiness) are left behind, which has been shown to limit plant growth [105].

The temperature affects porosity as well; the higher the temperature, the greater the porosity. This means that charcoal is not as good as biochar at retaining water and nutrients. Microbes have less surface area when there are fewer pores. As a result, using crushed up charcoal instead of biochar will not be as beneficial to your plants. Because charcoal is made at a lower temperature, it produces a less stable form of carbon, which means it does not provide the long-term carbon sequestration properties associated with biochar [99].

Carbon, which occurs naturally in wood, forms a crystalline structure at higher temperatures, according to research. That is, charcoal has a shorter lifespan in the soil than biochar, which can last hundreds, if not thousands, of years. As a result, it is less effective in the soil and less beneficial to the environment. Biochar made at higher temperatures performs better and sequesters more carbon [87]. The potential of extracting biogas from waste resources is shown in **Table 2**.

#### **5. Economic impact of resource reclamation**

Population growth resulted in modest increases in per capita income at the macro level. Economic activity in any of the world's poorest countries, on the other

#### *Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

hand, has stalled. This economic downturn coincided with significant (and, in some cases,) population growth, resulting in stagnant or decreasing per capita incomes [1]. Agricultural economics applies economic ideas to agriculture without taking into account the profession's economic, social, and environmental concerns. It's important to remember that agricultural economics encompasses a far larger spectrum of food and fiber-related activities than just farming. The agriculture sector accounts for around 12–15% of the nation's production when considered in this light [110].

The circular economy notion [111] is a valuable method of comprehending the waste management hierarchy's implementation in terms of its contribution to the green economy and other energy power recovery (EPR) initiatives. A circular economy is characterized as "closing the loop" between resource extraction and waste disposal throughout the economic cycle by applying waste avoidance, reuse, repair, recycling, and recovery strategies to minimize waste output and demand for virgin resources as production inputs. An economy that is meant to be restorative and regenerative to maintain the greatest utility and value of goods, components, and materials [112].

Recycling efforts account for a significant portion of waste reclamation. In a circular economy, the interchange of products and services is boosted. As the activities in the sector increase, the economic sectors of interest are impacted. This affects the income of all active participants in the economy. Cans and bottles may be recycled by consumers, shipping cardboard and unsold food can be recycled by businesses, and scrap materials can be recycled by manufacturers. Thousands of recycling brokers and processors exchange source-separated and aggregated materials, as well as treat waste to provide feedstock for manufacturers to employ as product inputs. This shows that waste recovery initiatives have a substantial global economic impact.

#### **6. Life cycle analysis (LCA) of waste resource reclamation**

The propensity of life is based on the creation of new cells and the elimination of old or expired ones. Another way of looking at life is as a process of ingesting nutrients-based materials and expelling waste. As a result, waste generation is a normal occurrence. Man's effort to bring rationality to waste generation and disposal procedures is known as waste management. LCA is defined by the Society of Environmental Toxicology and Chemistry (SETAC) [113] as "an objective process for evaluating the environmental burdens associated with a product, process, or activity, by identifying and quantifying energy and materials used, waste released to the environment, and evaluating and implementing opportunities to effect environmental improvements." LCA is a methodology for analyzing the environmental implications of a product, process, or service from the raw material production through the final disposal of wastes.

#### **6.1 Composition of household and farm wastes**

The composition of HMFSW from households, municipalities, and farms is influenced by a variety of factors including cultural traditions, lifestyles, eating preferences, climate, and income. Many diverse sources of solid waste were found by Yadav and Samadder [114] in families, municipalities, and crop farms. Family units, hostels, governmental and private organizations, and commercial centres all produce waste. Waste is created on the farm during harvest and post-harvest operations. Solid wastes can be categorized into biogenic solid waste (BSW) and non-biogenic solid waste (nBSW) based on their origins. Location, socioeconomic position, habits, environmental awareness, and other variables all influence the

frequency of one over the other [113]. The biogenic constituent of solid waste includes paper, packaging/cartons, wood, textiles, food leftovers and waste, yard trimmings, leather, and others; while the nBSW include rubber, polyethene tetrafluoride (PET), high-density polyethene (HDPE), polyvinyl chloride (PVC), low-density polyethene (LDPE), polypropylene (PP), polystyrene (PS), and other plastics. The biogenic component supports biogas production after some customized pretreatment steps.

The Life Cycle Analysis (LCA) process is most commonly utilized as a support tool in the strategic planning and decision-making process for Waste-to-Energy projects [113]. However, the Waste-to-Energy systems' inputs and outputs differ from one project to another; in particular, the waste composition and cost are highly dependent on the project's location. The WtE plant design and waste composition can have a considerable impact on efficiency and emissions.

#### **6.2 Flow characterization of materials**

Any country's waste management industry is under growing pressure to improve its environmental performance. Solid waste management (SWM) is essentially a local responsibility in most countries [115]. Low- and middle-income nations confront hurdles in terms of sustainable waste management strategies compared to higher-income countries due to a lack of resources and ability in local governments, as well as the ineffective execution of specialized regulations. As a result, nations with greater incomes are leading the way in creating sustainable waste management systems. Source reduction is the most prevalent waste management method in the sustainable waste management ladder.

In a stated mapping strategy, the material flow analysis (MFA) technique is utilized to characterize or quantify the efficiency of waste collection and disposal. Due to their complexity and volume, the system is divided into four subsystems to reflect the management of major waste streams: residual trash, commingled materials, source segregated dry recyclables, and source segregated food and garden wastes. The collected primary waste streams are the system's import flows, while secondary products and emissions are the system's export flows [116].

The use of integrated material flow analysis (MFA) and life cycle analysis (LCA) to make decisions in SWM systems is becoming increasingly popular. By acting as a great tool for assessing and controlling flows of wastes, secondary products, and residues, MFA on the levels of commodities aids in understanding the functioning of processes and the connections between processes in waste management [117]. LCA assesses the environmental advantages and disadvantages of waste management solutions. LCA examines system performance and allows for alternative comparisons as well as the identification of potential system improvements.

#### **7. Conclusion**

The increase in human population and the rural-urban drift has continuously placed a strain on fossil energy resources. Waste piles have increased across the globe with limited land space for landfills. Solid waste from the household, municipality and farm have an inherent energy content that could be harnessed to bridge the energy gap that has continued to get wider due to the increasing demand. The biogenic component of the solid waste is sorted for customized biochemical processes thereby accessing energy resources that could be used in homes or private and public institutions. Anaerobic digestion produces methane and carbon dioxide. However, the system could be tailored to produce hydrogen, which is an energy

*Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

resource of value. The circular economy is necessarily employed to cub the waste piles and to enhance environmental sustainability.

