Why Biogas Digesters Give Me Hope
At this season of gratitude and thanksgiving, I am very grateful to everyone who donated to my fund-raiser to subsidize a biogas digester for a group of farming families in Guane, right below Barichara. Thanks to all who contributed, I can now present them with $950 toward the cost of a small biodigester that will run on animal manures! And I am grateful to be connected with the Earth Regenerators movement, with plans to return to Barichara hopefully in January.
I’m also grateful for the abundant, clear, clean water that flows from these mountains in North Carolina, which seems even more precious as Barichara faces its dry season.
There is a permaculture principle: “The problem is the solution.” When you look deeply enough at any problem, one may find a solution lurking within it.
The problem
All organic wastes generate methane as they decompose. Methane is 86x more potent as a greenhouse gas than CO2 in a 20-year timeframe. Globally, livestock manures are responsible for about 10% of methane emissions. Each year, methane from livestock manure alone has the warming equivalent of 240 million tons of carbon dioxide, or the same as a year of emissions from 52 million cars. A great deal of organic wastes end up in landfills, where just a small fraction of the methane is captured. Food waste makes up over 20% of US landfills. In many countries, wood is used for cooking, leading to deforestation, and causing health problems due to smoky fires. Meanwhile, animal and human wastes are a threat to streams and pose health hazards. Farmers struggle to fertilize their crops, often relying on chemical fertilizers that damage soil and water. There is a better way! Biogas digesters, or biodigesters.
How they work
Biogas is created through a process of anaerobic digestion, whereby microorganisms break down plant and/or animal wastes under oxygen-free conditions. Biodigesters can be powered with animal manures, human waste, crop waste, kitchen and food waste. Woody waste high in lignins cannot be processed, as lignin does not break down in a biodigester. “Co-digestion” means using more than one feedstock, e.g., using cow manure but adding grass, fats, and oils in order to achieve the optimal carbon to nitrogen ratio, between 20–30:1. (Excess nitrogen can lead to ammonia, which inhibits digestion.)
Biogas is 50–70% methane, 30–40% CO2, plus water vapor and trace gases including hydrogen sulfide, which can be scrubbed out with filters. This gas can be used for cooking, heating, lighting, combined heat & power, or electricity generation, or to fuel cars. 20 liters of cow manure plus 40 liters of water generate 1 cubic meter of biogas, enough to cook 3 meals a day for a family of 4. (Just 5 liters of pig manure can create that amount.)
The other valuable product is an excellent liquid fertilizer, which when applied to the soil or as a foliar spray, increases crop yields up to 30% and prevents many plant diseases. Livestock bedding can be made from the dried solids. The optimum temperature within the digester for rapid production is 86–100 degrees F (30–38 C). This makes biodigesters easier to operate year-round in warmer climates, and above-ground construction is cheaper. In colder climates, some of the gas can be burned to heat the digester. The digester can be placed underground or under a greenhouse/hoophouse.
Other benefits: decreased odors, flies, and pathogens from manure, less methane emissions. There’s less water pollution from livestock waste, and less need for chemical fertilizers, improving the soil while saving farmers money. Nitrogen oxides from chemical fertilizers are even more potent than methane as a greenhouse gas, and runoff of nitrogen into waterways is harmful, causing eutrophication or algal bloom. And they destroy the natural soil life.
100 tons of food waste per day could create enough biogas to power up to 1400 homes. Shredding or pulping the food waste to increase surface area for the bacteria to decompose it, improves efficiency of biogas production.
History of biodigesters
In 1859, in Bombay, India, an early biogas digester plant was built in a leper colony; in 1895, England began using biodigesters to treat sewage, and used the gas to power street-lamps. In the early 20th century, Germany used biogas for fueling vehicles, for heating, and to light street-lamps. Obviously, this technology is not new.
Types
Mesophilic and thermophilic digesters: Mesophilic operates at lower temperatures (30–38 C), while thermophilic runs at 49–57 C. The latter is a faster process and produces more gas, with greater pathogen reduction, hence more suitable for human waste.
There are “batch” digesters and “continuous flow” digesters. The batch type is cheap and simple, but the continuous type yields a steadier flow of gas.
China is #1: Household or small farm digesters are now China’s largest producers of methane biogas, with 43 million in place by 2013. Over 70,000 people were employed to promote and build biogas digesters. To help meet China’s goal, subsidies for half of the digester cost were made available. In 2014 alone, the central and local governments invested the equivalent of US$35 million in digester engineering and construction.
India: Due to government support, by 2008 over a million rural households and small farms had biodigesters. Many households in rural India, as well as in some Central and South American countries, still depend on fuelwood for cooking, since cleaner fuels are not available or affordable to many. Average wood consumption per household is over 10 lb./day, a serious threat to forests and woodlands. Globally, the loss of forest cover results in increased greenhouse gas emissions, and is a significant contributor to climate change. Collecting firewood, traditionally a woman’s or child’s task, is extremely time and labor intensive, leaving fewer hours for school and other daily tasks. And as the forest recedes further, wood collection becomes an increasingly labor-intensive task.
The India Biogas project was developed by First Climate and Indian NGO INSEDA (Integrated Sustainable Energy and Ecological Development Association) and provides a sustainable solution to these problems. More than 4,000 households are provided with their own biogas plant to utilize the free and sustainable energy from animal manure. The biogas is used for cooking, household lighting and boiling water to prevent diseases.
Household-sized biogas plants cut greenhouse gas emissions by reducing use of firewood for cooking. In the project host states of Kerala and Madhya Pradesh, only 5–10% of firewood is from sustainable sources. To generate biogas, animal waste is mixed with water and then fed into the plant where it is digested over about 8 weeks. The gas is extracted via a valve located in the roof of the digestion tank. Constructed underground, the digester can operate for more than 20 years. The plants are built through locally available materials and labor, thus generating employment.
