**1. Introduction**

Among the increasing energy consumption, natural gas (mainly methane) demand is increasing. Methane (CH4 ) is created both in the natural environment and through various human activities. Derived from the decay of organic material, CH4 is easily produced and abundant. Although in most cases CH4 created from human activity cannot completely replace significant energy needs, it could lower the costs and decrease a facility's reliance on the electrical grid [1].

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. © 2018 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.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Therefore, biogas as a sort of renewable energy is gaining more attraction throughout several nations of the world [2]. Biogas is the gaseous emission produced by the breakdown of organic matter in the absence of oxygen. It is a mixture of CH<sup>4</sup> and carbon dioxide (CO<sup>2</sup> ) along with other trace gases (H2 S, H2 , SO2 , etc.). CH4 , the primary component of natural gas (98%), makes up 55–90% by volume of biogas (depending on the source of organic matter and conditions of degradation). CH4 is the only constituent of biogas with significant energy value. The inert diluents of CO2 and nitrogen lowers the calorific content of the gas, while the corrosive nature of hydrogen sulfide (H<sup>2</sup> S) wears down the anaerobic digester and pipes involved in the gas distribution. Biogas has a very wide industrial application range, includes heat combustion systems, motors, turbines, and fuel cells, and it can also be sold as a byproduct separately. Biogas can be generated by anaerobic treatment of organic wastes. In the past decades, researchers have been conducting massive experiments on evaluating the conversion of miscellaneous wastes such as animal manure, municipal solid waste, energy crops, municipal biosolids, and food waste to biogas [3, 4]. In this chapter, three kinds of wastes were selected for investigation: bleaching and pulping effluent from paper mill, brown grease from food waste, and corn stillage from the bio-ethanol plant.

The concentration of specific volatile fatty acids (VFAs) and total alkalinity (ALK) can give vital information on the status of AD processes. VFA is an important intermediate product

used to offset the excess VFA to keep the pH value at the stable level. System retention time, including hydraulic retention time (HRT) and solid retention time [(SRT), in solid digesters] may influence the system performance. A longer retention time comes with a higher organic mass removal, but it can also lead to possible VFA accumulation and decrease of system treatment efficiency. The required retention time for the completion of AD reactions varies with

Organic loading rate (OLR) is the measurement of the biological conversion capacity of the AD system. Feeding the system above, its sustainable OLR will result in low biogas yield due to the accumulation of inhibiting substances such as VFA [8]. Generally, OLR was calculated based on the concentration of chemical oxygen demand (COD) of volatile solids (VSs). The composition of OLR may contain biodegradable organic loading and refractory organic loading; this composition will affect the biogas yield and quality and the organic removal efficiency as well. Biogas production is one of the main purposes of AD process. Tracking the biogas production is a widespread online measurement in AD control systems. A low biogas production may indicate accumulation of some inhibitive intermediate compounds. The measurement of CH4 is important because it is the major energy output of the AD system. The concentration of tract

The technology of AD has developed in many aspects [8]. There are a lot of studies that use AD to treat different kinds of municipal, agricultural, and industrial wastes. Gunaseelan [9] has summarized the application of AD to over 100 kinds of wasted biomass to recover CH<sup>4</sup>

Appels et al. [10] have applied AD technology in wastewater treatment plant (WWTP) to treat

ters to save over 50% of the WWTP cost. Hansen et al. [11] have used a continuous stirred tank

kg-VS-1. Bouallagui et al. [12] and Zhang et al. [13] also applied a batch AD reactor to food waste. Angelidaki et al. [14] have defined the measurement protocol for biomethane potential (BMP). Furthermore, in the study of De Baere [15], the anaerobic treatment capacity of solid

To develop and extend the application of AD technique to large-scale fabrication plants and industries, three kinds of industrial wastes were selected to be treated in a pilot-scale AD process. The waste substrates include paper mill effluents (comes from different paper making processes), brown grease (a kind of common food waste), and thin stillage (a kind of intermediate from corn grain-to-ethanol process). All the selected waste substrates come from real industries and practical plants. The reason for choosing these industrial wastes included, firstly, for these selected wastes, the traditional treatment technique seems inefficient. For example, for paper mill effluents, the traditional treatment technique is activated sludge process, which could