One of the methods to ensure equilibrium in the energy economy is converting waste resources into value materials. Bioethanol, biogas, biohydrogen are some of the energy resources that can be extracted from the BSW; and because BSW is constantly produced from their sources, these energy resources are described as renewable. The residue that is left after extracting the energy resources can be turned into biochar, which is a resource that could be used to amend the soil for agricultural production.

#### **Acknowledgements**

The authors appreciate the support of the Durban University of Technology for funding this research focus area in Water and Wastewater. This work is also supported by the Green Engineering and Sustainability Group. The authors would like to acknowledge enabling atmosphere provided to harness the scientific information compiled and presented in this book chapter.

#### **Conflict of interest**

The authors declare that there is no conflict of interest.

#### **Nomenclature**


#### **Author details**

Donald Kukwa1 \*, Maggie Chetty1 , Zikhona Tshemese2 , Denzil Estrice1 and Ndumiso Duma3

1 Department of Chemical Engineering, Durban University of Technology, Durban, South Africa

2 Department of Chemistry, Durban University of Technology, Durban, South Africa

3 Department of Chemical Engineering, University of KwaZulu-Natal, Durban, South Africa

\*Address all correspondence to: tyokedroo@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Resource Reclamation for Biogas and Other Energy Resources from Household and Agricultural… DOI: http://dx.doi.org/10.5772/intechopen.101747*

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#### **Chapter 4**

## Role of Microbial and Organic Amendments for the Enrichment of Methane Production in Bioreactor

*Sharda Dhadse and Shanta Satyanarayan*

### **Abstract**

Studies were carried out on lab-scale levels for biogas production using two different wastewaters, that is, herbal pharmaceutical wastewater and food processing wastewater. A total of eight methane bacteria were isolated from cattle dung and mass culturing was carried out to study their feasibility in biogas escalation. Optimization of methane bacteria that could increase biogas production was identified. Among the methane bacteria, two species *Bacillus* sk1 and *Bacillus* sk2 were found to enhance the biogas production to a maximum level. Gas analysis showed CH4 content of 63% in the case of food processing wastewater and around 67% with herbal pharmaceutical wastewater. *Bacillus* sk1 was found to be more suitable for both wastewater and biogas production and was found to be 46.4% in food processing wastewater and 43.3% in herbal pharmaceutical wastewater. Amendment of *Bacillus* sk2 in food processing wastewater produces 39.7% and 30.3% of biogas in herbal pharmaceutical wastewater was observed. Enzyme Bacillidine™ (P-COGconcentrate aqueous base) was also tried but results were not very encouraging. Comparative studies on both the wastewater have been discussed in detail in this article.

**Keywords:** anaerobic digestion, herbal pharmaceutical wastewater, food processing wastewater, methanogenesis, *Bacillus* sk1, *Bacillus* sk2

#### **1. Introduction**

Due to industrialization and excessive exploitation of natural resources, as well as the population explosion at the global level affects the environment at large [1, 2]. Textile industries, municipal sewage, dairy waste, pharmaceutical industries, swine, and aquaculture sectors release wastewater on a regular basis [3, 4]. Wastewater contains a variety of unfavorable chemical components and microbes that show short- and long-term environmental and human health implications [5, 6]. Untreated wastewater if utilized directly for irrigation may cause undesirable implications in the environment and groundwater [7]. The challenges with wastewater treatment include high energy consumption and laborious work [8]. In recent decades, a new goal has gained attraction on resource recovery from wastewater paired with its treatment technologies.

Regarding the crisis of energy use, the widespread usage of fossils fuels may deplete in the next 50 years [9]. So, to cope with the future energy demand, it is critical to seek innovative renewable energy sources [10, 11]. Other technologies for harnessing renewable energy sources, such as solar, wind, hydraulic, and geothermal energy, have been created [12]. All of these technologies have been developed very well and are commercially accessible to meet rising energy demand to some extent. Using wastewater as a source of energy can also help to relieve pressure on other technologies. Fresh microbial biomass or residual biomass after lipid extraction can be used directly for bioenergy generation using dark fermentation (biohydrogen production), fermentation (bio alcohols), and anaerobic digestion (methane) [13–15].

Presently, the global pharmaceutical sector has been quickly expanding and contributing to great economic development. But on the other hand, it is generating significant environmental degradation by releasing effluents [16]. Pharmaceutical manufacturing based on chemicals employs a number of chemical processes that result in complicated effluent with high salt content and poor nutritional value that is difficult to biodegrade. The wastewater generated by various pharmaceutical businesses is not uniform, and the composition of each type of wastewater is impacted by the techniques used. Antibiotics, steroids, reproductive hormones, analgesics, beta-lactamides, antidepressants, detergents, as well as unspent solvent and heavy metals make up the majority of the substance [17]. The treatment of wastewater includes several processes that are usually expensive. Anaerobic digestion (AD) is a low-cost technique for treating organic wastes while simultaneously recovering energy in the form of methane [18, 19]. The efficiency of anaerobic digestion is determined by the cooperation of numerous microorganisms that conduct hydrolysis, fermentation, and methanogenesis [20, 21]. Anaerobic digestion (AD) is a waste-to-biomethane conversion technology that has been utilized to transform sewage sludge, agricultural/livestock residues, food wastes, and other organic waste streams into biomethane [22]. Many research studies have been undertaken for the past 10 years to optimize the digestion benefits in terms of biogas production, environmental effect, and reduction of waste [23].

Therefore, looking at the present scenario of energy demand in a developing country like India, it is very much necessary to switch over to bio-methanation, as it is the ultimate environment-friendly and sustainable way of progressive development. Our study aimed to produce biogas from two types of wastewaters namely herbal medicinal wastewater and food processing wastewater using cow dung and isolated microbial species.

#### **2. Materials and methods**

Samples of influent cattle dung slurry were collected and analyzed for various physicochemical characteristics. Similarly, effluent samples were also collected from an anaerobic conventional digester for their characterization after 38 days. The physical and chemical parameters were determined according to the Standard Procedures [24]. Two different wastewaters viz., herbal pharmaceutical and food processing were also collected and its treatability studies were carried out. Herbal pharmaceutical wastewater was tried to treat with Vermi filters that produce a nutrient biosolid and vermiwash that promotes the growth of plants [25, 26].

