Processing of Household Wastes

#### **Chapter 4**

## Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries

*Martina Pilloni and Tareq Abu Hamed*

#### **Abstract**

The world's rural population surpasses the three billion people mainly located in Africa and Asia; roughly half the global population lives in the countryside. Access to modern fuels is a challenge for rural people compared to their urban counterparts, which can easily access infrastructures and commercial energy. In developing countries rural populations commonly depend on traditional biomass for cooking and heating. A key strategy in tackling the energy needs of those rural populations is to advance their energy ladder from the inefficient, traditional domestic burn of biomass, organic waste, and animal manure. Governments and non-governmental institutions have supported small biogas digesters in rural areas, mainly in Asia, South America, and Africa, over the last 50 years. This chapter reviews the literature to offer an overview of experimental and theoretical evidence regarding the characteristics of design, construction material, feedstock, and operation parameters that made anaerobic digestion in small digesters a valuable source. Small-scale rural biogas digesters can generate environmental, health, and social benefits to rural areas with a net positive impact on energy access. Remarkable improvement in living standards was achieved with small inputs of the methane, produced via anaerobic digestion; however, challenges associated with lack of technical skills, awareness, and education remain and obstruct biogas' full potential in rural areas, mainly in developing countries.

**Keywords:** small-scale biogas installations, household biodigesters, rural livelihood, biogas in developing countries, energy access

#### **1. Introduction**

Anaerobic digestion is a technology that converts waste into energy. The produced biogas is considered as the primary energy output. The percentage of methane in the biogas is responsible for its calorific value, which is generally considered high [1]. Biogas can substitute oil, coal, and natural gas. Biogas can also be upgraded and directly used in natural gas pipelines and vehicles. The exploitation of fossil fuels and natural resources has increased greenhouse gas (GHG) emissions, deforestation, infertility of land, consumption, and water pollution. Biogas as a source of energy may help to mitigate those problems and reduce global warming. Moreover, using anaerobic fermentation to convert organic waste into fuel has many advantages over the use of crops to generate biofuels: it limits land use, food scarcity, and

biodiversity damage. Thus, biogas represents an ethical choice for energy production [2]. In terms of net energy generation, the methane from anaerobic digestion is considered competitive regarding efficiency and costs compared to other biomass energies [3], and it is better from an ecological point of view [4].

Those benefits are already attributed to anaerobic digestion and biogas technology worldwide; however, the contribution of small-scale biogas installations to rural areas in developing countries has a wealthier meaning, and this chapter is aimed to disclose and discuss such value.

The design of biogas technology varies depending on the country, climatic conditions, and the feedstock availability; moreover, it depends on the policy regulations such as waste and energy programs and energy accessibility and affordability. Thus, biogas production may vary from different ranging set-ups, from backyard systems to large industrial plants. In developing countries, the domestic small-scale biogas installations, also called household anaerobic digesters, are the most diffused systems in the rural areas [5]. Those systems volume generally ranges up to 10 m3 [6]. The digester size is limited by the available feedstock volume originated by the household and easily accessible; the most common feedstocks are manure from animal husbandries, food waste, small-agriculture waste, and sewage sludge. The household systems represent an effective strategy to enhance rural household life quality because it simultaneously advances sanitation and rural ecology and increases energy availability and incomes from the small agricultural activities [7]. The most common energy use of household biogas is for cooking and lighting [8]. Those systems have been successfully employed worldwide with governments and institutions' involvement, supporting household biogas' diffusion throughout subsidy schemes and programs of planning, design, building, and maintenance [9].

The chapter aims to offer an overview to the whole scientific community, to those already interested in biogas technologies but not expressly focused on developing countries and those who started to face the topic. It seems essential to attract new interest in biogas technology from practitioners involved in energy poverty and sustainable development for the Global South, the chapter is also directed to them.

#### **2. Methodology**

An overall evaluation of recent literature is used to compare relevant cases that disclose theoretical and practical assessments of small-scale biogas installations in rural areas. The literature review included only publications focused on developing economies; thus, papers were selected to achieve insights on the recent and current status of small-size biogas installations in such contexts. The information gathered is summarized here as principal aspects, designs, materials, and operations as they are applied to the most diffused small-scale and household installations in rural areas. Moreover, the literature data are compared to extract and discuss the relevance that small-biogas technology has for impoverished communities and the prevailing barriers that still slow down, or even prevent, biogas technology diffusion.

#### **3. Rural areas in developing countries: defining the context**

The world's rural population has been growing slowly since 1950. There are 3.4 billion people who live in rural areas around the world, 90% of them live in Africa and Asia. India (893 million) and China (578 million) represent 43% of the world's rural population. As the rural population worldwide became more sedentary and grew in population and density, the related environmental and public health problems

#### *Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

increased. The population growth determined an increase of consumption needs, and several effects are due to such increased demands. The more prevailing demand is the need for food that can be met through intensification and extensification of agricultural land use; these two responses to the increased food demand are often led by the lack of technological innovation and efficient practices. Indeed, if the land is available, the land extensification is more likely to happen; depending on geographical area, communities may cut trees in lowland forest, use highland slopes in high mountainous regions, or root out brushes in semi-arid zones. Thus, in the absence of environmental controls and adequate rural policies, as generally occurred in the past, the consequences have been deforestation, soil degradation, and desertification in areas already marked by poverty. The population growth determines an increase in energy demand for cooking and heating. In developing countries fuelwood is the cheapest and primary source of energy for cooking and heating. If fuelwood is available in the vicinity, local deforestation results, otherwise deforestation occurs elsewhere also at a long distance from the community [10]. Besides deforestation, which represents an urgent issue in the current climate change era [7], fuelwood's use creates other concerns that need attention. In terms of environmental concern, the diffused utilization of inefficient biomass source contributes to the greenhouse gas emissions [11]. Indeed, biomass as wood and charcoal, both used in poor rural areas, is not sustainable, and when it is partly burnt, it causes emissions that contribute to global warming [12]. As a health concern, because of the use of wood stoves by the rural households, a high level of exposure to Respirable Suspended Particulate Matter (RSPM) from the fuelwood stoves smoke generates health hazards mainly for women and children [13]. From the perspective of social-economic aspects, the women and children are the main fuelwood gatherers (even from long distance), and the fuelwood is collected at the expense of their labor, time, and drudgery [14], and it withdraws them from opportunities of education and incomes.

In developing countries, the rural areas suffer more than urban clusters from lack of basic infrastructure with low access rates to clean water, household sanitation [15], and waste management [16], which determine high public health risk, which is exacerbated by the continuous growth of population and density. The absence of such infrastructures drives rural communities toward practices that negatively affect their surrounding with contamination and pollution of land, water, and air due to unmanaged organic waste from the household and livestock [17, 18]. Practices of burning organic waste as animal dung and crop residues represent how rural communities meet their cooking and heating needs, although it is inefficient and detrimental for the health [19].

Rural areas also suffer from the limited or absent electricity supply and distribution infrastructures, so rural populations have low access to electricity. It was estimated that 770 million people in 2019 were without electricity access; in Africa in the year 2020 there were 592 milion people without electricity access, and the Sub-Saharan represents the region where the access deficit is higher [20]. Such a struggle in energy access drives rural populations to rely on traditional biomass resources or become dependent on imported fossil fuel derivates. However, as already described, these resources have negative impacts on health and the environment and weaken those economies which are already fragile [21].

#### **4. Developing countries: small-scale biogas programs for rural areas**

The attention to small-scale biogas technologies has increased in the last decades globally, with fast development and diffusion in rural areas in Asia, Africa, and Latin America [6]. The mass dissemination was dependent on central government

programs and long-term political support [22]. Between 1970 and 1985, China established a program for promoting and facilitating the installation of biogas in every rural household; the program brought the installation of 4.7 million household digesters by the end of 1988 [23]. A further increase was observed starting from the end of the 20th century, China registered more than 26 million biogas household installations in 2007 [5], and 43 million biogas users were counted in 2013 [24]. Since 1981, India had the National Project on Biogas Development (NPBD) with various training and development programs and financial support [25]. As a result of Governments' subsidies, over five million household biodigesters were installed in 2014 [26]. In Latin America, the introduction of biogas technologies for households was driven by the energy crisis in the 1970s when the Latin American Energy Commission (OLADE) prompted installations in several counties.

Moreover, the network Biodigesters in Latin America and the Caribbean (RedBioLAC) were created in 2009 to promote household, community, and farmscale digesters in Latin America [27]. Bolivia stands out among the Countries involved in the network, with over 1000 domestic biogas digesters installed in 2014 [28]. Many other small scale biogas programs were implemented for developing rural areas [19, 29]. In Africa, over 44% increase in domestic digesters installed between 2011 and 2012, and about 60,000 digesters were in Burkina Faso, Ethiopia, Kenya, Tanzania, and Uganda in 2015 [30].

In many other cases, the success of biogas implementation was due to the combination of governmental support and non-profit organizations. Netherland Development Organization (SNV), based in Netherland, had supported national biogas programs impacting more than 2.9 million people in different continents [31].

#### **5. Biogas production and potential in developing countries**

The biogas energy supply is a valuable sector for the bioenergy industry. In 2017, 1.33 EJ of biogas was produced globally, representing 2% of the total biomass produced for energy purposes, but it has the potential to develop much more. Europe leads in biogas supply for more than 50% of the global supply, Asia follows it with 31%, and America with 14% [32].

Although the developing countries displayed more barriers for biogas application, some countries such as China [33], South Africa [34], Ghana, Rwanda, and Tanzania [35] produce biogas from large scale institutional plants using similar technology implemented in developed countries.

However, in developing countries, biogas is predominantly produced on a small and domestic scale. In China, the 43 million small-scale biogas installations contributed to generating, together with the large-scale plants, about 15 billion m3 of biogas in 2014. It corresponds to 9 billion m3 biomethane; moreover, the annual potential was calculated around 200–250 billion m3 [28]. In Bangladesh, it was planned to build 100,000 small biogas systems by 2020, with an average c.a. 50 kW [36].

It is difficult for developing countries to find in the literature an exact number about the real contribution of small-scale biogas systems to the overall national renewable energy production. However, it should be noted that for the regions in which the energy access deficit is higher, domestic livestock biogas generation represents an enormous energy gain to move a step from the absolute energy poverty. For example, domestic biogas generation potential assessed in Nigeria showed an annual biogas projection of 138.7 X 106 m3 from livestock, equivalent to 0.48 million barrels of crude oil [37].

*Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

#### **6. Designs**

#### **6.1 Standard design systems**

Biogas is a sustainable and affordable technology for rural areas where it is more convenient to adopt cheaper and simpler anaerobic systems to benefit from biogas production [38]. The household systems are low cost, simple to operate and maintain, and often constructed using local materials. The selection of the biogas systems depends on the construction, design skill, and material availability. Moreover, the design depends on the type of feedstock, climatic conditions, and geographical location. Generally, those systems do not have control instruments and heating apparatus and serve at room temperature (psychrophilic or mesophilic temperature) [5]. In tropical countries, digesters are underground to take advantage of geothermal energy; meanwhile, in mountainous regions, the systems have a reduced amount of gas to avoid discrepancies between the hot and cold season biogas production [39]. Traditionally, the generated biogas is used for cooking and lighting; however, biogas for electricity is increasing [40].

