Biogas Digester

First, into a biogas digester or the post digester hydrogen is added to increase the methane yield.

From: Hydrogen Supply Chains, 2018

Chapters and Articles

Issues of Broader Concern for Engineers

Heinz C. Luegenbiehl, Rockwell F. Clancy, in Global Engineering Ethics, 2017

Biogas Digesters in Nepal: The Importance of Culture in User-Centered Design (Successes)

In 2008, the student chapter of EWB at the Technion—Israel Institute of Technology (hereafter Technion) worked closely with the 8000-person village of Namsaling, Nepal, to improve the design and creation of biogas digesters—devices used to produce gas for cooking and fertilizer for growing. Through consultation and work with local stakeholders, the student team gained a sense of the culture, needs, and values of those in Namsaling, resulting in the implementation of less costly digesters.

Biogas digesters can solve a variety of energy, environmental, and health issues in rural communities. Biowaste—animal and sometimes human excrement, along with weeds or other biological waste—are placed in the digester. As the material decomposes, it produces gas that can be pumped out and used as cooking fuel and to heat homes. The remaining waste can be used as a fertilizer for local farms and gardens. This gas reduces the amount of wood burned, therefore reducing deforestation and exposer to the toxic smoke and fumes produced by traditional wood-burning stoves, in turn reducing respiratory problems (Tugend, 2011). Therefore, the use of natural gas from biogas digesters contributes to environmental sustainability and the health of rural communities.124

When the Technion student project began in 2008, Nepal already had 200,000 biogas digesters in use (Stricker, 2010), although their construction cost considerable time and money. To build a digester of this kind, a large pit was dug and soil used to create a dome, often by the children of the community. Concrete was then laid over the dome, and soil removed to create the main chamber of the digester. Digging the pit, fashioning the soil dome, laying the concrete, and removing the soil afterwards required tremendous time and effort. Technion students believed they could design a cheaper, easier way of building biogas digesters.

Students made several trips to the village, “to work with villagers in defining and collecting data required for the design of sustainable and appropriate projects” (Lichtman, n.d.). Additionally, they worked closely with the Namsaling Community Development Center (NCDC), Biogas Sector Partnership (BSP), and families from Namsaling. The NCDC and families in Namsaling not only assisted in the development of a solution but also funded a third of the project (Tugend, 2011). With these partners, the team redesigned the dome mold used in the construction process.

Instead of using soil to build the dome, the team used bamboo—a material widely available in Namsaling. After the concrete on top hardened, the mold could be removed from the pit more easily and reused to create other digester chambers. This significantly reduced the amount of money and time needed to create digesters. After this new design was implemented, villagers reported a 36 kg reduction in daily wood use per family (Lichtman, n.d.). The Technion team's “deep acquaintance with the community” in Namsaling undoubtedly contributed to the success of this project (EWB, n.d.).

Students from Technion spent considerable time with the community stakeholders, learning more about their values and economic needs, for example, the Nepalese emphasis on family and respect for community members, which was important to the construction and use of the digesters. Additionally, the economic benefits associated with digester fertilizer are particularly significant: the fertilizer is used in Namsaling to grow important cash crops such cardamom and ginger (Namsaling village, n.d.). The success of this project emphasizes the importance of considering the values, needs, and circumstances of the Nepalese people affected by engineering aid projects. Even with the best of intentions, neglecting these considerations can result in the failure of engineering aid projects:

In your opinion, who is primarily responsible for the success of this project? Justify your response.

Did the financial contributions of the Namsaling community help this project to succeed? Why might the financial support of beneficiaries be helpful to the success of a project—versus projects funded entirely by external organizations?

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Waste Treatment Processes/Technologies for Energy Recovery

Rucha V. Moharir, ... Sunil Kumar, in Current Developments in Biotechnology and Bioengineering, 2019

3.4.1 Anaerobic Digestion

In this process a biogas digester is prepared (closed container) in which the segregation and feeding of the organic fraction takes place. In this digester, the biodegradation of segregated waste takes place under anaerobic conditions and in the presence of methanogenic bacteria, and as a result produces a methane-rich biogas. This generated biogas can be further used for cooking and for electricity generation, which can be processed through gas engines. The fully stabilized sludge that remains after anaerobic digestion can be further used as a soil conditioner. Depending on the composition of the input waste it can even be sold as compost.

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An integrated rural energy system in Sri Lanka

B.P. Sepalage, in Integrated Rural Energy Planning, 1985

Biogas component

The larger of the two biogas digesters was designed by Khadi and Village Industries Commission (KVIC) of Bombay, and produces approximately 80 m3 of gas per day. The other biogas digester, of Chinese design, is substantially smaller with a daily output of approximately 6 m3 of gas. The daily fuel requirement of the two plants is around 2400 kg of fresh dung obtained from the village.