#### **3. Isolation of anaerobic bacteria**

The potential bacterial species involved in biogas production were isolated from a fresh sample of cattle dung. During isolation, the sample was diluted as per *Role of Microbial and Organic Amendments for the Enrichment of Methane Production… DOI: http://dx.doi.org/10.5772/intechopen.102471*


#### **Table 1.**

*Different digester mixture with seed.*

requirement. The anaerobic agar medium was used for the selective isolation of the anaerobes. The spread-plate method was employed for bacterial-cell isolation. A total of 0.5 ml of diluted bacterial samples was spread onto an anaerobic agar plate. The plates were then incubated in an anaerobic jar provided with alkaline pyrogallol to make the environment free of molecular oxygen. Incubation was carried out for 72–96 h, at 37°C for bacteria proliferation.

Microscopic examination was carried out to study the presence of methane bacteria and their motility. A total of eight methanogenic cultures were isolated and detailed biochemical tests were carried out, such as the sugar fermentation test and IMViC test. Apart from these two tests Indole test, methyl red test, Voges Proskauer test, citrate utilization test, etc., were also evaluated. Enzyme like catalase test, oxidase test was performed to authenticate the presence of these enzymes. To confirm the methanogenic nature of the bacteria fluorescence test was carried out. Identification of the eight cultures of the methane bacteria was carried out by subjecting the isolates to scanning electron microscopy.

A total of eight isolates of bacterial species were obtained from the predigested cow dung slurry, which was inoculated for the comparative assessment of methane production individually by each species. The studies were conducted for two months, based on which the isolates 2 and 4 were contributing maximum. So, by taking these two isolates the experiment was designed by taking wastewaters from two different industries, namely the food processing industry and herbal pharmaceutical industry. Along with that, the enzyme *Bacillidine* was also taken for the experiment, which was isolated from the same material (pre-digested cow dung slurry). The details of different combinations taken for the experiment have given in **Table 1**.

#### **4. Experimental set up**

#### **4.1 Part 1**

Fresh cow dung slurry was prepared, for that, a total solid content was diluted in water to make a slurry of 1:1 ratio to get a total solid content of approximately 8.0% solids. Every digester was filled with 950 ml of diluted cattle dung slurry plus 50 ml of seed slurry from a working biogas plant. So, the working volume of digesters was

#### *Biogas - Basics, Integrated Approaches, and Case Studies*

kept to be 1 liter. A total of eight species of methane bacteria were isolated and they were subjected to mass culturing. Out of the nine digesters, one was kept as control with only cattle dung, while others were used for experimental purposes and named 1, 2, 3, 4, 5, 6, 7, and 8, respectively. These eight cultures individually were added (2 ml) to each of the above eight cattle dung digesters.

The digesters with maximum gas production were identified and further experimental work was initiated. Two bacterial species, that is, isolate 2 and isolate 4 resulted in maximum biogas production. The biogas production by individual species is given in **Figure 1**. DNA sequencings for 16s RNA studies of isolates 2 and 4 show that isolate 2 is *Bacillus* sk2 and isolate 4 is *Bacillus* sk1 (**Figures 2** and **3**).

**Figure 1.**

*Daily biogas production by eight types of isolates. \*C: control and 1, 2, 3, 4, 5, 6, 7, 8 are the isolates no 1, 2, 3, 4, 5, 6, 7, 8.*

**Figure 2.**

*Daily biogas production in food processing wastewater with Bacillus sk1, Bacillus sk2, and enzyme Bacillidine. \*FPW: food processing wastewater.*

*Role of Microbial and Organic Amendments for the Enrichment of Methane Production… DOI: http://dx.doi.org/10.5772/intechopen.102471*

**Figure 3.**

*Daily biogas production by herbal pharmaceutical wastewater with Bacillus sk1, Bacillus sk2, and enzyme Bacillidine. \*HPW: herbal pharmaceutical wastewater.*

#### **4.2 Part 2**

Eight digesters of 2-liter capacities were taken for two different wastewaters for different combinations with Bc (isolate 2) and Bt (isolate 4) and enzyme *Baccillidine* along with control as H and B. The biogas was collected in the inverted measuring cylinder of 2-liter capacity filled with 20% sodium sulfate [27]. Every day the digesters were manually shacked for 3–4 times a day and daily gas production was monitored. This situation was maintained for a period of 2 months till the gas production ceased completely. The digester where maximum gas production was obtained was selected for further experimental work using wastewaters as an organic amendment.

#### **5. Results and discussion**

There were many industrial wastewaters studied by anaerobic treatment by various authors. These wastewaters may have properties that accelerate the process of digestion. Some of the properties, such as temperature, pH, alkalinity, total ammonia nitrogen, volatile acids, total solids, total volatile solids, and phosphate, may also influence the enzymatic reaction of anaerobic treatment. In the present study,

both the wastewaters were containing plant materials as organic matter. Therefore, it was easily degrading when processed anaerobically.

Karray et al. [28] utilized anaerobic digestion of green algae *Ulva rigida* with sugar industry influent and tried to increase biogas generation. The results showed that this combination helps to compost algae with anaerobic sludge and water yielded the optimal inoculum for producing biogas and feeding an anaerobic reactor, providing 408 mL of biogas. When sugar co-substrate was employed, a maximum methane generation yield of 114 mL g−1 was received with 75% methane. Biogas was produced anaerobically from wastewater of the Colombian palm oil mill industry by Nabarlatz et al. [29]. Using two distinct inoculums, anaerobic digestion tests were carried out in batch mode to assess the effects of pH and inoculum to substrate ratio on anaerobic digestion. The best-suited inoculum was determined to be a 1:1 v/v mixture of urban WWTP (wastewater treatment plant) anaerobic sludge/pig manure at a ratio of 2 g volatile solids (VS) inoculum/g VS substrate, which produced the largest amount of accumulated methane, attaining 2740 mL methane without neutralizing pH. Anaerobic digestion of brewery wastewater to enhance biogas production using UASB (upflow anaerobic sludge blanket) reactor was carried out by Enitan et al., [30]. Using a modified methane generation model, 1.46 L CH4/g COD was generated. Similarly, Debowski et al. [31] investigated the anaerobic treatment of dairy wastewater in a multi-section horizontal flow reactor (HFAR) using microwave and ultrasonic generators. The study's findings in terms of wastewater treatment efficiency, biogas output, and economic analysis results demonstrated that the HFAR can compete with existing industrial technologies for food wastewater treatment [31]. Ounsaneha et al. [32], evaluated biogas generation during the digestion of municipal wastewater and food waste in semi-continuous and continuous operation with varying hydraulic retention times (HRTs). At 30 days of HRTs with a 10:90 ratio of municipal wastewater to food waste, methane outputs of 167.41 66.52 ml/g-Vs were observed in semi-continuous mode.