The most diffused systems in developing countries are fixed dome, floating drum, and plug flow type.

The fixed dome model is also called hydraulic digester (**Figure 1**) developed in China, where more than 45 million systems have been installed [6]; this type of system is also implemented in South Asia and Africa [31]. Typically, it consists of an underground digester and a dome-shaped roof. The digester's size depends on the amount of substrate available and the location; biodigesters are typically from 6 to 8 m3 and operate in a semi-continuous mode. The new substrate is added once a day, while an equal amount of decanted mixed liquid is removed [5]. The digester is built from bricks, cement and reinforced by concrete. The system has one central part, the digester, dedicated to the fermentation and located at a deeper level, and above the ground level, there are two rectangular openings on each side, and they act as the inlet and outlet points for the digester. At the top of the dome-shaped roof, there is a pipe that is the biogas outlet. The digester is filled through the inlet, while the outlet also plays the hydraulic chamber's role. During the process, the biogas is produced in the digester, and it fills the upper part called the storage part (i.e., the dome). The pressure generated by the biogas presses the slurry from the digester into the inlet and outlet tanks. When the gas is released, the slurry flows back into the digester. Over the decades, this model has been improved and new

**Figure 1.** *Scheme of fixed dome digester model.*

designs developed. In China, the digesters were modified with a hemispherical shape with a wall in the middle to increase the retention time and ensure a complete digestion process. Different fixed dome models were developed in India; first, the Janta model, a shallow system with a dome roof, has an inlet and an outlet above the dome equipped with the gas pipe. The Deenbandhu model, which is a modification of the Janta model, consists of two spheres; at the bottom, there is the fermentation unit, while at the top, there is the storage unit. In India, a low-cost model for light purposes was also designed with a vertical cylinder as a dome and with long inlet and outlet tubes [41]. In Pakistan, the French model digesters were installed; in this case, the digester is surrounded by a steel dome to prevent the loss in temperature [42]. Over the last years, alternative construction materials have been introduced to reduce labor costs and increase the system lifetime. Polymers and glass-fiber-reinforced plastics are used nowadays [43]. The fixed dome design is a reliable model with low maintenance and a long lifetime; for these reasons, it was implemented widely [31].

India developed the floating drum model (**Figure 2**); its design comprises a mobile inverted drum placed on the block digester with inlet and outlet connections through pipes located at the bottom. The digester is often partially underground. The drum acts as a reservoir; it can rise and fall along a guide pipe, depending on the produced biogas' volume. It produces biogas at constant pressure with variable volume. The weight of the drum applies the pressure required for the gas to flow through the pipeline. The digester generally is made of bricks and concrete. Meanwhile, the drum is made on metal or steel and coated with paints or bitumen to avoid corrosion, determining its lifespan. Galvanized metal and fiberglassreinforced plastics represent a suitable alternative to standard steel [39].

The plug flow type or tubular model (**Figure 3**) was developed as portable model. This model is widespread, especially in South America [44]. It comprises a narrow and long tank (length: width equals to 5:1) inclined and partially buried in the ground, with the inlet and outlet over the ground and at the opposite side. Due to the inclination, the digestate flows toward the outlet; it is a two-phase system where acidogenesis and methanogenesis may be longitudinally separated. To keep

**Figure 2.** *Scheme of floating drum digester model.*

*Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

**Figure 3.** *Scheme of tubular digester model.*

the process temperature adequate, the system needs insulation, and generally, a shed roof is placed on the top of the digester [39].

Comparing the tubular digester model with the fixed one, the fixed model can be fed with ratio manure: water 1:1, while tubular model 1:3, the former needs three times the amount of liquid [27]. Compared to the fixed dome, the plastic tubular digester has several advantages. It is a very low-cost model suitable to high altitude and low temperature, it is easy to transport and simple to install with lower investment costs, it needs less maintenance, and it is more environmentally friendly [45]. If the hard constructed models are compared from an economic point of view, for a capacity of 1–6 m3 , the cost of installation and the annual operational costs are the highest for floating model followed by fixed ones (i.e., Janta and Deenbandhu models). The floating type also has a longer payback period. With the increase of capacity, the cost of installation and the annual operational costs increase proportionally, and the payback period increases. It was shown that the Deenbandhu model (capacities from 1 to 6 m3 ) is the cheapest model [46].

Regardless of the model, the household biogas systems may include auxiliary equipment to mix and handle the slurry and gas. The gas equipment may comprise pipes, valves, manometers [47].

**Table 1** resumes the principal household biogas designs here described, including for each design, the advantages, the disadvantages, and the countries where it is mainly diffused.

The local conditions, biogas users' needs, waste, water, and land availability, are the criteria used to select the appropriate digester design in terms of volume and building materials [19]. Together with the different operational parameters, the design determines the biogas production and the quality of the digestate. As a decentralized energy resource, a poor design represents a particular limitation to users' adoption [50]. Moreover, sizing the digesters according to local needs and reducing the discrepancy between demand/production can avoid biogas' excessive production that often drives users to leak it into the surrounding environment purposely, and this causes a negative environmental impact [51].

#### **6.2 Prefabricated and low-cost digesters**

In recent years prefabricated systems were preferred for projects involving rural communities in developing countries. Those systems are also called "commercialized digesters" and often called "news digesters" because they involve new production materials, processes, and techniques. The main models generally used in developing countries are composite material digesters and bag digesters [9].

The bag-digester is also called balloon digester, tube digester, and it has a sealed soft plastic tubular structure. The long cylinder is generally made of polyvinyl chloride (PVC), polyethylene (PE) (**Figure 4**), or rubber. It was developed to address the construction problems with solid digesters (fixed and floating models).


**Table 1.** *Principal household designs used in developing countries (authors adaptation from literature sources).* *Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

Some Authors consider the bag digesters and the plug flow digesters different types, but actually, they are similar. In such a system, the biogas production is between 0.1 and 0.32 m3 biogas/ m3 digester/day, it equals the yield of traditional digesters used in India [52]. The bag-digester is more suitable in rural areas where the day temperature is above 20°C. This system has been widely applied in South and Central America [53], and at least 1 million low-cost PE plastic were installed in Vietnam with the Ministry of Agriculture and Rural Development. This system needs only two people for installation, and it can be easily transported, and for this reason, it was widely adopted for remote areas [9].

The composite material digesters are relatively new, originated in China, and well developed in East Asia countries [54]. The reinforced fiber plastic digesters represent a type of composite material digesters, and they can be manufactured through processes of resin transfer molding, sheet molding, and filament winding and they can also be built by hand (**Figure 5**). Such digesters are lightweight. Therefore, they can be easily transported and removed. They have long-term durability, good corrosion resistance to acid, high productivity, and high gas pressure (depending on the tightness). Several modified plastic digesters are also commercially available, and every model allows facile transportation. They are particularly suitable in rural

#### **Figure 6.**

*Commercial water tank (composite material digester) in Cambodia. Image courtesy: Shikun Cheng.*

#### **Figure 8.** *Typical portable digester for kitchen and green waste in Malaysia. Image courtesy: Shikun Cheng.*

areas subject to reconstruction due to rural and land reform policy. Examples are represented by water tanks (**Figure 6**) and compact high-rate digesters (**Figure 7** and **Figure 8**) designed for kitchen and garden waste disposal [9].

*Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

#### **7. Materials**

As already mentioned in the design's description, the construction may involve different building materials. For household systems, bricks are essential material for fabricating of the digester chamber for both fixed and floating models. Generally, high-quality bricks should be used in the fabrication; however, clinker bricks are the most suitable ones because of their properties: low-cost, low moisture content, high resistivity, low thermal conductivity, appropriate thermal mass, weather resistance, fire-resistance, and tolerance to acidic pH. The concrete stones are used for building the block or the whole structure of the bricks/cement biogas digesters, they are the cheapest construction material, and they fit for the biogas purpose because of their tensile strength, durability, fire resistance, the thermal and conductive properties. The cement is also used for plastering purposes and building the concrete digester block and both the inlet and outlet. The most advantageous concrete used for the biodigesters is the Portland cement concrete (PCC), which has good density, compressive, flexural, and tensile strength. However, the use of these traditional materials brings challenges and holds disadvantages. Often the structures made with bricks, cement, and concrete, crack due to the structural stabilization and the fluctuation of temperature, usually resulting in leakages. High-quality materials and highly skilled labors are needed to minimize these problems, but those two aspects are often unavailable in developing countries. However, in recent years also alternative construction materials have been introduced like polyvinyl chloride (PVC), high-density polyethylene (HDPE), or glass fiber reinforced plastics (GRP). The PVC is used due to its low cost for building the inlet and outlet and for the digester chamber (in the case of plastic models) despite its short lifespan. Mild steel bars are usually used for the construction of the cover and the digester chamber. For the gas pipes, several different materials have been used as metal (steel or copper) and plastic (HDPE, PVC), and for the valves, generally, ball valves are used [55]. Because the biogas system's durability and cost are directly linked with construction materials, the pre-built and low-cost digesters are preferred for installations in developing countries [56]. Generally, off-site models are made with materials with specific characteristics such as glass fiber reinforced plastics (GRP), which have lower coefficient thermal conductivity, a longer operational life, and lower maintenance costs than the concrete models [54]. Several innovative design types were produced (already discussed in section 6.2), and they are commercially classified as fiber-reinforced plastic, soft plastic, and hard plastic digesters [9].

#### **8. Influencing parameters**

The process of anaerobic digestion requires the right conditions to have adequate biogas production; the most influencing parameters are temperature, organic waste composition, the moisture content, the mixing, and the hydraulic retention time (HRT) [57]. The generally suitable substrates for biogas production in rural areas are agricultural and livestock residues, organic fraction of solid domestic waste, and domestic sewage sludge (i.e., human excreta and wastewater). The biogas yield depends on the quality, amount, and supply rate (continuous or semi-continuous) of feed materials (**Table 2**). The biogas production can be directly measured by calculating the pressure of each digestor's headspace [58]. Several parameters can be used for monitoring the value of feedstocks, such as the Dry Matter (DM), the carbon-to-nitrogen ratio (C:N), Total Solids (TS), and the Volatile Solids (VS). Overall, animal manure is an ideal feedstock because of its high moisture and


#### **Table 2.**

*Common Feedstocks used in household digesters (author adaptation from literature sources).*

volatile solids (VS) content and the buffering capacity, and also for its variety of microbial strains. The animal manures used in anaerobic digestion may vary according to the geographical area and local livestock practices [5, 30, 39].

The HRT always depends on temperature and substrate; however, there are no regulator instruments and no process of heating in the household systems that are generally installed in developing countries; thus, for each substrate, the optimum HRT should be found for best biogas yield because retention time affects the digestion process. The potential of cow dung, sheep, and pig manures in the plastic reactor was studied in Ethiopia, showing how at 25-28°C, a burnable gas with more than 60% of methane, was obtained from cow dung and sheep manure after 20 days of retention, while pig substrate needed more time [59]. In northern Brazil, the biogas production per kilogram of goat manure was ca. 54 L/kg in a modified floating model with a volume of 11.3 m3 [60].

