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The amount of human waste we generate each year is astounding. The United States and Europe, for example, combine to generate 40 million tons of sludge from sewage treatment. Converting this material to biogas and biosolids is a cleaner, cheaper, and more sustainable way to produce heat, electricity, and farming fertilizer than dumping it into a landfill. And the result doesn’t even stink.
Turning feces into fuel is not a new technology. Experts at the University of Adelaide in Australia point out that human excrement biogas was used to heat water in 10th century B.C. Assyria and 16th century C.E. Persia, generate power in 13th century China, and power gas street lamps in Victorian Britain.
In the United Kingdom today, dwindling domestic gas reserves, a dubious reliance on foreign energy imports, and a commitment to get 15 percent of its energy from renewable resources by 2020 has made human waste appealing again. This summer, British Gas will partner with Thames Water and Scotia Gas Networks to pipe human-excrement-generated methane directly into the homes of 130 U.K. families, replacing natural gas.
Here’s how they’ll do it: Feces flushed down the toilet will be transported to sewage processing plants where settlement tanks separate the sewage into clean water and sludge. Anaerobic digesters break down the sludge into solid, odorless waste and methane gas by fermenting it with bacteria. The waste is used as fuel or fertilizer while the gas travels to a biogas plant to be treated for impurities and turned into clean gas. The clean gas—which has the same odor as natural gas, if at all—is pumped back into the national energy grid no more than 23 days later and piped into homes.
The United Kingdom already has plants that convert human waste into electricity. But this would be the first to convert feces to gas, and the National Grid—the high-voltage electric power transmission network in Britain—believes the United Kingdom could meet half of its gas needs by implementing this practice statewide.
But it’s not just Britain that’s smelling the potential. The Kigali Institute of Science Technology and Management in Rwanda developed a prison-based biogas technology that converts prisoners’ feces from more than 15 prisons around the country into methane gas to meet half of the cooking and lighting needs in each facility. The prisoners then restock the gas supply with their excrement. Prisons have been overcrowded by 10 times their capacity since the end of Rwanda’s genocide, and with more than 120,000 prisoners in only 30 facilities, the prisons have significant energy and waste cleanup needs. This process has helped by reducing the annual wood fuel costs by 60 percent.
In India, Sintex Industries, a plastic and textile manufacturer, has created a new biogas digester to turn human excrement, cow dung, or food waste into cooking fuel and electricity. Government officials plan to end open-air defecation by 2012, so the biogas digesters are an intelligent solution. A one-cubic-meter digester can convert a four-person family’s waste into enough gas to cook three meals a day and provide fertilizer. While these small digesters are expensive for the majority of Indians—at roughly $425 a pop—experts say they will pay for themselves in less than two years and the government will subsidize a third of the cost.
But despite successes with this process in other countries, the United States is slow to get on board. It is not planning on building any new waste-to-energy plants, even though the federal government and 24 states can subsidize this type of renewable energy production according to the Environmental Protection Agency. The United States has more than 300 million people but only 87 plants that convert waste into energy, most of which are more than 15 years old. Denmark, in contrast, has only 5.5 million people and 29 plants, all of which are state-of-the-art facilities that can produce both heat and power.
Biomass fuels such as burning wood constitute roughly 4 percent of U.S. energy use—a good start to using this as an alternative to fossil fuels—and we do use cheap landfills that generate methane gas for more than 400 energy projects across the country. But hauling waste to landfills is expensive and the methane emitted onsite is about 20 times stronger than carbon dioxide.
Further, a 2009 study by the Environmental Protection Agency and North Carolina State University determined that waste-to-energy plants will not only curb greenhouse gas emissions but provide nine times the energy that landfills can. There’s no reason why we should flush all that energy down the toilet each time we go to the bathroom. It’s something to make a stink about.
Read more articles from the "It’s Easy Being Green" series