The initial feeding of the Indian biogas digester presented a problem due to the large quantity of dung required for the first feeding and the village's inability to provide this amount in a short period of time. Most of the initial dung requirements were met by a nearby government farm with a large cattle population.

The biogas produced by the two digesters is used to operate a 37.5 kVA engine generator working on 100% biogas and a 12.5 kVA dual fuel (diesel biogas) engine generator. Biogas is also used as a cooking fuel and for lighting purposes. The slurry, a rich organic manure, is sold to the village in bulk and a certain amount is also placed in containers and sold outside the village.

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Anaerobic fermentation process for biomethane production from vegetable waste

Zhao Youcai, Wei Ran, in Biomethane Production from Vegetable and Water Hyacinth Waste, 2021

1.6.3.2 Classified by number of steps

According to the number of biogas digesters connected with each other in the fermentation process system, it can be divided into single-stage, two-stage, and multistage fermentation.

1.

Single-stage fermentation

This refers to mixed fermentation with only one biogas digester (or fermentation device), and its fermentation process is only carried out in one fermentation digester. The equipment for single-stage fermentation is simple, but its condition control is difficult.

2.

Two-stage and multistage fermentation

In order to improve the digestibility and removal rate of organic matter, a two-stage or multistage biogas fermentation process has been developed. This type of fermentation is characterized by fermentation in two or more connected fermentation ponds. The raw materials are decomposed and gas is produced in the first fermentation pool over a certain period of time, then the feed liquid is transferred from the first fermentation pool to the second or other fermentation pools for further fermentation. The fermentation process has a long detention period and decomposes organic matter completely, but the investment cost is higher.

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BIOGAS

L.A. KRISTOFERSON, V. BOKALDERS, in Renewable Energy Technologies, 1986

Size of Biogas Digesters

In terms of size, biogas digesters have been developed to cater for a wide range of biogas demand.

1

Household plants are small-scale plants of about 8–10 m3 usually located in rural areas and depending on households for their inputs, control and utilization of outputs. This is the most common application of biogas technology and the one most referred to in this report.

2

Community-scale plants have capacities greater than 40 m3, are generally found in rural areas and depend on the co- operation of a number of households for their inputs, control and output utilization.

3

Plants associated with intensive animal rearing (chickens, pigs or cattle), or institutional plants which have pre-existing management systems, e.g. prisons, hospitals, schools.

4

Plants associated with the disposal of industrial effluent (e.g. distillery wastes).

The prospects for plants located wholly in the monetized sector (types 3 and 4) seem on the whole to be favourable, whereas plants located wholly or partly in the subsistence sector (type 1) sector appear to face particular problems.

The benefits of community-sized plants include: lower capital cost per m3 installed due to economies of scale, better operation and maintenance since it is possible to employ a full-time operator, ability to use organic wastes other than manure due to the larger size, generation of sufficiently large volumes of gas so that engines can be installed, and the possibility of achieving a more equitable distribution of benefits to the poor in the village. Furthermore, it is likely that higher gas yields could be expected due to addition of other organic wastes, better mixing and heating and closer operational control. At the moment there are only a handful of community-sized digesters in developing countries.

In general, it can be concluded that the community plants are usually more efficient than the household-scale plants due to their economies of scale and better associated operation and maintenance. However, such plants can be negatively affected by social problems relating to: rights to the biogas in relation to the organic material input from individuals in the community; rights to the slurry; the reduction in the amount of freely-available organic materials to the poorer sections of the community who depend on such materials for fuel and may have less access to the biogas than the richer sections; and difficulties in rapidly altering the lifestyles of a large group of people who will almost overnight have to change from using traditional fuels to a new and relatively unknown fuel. Such a plant could also bring monetarism to areas which were previously subsistence-oriented and immune from monetised life-styles - a factor that could ultimately exclude the community's poor from the benefits of gas supply. However,

Biogas digester with a rubber dome.

evidence from some of the few community plants now operational, especially from a case study in Nepal, suggests that these problems can be successfully overcome.

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BIOGAS PRODUCTION BY BIPHASE

Geoffrey Stanford, David Donohue, in Passive and Low Energy Alternatives I, 1982

CONVENTIONAL MULTI-PHASE (SINGLE TANK) SYSTEMS

The simplest design for a biogas digester is a single tank which is kept completely air- and water-tight. It is loaded with biomass and left to rot or biodegrade (these terms are synonymous). All the stages of biogas production, each with its own optimal conditions, occur in a precarious equilibrium within that single tank. This tank can be operated in different modes, depending on the loading schedule.

Batch flow: The simplest type of such a single-tank digester is the batch system. This is loaded once, then left alone to produce biogas. When biogas production falls off it is completely emptied and a new batch of biomass is loaded. The Chinese village units work this way.