S in produced biogas reflects the current presence and degradation of sulfide-

S has a certain amount of toxicity; thus, its concentration needs to

S substrates.

from those discarded organic mat-

yield of 0.022–0.188 m<sup>3</sup>

.


finally, and proper amount of ALK is

http://dx.doi.org/10.5772/intechopen.72292

253

Biogas Recovery from Anaerobic Digestion of Selected Industrial Wastes

in the AD process, which should be converted to CH4

different reactor types, temperature, and waste composition.

be cautious to not reach inhibiting levels when treating rich H2

the waste-activated sludge and successfully recovered CH4

waste in Europe was over 1 million tons in the year 2000.

reactor to treat high-ammonia swine manure and obtained a CH4

gases such as H2

containing compounds. H2

**1.3. Current research background**

#### **1.1. Introduction of anaerobic digestion (AD) process**

Anaerobic digestion (AD) is the consequence of a series of metabolic interactions among various microorganisms. It occurs in three stages: hydrolysis/liquefaction, acidogenesis, and methanogenesis [3, 5]. In these three stages, complex organic materials are converted to CH<sup>4</sup> and CO2 in the absence of O2 *via* activity of several groups of anaerobic microorganisms. Firstly, fresh organic matter was hydrolyzed to soluble particles. Afterwards, soluble organic matter was biodegraded to volatile fatty acids (VFAs) and alcohols by a heterogeneous microbial population called acidogens. Finally, a limited number of organic compounds were used as carbon and energy sources and to be transferred to CH4 by microbes called methanogens. AD process is an effective proven technology for handling and treating municipal or industrial wastes and effluents, for the generation of district heating and electricity supplies, as well as for clean environment.

#### **1.2. Important operating parameters in AD process**

During the AD process, many operating parameters must be controlled to optimize the microbial activity and keep the system efficiency stable and superior. Ideally, the performance of an AD process should be evaluated by observing those important parameters.

pH and temperature are important factors for keeping functional AD process. Generally, anaerobic process happens in neutral pH range (pH 6.5–7.6) [6], because anaerobic bacteria, especially the methanogens, are sensitive to the acid concentration within the digester and their growth can be inhibited by acidic conditions. Based on pH level, two temperature ranges, named mesophilic (30–45°C) and thermophilic (45–65°C), were commonly applied in industrial fields [7]. Redox potential (ORP) is a parameter to reflect changes in oxidizing or reducing agents; it represents the oxygen inhibition situation during the AD process. At the same time, the concentration of dissolved oxygen (DO) could also be monitored as an indicator of oxygen inhibition.

The concentration of specific volatile fatty acids (VFAs) and total alkalinity (ALK) can give vital information on the status of AD processes. VFA is an important intermediate product in the AD process, which should be converted to CH4 finally, and proper amount of ALK is used to offset the excess VFA to keep the pH value at the stable level. System retention time, including hydraulic retention time (HRT) and solid retention time [(SRT), in solid digesters] may influence the system performance. A longer retention time comes with a higher organic mass removal, but it can also lead to possible VFA accumulation and decrease of system treatment efficiency. The required retention time for the completion of AD reactions varies with different reactor types, temperature, and waste composition.

Organic loading rate (OLR) is the measurement of the biological conversion capacity of the AD system. Feeding the system above, its sustainable OLR will result in low biogas yield due to the accumulation of inhibiting substances such as VFA [8]. Generally, OLR was calculated based on the concentration of chemical oxygen demand (COD) of volatile solids (VSs). The composition of OLR may contain biodegradable organic loading and refractory organic loading; this composition will affect the biogas yield and quality and the organic removal efficiency as well.

Biogas production is one of the main purposes of AD process. Tracking the biogas production is a widespread online measurement in AD control systems. A low biogas production may indicate accumulation of some inhibitive intermediate compounds. The measurement of CH4 is important because it is the major energy output of the AD system. The concentration of tract gases such as H2 S in produced biogas reflects the current presence and degradation of sulfidecontaining compounds. H2 S has a certain amount of toxicity; thus, its concentration needs to be cautious to not reach inhibiting levels when treating rich H2 S substrates.