However, animal manure can make digestion slow because of its low content of carbohydrates [21], and it can generate a high concentration of ammonia, which is unfavorable for methanogens [61]. Mixing manure with other organic waste can create the optimum waste combination for the co-digestion process to improve the biomethane yield in terms of quality and quantity. Overall, the interaction within different waste streams directly determines the biogas yield [62]. In the co-digestion, the mixture of animal manure with an organic fraction rich in carbohydrates and low in ammonia has the remarkable ability to enhance biogas production. And vice versa, the agricultural residues with high VS, high fermentable constituents, and low moisture benefit from the co-digestion with animal manure or sludge due

#### *Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

to their high content of ammonia. Compared with reactors supplied with manure alone, the volumetric methane production can increase up to 65% in reactors fed with waste and 30% VS of crop residues such as straw, sugar beet tops, and grass [63]. Co-digestion showed promising results using several mixtures of food waste and dairy manure at 35°C; a manure/food waste ratio of 52/48% produced methane yields 311 L/kg VS after 30 days of co-digestion. In comparison to raw manure, food waste contained higher VS (ca. 241 g/kg) it means higher energy content, which is desirable with regards to biogas energy production [58].

According to the different methanogenic microorganism's growth temperatures, working temperature ranges can be defined as psychrophilic (under 25°C), mesophilic (30-40°C), and thermophilic (50-60°C). Anaerobic digestion is a process that is sensitive to temperature [64]. Because simple systems as those used in rural areas in developing countries work at ambient temperature, the HRT should be selected considering local temperature conditions to give bacteria adequate time to transform feedstock into biogas. Depending on the climatic condition, the HRT varies from 10 to over 100 days [65]. At high altitude as Peruvian Andes (psychrophilic conditions), HRT from 60 to 90 days is needed [66]. In such high-altitude and cold climates, the temperature fluctuation also represents a problem for biogas production. In Andean villages, the low-cost tubular digesters were adapted by substituting the roof with a greenhouse. However, it was not always successful in maintaining a digester slurry temperature higher than the ambient temperature [64].

On the other hand, positives results were obtained from the modification of a floating drum model in Indian villages located at an altitude of 1600 to 2200 m, where the diurnal temperature fluctuates from −8 to 35°C during a year. Such fluctuation results in the reduction of gas production during winter by 23–37%. An improvement of the insulation kept proper operating temperature. That was achieved by enfolding the system inside a greenhouse or using hollow bricks for the construction or placing straw insulation around the digester, or adding hot water in the input feedstock material. These modifications allowed a continuous biogas production around 1.6 to 2.6 m3 /day during the whole year [67]. Solar-biogas hybrid systems where a solar collector provided the heating have been proposed for maintaining the right temperature for anaerobic bacteria to produce biogas [68].

In tropical regions with mesophilic conditions, the HRT may range from 20–60 days [19]. In Bangladesh, the rural dome-type digesters showed a retention time of about 40–50 days from a single feedstock such as cows' manure [29]. In Nigeria, the total biogas produced from poultry and cassava wastes was 1.5 m3 after 42 days in a prototype polyethylene system of 1 m3 at the ambient temperature of 33.6°C [69].

It is important to retain that while the temperature will affect the biogas, the feedstock security (or availability) influences the operation of the system [70]. For fueling a household stove twice per day in a family of five persons, it is required manure from one pig, five cows, or 130 chickens to have approximately 1.5 m3 of biogas [6]. Gathering sufficient water and manure are among the limiting factors; in many parts of Sub-Saharan Africa, although the households possess adequate livestock, the grazing nature (nomadic, semi-nomadic, or free) may impede to gather manure to feed the biogas digesters [71]. A digester volume of 1.3 m3 /capita requires approximately 0.05 m3 /day of water for each cow and 0.01 m3 /day for each pig supplying manure to the digester. Such an amount of water can hardly be provided in areas of low water availability. In sub-Saharan countries, the water needed for digestion can be provided using recycled waters (gray water), such as domestic water, rainwater harvesting and aquaculture [72].

All rural small-scale and household digesters models require daily operation and maintenance. Everyday operations include the feeding, the handling of digestate, and the control of biogas outflow. Both brick and plastic tubular digesters are supplied with organic waste diluted with water in different proportions. The most challenging maintenance for the users comprises removing sludge from the digester, blocking possible cracks in the fixed digesters, and repairing damages in plastic systems [19]. Because installed digesters' functionality depends on continuous management and supervision of operation and maintenance, specific programs are often put in place to develop ownership and participation in using the biogas systems [73]. Sensitivity analyses demonstrated that small-sized digesters are more environmentally sustainable, if biogas leakage and release are avoided [51].

#### **9. The relevance of small-scale biogas systems to regional development of rural areas in developing countries**

The literature study discloses how small-scale biogas systems benefit the local family, village, and surrounding communities in rural areas in developing countries. Anaerobic digestion, even at the small-scale, represents an efficient waste treatment, and it offers a source of clean energy (biogas) suitable for cooking, heating, electricity generation, and a digestate with a high fertilizer value. It is a widespread opinion that anaerobic digestion implemented in poor rural areas may help in achieving several Sustainable Development Goals (SDGs), positive health impacts and sanitization, preservation of soil and water [74], reduction of greenhouses gas (GHG) emissions, gender empowerment and education [75], and accessible and affordable source of clean energy [76].

The use of biodigesters to treat human sludge and animal manure significantly improves the hygiene situation of rural areas that lack adequate infrastructure to collect and treat wastewater, unmanaged human and animal waste. The use of biodigesters can reduce infectious diseases such as diarrhea, cholera, and tuberculosis. Biodigesters also reduce the environmental impact (ecological, health, esthetic) of the spreading of waste in rural areas and reduce sewage danger percolating into the groundwater sources pumped for drinking water. Moreover, it contributes to the reduction of GHG emissions. It was calculated that processing the liquid and solid manure through anaerobic digestion reduces the potential impact from 4.4 kg carbon dioxide (CO2) equivalents to 3.2 kg CO2 equivalents if compared with traditional manure management [77].

Biodigesters represent a great alternative to the inefficient use of traditional biomass such as fuelwood, agricultural residues, and dried dung. Rural areas worldwide suffer from the loss of forest lands due to the illegal collection of firewood. The installation of biodigesters and the use of biogas can provide a substitute for firewood and save forests. Also, fuel oil and kerosene are widely used in rural areas for cooking and lighting purposes, especially in developing countries. Biogas is an excellent replacement for these fossil fuels and can save people hundreds of dollars every year. Besides that, countries with large amounts of rural areas are usually poor and oil-importing countries. The use of biogas can save those countries millions of dollars every year.

The use of biogas as a clean source of energy for cooking also includes important health benefits. It reduces exposure to indoor smoke and soot, reduces respiratory and eye diseases, reduces fatalities caused by carbon monoxide poisoning and offers a significant reduction of the RSPM in indoor environments.

Biogas use has many positive social outcomes on education and gender equality, and it generates employment opportunities for rural communities. The lack of enough lighting in rural areas in developing countries prevents students of all ages *Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

from having enough light to study or even be involved in any educational activities in the evenings. Biogas in gas lamps provide enough fuel for lighting and provide more study hours in the dark [78]. Moreover, in such poor areas, women are in charge of securing water and energy [67, 75, 79]. Having a biodigester at home will save women tens of hours of collecting firewood. This time can be used by women for other activities such as education and socializing. Also, burning biogas does not generate any particulate matter or soot that pollutes the houses, saving women cleaning time [21, 78]. Moreover, an increase in employment in rural areas was recognized as the positive impact of small-scale biogas installations. These news opportunities mainly involved women and professionals in education, environment, agriculture, and technical professions related to the building and maintenance of the systems.

The use of biodigesters reduces the use of chemical fertilizers. Along with the biogas, biodigester produces organic fertilizer rich in nutrients, such as nitrogen, potassium, and phosphorus. This organic fertilizer can replace commercial fertilizers and save farmers in rural areas thousands of dollars every year. Also, this liquid fertilizer can keep the use of water for irrigation. Thus, biodigesters maximize the valuable fertilizing properties of the recycled waste for agriculture; this benefit will lead and promote the local family's economic advancement.

#### **10. Biogas serves to reduce energy poverty in developing countries**

In some countries, rural people do not even have access to fossil oil and kerosene because of their price or shortage; those people are forced to meet their energy needs using traditional and inefficient resources. As described, such practices represent significant health, environmental, economic, and social issues for those communities. Within the context of sustainable development, nowadays, it is imperative to offer these disfavored regions access to clean, affordable, and renewable energy. Assisting people to transform the animal manure, crop residues, domestic waste into a more efficient energy carrier, such as biogas, provide clean and reliable energy, and conserve the local and global environment [21]. It is evident how biogas' decentralized production gives several opportunities for accelerating the transition to sustainable development and the circular economy with positive economic effects at the local-level livelihood [80]. Biogas is an energy source useful for people to meet their energy needs without using fossil fuel [8].

In Northern Brazil, a biogas volume of 1 m3 from manure was equal to 0.75 L of gasoline [60]. Small-scale biodigesters produce around 2–4 m3 /day biogas, sufficient to meet the cooking lighting needs of a family [62]. The biogas potential in Colombia showed that 80% of propane, which is used the traditional fuel, could be replaced by biogas; results showed that a low-cost tubular digester in polyethylene with a total volume of 9.5 m3 and feed with cattle produces enough biogas to supply cooking of five hours/day for five people [81]. In India, positive achievements were obtained using different design models simultaneously; it was possible to produce approximately 40.5 m3 biogas/day and supply the community of 48 households that had cooking needs of 0.85 m3 /day each [82]. In Bangladesh, about eight head of cattle per household were needed to cover the need for cooking gas, electricity, and drinking water [83]. In Nepal, 0.33 m3 of biogas fulfills the energy needs per capita per day [84]. In Israel, post-nomadic Bedouins families adopted a system of 7.5 m3 fueled with goat manure and straw that provided biogas for cooking and for powering a little refrigerator [85]. In Bali approximately 30 m3 biogas/month using cow manure can supply the energy need of a 5–6 people family size [86].

Small-size biogas technology embodies the opportunity to address the energy access issue for low-income developing countries [87]. Biogas digesters may reduce energy poverty [35, 88], and they provide clean energy for cooking and lighting for rural areas where energy infrastructures are missing [39]**.**

#### **11. Challenges of biogas systems in rural areas for communities in developing countries**

Despite all of the benefits biodigesters have for rural communities, some biogas systems in rural areas do not meet the expectations due to technology, maintenance, and technical support. All those aspects induce a discontinuity of digester operation as documented for China, in the Guizhou Province, 62.03% of household biogas were continuously operating while 36.72% were discontinued [89]. In some other cases, the challenges represent the reasons for technology's abandonment [90]. This section summarizes the challenges biogas systems are facing in rural areas.

