Ashden Conference 2018
Millions of people still use solid fuels like wood and charcoal to cook their food every day. This causes respiratory problems and puts a burden on the families who have to collect the wood. Biogas is an effective alternative, made from breaking down waste like animal dung or leftover food, it provides a sustainable source of clean fuel for cooking, lighting, or electricity.
When organic matter like animal dung, leftover food or human waste decomposes in the absence of oxygen, biogas, a mixture of methane and carbon dioxide, is produced. This process is known as anaerobic digestion, and as well as biogas it produces a semi-solid residue which is useful as a crop fertiliser. Biogas can be used to provide heat for cooking, for lighting or be fed into a gasoline engine to power an electrical generator.
The Ministry of Agriculture and Rural Development (MARD) in Vietnam and Netherlands Development Organisation (SNV) collaborated in Ashden Award-winning work to develop a nationwide biogas programme in Vietnam, in order to deal with the problem of waste produced by domestic pig farming and to create a new source of clean energy for rural families.
Ashden Award winner SkyLink Innovators were recognised for their work installing institutional biogas plants in schools in Kenya, as well as smaller domestic plants. Deforestation for firewood is a major problem in Kenya, and SkyLink’s plants reduce the demand for firewood as well as reducing CO2 emissions.
Indian consultancy BIOTECH, an Ashden Award winner in 2007, promotes the use of biomass plants to manage food waste and provide a source of electricity and biogas for cooking. This allows the safe, convenient disposal of waste for domestic users. Markets and councils are also able to use larger digesters, reducing disposal of food waste onto streets and allowing markets to run generators on the gas produced.
Appropriate Rural Technology Institute (ARTI) is a charity in India which won an Ashden Award for creating a small, cost effective plant which uses food waste to produce biogas. Each plant is made from two adapted plastic water tanks, with pipes to add waste food, remove liquid effluent and transport biogas to the kitchen. The biogas produced replaces the use of kerosene or LPG, and fuel savings mean that the initial cost is repaid within 2 years.
The cost of biogas plants varies greatly from country to country, because the costs of both materials (brick, concrete and plastic) and labour can be very different, but is usually $500 or more.
Using plastic or steel to pre-fabricate biogas plants usually increases the material cost but can substantially reduce the labour needed for installation.
The economic viability of biogas depends on the cost of the fuel being replaced, and whether there are other financial benefits. For example, MARD/SNV plant users can pay back the cost of a plant in about four years through savings in LPG, but even more quickly if the reduced need to buy fertiliser is taken into account.
The potential of biogas plants to reduce greenhouse gases (including methane from uncontrolled dung and sewage management as well as carbon dioxide) means that carbon-offset finance has been a source of funding for some biogas programmes.
Rural families often use animal manure as the feedstock for biogas: the plant needs to be topped up with a mixture of manure and water each day. The manure from two to four cows (or five to ten pigs) can produce enough gas for all average-sized household cooking needs, and sometimes for lighting too.
Ashden Award-winner BSP-Nepal is a good example of plants that use cattle manure, and Biotech in Kerala, South India, supplies food-waste plants for this urban market. A family or community using just its own food waste can replace between a quarter and a half of their cooking fuel.
Most household biogas plants replace wood for cooking, and this brings many benefits. Cooking fires and wood stoves produce high levels of indoor air pollution, which kills more than four million people across the globe each year. Biogas burns with a clean flame and cuts pollution to safe levels. Studies by BSP-Nepal found that households with biogas plants save three hours per day on average, and women benefit most. Biogas is available whenever it is needed and cooks food quickly.
Biogas plants that use human sewage improve hygiene and sanitation as well as providing cooking fuel. About two thirds of the cattle-manure plants supplied through BSP-Nepal have a household toilet attached as well, as do many of the pig-manure plants supplied through MARD/SNV.
In Rwanda, the Kigali Institute of Science of Technology, now known as the College of Science and Technology, built large biogas plants to manage sewage in prisons, which has improved hygiene and reduced pollution of nearby land where raw sewage used to be discharged.
The residue from dung-based biogas plants makes a good fertiliser with minimal smell. The fertiliser value can be improved by composting the residue with crop waste.
Biogas plants have huge potential to produce clean fuel from unhygienic, wet organic waste. There are many more rural and peri-urban areas where traditional dung-based plants could be used. There may be even more potential in towns and cities, where waste disposal and sanitation is becoming an increasing challenge as more people move to urban areas.
Interest is also growing in the use of larger plants for electricity generation and to supply gas grids. In the UK, Ashden Award winner Ecotricity is now developing anaerobic digestion plants to feed gas directly into the national gas grid.