#### **1.3. Current research background**

Therefore, biogas as a sort of renewable energy is gaining more attraction throughout several nations of the world [2]. Biogas is the gaseous emission produced by the breakdown

, etc.). CH4

(98%), makes up 55–90% by volume of biogas (depending on the source of organic matter

involved in the gas distribution. Biogas has a very wide industrial application range, includes heat combustion systems, motors, turbines, and fuel cells, and it can also be sold as a byproduct separately. Biogas can be generated by anaerobic treatment of organic wastes. In the past decades, researchers have been conducting massive experiments on evaluating the conversion of miscellaneous wastes such as animal manure, municipal solid waste, energy crops, municipal biosolids, and food waste to biogas [3, 4]. In this chapter, three kinds of wastes were selected for investigation: bleaching and pulping effluent from paper mill, brown grease from

Anaerobic digestion (AD) is the consequence of a series of metabolic interactions among various microorganisms. It occurs in three stages: hydrolysis/liquefaction, acidogenesis, and methanogenesis [3, 5]. In these three stages, complex organic materials are converted to CH<sup>4</sup>

Firstly, fresh organic matter was hydrolyzed to soluble particles. Afterwards, soluble organic matter was biodegraded to volatile fatty acids (VFAs) and alcohols by a heterogeneous microbial population called acidogens. Finally, a limited number of organic compounds were used

AD process is an effective proven technology for handling and treating municipal or industrial wastes and effluents, for the generation of district heating and electricity supplies, as well

During the AD process, many operating parameters must be controlled to optimize the microbial activity and keep the system efficiency stable and superior. Ideally, the performance of an

pH and temperature are important factors for keeping functional AD process. Generally, anaerobic process happens in neutral pH range (pH 6.5–7.6) [6], because anaerobic bacteria, especially the methanogens, are sensitive to the acid concentration within the digester and their growth can be inhibited by acidic conditions. Based on pH level, two temperature ranges, named mesophilic (30–45°C) and thermophilic (45–65°C), were commonly applied in industrial fields [7]. Redox potential (ORP) is a parameter to reflect changes in oxidizing or reducing agents; it represents the oxygen inhibition situation during the AD process. At the same time, the concentration of dissolved oxygen (DO) could also be monitored as an indica-

AD process should be evaluated by observing those important parameters.

in the absence of O2 *via* activity of several groups of anaerobic microorganisms.

and carbon dioxide (CO<sup>2</sup>

, the primary component of natural gas

by microbes called methanogens.

is the only constituent of biogas with significant energy

S) wears down the anaerobic digester and pipes

and nitrogen lowers the calorific content of the gas, while

)

of organic matter in the absence of oxygen. It is a mixture of CH<sup>4</sup>

S, H2

, SO2

along with other trace gases (H2

252 Advances in Biofuels and Bioenergy

value. The inert diluents of CO2

and CO2

as for clean environment.

tor of oxygen inhibition.

and conditions of degradation). CH4

the corrosive nature of hydrogen sulfide (H<sup>2</sup>

food waste, and corn stillage from the bio-ethanol plant.

**1.1. Introduction of anaerobic digestion (AD) process**

as carbon and energy sources and to be transferred to CH4

**1.2. Important operating parameters in AD process**

The technology of AD has developed in many aspects [8]. There are a lot of studies that use AD to treat different kinds of municipal, agricultural, and industrial wastes. Gunaseelan [9] has summarized the application of AD to over 100 kinds of wasted biomass to recover CH<sup>4</sup> . Appels et al. [10] have applied AD technology in wastewater treatment plant (WWTP) to treat the waste-activated sludge and successfully recovered CH4 from those discarded organic matters to save over 50% of the WWTP cost. Hansen et al. [11] have used a continuous stirred tank reactor to treat high-ammonia swine manure and obtained a CH4 yield of 0.022–0.188 m<sup>3</sup> -CH4 kg-VS-1. Bouallagui et al. [12] and Zhang et al. [13] also applied a batch AD reactor to food waste. Angelidaki et al. [14] have defined the measurement protocol for biomethane potential (BMP). Furthermore, in the study of De Baere [15], the anaerobic treatment capacity of solid waste in Europe was over 1 million tons in the year 2000.