Economic impact: The project supports households whose average monthly income of 10–20 USD per month. Utilizing biogas from livestock waste saves families money by replacing LPG or propane; and the liquid fertilizer produced helps increase the farms’ yield.
Health benefits: The project reduces hazardous wood smoke from traditional indoor stoves. The fumes cause eye infections and respiratory diseases such as asthma, pneumonia, bronchitis and emphysema. These diseases are common among both women and children, who have the most exposure to the smoke. Biogas is a clean and safe source of energy and helps to prevent further spreading of those illnesses.
Environmental gains: Slowing deforestation (for fuelwood) means reduced soil erosion, conservation of natural habitats, biodiversity protection, and climate change mitigation.
- Total emission reductions: 20,000 t CO2
- Number of households benefited by the project: 4,265
- Number of people affected: approx. 20,000
- Total amount of cow dung used to run all plants: 283 tons per day
- Annual savings of firewood/biomass: 15,000 tons
- Jobs created: more than 150
Source: India Biogas/First Climate
Germany had 8,625 digesters by 2014 — due to 1991 adoption of long-term contracts compensating investment in renewable energy generation. By end of 2013, 4.5% of Germany’s electricity came from biogas.
Latin America: www.Sistema.bio, based in Mexico, has distribution and training hubs on 5 continents including South America, India, and Africa. They are partnered with Ashoka, Heifer International, EPA, Nature Conservancy, USAID, UNDP, and more. They’ve received awards from the Bioneers, Buckminster Fuller Institute, and Ashden. Their above-ground biodigester model uses a geo-membrane. Sistema.bio reports that most small farmers recover the cost of the digester within 18 months after installation. This company states that a 30% reduction in global methane emissions will be possible if 400 million smallholder farmers used this technology. They sell and install the kits, sized based on the quantity of manure available; they teach proper use, and make 2 follow up visits to ensure all is working well. Sistema.bio offers a 10-year warranty and reports that a digester typically operates for 20 years.
Network of Biodigesters in Latin America and the Caribbean (www.REDBioLAC.org) brings together institutions involved in the research, development, dissemination and implementation of low-cost biodigesters in nine Latin American countries. Its members include manufacturers of biodigesters, NGOs, research centers and universities to share information and experiences, plus identify technical, environmental, social and economic barriers. They plan ways to spread the biodigester technology in different countries, systematize research and dissemination among partners and encourage policies related to biodigesters.
Africa: Over half of the developing world’s households cook primarily with wood, charcoal, coal, crop waste, or dung. A 2014 World Bank report estimated that over 700 million Africans use solid fuels as their primary fuel source, with 98% of households in rural areas depending on it. Burning solid fuels, plus inefficient and polluting cookstoves lead to major public health challenges, causing more premature deaths than HIV/ AIDS, malaria, and tuberculosis combined. The use of solid fuels can be expensive, and contributes to adverse environmental and climate change effects.
Africa Biogas Partnership Program (ABPP) works in Kenya, Tanzania and Uganda. ABPP, established in 2009, promotes adoption of biodigesters by rural households in sub-Saharan Africa. By 2017 over 27,000 households had a biodigester, half of them in Kenya. Additional benefits include increasing agricultural productivity by using bio-slurry, improving health, reducing deforestation, and adding to incomes.
Households report higher crop yields, reduced fuel consumption, fewer eye problems and respiratory symptoms. Benefits most appreciated are “easy cooking” and “saving time and money”. Households with biodigesters use 2–3 fewer tons of wood per year than similar households without biodigesters.
Water use: Green Heat, a Ugandan company, has created an on-farm system that produces biogas and fertilizer while reducing the demand for water by 80%. These are being promoted widely throughout Africa. Using a patented Slurry-Separation Technology, the Green Heat digesters can be fed with liquids including wastewater and even urine. Water is separated from waste matter and recycled back into the system. The SST dewaters slurry and converts it to solid fertilizer, which can then be applied directly to farmers’ fields. According to Green Heat, the dry fertilizer has boosted crop yields up to 270%. www.greenheatinternational.com
US: The US has only 2,200 operating biogas systems, less than 20% of the estimated potential. There are 1200 Water Resource Recovery Facilities treating sewage with biodigesters; over half of these use the biogas for heat or electricity, though some just flare it off. Among some CAFOs (concentrated animal feeding operations) there is a “renewable natural gas” movement to generate methane from them, but this provides greenwashing for unsustainable and inhumane practices that many believe should be outlawed.
Sewage treatment: Oakland’s East Bay Municipal Utility District uses biodigesters to process both sewage and food waste, generating up to 1300 kwh of electricity per ton of waste. EBMUD was the first wastewater facility in the nation to generate more electricity than the plant needs to operate in a year. It can generate more than 55,000 megawatt-hours annually.
In India, disposal of human waste in extremely cold terrains, railways and even in rural areas is a major concern. DRDO (Defense Research Development Organization) converts human waste into biogas; they report that pathogens are decreased by 99%. Biodigesters have been extensively fitted in rail coaches by Indian Railways with collaboration of DRDO. Biodigesters are suitable even for sub-zero temperatures of the Himalayan region, glaciers, plains and coastal regions. In addition to human excreta, they can also be used for kitchen and animal waste disposal.
Vehicle fuel: Biogas can be upgraded to biomethane by removing CO2, water vapor, H2S and other trace gases; it can then be used as a vehicle fuel. In Sweden, 38,600 vehicles run on it, including 25% of public buses.
“Waste” is sometimes just a resource we haven’t figured out how to use yet!