Initially, physicochemical parameters of seed slurry, herbal, and food processing wastewater were determined by the standard methods. The parameters that were determined included—pH, alkalinity (as CaCO3 mg/l), total ammonia nitrogen (mg/l), volatile acids (mg/l as CH3COOH), total solids (%), total volatile solids (%), and phosphate (mg/l). The pH of the seed slurry before the experiment was 6.91 indicating it was very less acidic and very close to the neutral pH. The alkalinity was found to be 1280 mg/l (as CaCO3). Total ammonia nitrogen was 105.28 mg/l. Total acids were determined as CH3COOH that was 312 mg/l. The percentages of total solids and total volatile solids were 5.50% and 3.60%, respectively. The data obtained are given in the tabular form in **Table 2**.


**Table 2.**

*Physicochemical characteristics of herbal and food processing wastewater.*

#### *Role of Microbial and Organic Amendments for the Enrichment of Methane Production… DOI: http://dx.doi.org/10.5772/intechopen.102471*

The physicochemical characterization of herbal processing wastewater (HPW) and food processing wastewater (FPW) was done where the same parameters were determined as in the seed slurry. The pH of FPW was 6.07, slightly higher than that of HPW in which the pH was found to be 6.78. The total ammonia nitrogen in the HPW was 20 mg/l, while that in FPW was 28.40 mg/l. Volatile acid in HPW was 60 mg/l, whereas in FPW the amount was comparatively very higher at about 384 mg/l. Total solids in HPW and FPW were 14% and 10.20%, respectively. Total volatile solids in HPW were found to be 7.10% and in FPW it was 3.40%. The amount of phosphate in HPW and FPW was found to be 2328 mg/l and 2067 mg/l, respectively. All the data obtained by characterization of HPW and FPW is shown in tabular form in **Table 2**.

Two sets of different digester mixtures were prepared for the experiment. In the first set food processing waste (FPW) water was used, whereas in the second set herbal processing wastewater (HPW) was used to make the digester mixtures with seed slurry. Each set contained four different digester mixtures. One mixture was prepared by mixing 200 ml of seed slurry and 800 ml of wastewater only. Another mixture contained 200 ml seed slurry, 800 ml wastewater, and isolate no. 2, that is, *Bacillus cereus* (Bc). The third kind of mixture contained 200 ml seed slurry, 800 ml wastewater, and isolate no. 4, that is, *Bacillus thuringiensis* (Bt). In the fourth kind of mixture enzyme, *Bacillidine* was added to 200 ml seed slurry and 800 ml wastewater. In this mixture, isolates 2, 4, and enzyme (2 ml) were mixed in each reactor. Hence four kinds of mixtures were there and the total numbers of eight digester mixtures were prepared using FPW and HPW. The above-mentioned information is summarized in **Table 1**.

The sets prepared were used in the experiment and kept for 45 days for biogas production. After 45 days the physicochemical parameters of all eight mixtures were determined. The same parameters were determined that were found initially. The pH of the four FPW effluents was slightly acidic to almost neutral. The alkalinity was between the range of 350–580 mg/l. The total ammonia was found in between 142 and 168 mg/l. Volatile acids were in the range of 168–276 mg/l. Total solids in the four mixtures were found in the range of 8–9%. Total volatile solids were between 6 and 7.2%. The pH of the four HPW effluents was slightly acidic compared to those of FPW. All the mixtures were ranged from 6.38 to 6.72. The alkalinity was between the range of 236–450 mg/l. The total ammonia was found in between 32 and 70 mg/l. Volatile acids were in the range of 120–218 mg/l. Total solids in the four mixtures were found in the range of 8.4–8.9%. Total volatile solids were between 5.7 and 8%.

#### **6. Selection of isolates**

The second part of this experiment showed that isolate no. 2, 8, and control were continued up to the 45th day, while isolate no. 4 and 7 has stopped on the 42nd day. Isolate no. 1 and 6 were stopped on the 40th day and isolate no 3 and 5 were stopped on the 36th day. On the 45th-day total biogas production was found to be 6080 ml in control, whereas in isolate 1, 3, 5, 6, 7, and 8 it was 2115 ml, 3595 ml, 1515 ml, 5430 ml, 5555 ml, and 5445 ml, respectively. The reactor containing isolate no. 2 was able to produce 6470 ml and the reactor with isolate no. 4 was able to produce 6900 ml of biogas, which was subsequently higher than isolate no. 2. So, it proves that isolate no 2 produces 6.4% and isolate no. 4 produces 13.5% more biogas as compared to control. **Figure 1** shows that isolate no. 4 was having the highest peak on the 13th day with production of 900 ml of biogas. Therefore, isolate no. 2 and 4 were selected for further studies.

A fluorescence test was conducted for the identification of methanogenic bacteria having the F420 coenzyme, which depicts blue-green fluorescence by methanogenic bacteria and was easily differentiated from the white-yellow fluorescence observed in non-methanogenic bacteria. The isolate no. 2, 6, 7, and 8 indicated the blue-green fluorescence in ultraviolet light depicting the presence of methanogenic bacteria, whereas isolate no. 1, 3, 4, and 5 indicated the negative fluorescence activity.

#### **7. Efficient isolate along with organic additive**

The experiment conducted to prove the efficiency of isolats no. 2 and 4 along with the organic additives like food processing wastewater and herbal pharmaceutical wastewater were continued till the complete anaerobic digestion took place. The digester mixtures were prepared as given in **Table 1**. After completing anaerobic digestion, the physicochemical analysis shows that they are well within the limits as per standards. The physicochemical characteristic of seed slurry and wastewater is given in **Table 2**. Initial characteristics of seed slurry, herbal, and food processing wastewater were determined by the standard methods. The parameters included were pH, alkalinity (as CaCO3 mg/l), total ammonia nitrogen (mg/l), volatile acids (mg/l as CH3COOH), total solids (%), total volatile solids (%), and phosphate (mg/l). The pH of the seed slurry before the experiment was 6.91 indicating it was very less acidic and very near to the neutral pH. The characterization of herbal processing wastewater (HPW) and food processing wastewater (FPW) showed the pH of FPW was 6.07, which was slightly higher than the HPW in which the pH was found to be 6.78.