In cold rural areas, biogas system owners lack the right technology to maintain the thermal conditions for a high rate of biogas production [57]. The people in these areas face this challenge, especially in winters where energy need is higher than in other seasons. As described above, the household biogas digesters are made of bricks or concrete and built just under the ground surface where the digesters' temperature is very close to the ambient temperatures. Thus, without appropriate heating or hybrid technologies, the household biodigesters' efficiency remains low and unstable under these conditions. Design solutions have been developed to maintain the right temperature for biogas production, such as insulating the digesters or combining with other heating technology (i.e., solar water heaters). However, these solutions may cause a burden for people in rural areas.

The lack of technical knowledge and building capacity in rural areas is another critical factor that leads to low biogas production rates. People in rural areas lack access to formal education, awareness of environmental issues, agricultural techniques, and appropriate knowledge on how to run the biodigesters. In some countries, farmers get governmental financial supports to construct biogas systems. In many cases, this governmental support is not accompanied by technical support and safety measures to adequately manage the biodigesters [21, 26, 78, 91]. Also, the lack of knowledge about the ratio between the size of the biodigester and the volume of organic waste can lead to low biogas production rates and digestate pollution near the biodigester. That may cause odor emissions, eutrophication of surface water, and pollution of groundwater. As described below, only a rational design of the small-scale system, along with a proper build, continuous cleaning, and maintenance, affects the productivity and the environmental footprint of the system [51].

In general, rural areas are located in remote zones where it is difficult to reach and run educational programs and maintenance. Also, the lack of governmental follow-up and capacity building programs leads to poor maintenance and operation of the biogas plants.

The inadequate use of liquid fertilizer may attract flies and mosquitoes to the biodigester and cause a challenge for the biodigester users. Also, this may create adverse publicity of biogas plants among people.

Low or discontinuous biogas production due to improper operation of the biodigester, technical barriers, lack of feedstock (animal manure or food waste), and low level of awareness may lead to an inadequate supply of biogas. Thus, people in rural areas are discouraged from using the biodigesters on a daily or seasonal basis. It may lead to low adoption rates in rural areas and force people to switch to more reliable fuel sources.

*Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

#### **12. Conclusion**

The chapter presents the effective implementation of small biogas digesters in rural areas in developing countries. Small Biogas digesters represent a tool to achieve rural areas' sustainable development, giving access to clean and affordable renewable energy. The use of biodigesters in poor rural areas serves as an environmentally friendly way to reduce fossil fuels and traditional biomass and reduce indoor and outdoor air pollution. Also, the use of biogas can significantly reduce organic waste in poor rural areas. Design, construction materials, feedstock operational modes vary accordingly with the geographical location of biogas installation. The systems installed in rural areas are simple and mainly for domestic uses. The biogas yield can be controlled and increased by controlling the retention time and modulating feedstock composition in a co-digestion process using manure and other organic waste. Despite the potential and the wide range of benefits that rural areas can acquire from the small-biogas digesters, several potential problems limit the diffusion of small-scale anaerobic digesters in rural areas in developing countries. They include the lack of construction and maintenance skills, awareness of users, and the inadequacy of design to meet the actual biogas (energy) need. For biogas systems to succeed and be used in rural areas worldwide, governments should strengthen current policies and develop new policies and regulations to motivate people in rural areas to install biodigesters. These policies should focus on the comprehensive sustainability of the biogas systems. The policies should include incentives and procedures for constructing the biogas digesters and comprise tools to support the systems' management.

#### **Acknowledgements**

The authors wish to thank Dr. Shikun Cheng for the kind permission to use prefabricated biodigesters photos.

#### **Conflict of interest**

The authors declare no conflict of interest.

*Anaerobic Digestion in Built Environments*

### **Author details**

Martina Pilloni1 \* and Tareq Abu Hamed2,3

1 University of Cagliari, Cagliari, Italy

2 Arava Institute for Environmental Studies, Kibbutz Ketura, Israel

3 Dead Sea and Arava Science Center, Israel

\*Address all correspondence to: martina.pilloni@gmail.com

© 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.

*Small-Size Biogas Technology Applications for Rural Areas in the Context of Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.96857*

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#### **Chapter 5**

## Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation for Biogas Production

*Godwin Glivin, Mariappan Vairavan, Premalatha Manickam and Joseph Sekhar Santhappan*

### **Abstract**

Environmental effects from traditional energy sources and government regulations, necessitate the use of alternative energies like biogas for many uses including drying and refrigeration. Biowaste produced in educational institutions will not be uniform over the year. The non-uniform supply of biowastes, the absence of studies on bio digestion of likelihood biomass, the unreliability of energy from such conversion and the profitability of its usage in most applications are some of the factors to be considered while implementing this technology. In this regard, theoretical and experimental evaluations were carried out to accurately forecast biogas generation capabilities in educational campuses for obtaining biofuels with quantity and efficiency. It is observed that biogas generation with 52 to 58% methane content can be possible during an academic year. The quality of biogas shows that it is appropriate for almost any application. A broader analysis on different types of biogas digesters was conducted for their suitability in academic institutions. The economic benefits are analyzed for incorporating three biogas digesters namely KVIC, Fiber Reinforced Plastic (FRP) type and JANATA. There are some encouraging results to confirm the economic feasibility of biogas plants including positive net present value. Biogas generation with digesters of capacities varying between 25 and 450 cubic meter shows payback periods varies from 3.18 to 7.59 years, which confirms that it is profitable to use digesters in this range of capacities.

**Keywords:** biogas, biodigester types, economic analysis, payback period, non-uniform loading rates

#### **1. Introduction**

#### **1.1 Renewable energy: current scenario**

The environmental factors and depletion of conventional energy sources create a huge demand for technologies to substitute conventional fuels. Renewable Energy Sources (RES) such as solar, wind, tidal and biomass are available abundantly and they can be harvested without environmental degradation. The International Energy Outlook (IEO) states that the global primary energy demand will increase to 48% between 2012 and 2040 [1]. The share of non-renewable energy (liquid fuels, coal, natural gas and nuclear) will decrease from 91% in 1990 to 84% in 2040. However, renewable energy sources will continue to grow and catering from 9% of the world's energy demand to 16%. The share of primary energy sources in the world's energy generation also points a decrease in the non-renewable energy's share in electricity generation from 78–71% in 2040.

The growth of installed capacity of renewable energy sources in India shows that the country had gone up from 7.8% in 2008 to 15.9% in 2016 with the generation mix of wind power (57%), solar power (18%), biomass (15%), small hydro (9%) and waste to energy (1%). Waste to energy is one of the new classifications among the energy mixes in the country. Among the various renewable energy conversion technologies, biochemical conversion is one of the best techniques to convert biowaste to useful form of energy (biogas). This low-cost technology can convert any organic wastes to biogas which can be further used as a fuel for cooking, lighting, power generation, etc. Anaerobic Digestion (AD) is one of the RES conversion processes which is capable of handling 90% of moisture content [2]. The end product of the AD is biogas which is comprised mainly with CH4 and CO2. CH4 is the combustible gas with an energy content of 50 5 MJ/kg which can be utilized for heating, power generation and other applications related with gaseous fuel [3].

The AD process involves four steps (hydrolysis, acidogenesis, acetogenesis and methanogenesis) which is effected by methanogens such as hydrogenotrophic and acidogenic [4]. The organic content consists of various particulate as well as water insoluble polymers, hence the polymers are not accessible for the microorganisms directly [5, 6]. During the first step i.e., hydrolysis the insoluble polymers break down to soluble oligomer and monomer. This is caused by the strains of hydrolytic bacteria which releases hydrolytic enzymes [7]. Carbohydrates, lipids, and proteins are converted to sugars, long-chain fatty acids, and amino acids. In the next step i.e., acidogenesis the soluble molecules are converted to C02 and H2 along with acetic acid, propionic acid, ethanol, and alcohols. Other acids which are produced apart from acetic acid, propionic acid, ethanol are due to *Actinomyces, Peptostreptococcus anaerobius, Clostridium* and *Lactobacillus* respectively [8]. With the support of proton reducing agent the long volatile fatty acids as well as alcohols will oxidize to acetic acid and H2 during acetogenesis (third step) [9]. During the last stage (methanogenesis) methanogens are generated namely *hydrogenotrophic* and *acetoclastic* [10, 11]. This is caused by the reduction of CO2 to H2 as well as scrubbing of sliced acetic acid which is formed in the third stage. The biochemical conversion process involved in the AD is shown in **Figure 1**.

#### **1.2 Biogas production and utilization**

The data obtained from the year-wise installed capacity in MW of bio-power energy sources for power generation in India reveals that the installed capacity of bio-power energy sources has been on the increase every year and the same can be utilized for about 70% of the rural basic energy needs in India [12]. Bio-power produced by thermochemical (biomass gasification) and biochemical (biogas) conversion techniques contributes significantly to India's rural energy supply. According to a 2012 World Bank report, waste is classified as organic, paper, plastic, bottles, metals, among others. For most solid waste preparation purposes, these six categories are normally appropriate. Studies in the field of biowaste utilization in Europe showed high initial cost for the implementation; however, such cost could be reduced by intensive research on process integration and intensification. The ministry of MNRE, India has set a target of 10 GW of bio-power capacity by 2022 [13]. A huge potential is observed for employing anaerobic digestion as waste

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

**Figure 1.** *Anaerobic digestion process.*

management method and energy production technology in India and the rest of the world [14].

Realizing the potential of biogas as future energy source, many studies were conducted on biogas generation, utilization, and applications. The canteen and mess wastes which are rich in organic content could be used effectively for waste utilization and energy generation. The series of experiments conducted by varying HRT and OLR showed that with at Hydraulic Retention Time (HRT) of 20 days and 100 kg TS m3 d<sup>1</sup> , the methane content of 50% with 0.981m<sup>3</sup> kg<sup>1</sup> VS could be achieved [15]. A test conducted with mesophilic tubular digester for generation of biogas showed that fruits and vegetable wastes were used as feedstock. Variations in HRT and feed concentration were used to assess the digester's efficiency. With a feed concentration of 6% TS and a 20-day HRT, the digester's efficiency was found to be the highest [16]. An experiment was conducted with pig manure in Anaerobic Batch Reactor (ABR) for hydrogen generation in two stages for pH values 5.0, 5.5 and 6.0. The OLR was taken as 96.4, 48.2 and 32.1 kg VS m<sup>3</sup> d<sup>1</sup> whereas HRT was maintained as 12, 24 and 36 h. It was noted that at 12 h HRT and 96.2 kg VS m<sup>3</sup> d<sup>1</sup> OLR, the hydrogen concentration was at the maximum [17].

An analysis was carried out to check the stability and performance of anaerobic digestion with varying HRT and OLR. The analysis showed a decrease in methane yield with the increase in OLR as well as a decrease in HRT for low OLR

(0.1 g VS<sup>1</sup> d<sup>1</sup> ). At high HRT (25 days), the methane yield was maximum [18]. Codigestion of food waste and fruit-vegetable waste was performed in single-phase and two-phase digesters. By varying the OLR, authors concluded that single-phase digester could produce more methane than two-phase for low OLR [19]. According to reports, co-digesting food waste with cattle manure will boost biogas production and methane yield [20]. The performance of biodigesters under overload conditions was evaluated based on two case studies. To study the interrelation between biomass population dynamics and digester stability, Anaerobic Digestion Model 1 (ADM1) was utilized. The study showed that the digester did not function in high OLR conditions [21]. The techno- economic study of a combined bioprocess, based on solid state fermentation for fermented hydrogen generation from food waste was conducted. The outcome shows that five years Pay Back Period (PBP), 26.75 percent Return on Investment (ROI) and 24.07 percent and Internal Rate of Return (IRR) respectively could be possible [22].

