A few minutes walk from Ghana's most luxurious hotel, which has hosted Tony Blair and Queen Elizabeth in the capital city of Accra, stands a boy - probably no more than 10 years old - watching four pigs bathe in a stream of raw sewage running into the ocean.

He has walked 20 metres down to the sand from a cluster of huts perched on the bank, where he lives with other squatters, surviving with no access to running water or sanitation.

Despite the fact that locals regularly swim and surf in the water, Accra's beach would no doubt fail any environmental health assessment.

Most of the sewage generated by nearly four million people in the city is untreated, leading to diseases such as cholera. Pieces of asbestos lay strewn across the sand from broken pipes, amid old clothes, shoes and discarded televisions. The bank behind the beach is woven so thickly with dirty plastic bags, that the earth is barely visible beneath it.

But now scientists at Columbia University hope that a new refinery opening this autumn will clean up the water supply through a green energy project, using a new waste-to-energy technology.

Kartik Chandran, an associate professor of earth and environmental engineering at Columbia Engineering, was awarded $1.5m from the Bill & Melinda Gates Foundation earlier this year to develop a bioprocess technology capable of transforming fecal sludge into biodiesel, creating what he describes as the "next-generation urban sanitation facility".

Chandran explained that the technology converts organic compounds in fecal sludge to biodiesel and methane, using bioprocesses that could prove cheaper than current biodiesel refinery practices.

"Thus far, sanitation approaches have been extremely resource- and energy-intensive and therefore out of reach for some of the world's poorest but also most at-need populations," he said. "This project will allow us to move forward and develop practical technologies that will be of great value around the world."

Accra has a poor sewage infrastructure, so the sludge will be collected by tanker trucks from the public latrines used by most residents and delivered to the refinery.

Chandran explained that the plant could produce up to 260 gallons of biodiesel daily, which will then be sold to a local oil company.

"That's not quite enough to break even financially, but we should steadily increase our output as we fine-tune our technical design," he told Columbia University's magazine.
 
The grant from Bill & Melinda Gates Foundation will be used to build and operate the refinery for two years. After that Chandran hopes to set up a social enterprise to expand the use of bioprocess technology globally, especially in developing economies. He added that he hopes to encourage local entrepreneurs and investors to launch their own refineries.

"The model that we're going to demonstrate could be beneficial anywhere in the world," he said. "But in a country where sanitation projects are said to be unaffordable and impractical, it could literally save lives."