Two sets of different digester mixtures were prepared for the experiment. In the first set food processing waste (FPW) water was used, whereas in the second set herbal processing waste (HPW) water was used to make the digester mixtures with seed slurry. Each set contained four different digester mixtures. The mixture was prepared by mixing 200 ml of seed slurry and 800 ml of wastewater with an inoculum of isolate, which was given in **Table 1**.

The digesters containing food industrial wastewaters were continued for 43 days, while digesters of herbal pharmaceutical wastewaters were continued for 58 days. The physicochemical characteristics of completely digested effluents were given in **Table 3**. Results indicated pH in the range of 6.58–7.08 and volatile acid to alkalinity ratio well below 0.8 indicated good buffering. Total ammonia nitrogen was well within the limits indicating the efficient working of reactions takes place. In no instances, there was any alarming increase in either volatile acid or total ammonia nitrogen shows that the system was well-balanced methane activity. This was due to the presence of higher organic content in the wastewaters.

The characteristics of effluents after 45 days of food processing wastewater and herbal pharmaceutical wastewaters were given in **Table 3**. The pH of the four FPW effluents was slightly acidic to almost neutral. The alkalinity was between the range of 350–580 mg/l, with total ammonia as 142–168 mg/l. Whereas, volatile acids were in the range of 168–276 mg/l. Total solids in the four mixtures were found in the range of 8–9%. With total volatile solids in between 6 and 7.2%.

The pH of the four HPW effluents was slightly acidic compared to those of FPW. All the mixtures were ranged from 6.38 to 6.72. The alkalinity was between the ranges of 236–450 mg/l. The total ammonia was found in between 32 and 70 mg/l. Volatile acids were in the range of 120–218 mg/l. Total solids in the four mixtures were found in the range of 8.4–8.9%. Total volatile solids were between 5.7 and 8%. The effluent of FPW and HPW showed minimized total solids after exhausting the bioreactors.

*Role of Microbial and Organic Amendments for the Enrichment of Methane Production… DOI: http://dx.doi.org/10.5772/intechopen.102471*


**Table 3.**

*Characteristics of effluents with herbal pharmaceutical wastewater (HPW) and food processing wastewater (FPW).*

#### **8. Methane production**

The microbial activity may get affected by some of the factors in an anaerobic digester. The design of the reactor, temperature, pH, C:N ratio, and wastewater characteristics along with the composition of complete seed material. Some of the methanogens belonging to the order viz., methanosarcinales, methanosarcinaceae, and methanosaetaceae may often be detected in accelerating methanogenicity.

Ho and Sung [33] investigated methanogenic activity in anaerobic membrane bioreactors (AnMBRs) used to treat synthetic municipal wastewater. The methanogenic activity profiles of suspended and attached sludge in AnMBRs treating synthetic municipal wastewater at 25 and 15°C were investigated using the specific methanogenic activity (SMA) assay. On day 1, AnMBR 1's methanogenic activity was 51.8 ml CH4/g VSS d, but by day 75, it had grown by 27% to 65.7 ml CH4/g VSS d. The methanogenic activity of AnMBR 2 sludge, on the other hand, was lower than that of AnMBR 1. Silva et al. [34] looked at the effects of pharmaceuticals like Ciprofloxacin (CIP), Diclofenac (DCF), Ibuprofen (IBP), and 17α-ethinylestradiol (EE2) on the activity of acetogens and methanogens in anaerobic communities. The majority of these compounds end up in wastewater treatment plants. The specific methanogenic activity was unaffected at doses of 0.01–0.1 mg/L. Acetogenic bacteria were sensitive to CIP concentrations more than 1 mg/L, whereas DCF and EE2 toxicity was only identified at concentrations greater than 10 mg/L, and IBP had no effect at any concentration. Acetoclastic methanogens were more sensitive to these micropollutants, being affected by all of the pharmaceutical chemicals tested, but to varying degrees. When compared to acetoclasts and acetogens, hydrogenotrophic methanogens were unaffected by any concentration, showing that they are less sensitive to these chemicals. CIP had the greatest impact on microbial communities, followed by EE2, DCF, and IBP, but the responses of the various microbial species

differed [34]. The co-digestion of mixed sludge from wastewater treatment plants and the organic fraction of municipal solid trash were explored by Keucken et al. [35]. When co-digesting mixed sludge with organic fraction at a 1:1 ratio, based on the volatile solids (VS) concentration, the results reveal rapid adaptability of the process and an increase in biomethane output of 20–40%. The microbial community is also affected by the introduction of organic fractions. The methanogenic activity grows and adapts to acetate decomposition under 50% co-substrate and constant loading circumstances (1 kg VS/m3 /d), while the community in the reference reactor, which does not have a co-substrate, remains unaffected. The methanogenic activity in both reactors increases when the load is increased (2 kg VS/m3 /d), while the composition of the methanogenic population in the reference reactor remains unchanged [35].

Isolate no. 4 was found to be more suitable for herbal wastewater than food processing wastewater because biogas production was almost double in the case of herbal pharmaceutical wastewater. Enzyme Bacillidine™ (P-COG-concentrate aqueous base) was also tried but results were not very encouraging. In the case of herbal pharmaceutical wastewater also the increase in biogas production was very significant with isolate 2 with total gas production of 3085 ml as compared to 2068 ml in the case of food processing wastewater.

The bioreactor with food processing wastewater and only sterilized seed was able to produce the biogas up to the 18th day, which was 2090 ml. However, the bioreactor with Bc was able to produce the biogas for 38 days with 2920 ml, which was almost 39.7% higher than the control, while the bioreactor with Bt was able to produce 3895 ml of biogas in 43 days, which was 86.4% higher than the control. In the case of enzyme Baccilidine, the biogas production was observed to be 2320 ml in 39 days, which was only 11.0% higher than the control. **Figure 2** shows that food processing wastewater produces 2090 ml of biogas in 43 days, but bioreactor amended with the culture of Bc produces 2920 ml of biogas that was 39.7% more and Bt amended bioreactor producing 3895 ml of biogas, which was 46.4% more than control. In the case of enzyme *Baccillidine***,** only 2320 ml of biogas was produced, which was only 10.2% higher than the control.