#### **1.3 Scope and aims of the work**

Many studies reported the production and utilization of biogas for various applications. In most of them, technical and economic viability of biogas plants for the utilization of biogas in various applications was studied for a stable organic loading in biodigesters. Despite the high potential for biogas use in educational facilities, only a few studies have been conducted to determine the technoeconomic feasibility of using biogas technology in this field [23–25]. This is mainly due to the variation of student and staff population throughout a year, and the nonuniform generation of organic waste. Furthermore, in order to improve the accuracy of the forecast, the quality and quantity of biogas produced from various biowastes available in this area must be investigated. Hence, this current research focuses on predicting technological and economic influences, as well as their effect on the deployment of biogas plants in a few educational institutions in India's southern region. The following objectives have been established to scientifically research the feasibility of using biowastes available in educational institutions in the selected area, as well as to determine the effect of non-uniform loading on digester's efficiency and economic viability.


#### **2. Methodology**

#### **2.1 Grouping of biowastes and selection of biogas plants**

Anaerobic digestion based waste management technology has an enormous significance in India because of the vital role of waste disposal methods as well as its role as a renewable energy source for cooking, lighting, electricity generation, and so on [26]. The anaerobic digestion process utilizes a variety of biowastes from various sources including municipal solid waste, households, institutions, and industry. The generation of biogas from anaerobic digestion of biowaste in

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

educational institutions is projected to play a significant role in ensuring rural and urban prosperity [27]. As a result, institutions in and around the southern part of India were chosen for this research, where biogas will substitute 35 percent to 40 percent of the traditional fuel used for cooking. The institutions in this region were categorized based on the student population, and the potential of biowastes and their availability throughout a year were studied. The strategy followed to select the biowaste and the digestion systems has been shown in **Figure 2**.

#### **2.2 Categorization of institutions**

More accurate research is possible in educational institutions because the large number of students living in the campus offers numerous opportunities for biogas production. Based on the population of students and staff, the institutes situated in southern part of India (the region selected for this study) were categorized as A, B, C, D and E as mentioned in **Table 1**. The population details were collected based on the published data of the respective institution.

**Figure 2.**

*Flow chart for the procedure involved in the grouping of biowastes and the selection of biogas plants.*


**Table 1.**

*The various categories of institutions according to population range.*

#### **2.3 Selection of biowastes for this study**

A survey was conducted with the required questionnaire to select the biowaste samples. Biowaste details such as amount, consistency, and varieties were discovered through the survey. The type of institution, academic schedule, population of students and staff living on and off campus, biowaste generation sources, conventional cooking fuel, and other relevant factors dominated questionnaire's development. Personal information of people was also included. The data reliability was verified with relevant authorities.

#### *2.3.1 Potential of biowaste sources*

Sewage sludge (SS), food waste (FW), leaves, cotton waste, paper waste, and other biogas energy sources have been reported. **Table 2** shows the estimated data of a sample.

On a regular basis for different academic schedules, a survey on food waste supply in a group 'A' institution was performed. This research looked at the most traditional food menu trends used by different institutions. Food wastes produced before and after cooking were also taken into account. **Table 3** shows the specification of category 'A' institution.

**Table 4** shows the common biowastes and the percentage of biowaste generated in a category 'A' institution. The samples were collected in the hostels before dumping. Separate buckets were kept for collecting the different food wastes. The students and staff members were instructed to dump the leftover food accordingly. It was observed that the availability of some wastes like fruit waste, meat waste and fish waste was low but their quantity in total waste had been checked at least twice a


#### **Table 2.**

*The data grouped for a category 'A' institution.*

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*


**Table 3.**

*The data grouped for a sample category 'A' institution.*


#### **Table 4.**

*Sample data for biowastes generated in a category 'A' institution on 100th day.*

month to find any major deviation. The observation showed that the variation was not significant. Hence such wastes were added along with mixed rice waste.

Among the numerous biowastes generated in the study area, Rice Waste (RW), Mixed Rice Waste (MRW), and Vegetable Waste (VW) were some of the potential biowastes available. Therefore, they were selected for the anaerobic digestion. Meat, fish, potato, and rice wastes, left out after consuming were used in MRW. **Table 5** shows the grouped-biowastes used as feedstock for biogas generation. Other biowastes, apart from VW and RW, were mixed with MRW due to insufficient availability.

#### **2.4 Measurement of biowaste properties**

The important parameters which control biogas generation are pH, VS and TS, therefore these properties were experimentally measured as per the standard procedure discussed below [28].


**Table 5.** *Biowastes grouping for category 'a' institution.*

#### *2.4.1 Total solids*

The following technique was used to assess the feed's TS according to APHA guidelines [28]. 50 g of each biomass was placed in pre-weighed porcelain vessels and heated at 60°C for 24 hours and then at 103°C for 3 hours in a hot air oven. The weight of the dry samples, as well as the container, was determined in a weighing balance with a precision of 0.001 g. A sample's TS percentage was determined as follows:

$$\text{TS} = \left(\frac{\text{W}\_d}{\text{W}\_\text{w}}\right) \cdot \mathbf{100} \tag{1}$$

The dry and wet sample weights are Wd and Ww, respectively.

#### *2.4.2 Volatile solids*

The standard formula for determining the VS of feed materials was used. The oven-dried samples were dried at 550°C � 50°C and ignited fully inside the muffle furnace. The desiccator's cooled samples were measured, and VS was determined using the Eq. (2).

$$\text{VS} = \left[\frac{(W\_d - W\_d)}{W\_d}\right].\text{100}$$

where Wd is the dry sample weight, and Wa is the dry ash weight.

#### *2.4.3 pH*

The pH of biowastes Cow Dung (CD), RW, MRW, and VW was measured at least once in a day using a pH electrode with 0.05 percent accuracy. The samples were taken from the slurry until where it was fed to the digesters. A pH electrode dipped in the inoculum was used to test pH of digesters on daily basis. **Table 6** shows chemical properties of the four types of biowastes used in this study. Eqs. (1) and (2) were used to measure the values of TS and VS. The validity of experiments was verified after the findings were compared to literature.

#### **2.5 Biogas plants commonly used in India**

In India, more than seven models of biogas plants are available and they are being used in various parts of the country according to the requirement of a particular area [35]. This study examines the feasibility of applying appropriate model in educational institutions from Khadi and Village Industries Commission (KVIC),


**Table 6.** *Characterization of feedstock.* *Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

JANATA, and Fiber-Glass Reinforced Polyester (FRP) [36]. These three models were selected based on the ease in construction as well as operation compared with other models. The selection of biogas plant model varies for all institutions based on the nature and activities of the students. For selected category of institutions these three models were considered.

#### *2.5.1 Biogas Plant: Khadi and Village Industries Commission*

This type of biogas plants consists of a floating drum made of steel, fiber glass reinforced polyester or high-density polyethylene. Its underground digester tank is made of bricks and cement as shown in **Figure 3**. The floating drum which moves up and down according to the biogas generation serves as the gas holder. The major disadvantage of these models is high maintenance due to corrosion of drum which leads to regular coatings. The rainwater should be prevented from entering the tank as it corrodes the steel. The advantage is seen when the same model floating drum is made of fiber glass reinforced polyester or high-density polyethylene, it can work efficiently without affecting the digestion process but it makes the biogas plant more expensive. The life of the plant is found to be 15 years [37].

#### *2.5.2 Biogas plant: JANATA*

The fixed dome instead of the floating drum, as seen in **Figure 4**, distinguishes this from KVIC model. Initial cost of dome is lower than that of KVIC model since it is constructed by bricks, blocks, and cement. The major disadvantage of this model is making a gas tight dome because in such models, leaks are observed in the cracks formed in the dome due to poor construction. Thus, this type of biogas plants required skilled supervisors and labourers for construction. This kind of small-scale biogas plant has a lower cost, making it a good choice for institutions in categories A, B, and C. A long life of 20 years or more can be expected due to non-corrosive parts used in construction [37]. Compared with other two models, this model has the largest life span.

#### *2.5.3 Biogas plant: fiber-glass reinforced polyester*

The FRP model biogas plants as shown in **Figure 5** are most used in household applications in both rural and semi-urban parts of India. FRP is used in the

**Figure 3.** *Biogas plant with floating-drum and cylindrical digester (KVIC model).*

**Figure 4.**

*Brick-reinforced fixed-dome biogas plant (JANATA model).*

#### **Figure 5.**

*Biogas plant with floating drum made by fiberglass reinforced polyester.*

construction of digester tank, floating drum, and water jacket. PVC pipes are used for inlet and outlet pipes, and the central guide pipe is made of GS. Unlike other models, these biogas plants are placed above earth due to smaller in size. The maximum size of this type of biogas plants is limited to 1 to 12 m<sup>3</sup> . The FRP model biogas plants are portable and can be easily maintained. The investment cost is less, and such models are more attractive for small scale applications. The space occupied by this model is one of the disadvantages compared with other two models. An average of 10 year life span has been reported for this model [23].

#### **2.6 Mathematical modeling**

Educational institution is a place where the generation of biowaste is high during academic schedule whereas low in non-academic schedules. This non-uniformity in biowaste availability affects the loading rate which results in reduced methanogens activity. Hence, by understanding the performance of digesters with available

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

biowastes throughout a year, the minimum and maximum production of biogas in various academic schedules can be predicted. Further, it can be used to design the capacity of a biogas plant toward efficiently manage the variations in daily yield. As part of a theoretical simulation, a study was conducted to predict biodigesters' efficiency and their effect on non-uniform loading. The equations that state the mathematical representation of biochemical reactions are used for the analysis in Anaerobic Digestion Model 1 (ADM1). Therefore, ADM1 toolbox was adopted to represent the complete metabolic network of an anaerobic digestion [11]. This toolbox aids in determining the system's operational conditions as well as its behaviour. Moreover, it could help in the design of biogas plants of large scale.

The various steps used for the simulation are depicted in **Figure 6**. The simulation process starts with the selection of biowastes for anaerobic digestion. The properties such as pH, TS, VS, and moisture content (MC) of biowaste were studied through APHA procedures and taken as input parameters [38, 39]. The temperature levels, digester tank scale, and simulation phase were chosen from the respective inbuilt parameter control menus. Then the simulation was carried out in steps of a day, and the quality and quantity of the biowaste were measured. If the measured quality of methane was less than 50% the biowaste was rejected and a new one was selected for the simulation.

