Kampala — HUMAN excreta and urine are now an asset to farmers because they are a cheap source of biogas energy. The two offer the best biogas followed by pig and cattle dung.
Banana peels, poultry droppings, water hyacinth and algae are the other organic raw materials that generate biogas. Banana peels and water hyacinth should be mixed with cow dung and poultry droppings to give off good gas after putting them out to dry under the sun for two days to reduce the amount of sap.
Andrew Ndawula, a technician subcontracted by Heifer International Uganda (HIU), revealed this during the recent tour of Heifer biogas beneficiaries by Dr. Sahr Lebbie, the Heifer International vice president of the Africa programme, based in USA.
Heifer International is a worldwide NGO whose mission is to work in partnership with others to end hunger and poverty and to care for the earth through sharing livestock and knowledge. Its main goal is to improve food security and the income of needy households, while focusing on the family, gender and environmental protection through sustainable agriculture.
In conjunction with its partners, HIU has initiated the construction of biogas plants among beneficiaries after realising that deforestation is a serious threat to the environment.
"Biogas will slow down the rate of deforestation and its by-products are utilised to improve soil fertility," said Lebbie. He added that biogas also indirectly reduces the burden of women and children fetching firewood from long distances.
Biogas is an inflammable gas produced by bacteria during bio-digestion fermentation of organic materials. This occurs under airless condition in an air tight container called a digester. It is composed of methane gas (60-65%) and carbon dioxide (35-40%). Biogas from animal excreta contains 60-90% methane and is combustible if the methane is more than 50%. In this range, biogas burns without further purification.
"There are three models and different sizes of biogas plants: floating, polythene tubular system and the Chinese fixed dome. "The fixed dome is the most common and economical plant constructed for HIU beneficiaries," said Ndawula.
The smallest size of fixed dome is 6-cubic metres (cu/m), and the largest is 100cu/m. Thirty cu/m and above are for institutions or large farms. The fixed dome is of two types; bricks/blocks type and cast systems. The price of cement, bricks and galvanised pipes put the total cost of the plant high.
The 6 and 8cu/m plants pressure prepares a simple meal in 24 hours if both the cow and plants are well fed and maintained. The digester should not be under- or over-fed by raw materials in order to have constant pressure supply to the house. The 12cu/m plant can be maintained by two or three well fed zero-grazed cows. Gas can light one lamp and a twin-burner for a family of 8-10 people.
However, the 16cu/m plant can be maintained by three to six cows. Its pressure can run three burners and two lamps. People owning animal farms should go for 30cu/m plant. Ten and more cows can sustain the plant that runs about five lamps, a canteen burner (commercial) and a twin-burner. This type of plant has two expansion chambers that maintain constant pressure.
Ndawula noted that 75 to 100cu/m have been built in Kenya and Tanzania by institutions such as universities. "I have approached a number of institutions in Uganda to put up similar plants, but they are skeptical," he added.
In China, Kenya and Tanzania institutions mix human and animal excreta, giving off good grade methane, while some institutions in China make biogas from only human excreta.
The polythene tubular chamber is either buried underground or left on top. It is a simple design, easily adoptable and cheap, compared to other biogas energy sources to the rural communities and low-income earners. Despite, its advantages it has not been fully successful because of fragility.
The tubular digester was first developed in Colombia in 1980s and then introduced in Vietnam, Tanzania, Kenya and finally to Uganda by Dr. Sarwatt of Morogoro University, Tanzania, in 1996.
Biogas plants behave differently in different areas due to varrying temperatures. During the cold or rainy weather, decomposition of materials slows down because of low temperatures. In the dry season, clients also register a low supply of cow dung due to scarcity of pasture.
The digester is the first chamber and stores the raw materials that undergo fermentation. Biogas accumulates on top of the raw materials before it sent to kitchen. In order to have a continuous gas production, the digester should be fed daily in the morning and in the evening through the two mixing chambers outside the cattle enclosure.
Before mixing, anything that does not rot, for instance stones and wood are removed. The dung and urine must be mixed in equal amounts.
The exotic cow gives one wheel-full of dung when well fed. In order to avoid pressure dropping, the recommended piping from the plant is 50metres.
Patrick Nalere, the HPI country director, said biogas technology gives off clean energy. "Its keeps the environment free of organic wastes, is convenient, time-saving and reduces smoke-related illnesses often associated with the use of firewood," he added.
"If the majority of Ugandans adopted biogas, we would preserve our biodiversity. People should exploit decomposing raw materials, which are free. Biogas plant maintenance is not regular, constant energy, no load shedding, local technicians are available, appliances are now locally-made and there is no metering. Therefore, no monthly power tariffs," said Nalere.
Biogas is used for cooking, lighting pressure lamps, in four-stroke engines, as fuel to supplement part of fuel compression engines and to run liquid absorption refrigerators.
The byproduct, 'slurry', is rich in nutrients that improve soil and fish farming. Its mechanism is clear and producing biogas is simple.
Ashram and Safinah Wasswa, the latest beneficiaries from Nakabago parish, Goma sub-county in Mukono district, said whatever development seen at home is a result of HIU.
"We received our heifer in 2000 and it has done a lot to transform our life. We get about 20 litres of milk daily and biogas. We had a small piece of land, but it has been increased to 210ft x200ft, and also bought a motorcycle. We have also built a big house and are in the process of setting up a poultry project," they noted.
The Wasswas' soils were depleted of nutrients, but for the last few years, the plant yields have picked up. With eight children, they were living an impoverished life before 2000. They occupied a plot of land of 50x100ft. "With the grace of God, Heifer pulled us from the pangs of absolute poverty," they said.
Kintu and Joyce Kiwanuka from Nsambwe B, Nyenje parish, Ggoma sub-county in Mukono district are also among the recent beneficiaries. Mary Nakabugo and Jackson Sezibwa from Ntaawo, from Mukono district were the first plant beneficiary Lebbie visited.
Lebbie noted that their dreams have been turned to reality. "I feel good. It gives me zeal and energy to fight for more funds to help the needy. The government cannot do everything."
Ndawula's experience goes way back in 1989. He has worked with a number of international organisations like ADRA Uganda, UNFA, ADF and individuals. His first biogas plant in Kabale was commissioned by the first lady, Janet Museveni, and still serves the beneficiaries.