Similar results were observed in the case of herbal pharmaceutical wastewaters also. **Figure 3** shows that the bioreactor containing only wastewater and seed was able to produce 3205 ml of biogas in 45 days, whereas the bioreactor containing isolate 2 was able to produce 4600 ml of biogas in 44 days that was 43.5% higher than the control and the bioreactor containing isolate 4 was able to produce 5650 ml of biogas in 58 days, which was 76.3% higher than the control.

Enzyme *baccilidine* was able to produce only 2930 ml of biogas in 27 days, which was 8.6% lesser than the control. Hence it has been proved that the Bt contributes more than Bc for the biogas production, while enzyme *baccilidine* attenuates the biogas production in overall processes. In the case of enzyme *Baccillidine,* it produced only 2750 ml (14.0% less than control) of biogas.

#### **9. Conclusion**

Looking at the present scenario of the energy crisis and the environmental damage that occurs due to the use of nonrenewable sources of fossil fuel, it is the need of an hour to switch over to the use of renewable sources of energy. In the present studies, the herbal pharmaceutical wastewater and food industry wastewater were rich in organic content, which promotes the anaerobic biodegradability with a maximum production of methane by inoculating the specific bacteria isolated from the cow dung. Only cow dung seed is not able to produce more biogas as compared

*Role of Microbial and Organic Amendments for the Enrichment of Methane Production… DOI: http://dx.doi.org/10.5772/intechopen.102471*

to isolated microbes. *Baccilus* sk1 (Bt, isolate no. 4) was highly capable of methane production rather than *Bacillus* sk2I (Bc, isolate 2). Therefore, the culture of *Bacillus* sk1 became the best enhancer of biogas production. Such inoculums can be cultured on large scale and may be utilized for future energy generation.

### **Acknowledgements**

The author is grateful to University Grant Commission (UGC) for providing the fellowship.

#### **Author details**

Sharda Dhadse\* and Shanta Satyanarayan CSIR-National Environmental Engineering Research Institute, Nehru Marg, Nagpur, India

\*Address all correspondence to: sn\_dhadse@neeri.res.in

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 5**

## Global Fertilizer Contributions from Specific Biogas Coproduct

*Sammy N. Aso, Simeon C. Achinewhu and Madu O. Iwe*

#### **Abstract**

The impact of Haber-Bosch process on modern agriculture is prodigious. Haber-Bosch process led to invention of chemical fertilizers that powered green revolution, minimized food scarcity, and improved human and animal nutrition. Haber–Bosch process facilitated agricultural productivity in many parts of the world, with up to 60% of crop yield increase attributed solely to nitrogen fertilizer. However, Haber-Bosch fertilizers are expensive, and their poor use efficiency exerts adverse external consequences. In European Union for example, the annual damage of up to € 320 (US\$ 372.495) billion associated with chemical fertilizers outweighs their direct benefit to farmers, in terms of crops grown, of up to € 80 (US \$ 93.124) billion. A substitute for chemical fertilizers is therefore needed. In this chapter, external costs of chemical fertilizers are highlighted. The capability of liquid fraction of cassava peeling residue digestate to supplant and mitigate pecuniary costs of chemical fertilizers required for production of cassava root is also analyzed and presented. Results indicate that about 25% of fund used to purchase chemical fertilizers required for cassava root production could be saved with the use of liquid fraction of cassava peeling residue digestate. The pecuniary value is estimated at US\$ 0.141 (≈ € 0.121) billion for the 2019 global cassava root output. This saving excludes external costs associated with Haber-Bosch fertilizers such as ammonia air pollution, eutrophication, greenhouse gasses emissions, and contamination of potable water supply reserves. Consequently, liquid fraction digestate could reduce the cost of cassava root production, as well as minimize adverse health and environmental consequences attributed to chemical fertilizers.

**Keywords:** anaerobic digestion, biogas, cassava peeling residue (CPR), chemical fertilizer, circular economy, cost savings, digestate, eutrophication, Haber-Bosch process

#### **1. Introduction**

The impact of Haber-Bosch process on modern agriculture may not be overemphasized. It led to the invention of inorganic fertilizers that powered global green revolution, minimized food scarcity, and improved human and animal nutrition. In his noble lecture, Fritz Haber (The 1918 noble laureate for chemistry; for the Haber-Bosch process) alluded that his impetuses for creation of ammonia from

the elements were to meet increasing human food requirements, and replenish soil nitrogen extracted by harvested crops when he concluded: "*Let it suffice that in the meantime improved nitrogen fertilization of the soil brings new nutritive riches to mankind and that the chemical industry comes to the aid of the farmer who, in the good earth, changes stones into bread*" [1]. Haber–Bosch process has facilitated agricultural productivity in many parts of the world, with up to 60% of crop yield increase attributed solely to nitrogen fertilizer [2]. It has been estimated that between 1908 and 2008, Haber–Bosch nitrogen enabled the number of humans sustained per hectare of arable land to increase from 1.9 to 4.3 persons [3]. However, poor nitrogen use efficiency (NUE) of the same fertilizer that laid the golden benefits has deposited unintended adverse consequences to environmental systems [4]. Impacts of poor NUE may manifest at local, regional, and global scales [5], thereby placing air, soil, and water quality and safety, as well as human and animal health in jeopardy. Environmental and ecosystem services disruptions due to fertilizer use in agriculture have been reported worldwide. These include impairments of eco-diversity, recreational use of freshwaters, lakefront property values, and drinking water supply sources [6, 7]; loss of tourism benefits to coastal communities, [8, 9]; greenhouse gas (GHG) emissions and climate perturbation [10]; as well as air quality degradation [11].