#### **2.7 Experimental setup**

**Figure 7** shows a schematic diagram of the experimental system included in the analysis. It holds a digester tank which is surrounded by a water jacket. The floating drum, known as gas holder, is fixed in such a way that it can move up and down based on the generation of biogas. The water jacket holds the floating drum and prevents the

**Figure 6.** *Flow chart of the simulation procedure.*

#### **Figure 7.** *Schematic diagram of the experimental setup.*

leakage of biogas and odor of inoculum. A stainless-steel central guide is mounted in the centre of the digester tank to ensure smooth flow of the floating drum. To load biowaste and drain digestate, inlet and outlet pipes are provided appropriately. Drainpipes are also provided to clean the digester tank and water jacket. Suitable arrangement is made in the floating drum to transfer the biogas for any application.

To calculate the quantity and consistency of the biogas, a thermal gas flow metre (mass flow measurements of liquids) with a 0.5 percent Full Scale (F.S) accuracy and a multi gas analyzer (NUCON) with 0.3 percent accuracy are attached in the gas line. A pH electrode and temperature sensors are dipped inside the inoculum. The manifold connects all the digesters with the instrumentation panel.

#### *2.7.1 Experimental procedure*

Initially Cow Dung (CD) was filled in all the four digesters for the generation of methanogens with an HRT of 55 days. After confirming the complete digestion of CD, the required quantity of biowastes collected from the educational institution of category A was loaded for 30 days with the same quantity per day. The quality and quantity of methane generated per day was measured using the multi gas analyzer and thermal gas flow meter. The pH and temperature of the feedstock during digestion process were also measured at regular intervals and their averages were calculated. During this trial study, the temperature was observed between 29–34°C. **Figure 8** depicts a photographic image of the digesters used in the experimental setup as mentioned in **Table 7**.

After the trial study the same digesters were used for the pilot study for 365 days. However, the loading was varied according to the non-uniformity in the availability of biowastes. Since the total quantity of biowastes generated inside the campuses cannot be digested completely with the small digesters, only 10% of each type of waste was taken every day and the same was used for loading the digester. Thus, the impact of non-uniform generation of biogas was incorporated in the pilot study. The results were used in the prediction of quality and quantity of biogas generated for the proposed systems.

#### **2.8 Economic study**

The economic feasibility of a biogas plant for non-uniform loading is also important to confirm the selection of any type. As a result, the economic study was *Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

**Figure 8.** *Experimental setup of different capacity biogas digesters.*


#### **Table 7.** *Summary of the experimental design.*

done using Capital Cost (CC), Annual Operating Cost (AOC), Payback Period (PBP), Net Present Value (NPV), and Life Cycle Cost (LCC). For this study, standard equations from previous studies have been chosen [37, 40]. Based on the pilot study performed in category 'A' institution, the biogas produced per person per day was determined and found vary from 0.014 to 0.019 m<sup>3</sup> . A mean value of 0.015 m<sup>3</sup> per person was taken into consideration. Methane content was found as 53%. The capacity of the biogas plant for each category was calculated using the mean value. The quality and quantity of biogas generated over the course of a year were also determined using primary data.

The biogas plant's volume (size) for an institution is determined by the availability of biowaste and the biogas yield from it. Using data from a pilot study conducted in category "A" institution, the supply of biowaste in the other categories of institutions over the span of a year was calculated and plotted in **Figure 9**. It is observed that the capacity of the biogas plant for each category varies between 25 m<sup>3</sup> and 450 m3. The calculations were carryout based on the average values taken from the population range as mentioned in **Table 1**. Hence, different types of biogas plants are required for each institution based on certain parameters such as geographical location, climatic condition, transportation and so on. Hence, the specifics of the different biogas plants available in India were investigated.

#### *2.8.1 Selection of biogas plants in an economic analysis*

The three types of biogas plants namely KVIC, JANATA and FRP were considered in this economic analysis. These models were selected based on the geographic

**Figure 9.** *Estimation of the biowaste availability for all categories.*

location and the capacity of waste in an institution. Because of the simplicity of design and construction, KVIC models are the best choice for higher capacity biogas plants. The KVIC model plants suffer from a disadvantage in hilly areas because of the rusting in floating drum according to various climatic changes. JANATA model biogas plants, on the other hand, which are entirely made of bricks, resist rusting and are thus strongly recommended. Due to portability feature, FRP models are highly suggested for less capacity requirement. The initial investment is one of the major concerns for these types of biogas plants. Due to such concerns, the various economic factors are studied and discussed below.

#### *2.8.1.1 Capital cost*

The cost of the digester, construction costs, and government subsidies are all included in the CC of the Biogas Plant (BGP). Eq. (3) is used to calculate the capital expenditure.

Capital Cost ¼ Cost of the biogas plant þ Installation cost of biogas plant (3)

#### *2.8.1.2 Running cost*

The operating and repair costs as well as the annual depreciation value, contributes to the plant's running expense. The cost of maintenance is estimated to be 2% of the plant's capital cost. (Jatinder & Sarbjit, 2004). For KVIC, JANATA, and FRP models, the life span was assumed as15, 20, and 10 years, respectively. The measurements are dependent on a handling fee of Rs 0.40 per kg for biowaste, which covers shipping and labour costs.

Running Cost ¼ Cost of the biowaste used þ cost of maintenance and operation of biogas plant þ cost of manpower*=*labour þ transportation charge þ depreciation value (4)

#### *2.8.1.3 Payback period*

The economics of a biogas plant includes the calculation of the payback period to substitute the LPG cooking stoves with biogas-based cooking stoves. It has been calculated as

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

$$Payback\ period = \frac{\text{Cost of Intallation}}{\text{Annual Profit}} \tag{5}$$

Where, Annual profit is the difference between the annual income and the annual operational cost of the BGP.

#### *2.8.1.4 Net present value*

The present value of a system's spending and operating costs over its lifespan is known as the net present value (NPV). NPV is one of the main economic factors for comparing the energy conversion systems. The difference between the present value of the benefits and the costs resulting from an investment is the net present value of the investment. It is calculated by,

$$NPV = \left[ \text{S.} \left( \frac{(\mathbf{1} + i)^n - \mathbf{1}}{i(\mathbf{1} + i)^n} \right) \right] - \text{CC} \tag{6}$$

Where, 'S' - benefits at the end of the period, CC - initial capital investment, i annual interest rate (12%).

The below are the approval conditions for an investment project as determined by the NPV method:


#### *2.8.1.5 Life cycle cost*

Another significant economic metric is the system's LCC, which accounts for all expenses involved with the system over its lifetime by considering the worth of money. The Life Cycle Cost Analysis (LCCA), which considers the initial costs, operation costs, repair costs, replacement costs, and salvage prices, is a valuable method for determining whether the selected biogas plants could be installed in educational institutions. A life cycle of 15, 20 and 10 years were assumed in calculating the Present Worth Cost (PWC) of KVIC, JANATA and FRP biogas plants [41].

$$\text{LCC} = \text{Initial costs} + \text{POC} + \text{PMC} + \text{PRE} + \text{PSV} \tag{7}$$

where, POC – present worth cost of the operating cost. PMC– present worth cost of the maintenance cost. PRE– present worth cost of the replacement cost. PSV– present worth cost of the salvage value.


**Table 8.**

*The relations used to calculate selected economic parameters.*


**Table 9.**

*Economic parameters for the analysis.*

**Tables 8** and **9** lists the several parameters that are incorporated in the economic analysis.

#### **3. Results and discussion**

#### **3.1 Pilot study: influence of non-uniform loading rate**

The non-uniform generation of biowaste in an educational institution for 365 days was studied to check the performance in terms of methane content and biogas yield. To understand the different academic schedules the study period has been divided into four phases as mentioned in **Table 10**.

According to academic schedules, the biowaste generation per day during maximum population was found as 70 kg, 280 kg, 120 kg and 80 kg for CD, MRW, RW and VW, and during minimum population it was 70 kg, 120 kg, 60 kg and 20 kg respectively. 10% of each biowaste was taken for the loading throughout a year as shown in **Figure 10**.

The biogas yield was observed for all the biowastes during different phases according to the loading pattern. To study the deviation of this biogas yield from uniform loading, a constant loading was assumed as shown in **Table 11** and the yield was predicted. The methane content obtained for both the uniform and nonuniform loadings of RW, MRW and VW is shown in **Figure 11(a)**-**(c)**. The figures show that the average methane content for simulation and experimental studies is 52% and 53% for RW, 55.69% and 54.85% for MRW and 52.28% and 53.26% for VW respectively.

#### **3.2 Biogas yield prediction for various categories**

The pilot study shows that the theoretical and experimental results are similar as shown in **Figure 12(a)**. Therefore, the current approach could be followed for


**Table 10.**

*Definition of phases according to academic schedule.*

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

#### **Figure 10.**

*Loading pattern of biowastes for 365 days.*


#### **Table 11.**

*Biogas yield during various phases according to academic schedules.*

forecasting the biogas yield for different loading rates as shown in **Figure 12(b)**. The yield for each category was determined by academic schedules and biowaste availability.

#### **3.3 Installation and annual operational costs for different biogas plant models**

The installation cost and AOC of KVIC, JANATA, and FRP model biogas plants are reviewed for different categories (A to E) as shown in **Figure 13**. The costs of construction, installation, annual service, and other costs are estimated based on the current market price prevailing in the southern part of India.

The Indian government offers subsidies for household digesters regardless of their use. Commercial digesters, on the other hand, are only eligible for subsidies if they are used for power generation. As a result, the subsidy is not considered in this research. The emphasis of the investigation is on the selection of an appropriate biogas plant for non-uniform loading, and its contribution to the reduction of LPG consumption. FRP model has the highest average cost per cubic metre, followed by KVIC and JANATA. The pattern is due to constraints in plant size (12 m<sup>3</sup> ) and the need for more units. The cost of the KVIC model is higher than JANATA model which may be due to the cost of gas holder. The cost of a gas holder in the KVIC model is high since the steel body needs frequent maintenance; besides, its susceptibility to corrosion. The investment cost is high even though the same gas holder is replaced with FRP. However, the cost of installation for KVIC model decreases steadily from category A to category E, whereas the cost of installation for JANATA

**Figure 11.**

*(a) Methane content in biogas for rice waste. (b) Methane content in biogas for mixed rice waste. (c) Methane content in biogas for vegetable waste.*

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

**Figure 12.** *(a) Biogas yield of pilot plant for 365 days. (b) 365-day biogas yield for categories A, B, C, D, and E.*

**Figure 13.** *Installation cost per cubic metre of various biogas plant models.*

model is almost same for both categories. **Figure 14** depicts the annual operating cost per cubic metre capacity of all biogas plants in each segment. The FRP model seems to have the highest operating costs, followed by KVIC and JANATA models. The running cost per cubic metre volume for both groups is almost the same for corresponding types and capacities.

#### **3.4 Payback period**

The payback period (PBP) of all digesters in various categories has been investigated and is depicted in **Figure 15**. The study reveals that as the volume of the biogas plant increases, PBP decreases, which is consistent with many research findings [45]. The FRP model demands the largest PBP for all categories ranging from 25 to 450 m<sup>3</sup> due to its high construction and operating costs. The KVIC models are well-known for being the most optimal for the production of biogas plants of any size. Though the JANATA style biogas plants are more difficult to build than the other two types, they are very feasible in educational institutions. The payback period for a system with non-uniform loading is 44 to 57 percent

**Figure 14.** *Annual operational cost per cubic metre of various biogas plant models.*

**Figure 15.** *Payback period for biogas plants for all categories.*

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

longer than for a system that is fully loaded during the year. As a result, if the design and development process is carried out by an expert, the installation of JANATA biogas digester in educational institutions is highly feasible.