To develop and extend the application of AD technique to large-scale fabrication plants and industries, three kinds of industrial wastes were selected to be treated in a pilot-scale AD process. The waste substrates include paper mill effluents (comes from different paper making processes), brown grease (a kind of common food waste), and thin stillage (a kind of intermediate from corn grain-to-ethanol process). All the selected waste substrates come from real industries and practical plants. The reason for choosing these industrial wastes included, firstly, for these selected wastes, the traditional treatment technique seems inefficient. For example, for paper mill effluents, the traditional treatment technique is activated sludge process, which could remove up to 90% of biochemical oxygen demand (BOD) but the chemical oxygen demand (COD) removal efficiency is just in the range of 20–50% [16–19]. Secondly, the United States Environmental Protection Agency (US EPA) have strict and specific policies about these industrial wastes, such as the US EPA CMOM (capacity, management, operation, and maintenance program, including grease control program), the US EPA final pulp and paper cluster rule and amendments, the US EPA CWA (Clean Water Act), the FOG ordinance/FOG management policy, and so on. That could be considered as the driving force to push industries to treat these wastes before discarding. Finally, these materials from industrial waste contain high organic content, which means they have the potential to be treated anaerobically as the energy feedstock.

conversion of waste streams such as animal manure, municipal solid wastes, energy crops, municipal biosolids, and food wastes to biogas [43–46]. In Europe, there are over 50 waste treatment plants using these materials to produce biogas [16, 45, 46]. For instance, ~15% of organic wastes are being converted annually in Germany [47]. The practice of converting wastes to energy provides a two-fold benefit of environmental protection and energy recovery. Brown grease (BG) is a mixture consisting of trapped grease, sewage grease, and black grease collected in grease interceptors (traps) of restaurants and food industries [48]. In the United States, there are 1.84 million tons of BG produced every year [49]. Most collected BG eventually ends up in landfills. The landfill cost for BG is ~5 cents per pound [50]. This results in a very high direct disposal cost. In addition, the moisture content in BG can lead to soil and water pollution, making the soil sterile and unable to support plant life [51]. Because of these drawbacks, the European Union enacted a general ban on landfilling organic waste in 2005

Biogas Recovery from Anaerobic Digestion of Selected Industrial Wastes

of CH4

States annually by converting the generated BG into biogas [53]. This is a substantial amount of renewable bioenergy. Recovering the energy and eliminating the waste input to landfills

AD is a treatment process capable of producing biogas from organic wastes. The benefits of anaerobic digestion include smaller reactor size in terms of organic loading, lower air emissions, and a smaller amount of generated sludge compared to aerobic biological treatment [55]. Greasy wastes such as BG have been added as a lipid-rich cosubstrate in earlier AD studies for sewage sludge [56–58], municipal wastewater [59–61], and the digestible fraction of municipal solid wastes [62]. Typically, it is blended at 2–50% of the primary substrate's organic loading to improve the biogas yield and methane content [56–62]. However, higher lipid loading (>50% of the substrate) can cause long-chain fatty acid (LCFA) inhibitions [55, 61, 62], scum and foam formation, and fat clogging problems [56]. To our knowledge, there are few studies devoted to investigating the degradability and biogas production using BG alone.

Based on the increased demand of renewable energy, bio-ethanol as an alternative energy source was considered and has enormous economic and strategic advantages. In the past decade, the national total annual fuel-grade ethanol production has increased from 1.77 billion gallons (in 2001) to 13.95 billion gallons (in 2011). In 2005, 67% of this ethanol was produced from dry mill corn [63], and this percentage has kept on increasing because of the low

In a typical bio-ethanol production process, corn mash has been fermented and distilled to produce high purity ethanol, and the fermentation residue is called whole stillage, which is centrifuged to produce wet cake (precipitate) and thin stillage (supernatant). About 50% of the thin stillage is recycled as backset. The remainder is further concentrated by evaporation to produce syrup and blended with dried wet cake to create a feed product known as distiller's dry grain with soluble (DDGS). The effluent of evaporation process was purified and

could be produced in the United

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255

[52]. An earlier study suggested that 14 × 10<sup>6</sup> m3

**2.3. Stillage from corn-to-ethanol process**

cost of this technology [64].

recycled as water reuse.

yields both economic and environmental benefits [54, 55].