Ammonia (NH3) air pollution from animal husbandry, fertilizer production and application has also been documented and reported [12–14]. About 94% of NH3 emissions in Italy emanate from agricultural operations [15], and in 2013 and 2018, agriculture contributed 93% of all ammonia emissions in the European Union [16, 17]. In the United States, agricultural runoff and drainage accounts for 89% of the total nitrogen inputs into the Mississippi River [18], contributing to hypoxic zone of the Gulf of Mexico [19]. In France, about 89% of residual nitrogen contamination of water resources and marine environments is attributed to mineral fertilizer and animal manure [8]. Similarly, nitrate contamination of surface and ground water is associated with agricultural use of fertilizers and manures [7, 8, 20–23]. Nitrous oxide (N2O) is a greenhouse gas that contributes to stratospheric ozone shield depletion and climate change [10]. Nitrogen fertilizer and manure contribute 92% of all N2O attributable to agriculture in the USA [24, 25]. In Italy and China, fertilizer accounts for about 68% of annual N2O emissions [15, 26]. Chemical fertilizer and manure are major contributors to external costs such as eutrophication and acidification of ecosystems [21, 27–30]. Annually, up to € 320 (US\$ 372.495) billion damage is associated with the use of nitrogen fertilizers in the European Union compared to direct economic benefit to farmers, in terms of crops grown, estimated at up to € 80 (US\$ 93.124) billion [31]. Report currency, € 1.0 ≈ US\$ 1.164 based on currency converter site: https://www1. oanda.com/currency/converter/as at Friday 22nd October 2021. Furthermore, inorganic fertilizers are not cheap, and may be used in large quantities. As at the second week of September 2021, the cost of 1 kg of nutrient fertilizer could range from ≈ US\$ 0.375 for liquid nitrogen (as urea) to US\$ 0.807 for dry phosphorus (as P2O5) [Ramsdell F&M Ltd. Brookings, SD USA]. In 2019, approximately 188.54 x 10<sup>9</sup> kg nutrient fertilizers (including 107.74 x 10<sup>9</sup> kg N, 43.41 x 10<sup>9</sup> kg P2O5, and 37.39 x 10<sup>9</sup> kg K2O) were consumed in agricultural production globally [32].

Due to outlined adverse effects and financial exigencies of chemical fertilizers, a more sustainable, environmentally benign, and cost-effective fertilizer system is desired. Digestate in the context of circular economy could play a prominent role. In this chapter, cost implications of using liquid fraction (LF) of cassava peeling residue (CPR) digestate, to supplement chemical fertilizers required for cassava root production are analyzed and presented (**Figure 1**).

*Global Fertilizer Contributions from Specific Biogas Coproduct DOI: http://dx.doi.org/10.5772/intechopen.101543*

**Figure 1.** *Graphical representation of the objectives and summary of this chapter.*

### **2. Anaerobic digestion and digestate for circular economy**

Circular economy is a credible intervention tool to minimize GHG emissions, limit global warming and ecosystem degradation. The circular economic model maximizes material and product conservation; prudent consumption; eco-friendly biorefinery; recyclability and reusability; green- smart mobility and renewable energy; systems thinking, innovative business models and policies; wasteless design and zero waste cities, as well as generation of useful products out of waste [33–40]. Anaerobic digestion (AD) is a responsive technology that could rise to the occasion. In the context of biorefinery platform, sustainability, and circular economy, AD transforms organic matter to two major coproducts: biogas fuel and digestate [41]. Digestate has soil amendment and biofertilizer potentials.

Digestate enhances soil biological stability and enzymatic activities [42]; enriches microbial biomass [42, 43]; abates nutrients leaching and remediates metal contaminants [43–45]; conditions the soil and boosts plant nutrients, stimulates growth of beneficial microbes, improves buffering capacity, and physical properties such as texture, aeration, bulk density, hydraulic conductivity, and moisture retention capacity [46–49]. In comparison to chemical fertilizers, digestate biofertilizers offer better ecosystem services, values, and life cycle assessment accounting [50]; including lower energy consumption [51–53], lower ammonia air pollution [15],

lower GHG emissions [53–55], better soil carbon sequestration [54, 56], reduced soil erosion [54, 57, 58], and increased biodiversity [59].

To exploit these benefits and advantages, various organic substrates have been used for digestate creation via the AD process. At least 120 items have been identified in published scientific literature [41], but CPR is not one of them. Indeed, there is scarcity of information on nutrient content, speciation, agronomic properties and values of LF of digestates from AD of single feedstocks in general [60]; and LF of digestate derived from AD of CPR as single feedstock in particular [41, 61].

#### **3. Nutrient content of liquid fraction (LF) of cassava peeling residue (CPR) digestate**

The only information on primary macronutrients (i.e., nitrogen (N), phosphorus (P), and potassium (K)) content of LF digestate of CPR as sole feedstock found in literature is presented in **Table 1**. For perspective, the values are compared with LF of digestates derived from other feedstocks in **Tables 2**–**4** respectively for N, P, and K. The values for each Table are presented in descending magnitude order. It can be seen that LF of CPR digestate is high in N and K, but low in P. Apart from livestock manure, most LF digestates with higher nutrient values are derived from AD of multiple feedstocks (**Tables 2**–**4**). Co-digestion of feedstocks may benefit from coactive effects.


**Table 1.**

*Macronutrients (N, P, K) content of liquid fraction of CPR digestate [41].*



#### *Global Fertilizer Contributions from Specific Biogas Coproduct DOI: http://dx.doi.org/10.5772/intechopen.101543*

#### **Table 2.**

*Comparison of nitrogen (N) content of liquid fraction of digestate derived from various feedstocks.*


#### *Biogas - Basics, Integrated Approaches, and Case Studies*


#### **Table 3.**

*Comparison of phosphorus (P) content of liquid fraction of digestate derived from various feedstocks.*


#### **Table 4.**

*Comparison of potassium (K) content of liquid fraction of digestate derived from various feedstocks.*

#### **4. Estimation of fertilizer credit for liquid fraction (LF) of cassava peeling residue (CPR) digestate derived from one metric ton (1000 kg) cassava root**

The nutrient values presented in **Table 1** are for digestate derived from 800 g CPR accumulated in the 3 L working volume of AD reactor [41, 61]. Therefore, total nutrient credits for the 800 g CPR are:

N = 573 mg/L 3 L = 1719 mg (1.719 g).

P = 31 mg/L 3 L = 93 mg (0.093 g).

K = 1066 mg/L 3 L = 3198 mg (3.198 g).

With the nutrients credit for 800 g (0.8 kg) CPR established, estimation of corresponding nutrient credit for CPR generated from 1000 kg cassava root becomes possible. It has been reported that CPR constitutes about 19% mass fraction of fresh cassava root [98]. Consequently, 1000 kg cassava root would yield 190 kg CPR. Hence, N, P, and K fertilizer credits for CPR generated from 1000 kg cassava root are estimated as:

N = 190 kg/0.8 kg 1.719 g. P = 190 kg/0.8 kg 0.093 g. K = 190 kg/0.8 kg 3.198 g. The results are presented in **Table 5**


**Table 5.**

*Nutrient credit for LF of digestate of CPR derived from 1000 kg cassava root.*

#### **5. Capability of liquid fraction (LF) of cassava peeling residue (CPR) digestate to supplant chemical fertilizer in cassava root production**

Cassava crop is forbearing of harsh growing conditions such as drought, acidic soil, marginal land, varied elevation, swings of temperature and rainfall [99, 100]. However, research has shown that cassava is also responsive to adequate soil fertility and fertilizer application [101–103]. The equivalent root productivities in response to three cases of chemical fertilizer input are presented in **Table 6**.


