Amy Lee, The New York Times (October 25, 2011)
In developing countries where domestic animals are ubiquitous and sewage systems rare, biogas technology — in this case methane derived from feces — can provide both valuable fuel and improved sanitation.
Unlike directly burning animal dung, the methane is clean-burning and odorless. And the technology has benign byproducts: reductions in deforestation and disease.
Dalla, a village of a hundred or so mud-walled, thatch-roof huts, clusters along a narrow dirt road a few kilometers from the forests of the Bardiya National Park in southwest Nepal. Buffaloes and cows lounge under thatch lean-tos to escape the hot sun. But unlike typical villages, Dalla’s approximately 550 residents use biogas for cooking in place of wood.
Biogas can also work in urban areas and with human waste. A few hours from Mumbai, a sprawling public toilet complex serving visitors to the temple of the Indian guru Sai Baba generates enough biogas to provide back-up power for the temple complex, which occupies almost a hectare, or two acres.
There are clear environmental benefits to using biogas, for both forest conservation and combating climate change. An average home biogas system can reduce firewood use by about 4.5 tons each year, which translates into 4 tons of greenhouse gas emissions, according to the World Wildlife Fund.
Jeet Bhadur Tharu, a 53-year-old farmer in Dalla, says almost all of his family’s cooking fuel comes from methane piped into the kitchen from an air-tight pit of dung and excrement dug beneath his backyard.
In the hut that is his kitchen, Mr. Tharu turns a valve on a narrow pipe and lights a burner on the floor; a strong blue flame instantly appears.
Before using biogas, Mr. Tharu’s family of five needed five to seven kilograms, or 11 to 15 pounds, of wood each day for cooking. The time-consuming task of gathering wood fell to his wife and daughters who cook in the small, unventilated kitchen. More than 1.5 million people worldwide die each year from diseases like lung cancer and childhood pneumonia caused by indoor air pollution from unventilated cooking fires, according to the World Health Organization.
Mr. Tharu’s wife and daughters “couldn’t always get dry wood,” he said: “It was very smoky, hard for women. Hard for eyes, and coughing. A lot of laundry to wash because clothes got very dirty. Now it’s better.”
There is no stigma attached to using biogas derived from the toilet and his buffaloes and cows for cooking, Mr. Tharu added.
In the Terai, Nepal’s thickly forested south, 61 percent of the people rely on wood for cooking, as fuel like liquid petroleum gas is too expensive for them, according to the World Wildlife Fund. Meanwhile there are 4.5 million cattle in the Terai that produce tons of dung each year. Most rural areas lack sewage systems.
Given this equation, it is not surprising that the government of Nepal, through its Alternative Energy Promotion Center, has helped build 200,000 biogas systems across the country and has set itself an ambitious target to eventually reach two million. The World Wildlife Fund supported the construction of 7,500 of the existing biogas systems in Nepal, including the ones in Dalla village.
The technology for a home biogas plant is simple and low-tech. Dig a pit ranging in size from 4 to 10 cubic meters, or 140 to 350 cubic feet (the average size is 6 cubic meters), line it with concrete and fit it with an air-tight concrete cover. Place animal dung and water into a round, concrete mixing bowl. A metal crank blends the concoction and pushes it into a pipe that feeds into the underground pit. Nearby, build a simple latrine made of concrete and bricks; gravity and water push human excrement into the same pit threough a pipe.
Deprived of oxygen, the waste mix decomposes, giving off methane, which flows under its own pressure into a narrow PVC pipe leading into the kitchen.
Another byproduct of this anaerobic process is pathogen-free manure, which flows out of the pit when it fills up, and can be used by farmers as fertilizer.
Ugan Manandhar, program manager with the World Wildlife Fund in Nepal, says biogas systems require little maintenance and are safer than combustible tanks of liquid petroleum gas. Villagers are taught to use only dung and water in their biogas plants — no chemicals or plastic should go into the pit. They are given a basic training to fix faulty pipes, though Mr. Tharu says there have been no problems with his biogas system since its installation two years ago.
Still, biogas systems are expensive for “middle poor” people like Mr. Tharu. It costs about $550 to build a home biogas system, including quality-control audits and a toilet. Most of that expense is paid by a combination of government subsidies and financing programs for villagers.
For now, biogas systems do not work in the colder conditions of Nepal’s Himalayan ranges, since the bacteria involved need warmth to thrive and multiply. Mr. Manandhar of the World Wildlife Fund says research is being done on insulation for biogas plants that could function at higher altitudes.
On the other hand, biogas plants can work well in urban areas, where their waste treatment role makes them doubly useful. Since 1970, Sulabh International, a nongovernmental organization based in Delhi, has helped build more than a million affordable latrines, which work without running water. Barely a third of India’s 1.2 billion people have access to hygienic latrines, and hundreds of millions have no choice but to relieve themselves in the open, which easily leads to the spread of disease.
Across India, Sulabh has built 200 biogas plants attached to toilets that are approved by the Indian government’s Ministry of Non-conventional Energy Sources. Some are powered by large public toilet facilities used by thousands of people each day. The biggest is in Shirdi, about four hours’ drive from Mumbai, which serves up to 7,000 people a day. The city is home to a temple devoted to the guru Sai Baba that attracts up to 100,000 visitors a day. With funds from a trust established by Sai Baba, who died in April of this year, Sulabh built what it describes as an “aesthetically exquisite and visually appealing, colorful toilet-cum-bath complex,” with 120 toilets and 108 “bathing cubicles.” Biogas from human waste runs lights at the complex during power failures.
Bindeshwar Pathak, founder of Sulabh, argues that biogas technology is inherently safe, and so far there have been no accidents from leaks at Sulabh’s biogas plants, he says. The organization has also helped build sanitary facilities in a dozen African countries including South Africa and Ethiopia, as well as in Laos, Bangladesh and Afghanistan.
In Kabul, where the city’s infrastructure is in shambles, five Sulabh community sanitary complexes with biogas plants, financed by the Indian government, were formally opened in 2007 in the presence of Mr. Pathak, the mayor of Kabul, the Indian ambassador to Afghanistan and other dignitaries.
The underground pits remain warm enough even during Kabul’s cold winters for bacterial decomposition to continue, and the design has attracted interest from U.S. Army engineers, who are considering building 40 similar complexes elsewhere in Afghanistan, according to Mr. Pathak.
“Biogas technology from human waste has multiple benefits: sanitation, bioenergy and manure,” Sulabh emphasizes. And in Afghanistan, the unlikely benefits of dung could include an unconventional aid to diplomacy, too.