Biogas power

Biogas is a gaseous mixture generated during anearobic digestion processes using waste water, solid waste (e.g. at landfills), organic waste, and other sources of biomass. Biogas can be upgraded to a level compatible with natural gas (‘green gas’) by cleaning (removal of H2S, ammonia and some hydrocarbons from the biogas) and by increasing its methane share (by removing the CO2). The resulting green gas can subsequently be delivered to the natural gas distribution grids. In developing countries, biogas could be an interesting energy option, in particular for those countries that rely heavily on traditional biomass for their energy needs.

Responds to the following needs

Diversification of energy sources
Cleaner energy sources
Reduced GHG emissions

Suitable for

Industry with organic residues
Small-scale biogas suitable for off-grid rural areas

Relevant CTCN Technical Assistance

Introduction

Biogas is a gaseous mixture generated during anearobic digestion processes using waste water, solid waste (e.g. at landfills), organic waste, e.g. animal manure, and other sources of biomass (Welink et al., 2007). Anaerobic digestion is the biological degradation of biomass in oxygen-free conditions. In the absence of oxygen, anaerobic bacteria will ferment biodegradable matter into methane (40-70%), carbon dioxide (30-60%), hydrogen (0-1%) and hydrogen sulfide (0-3%), a mixture called biogas. Biogas is formed solely through the activity of bacteria. Although the process itself generates heat, additional heat is required to maintain the ideal process temperature of at least 35°C. In comparison, the methane component of natural gas could amount to over 80%. In nature, biogas is generated at the bottom of stagnated ponds, lakes, swamps or in the digestive system of animals (Jepma et al., 2006).

Biogas can be produced on a very small scale for household use, mainly for cooking and water heating or on larger industrial scale, where it can either be burnt in power generation devices for on-site (co)generation, or upgraded to natural gas standards for injection into the natural gas network as biomethane or for use directly as gaseous biofuel in gas engine-based captive fleets such as buses. The feedstock, e.g. animal dung or sewage, is converted to a slurry with up to 95% water, and – for small-scale applications – fed into a purpose-built digester. Digesters come in many forms and sizes, which may range from 1 m³ for a small household unit to some 10 m³ for a typical farm plant and more than 1,000 m³ for a large installation. Biogas production in such cases can be both continuous and in batches with digestion taking place for a period from ten days to a few weeks.

A small domestic biogas system will typically consist of the following components (EPA, 2010):

Manure collection: raw, liquid, slurry, semi-solid and solid manure can all be used for biogas production.
Anaerobic digester: The digester is the component of the manure management system that optimizes naturally occurring anaerobic bacteria to decompose and treat the manure while producing biogas.
Effluent storage: The products of the anaerobic digestion of manure in digesters are biogas and effluent. The effluent is a stabilized organic solution that has value as a fertilizer and other potential uses. Waste storage facilities are required to store treated effluent because the nutrients in the effluent cannot be applied to land and crops year round.
Gas handling: piping; gas pump or blower; gas meter; pressure regulator; and condensate drain(s).
Gas use: a cooker or boiler.

For applications on a larger scale, feedstocks such as sewage sludge from waste water treatment plants, wet agricultural residues and the organic fraction of municipal solid waste (MSW) can be collected and used. Biogas can be used for all applications designed for natural gas, given a certain upgrading of its quality (IEA Bioenergy Task 37, 2005).

Feasibility of technology and operational necessities

Small scale applications

Small scale biogas for household use is a simple, low-cost, low-maintenance technology, which has been used for decades across the developing world. Such small-scale applications are mostly implemented through programmes supported by governments. In such cases, it usually concerns rural areas and communities without connection to the grid. Although some cattle would be needed to feed the digester (about seven) and water needs to be available as well, other requirements are rather low.

Data on biomass use is often hard to access and difficult to evaluate because of the diversity in consumption patterns, differences in units of measurement, the lack of regular surveys and the variation in heat content of the different types of biomass.

The switch to biogas in cooking is not without challenges. According to the IEA, with an increase in income, households do not simply switch from one fuel to another. The use of multiple fuels in parallel may enhance energy security compared to reliance on a single fuel or technology. Besides, traditional food preparation processes are not easily being overhauled because of taste preferences and the familiarity of cooking with traditional technologies. Nevertheless, in the long run and on a regional scale, households in countries that become more wealthy are generally projected to shift from cooking exclusively with biomass to using more efficient technologies, amongst which biogas can be one option (IEA, 2006, 2008).