#### **3.5 Net present value**

The net present value of installing biogas digesters in different types of institutions has been estimated and shown in **Figure 16**.

The NPV of an investment is the difference between the present value of the gains and the present value of the costs arising from the investment. The NPV increases as the scale of the biogas plants increases. The biogas plant project could be preferable for implementation in academic institutions based on NPV selection criteria. The results show that the uniformity in loading produces more useful data than non-uniform loading. However, non-uniform loading rate values indicate that those digesters could be effectively applied in institutions with differing academic schedules.

#### **3.6 Life cycle cost**

The most cost-effective solution among competing alternatives that are equally suitable for deployment on technical grounds is determined by a LCC study. As a result, the LCC for uniform and non-uniform loading rates was measured and plotted in **Figure 17**, demonstrating that the LCC of JANATA is the most preferred alternative when compared to the other two versions. However, according to the literature [46], KVIC is recommended because the design and development of larger JANATA model biogas plants is difficult.

#### **3.7 Cost per unit of electricity**

The various cost involved in the electricity generation from biowaste available in an educational institution and its equivalent quantity LPG were calculated per year and show in **Figure 18**. The cost of unit electricity was obtained from the following Eq. (8).

**Figure 16.** *Net present value of biogas plants for all categories.*

**Figure 17.** *Lifecycle cost for per cubic meter with uniform and non-uniform loading rates.*

**Figure 18.** *Comparison of unit cost of electricity from biogas, LPG and grid.*

Unit cost of electricity generated <sup>¼</sup> ð Þ *Investment cost* <sup>þ</sup> *maintenance cost per annum Total units generated per annum* (8)

#### **4. Conclusions**

The yield of biogas and the efficiency of its production from biowaste of educational institutions, such as rice waste, mixed rice waste, and vegetable waste, were investigated to determine the effect of nonuniform feeding of digesters on the technical and economic viability. As less than 5% of the experimental values were different from the expected content of CH4 in biogas, the proposed simulation method was found appropriate. Although the biowaste's pH before loading was less than 5, the inoculum's pH was 6.5 to 7.5; thus, the sufficient pH for optimum gas production could be preserved in this method. For all biowastes, the calculated parameters such as total solids, volatile solids and humidity were found within the

*Techno Economic Studies on the Effective Utilization of Non-Uniform Biowaste Generation… DOI: http://dx.doi.org/10.5772/intechopen.98314*

best suited range of anaerobic digestion. The biogas produced from all biowastes contained 52 to 58% methane which shows that biowastes generated in educational institution included in this study can be used for all types of applications such as electricity generation, lighting and cooling. The amount of biogas generation was affected by population; however, the content of methane in biogas was not affected. In an educational institution, the amount of biogas generated by person per day was 0.014 m<sup>3</sup> to 0.019 m<sup>3</sup> all year. The PBP was 50% higher for both models than that of uniform loading. For the installation in category A, B, C and D institutions based on the PBP, JANATA biogas plants is attractive. JANATA and KVIC are suggested for E group of institutions. The optimistic NPV for the three models and the five separate biogas plant capacities indicates the economic viability of all the designs.

#### **Author details**

Godwin Glivin<sup>1</sup> \*, Mariappan Vairavan<sup>2</sup> , Premalatha Manickam<sup>1</sup> and Joseph Sekhar Santhappan<sup>3</sup>

1 Department of Energy and Environment, National Institute of Technology Tiruchirappalli, Tamilnadu, India

2 Department of Mechanical Engineering, National Institute of Technology Tiruchirappalli, Tamilnadu, India

3 Department of Engineering, University of Technology and Applied Sciences, Shinas, Oman

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

© 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.

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#### **Chapter 6**

## Innovative Designs in Household Biogas Digester in Built Neighbourhoods

*Isaac Mbir Bryant and Martha Osei-Marfo*

#### **Abstract**

Most household biogas digesters operate on continuous automatic stirring modes. Often, these digesters rely on electrical energy for their continuous operations which are often mesophilic. Rarely do manually-stirred discontinuous household biogas digesters operating on hyper-thermophilic conditions exist. This work seeks to highlight some innovative designs in a household biogas digester piloted in Terterkessim slum in the K.E.E.A. Municipality of the Central Region, Ghana. A pyramidal dome-shape biogas digester was constructed on an abandoned septic tank using blocks and concrete. The digester has a rectangular sub-surface base and a pyramidal gas holder above the surface of the soil. The digester has a two-blade manual stirrer, a ball bearing affixed at the bottom and a handle to manually mix the content of the digester. In order to heat the content of the digester to a hyperthermophilic condition for hygienising the digestate, a solar-photovoltaic was installed on the roof of a toilet connected to the household biogas digester.

**Keywords:** Solar photovoltaic, manual stirrer, hyper-thermophilic, household, biogas digester

#### **1. Introduction**

In Sub-Saharan Africa and especially Ghana, the use of renewable energy such as biogas is highly under-developed [1] thus accounting for the country's overreliance on natural gas and other fossil-based fuels for electrical power generation [1]. It is, therefore, very crucial for Ghana to expand the production of renewable energy such as biogas from food wastes, black water (BW) (waste water comprising human faeces, urine and flush water) for both industrial and household consumption. Consequently, coming up with an innovative and good technological design for household biogas production is very imperative. The choice of the type of reactor and the innovative designs that can be made for efficient technological processes of a household biogas digester in a built is crucial. This is because of the financial repercussions for the citizens (for example, affordability) and its technical complexity for operation and maintenance. In addition, the efficiency and the applicability to the populace especially, in a developing country like Ghana are some of the reasons the choice of a particular innovative design cannot be overlooked. In Ghana, different energy mix is used for various applications such as domestic/residential, non-residential and other industrial facilities (**Figure 1**) [2]. The greatest

#### **Figure 1.**

*Percentage contribution of different energy sources used in Ghana. NB: Renewable energy (RE) in Ghana comprises solar energy, energy from biogas, wind energy and biomass energy.*

percentage of the energy generation in Ghana is from thermal energy source (61%), followed by hydro-electric power (38%) and 1% making up renewable energy sources such as biogas, solar energy, wind energy and biomass [2].

Different treatment technologies such as Membrane Bioreactor (MBR), Anaerobic Membrane Bioreactors (AMBRs), advanced fluidized bed (AFB) reactors, EGSB and IC® [3] and UASB reactor [4], continuous stirred tank reactor (CSTR) [5] fixed-dome biogas digester (Deenbandhu type) [6, 7] have already been used for biogas production using different substrates and treatment parameters. However, most of these digesters, even though may be modern, did not incorporate other innovative designs that will make them affordable, less technically complex, efficient and easily applicable. This work seeks to address some of these innovative technological missing gaps for easy adoption and implementation, especially, by households in tropical developing countries.

However, single-stage systems are considered to be simple, easy to design and less expensive to be constructed and operated making them common in the anaerobic treatment technology applications [8, 9] Considering small scale anaerobic treatment systems, single-stage reactors have been often used compared to large scale reactors (with a capacity of more than 50 000 tons/year) that use multi-stage systems [7]. According to [7], a fixed-dome (Deenbandhu type) is a closed-dome shaped digester which has an immovable rigid gas-holder. It has an influent inlet and a displacement pit called the compensation tank where the effluent and the digestate exit the reactor. The gas holder is designed to be on top of the digestate in the reactor. With a closed gas valve, higher production of biogas could cause a displacement of the digestate into the compensation tank [6, 7].

The choice of a fixed-dome biogas digester plant for the pilot-scale study in this research for the treatment of household BW in Terterkessim slum in Elmina - Ghana, is based on the following reasons: the user interface is directly connected to the biogas digester [6], the digester can work with or without urine, the reactor can be built underground protecting it from temperature variations [7] and also implies little space is required (making it feasible in a densely

*Innovative Designs in Household Biogas Digester in Built Neighbourhoods DOI: http://dx.doi.org/10.5772/intechopen.97210*

populated area like a slum) [6]. Other advantages include: the reactor functions on a wide range of organic input such as animal manure, kitchen waste and BW. Thus, co-digestion would be done to enhance biogas production. It also supports pour flush toilet system (less water used – concentrated BW, higher biogas production), surrounding soil help to counter the in-built pressure in the reactor, moderately not expensive (the use of local materials and labour), has a life span of between 15 to 20 years as there is no corrosion [7].

#### **2. Location for the construction of household biogas digester**

The household biogas digester was constructed in Terterkessim slum in Elmina, a coastal town and the administrative capital of the Komenda Edina Eguafo Abirem (K.E.E.A.) Municipality of the Central Region of Ghana [10]. Elmina is bordered to the South by the Gulf of Guinea, West by Bantoma, East by Abakam and North by Bronyibima townships [10]. Elmina lies within latitudes 5o 05' North and 5o 60' North and longitudes 1o 20' West and 1o 22' West (**Figure 2**). The town is one of the biggest fishing hubs of Ghana and thus, the major occupation in the town is fishing. The presence of Brenya lagoon, which stretches and overflows (during high tides) to Terterkessim slum, has also made some of the inhabitants to be involved in salt production at commercial quantities. Temperatures are generally high with average being 27°C and annual rainfall ranging between 750 mm to 1000 mm. The vegetation are mostly shrubs and grasses [10]. The town has a total population of approximately 34000, of which about 7600 of the Inhabitants live in Terterkessim slum where the household biogas digester was constructed (Personal Communication with Mr. Damptey- K.E.E.A. Municipal Environmental Health Officer, 2016).

The construction of a household biogas digester connected to a household toilet facility was imperative to help curb the issue of open defecation in the slum due to

#### **Figure 2.**

*Map of Ghana showing the district map of the study area, Elmina. Source of the map: Adade, F. (2016). GIS, Department of Fisheries and Aquatic Sciences (DFAS), University of Cape Coast, Cape Coast-Ghana.*

lack of public toilets in the community. In addition, the only available toilet facility in the community was in a very bad state. Furthermore, most individual households in the Terterkessim slum do not have household toilet facilities, thus giving the residents the impetus to defecate in the open gutters, lagoon and even in and around the salt ponds. Thus the construction of a household toilet facility connected to a biogas digester with innovative designs for both biogas production and disinfection of digestate was imperative for the Terterkessim urban slum in Elmina.

#### **2.1 Innovative designs for household biogas digesters**

The household biogas digester was constructed on an abandoned septic tank thus, it received a lot of modifications to enhance its functionality and efficiency. The innovative designs introduced in the household biogas digester constructed included construction of pyramidal-dome-shape biogas digester, introduction of pour-flush water closet (WC) toilet seats and introduction of manual stirrer in the digester. Other innovative modifications in the household biogas digester built in Terterkessim slum included, adoption of solar photovoltaic to heat the digester to a hyper-thermophilic condition and co-digestion of BW and kitchen food wastes will be highlighted.