Plug flow: A plug flow system consists of a rectangular tank. Fresh biomass is added on a regular basis at one end, and the same amount is wasted from the other end. Most on-farm installations for cattle and swine manure in the USA work this way.

High rate: A high rate system is essentially identical to plug flow, only it is stirred. This creates more rapid biogas production in a smaller tank, but requires additional equipment and energy inputs. The sludge is often allowed to settle in a second tank, and then returned to the first tank — this to retain in the system the methanogens that are sticking to the sludge particles. Most anaerobic digestors for sewage sludge work this way.

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Technical development and a pilot trial for anaerobic digestion of water hyacinth

Zhao Youcai, Wei Ran, in Biomethane Production from Vegetable and Water Hyacinth Waste, 2021

5.11.3 Utilization of biogas slurry

At present, biogas produced by the biogas digesters in rural areas is mainly used for the following reasons. (1) Biogas slurry is a kind of quick-acting fertilizer and is suitable for topdressing in vegetable fields or dry fields under irrigation. (2) Biogas slurry contributes to crop disease resistance and pest control. The use of biogas slurry for extraroot topdressing or foliar sprays allows nutrients to be directly absorbed by crop stems and leaves and participates in photosynthesis, thereby increasing yield and improving quality, while at the same time enhancing resistance to disease and acting as an antifreeze. (3) Biogas slurry is used as an additive to feed for livestock and poultry. Biogas slurry contains of macro- and trace elements, with an especially rich amino acid content has soluble nutrients, and is easy to digest and absorb to meet the growth needs of livestock and poultry. (4) The use of biogas slurry to feed fish will not only increase production and reduce costs, but also reduce the incidence of disease. The nutrient content of biogas slurry is easily absorbed by plankton, promoting their growth, improving water quality, reducing the consumption of dissolved oxygen, avoiding the occurrence of pan-sugar phenomenon, and eliminating parasite eggs and pathogens caused by fresh livestock and poultry manure, which may cause fish disease. (5) Soaking with biogas slurry, as biogas slurry contains a large amount of ammonium, phosphorus, potassium, and other trace elements required by ammonium humate, various vitamins, auxins, and crops, and a variety of active substances secreted by microorganisms. These soluble nutrients will have different degrees of penetration due to infiltration. The seeds absorbed by biogas slurry can effectively activate the enzyme sources in embryos and endosperm, enhance the enzymatic activity, promote sprouting, stimulate growth, accelerate nutrients from dormant seeds and even seedlings, and promote metabolism. Soaking seeds with biogas slurry can provide increase the seed germination rate and yield.

In this pilot test, the biogas produced by the biogas digester was first digested by primary oxidation ponds and then entered fish ponds. The biogas slurry was rich in nutrients, and a large amount of plankton could be produced in a short period of time for filter-feeding. The fish feed on these plankton thereby accelerating the growth of the fish. One week after the biogas slurry entered the fishpond, the water in the pond became light green, the pH was between 6.5 and 7.5, and the water quality COD at the outlet was determined to be less than 100 mg/L, indicating that the biogas slurry was passing through. After use in oxidizing ponds and fish ponds, not only can they provide rich nutrients for fish, but also the effluent COD value can reach the first-level discharge standard.

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Decentralized biogas plants: status, prospects, and challenges

T.E. Rasimphi, ... P. Mhlanga, in Handbook of Biofuels, 2022

24.5.1 Biogas digester types

There are industrial digesters and small-scale biogas digesters all around the world, and these can be classified into fixed-dome plants, floating-drum plants, balloon plants, horizontal plants, earth-pit plants, and ferrocement plants.

Anaerobic digestion takes place in a digester, and these digesters are designed in a way that they do not allow air to enter (anaerobic digestion); that is to say, they are airtight. Geographic location often determines the design of the digester, and the availability of substrate and climatic conditions also contribute to choosing the design. For example, floating drum digesters are made from concrete and steel, and fixed dome digesters, which are mostly used in China, are constructed from bricks and cement, whereas balloon digesters are made from polyethylene foils with porcelain pipes as the inlet and outlet (Bond and Templeton, 2011). Fig. 24.2 shows three types of digesters, namely the fixed dome digester, the Indian floating drum, and balloon digester (Bond and Templeton, 2011), and they range in volume from 2 to 10 m3. The design operation of these digesters is simple: the feedstock enters through the inlet into the digestion chamber and, after digestion, comes out through the outlet where the slurry can be collected.

Figure 24.2. Common digester designs in the developing world. Bottom right: fixed dome digester (Chinese type). Top right: flexible balloon (Indian type). Bottom left: floating drum.

Data from Bond, T., Templeton, M., 2011. History and future of domestic biogas plants in the developing world. Energy for Sustainable Development 15, 347–354.

