Household Biogas Digesters—A Review
Abstract:This review is a summary of different aspects of the design and operation of small-scale, household, biogas digesters. It covers different digester designs and materials used for construction, important operating parameters such as pH, temperature, substrate, and loading rate, applications of the biogas,the government policies concerning the use of household digesters, and the social and environmental effects of the digesters. Biogas is a value-added product of anaerobic digestion of organic compounds. Biogas production depends on different factors including: pH, temperature, substrate, loading rate, hydraulic retention time (HRT), C/N ratio, and mixing. Household digesters are cheap, easy to handle, and reduce the amount of organic household waste. The size of these digesters varies between 1 and 150 m3. The common designs include fixed dome, floating drum, and plug flow type. Biogas and fertilizer obtained at the end of anaerobic digestion could be used for cooking, lighting, and electricity.
Keywords:biogas; household digesters; bioenergy; waste management; fixed dome digesters; floating drum digesters; plug flow digesters
1. Introduction
Due to the increasing prices of fossil fuels and taxes on energy sources, finding alternative, clean
and economical sources of energy has nowadays become a major concern for households’ and nations’
economies. In addition, economic prosperity and quality of life, which are linked in most countries to
per-capitaenergy consumption, is a great determinant and indicator of economical development
Energy demand is a critical reason for extensive climate change, resource exploitation, and also
restricts the living standards of humans [5,6]. By the time fuel and fertilizer reaches rural areas, the end price is relatively expensive due to high transport costs, leaving people to find alternative resources other thanoil [7]. Starke [8] reported wood as the traditional source of fuel to produce energy for domestic purposes for 2.5 billion people in Asia. Many of the rural communities in developing countries are forced torely on the traditional energy sources such as firewood, dung, crop residues, and paraffin. These traditional methods are often expensive and/or time-consuming [9–11]. Cooking accounts for 90% of energy consumption in the households of developing countries [12]. Furthermore, access to electricity in rural areas is relatively scarce [13]. Biogas is a substitute for firewood and cattle dung that can meet the energy needs of the rural population [14,15]. Biogas is a renewable source of energy that can be used as a substitute for natural gas or liquefied petroleum gas [16]. There are different models to assess the energy content of different energy sources, which includes water boiling test, controlled cooking test and kitchen performance test [17]. The energy content of 1.0 m3 of purified biogas is equal to 1.1 L of gasoline, 1.7 L of bioethanol, or 0.97 m3 of natural gas [16]. The application for rural and urban waste biogas production is widely spread. It is a challenge for engineers and scientists to build an efficient domestic digesters with the materials available, at the same time taking the local and economical considerations into the account. Although many digesters have been built, additional research and awareness are needed to meet the changing needs and conditions [18]. Biogas production can be carried out in very small reactors ranging from100-mL serum bottles in the lab up to 10,000 m3large digesters as normally used, for example, in Europe. This review deals with a summary of different household biogas digesters, their operating parameters, cost and materials used to build them, startup, and maintenance, the variety of applications employed, and associated social and environmental effects.
Biogas
Biogas, the metabolic product of anaerobic digestion, is a mixture of methane and carbon dioxide with small quantities of other gases such as hydrogen sulfide [19,20]. Methane, the desired component of biogas, is a colorless, blue burning gas used for cooking, heating,and lighting [21]. Biogas is a clean, efficient, and renewable source of energy, which can be used as a substitute for other fuels in order to save energy in rural areas [22]. In anaerobic digestion, organic materials are degraded by bacteria, in the absence of oxygen, converting it into a methane and carbon dioxide mixture. The digestate or slurry from the digester is rich inammonium and other nutrients used as an organic fertilizer [11,23–27]. Methane formation in anaerobic digestion involves four different steps, including hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Different bacterial/archaea communities work in a syntrophic relationship with each other to form methane. In hydrolysis, complex carbohydrates, fats, and proteins are first hydrolyzedto their monomeric forms by exoenzymes and bacterial cellulosome. In the second phase (acidogenesis), monomers are further degraded into short-chain acids such as: acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caprionic acid,lcohols, hydrogen, and carbon dioxide. During acetogenesis, these short-chain acids are converted into acetate, hydrogen, and carbon dioxide. In the last phase, methanogens convert the intermediates produced into methane and carbon dioxide. Almost one-third of methane formation is due to reduction of carbon dioxide by hydrogen
Download full research Paper Household Biogas Digesters
Karthik Rajendran *, Solmaz Aslanzadeh and Mohammad J. Taherzadeh
School of Engineering, Universityof Borås, Borås 50190, Sweden;
E-Mails: Solmaz.Aslanzadeh@hb.se (S.A.); Mohammad.Taherzadeh@hb.se (M.J.T.)
