Turning human waste into energy

Waste not, want not
Plastics maker Sintex seeks to solve India's energy and sanitation problems in one stroke - with an at-home biogas digester.
By Jeremy Kahn

A Sintex digester can turn manure into fuel for cooking and electricity.

(Fortune Magazine) -- Sintex Industries, a plastics and textiles manufacturer in Gujarat, India, is betting it can find profit in human waste. Its new biogas digester turns human excrement, cow dung, or kitchen garbage into fuel that can be used for cooking or generating electricity, simultaneously addressing two of India's major needs: energy and sanitation.

Sintex's digester uses bacteria to break down waste into sludge, much like a septic tank. In the process, the bacteria emit gases, mostly methane. But instead of being vented into the air, they are piped into a storage canister.

A one-cubic-meter digester, primed with cow dung to provide bacteria, can convert the waste generated by a four-person family into enough gas to cook all its meals and provide sludge for fertilizer. A model this size costs about $425 but will pay for itself in energy savings in less than two years. That's still a high price for most Indians, even though the government recently agreed to subsidize about a third of the cost for these family-sized units. "We want to create a new industry for portable sanitation in India that's not available now," says S.B. Dangayach, Sintex's managing director.

Government officials plan to end open defecation by 2012 (hundreds of millions of Indians use railroad tracks or other outdoor locales instead of toilets) and say biogas plants are part of the solution. A.R. Shukla, a scientific advisor in the Ministry of New and Renewable Energy, says India could support 12 million such plants, but only 3.9 million - mostly pricier models big enough to accommodate entire villages - have been installed to date. And last year the government fell far short of its target for new installations.

The future can be glimpsed on a dusty, rutted road in a poor South Delhi neighborhood. Here 1,000 people use an immaculately clean public toilet constructed by a nonprofit foundation, the Sulabh Sanitation Movement. The biogas digester attached to toilets provides cooking gas for a 600-student school and vocational-training program the foundation runs. In the past, nongovernmental organizations like Sulabh were the only ones offering biogas digesters.

But Sintex is hoping cities, real estate developers, building managers, and hospitals will jump at a ready-made way to harness the same energy.

Biogas digesters are just a small fraction of Sintex's business. The company has installed only about 100 of them. But it plans to increase investment and production tenfold in the coming year. That growth potential has helped Sintex stock more than double this past year. Human waste may be a stinky business, but to investors it smells like money