Large-scale applications

Industrial applications are designed to process large amounts of feedstock into biogas, which requires a well-developed logistical system for feedstock collection and effluent disposal. Because of costs associated with feedstock collection, the viability of such plants depends on the availability of very cheap or free feedstock such as sewage sludge, manure, agricultural residues or organic fractions of municipal solid waste. Decentralized farm-size units are increasing productivity by supplementing their feedstock with agricultural residues or crops (IEA Bioenergy, 2009).

How the technology could contribute to socio-economic development and environmental protection

Small scale applications

Social benefits

Smoke-free and ash-free kitchen, so women and their children are no longer prone to respiratory infections;
Women are spared the burden of gathering firewood;

Environmental and health benefits

Keeping manure and waste in a confined area and processing themin the digester reduces the amount of pollutants in the immediate environment and increases sanitation;
Households no longer need to extract wood for cooking, which can reduce deforestation levels where people heavily rely on woodfuel;
The sludge remaining after digestion is a good fertilizer, increasing land productivity (and farm incomes).
The release of methane is avoided thus contributing to climate mitigation. A single, small scale biodigester reduces between 3 and 5 tCO₂-eq./year. Most of the biogas has a methane component of 50 to 60%, a CO₂ component of 35 to 50%, and a relatively small amount of hydrogensulfide (H₂S) and ammonia. In comparison, the methane component of natural gas could amount to over 80%.

Economic benefits

Buying (fossil) fuel resources (e.g. kerosene, LPG, charcoal or fuel wood) is no longer needed
Switching from traditional biomass resources (e.g., in developing countries) or fossil fuels (e.g. in industrialised countries) to biogas fired generation capacity improves security of energy supply (locally as well as nationally or regionally) as the feedstock can mostly be acquired locally

Possible negative aspects of the biogas installations are the possible reduction in soil fertility since animal dung is now used as feedstock for the biogas installation instead of for fertilisation. This aspect can be addressed by using the bioslurry that remains as a side-product of the biogas production process for soil fertilisation. Another potential problem is related to the possible build-up of pathogens (worms, protozoa and some fatal bacteria such as salmonella) in the biogas system. A study carried out for biogas systems in Nepal has shown that some pathogens were present in the bio-slurry. Studies have been undertaken to explore whether the biogas systems could enhance the breeding of mosquitoes. However, no direct relation was found between biogas production and mosquito breeding (Netherlands Ministry of Foreign Affairs, 2007).

Large scale applications

Industrial scale digesters also offer a number of benefits

Biogas can contribute to replace fossil fuels, thus reducing the emission of GHGs and other harmful emissions;
By tapping biogas in a biogas plant and using it as a source of energy, harmful effects of methane on the biosphere are reduced;
Industrial estates can, by processing their waste in a biogas plant, fulfill legal obligations of waste disposal while at the same time, generate energy for production processes, lighting or heating;
Municipalities can use biogas technology to solve problems in public waste disposal and waste water treatment
It’s a natural waste treatment process;
Requires less land then anaerobic composting;
Reduces disposed waste volume and weight to be landfilled;
It generates high quality renewable fuel proven to be useful in a number of end-use applications
It significantly reduces GHG emissions
It maximizes recycling benefits
Considering the whole life-cycle, it is more cost-effective then other waste treatment options (IEA Bioenergy, Task 37, 2005).

Product examples

Biodigesters [East Africa Climate Innovation Network (EACIN)]
Biodigester for biogas production [Gbolawande Nigeria Limited]
Biogas production from protein-rich materials [Oklahoma State University]
Biogas Booster [TechnologieAllianz e. V.. Germany]
Compost and Biogas from Organic Waste Materials [University of California Davis]
Domestic Waste Biogas System [East Africa Climate Innovation Network (EACIN)]
Production of Biogas by Dry Fermentation [BEKON Energy Technologies GmbH Co KG, Germany]
Renewable energy- Landfill gas and biogas utilization [Ministry of Economy, Israel]

References

EPA (2010): AgSTAR Handbook: A Manual for Developing Biogas Systems at Commercial Farms in the United States, available online at [[5]]
IEA Bioenergy Task 37 (2005): Biogas Production and Utilization, available online at [[8]]
IEA, (2006): Energy Technology Perspectives - Scenario and Strategies to 2050, in support of the G-8 Plan of Action, Paris, France.
IEA, (2008): Energy Technology Perspectives - Scenarios and Strategies to 2050. International Energy Agency, Paris, France.
Jepma, C.J. and Nakicenovic, N. (2006): Sustainable Development and the Role of Gas, EDReC/IIASA/IGU.
Netherlands Ministry of Foreign Affairs (2007). Clean and sustainable? An evaluation of the contribution of the Clean Development Mechanism to sustainable development in host countries, IOB Evaluations, no. 307, the Hague, the Netherlands.