#### **2.2 Construction of pyramidal-shape biogas digester**

A single-stage household biogas digester was constructed with 6-inch-blocks (moulded sand, cement and water), reinforced with concrete material and plastered with mortar. The concrete material was made of 10 head pans of quarry sand, 10 head pans of 0.5-inch stones (igneous type), 2 bags of rapid strength Portland cement and 10 L of tap water. Additional mortar and water-proof cements like FEB TANK (UK) were used to stop all water leakages into the reactor chambers. The mixture of the mortar was 1 bag of Portland cement (50 kg), 6 head pans of quarry dust, 1 head pan of eroded sand and 2 kg of waterproof FEB TANK cement. About 10 L of water was added and homogenised into a thick paste of mortar for the reinforcement of the weak walls and floor based on the specifications by the manufacturer of the FEB TANK waterproof cement.

The reactor was a modified form of a circular fixed-dome biogas digester with the circular dome modified into a pyramidal-shape roof for biogas storage. The pyramidal shape roof was done instead of the circular dome because the base of the reactor was rectangular, consequently, a pyramidal shape roof on the rectangular base would ensure airtightness. This was because the rectangular base had corners which a circular dome shape could not perfectly fit on without leakages. Ten pieces of 14-ft Wawa wood of dimensions 2-in by 4-in as well as 15 pieces of 14-ft Wawa wood of dimensions 2-in by 2-in were used for the construction of the gable of the pyramidal dome shape of the biogas digester fastened with 3-in concrete nails. The skeletal structure of the pyramidal-shape roof of the biogas digester was covered with 5 pieces of ¼-plywood. A black thick polythene bag was used to cover the plywood before the concrete layer was formed on the reactor (**Figure 3**). The 6-in (15.24 cm) concrete layer for the roof of the SSHTABD was made of 15 pieces of 0.6-in (1.5 cm) diameter iron rods, 1.5-in (3.8 cm) diameter stones (igneous type) and sand (both coarse and fine). A manual stirrer with four (4) galvanised metal blades of dimensions 15 cm by 30 cm each was affixed into the household biogas digester (**Figure 4**). The rotating metal rod of the stirrer was welded into two ball bearings (one affixed to the bottom of the concrete and the other at the top of the metal rod just beneath the pyramidal shape) to enhance easy rotational movement when manually stirred.

*Innovative Designs in Household Biogas Digester in Built Neighbourhoods DOI: http://dx.doi.org/10.5772/intechopen.97210*

**Figure 3.** *Construction of a pyramidal-shape biogas digester insulated with black polythene bag.*

**Figure 4.** *Manual stirrer in the biogas digester.*

#### **2.3 Pour-flush water closet toilet**

Two pour-flush water closet (WC) toilet seats were installed in each of the toilet unit connected to a household biogas digester (**Figure 5**). Polyvinyl chloride (PVC) pipes of diameter 4-inches were connected to the toilet seats and into the main chamber of the digester. Adjoining pipes from the WC into the digester were

**Figure 5.** *A 3-litre pour-flush toilet seat connected to the biogas digester.*

connected using 4-inch Tee, 4-inch 45o and 4-inch 90o pipes. The influent pipe was inserted into the reactor to a depth of 450 mm above the floor of the reactor. This was done to ensure that the influent fully covered the pipe to avoid any biogas leakage through the influent pipe. An inlet pipe with a cover was also connected to the influent pipe carrying faecal materials to enhance co-digestion processes (**Figure 6**).

#### **2.4 Manual stirrer**

Most biogas digesters that operate in a continuous mode and use stirrers that rely on electrical energy for stirring the digesters. In this design, a manual stirrer was introduced into the household biogas digester for discontinuous stirring by the users in the household. The users were educated and trained to manually stir the digester anytime they visited the toilet. In this way, it was ensured that the old and new feedstock would easily mix to enhance faster digestion. The manual stirrer with four (4) galvanised metal blades of dimensions 15 cm by 30 cm each was affixed into the household biogas digester. The rotating metal rod of the stirrer was welded into two ball bearings (one affixed to the bottom of the concrete floor of the digester and the other at the top of the metal rod just beneath the pyramidal shape) to enhance easy rotational movement when manually stirred (**Figure 4**).

#### **2.5 Installation of solar-photovoltaic for heating the digester**

A high quality 50 W offgridtec® autarkic mono photovoltaic panel of dimensions 60.5 cm x 47.5 cm (0.3 m2 ) was installed on the roof of the toilet connected to the SSHTABD for heating. The photovoltaic panel was offgrid with model number 3–01-001260 and had a voltage of 22.3 V (made by offgridtec® AGM GmbH, CMK ENERGY, Germany). The photovoltaic panel was connected to a solar charge controller (Stecca PR1010 756.477 by Solar Electronics, PV offGrid, PV Autarke

*Innovative Designs in Household Biogas Digester in Built Neighbourhoods DOI: http://dx.doi.org/10.5772/intechopen.97210*

**Figure 6.** *Pipe connections from the pour-flush toilet into the innovative household biogas digester.*

systeme, made in EU) via solar cables. The charge controller was connected to a 12 V/30 A/20 Hours offgridtec AGM gel battery series (by offgridtec AGM GmbH, Germany). The battery had a constant voltage charge and voltage regulation with cycle use of 14.5–14.9 V at 25°C and standby use of 13.6–13.8 V at 25°C. The battery was connected to an NP series pure sine wave inverter (Model number NP 300, made by Solartronics, Leipzig-Germany) which had a maximum peak power of 600 W and an average current of 300–400 W. It also had an input voltage of 12 V and an output voltage of 230 V ˜ 50 Hz and efficiency of 84–94% (**Figure 7**).

#### **2.6 Installation of galvanised copper pipes into kitchen**

Galvanised copper pipes were used to connect the SSHTABD to the kitchen of the household where potential biogas to be produced was to be used. The copper pipes had diameter of 2 cm. Stop corks or valves were installed at adjoining points to regulate the flow of biogas into a biogas bag to monitor the daily biogas production. The copper pipe was laid into the walls of the restroom to the kitchen at an angle of 45o in order to ensure that all water vapour that could form during the operation of the SSHTABD would trickle down by gravity into a collection tube to be discharged (without losing biogas from the reactor) (**Figure 8**).

**Figure 7.** *Components of solar-photovoltaic system installed on the biogas digester.*

**Figure 8.** *Installation of galvanised copper pipes for tapping biogas into kitchen.*

#### **2.7 Detailed description and performance of innovative household biogas digester**

The single-stage innovative household biogas digester constructed in Terterkessim slum composed of 3 chambers which were originally designed for a septic tank system. The septic tanks were connected to a two-unit toilet meant for that household. The first chamber was the biggest and was converted into the main single-stage household biogas digester in which the AD process occurred. It had a total volume of 8.64 m3 . Adjoining the main reactor was a compensation tank which had a tunnel from the main digestion chamber. The compensation tank was about 3.17 m3 . Within the compensation tank were steps designed to help with settling of particles as well as directing clear effluent to be discharged into the next chamber, the effluent collection and storage tank. The effluent collection and storage tank had a total volume of 4.52 m3 . It had an effluent discharge pipe for overflow into a collection container for agricultural usage. An average COD removal of 97.6% was recorded for the digester. The operational parameters for the innovative household biogas digester were a mean temperature of 37°C, average daily flow rate of 182.1 L/d and mean HRT of 51.3 days. The mean daily volumetric loading rate and mean daily organic loading rates of 0.97 kgCOD/(m3 .d) and 0.06 kgVS/(m3 .d), respectively, were also recorded for the digester. These operational values for the biogas digester gave an implication the digester had more potential of receiving more organic load for treatment daily. The digester could produce about 2.52 Nm3 CH4/(kgCOD.d) which could be burnt for at least 8 hours for purposes such as cooking and heating in the households in the slum. This high value was recorded because of the simultaneous conversion of food waste and human faeces into biogas.

### **3. Conclusions**

Manually-stirred discontinuous household biogas digesters which also operate on hyper-thermophilic conditions for anaerobic digestion processes rarely exist. In this study, the objective was to highlight some innovative designs in a household biogas digester piloted in a slum called Terterkessim in the K.E.E.A. Municipality of the Central Region of Ghana. A 2-seater toilet compartment was constructed on a pilot manually-stirred, fixed pyramidal-dome-shaped single-stage household biogas digester for a compound house of 32 persons in the Terterkessim slum. The pyramidal dome-shape biogas digester was constructed on an abandoned septic tank meant to contain faeces from the toilets. Blocks and concrete were used for the construction. The digester has a rectangular sub-surface base and a pyramidal gas holder above the surface of the soil. It also has a two-blade manual stirrer, a ball bearing affixed at the bottom and a handle to manually mix the content of the digester. A solar-photovoltaic was installed on the roof of the toilet connected to the digester to heat the content to a hyper-thermophilic condition for hygienising the digestate.

The innovative household biogas digester has a potential to produce about 2.52 Nm3 CH4/(kgCOD.d) which could be burnt for at least 8 hours for purposes such as cooking and heating in the household. With average daily flow rate of 182.1 L/d and mean HRT of 51.3 days, 97% of the influent was removed. Consequently, this innovative household biogas digester can be employed in already existing residential facilities or new residences for wastewater treatment at the household level and energy recovery from the waste.

### **Acknowledgements**

We wish to acknowledge the contributions of all laboratory and technical staff of the School of Agriculture laboratory in the University of Cape Coast Technology Village for their immense contributions during the laboratory analyses.

### **Conflict of interest**

"The authors declare no conflict of interest."

### **Notes/thanks/other declarations**

We declare that the information provided in this Book Chapter form part of the data and work obtained by the corresponding author of this scholarly work and needs no copy right declaration. In addition, the authors wish to declare that the research was not funded by any organisation.

We wish to thank all labourers and artisans who supported with the construction of the household biogas digester.

*Anaerobic Digestion in Built Environments*

### **Author details**

Isaac Mbir Bryant1 \* and Martha Osei-Marfo2

1 Department of Environmental Science, School of Biological Sciences, University of Cape Coast, Cape Coast, Ghana

2 Department of Water and Sanitation, School of Physical Sciences, University of Cape Coast, Cape Coast, Ghana

\*Address all correspondence to: ibryant@ucc.edu.gh

© 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.

*Innovative Designs in Household Biogas Digester in Built Neighbourhoods DOI: http://dx.doi.org/10.5772/intechopen.97210*

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### *Edited by Anna Sikora*

Anaerobic digestion of biomass to biogas, commonly occurring in natural anoxic ecosystems, is an excellent method for utilizing wastes and producing green energy. This book presents examples of local installations of AD, or their proposals, located at small factories, workplaces, and in rural areas and housing complexes. The facilities consider the specific nature of the region, site conditions, and specificity of the utilized wastes. They protect the environment and ensure dispersed energy production. The latter is of great economic significance due to its closeness to end customers. Small local installations expand the pool of renewable energy on a global scale.

Published in London, UK © 2021 IntechOpen © Martina Birnbaum / iStock

Anaerobic Digestion in Built Environments

Anaerobic Digestion

in Built Environments

*Edited by Anna Sikora*