**Table 6.** *Nutrient requirements for cassava root production (Derived from ref. [102]).*

From the atomic weights of P, K and O, the elemental nutrient equivalent of the oxide forms (P2O5 and K2O) could be computed with the equations:

$$\mathbf{P} = \mathbf{0}.43\mathbf{\overline{7}} \text{ (P2OS)}\tag{1}$$

$$\mathbf{K} = \mathbf{0.830} \text{ (K2O)}\tag{2}$$

Consequently, the total P and total K corresponding to the total N required for the three cases of cassava root production outlined in **Table 6** are estimated and presented in **Table 7**.

Based on nutrients required to produce one metric ton (1000 kg) of cassava root shown in **Table 7**, and the nutrient credit for LF of digestate of CPR generated from 1000 kg cassava root presented in **Table 5**, the capability of LF of CPR digestate to supplant chemical fertilizer in cassava root production is estimated and outlined in **Table 8**. The proportion of production nutrient substituted range from about 23–30% for nitrogen; 5–11% for phosphorus; and 21–40% for potassium.


**Table 7.**

*Elemental nutrient requirements for cassava root production (Derived from Table 6).*

#### **6. Cost analysis**

From the mean nutrient values in **Table 8**, about 25, 8, and 28% of N, P, and K respectively required for production of 1000 kg cassava root, and sourced from inorganic fertilizers are supplanted by liquid fraction of CPR digestate. The cost implications are analyzed and presented in **Table 9**. The analyses indicate that about 25% of the total financial cost of inorganic fertilizers is supplanted by liquid fraction of CPR digestate (**Table 9**).


*Global Fertilizer Contributions from Specific Biogas Coproduct DOI: http://dx.doi.org/10.5772/intechopen.101543*


#### **Table 8.**

*Capability of liquid fraction of CPR digestate to supplant chemical fertilizers required for cassava root production (Estimate based on Tables 5 and 7).*


*\*Unit cost of liquid fertilizer derived from price data supplied by Ramsdell F&M Ltd. Brookings, SD USA. (Price as at 13th September 2021).*

#### **Table 9.**

*Cost implications of supplanting chemical fertilizers with liquid fraction of CPR digestate in cassava root production.*

#### **7. Global fertilizer savings from liquid fraction (LF) of cassava peeling residue (CPR) digestate**

In 2019, a total of 96 recorded countries/territories produced about 303.569 x 10<sup>9</sup> kg cassava root globally. The output ranged from 5000 kg for Maldives to 59.194 109 kg for Nigeria [104]. At 19% CPR mass fraction composition, 57.678 <sup>10</sup><sup>9</sup> kg of CPR would be generated from the global root output. This quantity of CPR could be transformed to biogas and digestate via AD. Whole digestate could be separated into liquid and solid fractions using appropriate technologies [41]. The liquid fraction of CPR digestate could then be utilized to supplant inorganic fertilizers required for cassava root production. The cost data generated

and presented in **Table 9** are applied to estimate the pecuniary value of global fertilizer savings from liquid fraction of CPR digestate substitution of chemical fertilizers. The results for each of the 96 countries/territories that produced cassava root in 2019 are presented in **Table 10**. Total global cost savings is about US\$ 141.019 (€ 121.130) million. The range is from US\$ 2.323 (€ 1.995) for Maldives, to US\$ 27.498 (€ 23.620) million for Nigeria.





#### **Table 10.**

*Global fertilizer savings from liquid fraction of CPR digestate.*

#### **8. Conclusion**

Haber-Bosch process facilitated the existence of inorganic fertilizers that revolutionized crop yield, improved nutrition, and enhanced food security. However, external costs associated with the production and application of inorganic fertilizers in agriculture are prodigious. Air quality degradation, climate perturbation, eutrophication, harmful algal blooms, ocean dead zones, pollution of surface water bodies and groundwater aquifers used as potable water supply sources are notable examples. Anaerobic digestion in the context of circular economic paradigm could provide viable solution. Anaerobic digestion transforms organic wastes and residues to beneficial biogas fuel and digestate biofertilizer. This chapter analyzed and presented the cost implications of liquid fraction of cassava peeling residue (CPR) digestate to supplant chemical fertilizers required for cassava root production. About 25% of fund used to purchase the chemical fertilizers required for cassava root production could be saved with the use of liquid fraction of CPR digestate. The global pecuniary saving is estimated at US\$ 0.141 (€ 0.121) billion for year 2019 cassava root output. Thus, exploitation of liquid fraction of CPR digestate would save 25% pecuniary cost of inorganic fertilizers required for cassava root production, as well as attenuate afore mentioned external costs correlated with the production and application of the inorganic fertilizers.

*Perspectives*: There is severe scarcity of data on the speciation of nutrients content of digestates derived from anaerobic digestion of CPR as single feedstock. The few studies reported in available literature focused on biogas potentials of CPR co-digested with other substrates such as animal manures. The reports did not indicate any data on generated digestate. For future perspectives, experimental questions could address systematic studies to characterize the nutrient speciation in digestates derived from CPR as mono feedstock. Findings may not only corroborate the fertilizer values of CPR digestate reported in this chapter, but also establish CPR's nutrients influence and contribution when co-digested with other feedstocks. Furthermore, the work for this chapter searched, and could not find any study on

the effects of CPR digestate on crop performance. Agronomic experiments designed with CPR digestate as bio-fertilizer, would provide valuable knowledge and insight on the suitability and practical impact of CPR digestate on yield and other performance indicators for cassava, and perhaps other crops.

#### **Author details**

Sammy N. Aso1 \*, Simeon C. Achinewhu<sup>2</sup> and Madu O. Iwe<sup>3</sup>

1 Food Engineering Laboratory, Rivers State University, Port Harcourt, Nigeria

2 Department of Food Science and Technology, Rivers State University, Port Harcourt, Nigeria

3 Department of Food Science and Technology, Michael Okpara University of Agriculture, Umudike, Nigeria

\*Address all correspondence to: sammyasso@yahoo.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Global Fertilizer Contributions from Specific Biogas Coproduct DOI: http://dx.doi.org/10.5772/intechopen.101543*

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Section 2