*Author to whom correspondence should be addressed; E-Mail: Karthik.Rajendran@hb.se;
Tel.: +46-33-435-4855; Fax: +46-33-435-4008.
Received: 11 May 2012; in revised form: 27 July 2012 / Accepted: 30 July 2012 /
Published: 8 August 2012
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| Bio gas digester |
Abstract:This review is a summary of different aspects of the design and operation of small-scale, household, biogas digesters. It covers different digester designs and materials used for construction, important operating parameters such as pH, temperature, substrate, and loading rate, applications of the biogas,the government policies concerning the use of household digesters, and the social and environmental effects of the digesters. Biogas is a value-added product of anaerobic digestion of organic compounds. Biogas production depends on different factors including: pH, temperature, substrate, loading rate, hydraulic retention time (HRT), C/N ratio, and mixing. Household digesters are cheap, easy to handle, and reduce the amount of organic household waste. The size of these digesters varies between 1 and 150 m3. The common designs include fixed dome, floating drum, and plug flow type. Biogas and fertilizer obtained at the end of anaerobic digestion could be used for cooking, lighting, and electricity.
Keywords:biogas; household digesters; bioenergy; waste management; fixed dome digesters; floating drum digesters; plug flow digesters
1. Introduction
Due to the increasing prices of fossil fuels and taxes on energy sources, finding alternative, clean
and economical sources of energy has nowadays become a major concern for households’ and nations’
economies. In addition, economic prosperity and quality of life, which are linked in most countries to
per-capitaenergy consumption, is a great determinant and indicator of economical development
Energy demand is a critical reason for extensive climate change, resource exploitation, and also
restricts the living standards of humans [5,6]. By the time fuel and fertilizer reaches rural areas, the end price is relatively expensive due to high transport costs, leaving people to find alternative resources other thanoil [7]. Starke [8] reported wood as the traditional source of fuel to produce energy for domestic purposes for 2.5 billion people in Asia. Many of the rural communities in developing countries are forced torely on the traditional energy sources such as firewood, dung, crop residues, and paraffin. These traditional methods are often expensive and/or time-consuming [9–11]. Cooking accounts for 90% of energy consumption in the households of developing countries [12]. Furthermore, access to electricity in rural areas is relatively scarce [13]. Biogas is a substitute for firewood and cattle dung that can meet the energy needs of the rural population [14,15]. Biogas is a renewable source of energy that can be used as a substitute for natural gas or liquefied petroleum gas [16]. There are different models to assess the energy content of different energy sources, which includes water boiling test, controlled cooking test and kitchen performance test [17]. The energy content of 1.0 m3 of purified biogas is equal to 1.1 L of gasoline, 1.7 L of bioethanol, or 0.97 m3 of natural gas [16]. The application for rural and urban waste biogas production is widely spread. It is a challenge for engineers and scientists to build an efficient domestic digesters with the materials available, at the same time taking the local and economical considerations into the account. Although many digesters have been built, additional research and awareness are needed to meet the changing needs and conditions [18]. Biogas production can be carried out in very small reactors ranging from100-mL serum bottles in the lab up to 10,000 m3large digesters as normally used, for example, in Europe. This review deals with a summary of different household biogas digesters, their operating parameters, cost and materials used to build them, startup, and maintenance, the variety of applications employed, and associated social and environmental effects.
Biogas
Biogas, the metabolic product of anaerobic digestion, is a mixture of methane and carbon dioxide with small quantities of other gases such as hydrogen sulfide [19,20]. Methane, the desired component of biogas, is a colorless, blue burning gas used for cooking, heating,and lighting [21]. Biogas is a clean, efficient, and renewable source of energy, which can be used as a substitute for other fuels in order to save energy in rural areas [22]. In anaerobic digestion, organic materials are degraded by bacteria, in the absence of oxygen, converting it into a methane and carbon dioxide mixture. The digestate or slurry from the digester is rich inammonium and other nutrients used as an organic fertilizer [11,23–27]. Methane formation in anaerobic digestion involves four different steps, including hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Different bacterial/archaea communities work in a syntrophic relationship with each other to form methane. In hydrolysis, complex carbohydrates, fats, and proteins are first hydrolyzedto their monomeric forms by exoenzymes and bacterial cellulosome. In the second phase (acidogenesis), monomers are further degraded into short-chain acids such as: acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caprionic acid,lcohols, hydrogen, and carbon dioxide. During acetogenesis, these short-chain acids are converted into acetate, hydrogen, and carbon dioxide. In the last phase, methanogens convert the intermediates produced into methane and carbon dioxide. Almost one-third of methane formation is due to reduction of carbon dioxide by hydrogen
Download full research Paper Household Biogas Digesters