Despite the slow progress of biogas adoption programs, especially in Africa, the future predictions are promising. Apart from energy provision, pollution treatment is also another factor that digesters have been constructed for in several countries, including Ghana, Kenya, Tanzania, Rwanda, and South Africa (Amigun et al., 2012). From 2007 to 2011, 4000–5000 digesters are estimated to be constructed in Tanzania through the help of the Tanzania Biogas Development Program (Maree et al., 2007). Most of the digesters constructed in Africa are Chinese fixed dome digesters because of their advantages. The digesters are buried underground, which gives them an advantage because they are fixed, and there are also no rusting steel parts, extending the longevity of the biodigester (Amigun and Von Blottnitz, 2010). The biodigester is buried underground, and this protects them from any physical damage they may incur. Proper care is required as routine inspection, and if needed, repairing the pipes and fittings. But the fittings need limited maintenance.

The digesters constructed in several sub-Saharan countries served as pilot and demonstration projects. This was done to test the ease of use of small-scale biogas technology (Hivos, 2019). Such countries like Tanzania, Ivory Coast, and Burundi have produced biogas from animal and human waste using the Chinese fixed dome digesters and the Indian floating cover digesters (Omer and Fadalla, 2003).

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The role of techno-economic implications and governmental policies in accelerating the promotion of biomethane technologies

Dhamodharan Kondusamy, ... Karthik Rajendran, in Emerging Technologies and Biological Systems for Biogas Upgrading, 2021

16.3.6.6 China

It was after the 1970s that the biogas industry grew in China at a rapid pace and biogas digesters were installed in rural areas (Gu et al., 2016). This was supported by government measures aimed at overcoming the energy scarcity problems faced in these areas. The development of biogas infrastructure has been made a part of the long-term national developmental schemes by the government (Jiang et al., 2011). Since 2003, the government of China has been boosting the AD industry by direct financial support ranging from 1000 million CNY (China Yuan) in 2003–2005 to 2500 million CNY in 2006–2007. The Renewal Energy Law was introduced in 2006 to drive the biogas engineering projects and the financial aid reached 5000 million CNY in 2010 (National People’s Congress NPC, 2005; Ministry of Agriculture MOA, 2007). This was instrumental in boosting an increase in AD projects from 2300 in 2003 to 10,000 in 2013 (Gu et al., 2016). After 2009, China increased its support to the AD industry through subsidies covering up to 45% of the total project cost, along with introducing FITs. To improve the performance of existing plants, local biogas service systems were set up. China has a target of achieving 44 Giga cubic meters biogas production by 2020 of which a minimum household share of 30 Giga cubic meters is expected (National Development and Reform Commission NDRC, 2007).

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Sustainable Water & Energy Systems

Elisa Puzzolo, Daniel Pope, in Encyclopedia of Sustainable Technologies, 2017

Renewable gaseous and liquid fuels for cooking: biogas and ethanol

Biogas is a renewable gas generated by the anaerobic digestion of biowaste including manure and agricultural feedstock in household biogas digesters. Biogas is mainly composed of 50%–75% methane (CH4) and 25%–50% carbon dioxide (CO2) along with other trace components, depending on type of feedstock and operating condition of the digester. Biogas can be used for all household energy needs. Its production is dependent on multiple necessary conditions, including adequate livestock/feedstock, consistent access to sufficient water supply, and sufficient labor to manage the digester on a daily basis. Anaerobic digestion occurs under normal temperatures and costly enhancements are needed for adequate biogas production in colder climates (Bond and Templeton, 2011). Biogas digesters can vary in type, size, and construction materials. High-quality biogas units can operate for several decades if properly maintained. The plant can be integrated with latrine and hygiene facilities improving sanitation. A useful by-product from biogas production is fertilizer slurry, which can be used to enhance agricultural productivity. One of the barriers to the widespread diffusion of this clean fuel is the high installation and maintenance cost. In countries like Nepal, India, and China, biogas programs have been successful because of substantial financial and technical support provided by the government and various nongovernmental agencies (Puzzolo et al., 2016).

Ethanol is a liquid fuel produced by alcoholic fermentation of a variety of feedstock including sugars, starches, and cellulosic materials. The ethanol–water mixture produced after fermentation is further purified by distillation. Ethanol yields vary significantly according to the feedstock used. Ethanol is among the cleanest of household fuels when burned in proper cooking appliances. Cooking with ethanol requires hydrous fuel; denaturating agents and colorants are usually added to discourage users from drinking it as an alcoholic beverage (Puzzolo et al., 2016). Ethanol as a household fuel is commercially available in a relatively discrete number of countries across SSA, South-Asia, and Latin-America and the largest number of households using alcohol stoves are in refugee camps. Efforts to expand ethanol use are underway in several countries including Ethiopia, Kenya, and Madagascar. However, strong and consistent policy is needed to ensure appropriate fuel taxation and to avoid land competition with agricultural production if the fuel is locally sourced (Puzzolo et al., 2016).

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