What can you do with sewage? Take your pick. You can grow crops with its nutrients; you can cook rice with its gas; you can drink it, once properly cleaned. None of this is revolutionary. In the 19th century, Paris’ finest restaurants got their vegetables from a farm that fed its crops with sewage. Around the same time, a sewage farm in Pasadena, California, had widespread fame for its walnuts. Grandmothers still remember when men came to buy the family pee, because urine cleaned cloth and leather. But look at the numbers now. Out of 16,000 wastewater treatment facilities in the US, only 106 turn the gases sewage produces into anything useful, though only 500 could produce enough energy to power 340,000 homes. The Chinese would find this baffling. They have used shit as fertilizer for 4,000 years. They have 18 million households transforming the contents of latrines into energy to cook with. They know shit is wealth, not waste. Luckily, they are not alone.
At Butare Prison, a couple of hours’ drive south of Rwanda’s capital, Kigali, it is almost lunchtime. Carrying machetes, similar to the ones they probably used during Rwanda’s 1994 genocide, a group of prisoners heads into the prison compound from its work detail in the nearby banana plantation. The kitchens have been working since 5am, because there are 8,364 prisoners to feed, twice a day. It is hard work, but it used to be harder, because it used to be blinding.
The only country in the world that powers most of its prisons with their inmates’ shit.
Rwanda is an extraordinary place. It is possibly the most orderly country in Africa, where streets are clean and roads don’t have potholes. It has banned plastic bags. It has kept the peace for 17 years, since some of its citizens decided to murder 1 million other citizens – often their neighbors, friends or relatives – during the 100 days of Rwanda’s 1994 genocide. And it is also the only country in the world that powers most of its prisons with their inmates’ shit.
Biogas is a mixture of methane and carbon dioxide that is given off when bacteria are added to sewage. The bugs break down organic matter, giving off gas. It is not revolutionary: Marco Polo saw biogas being used in 13th-century China. Nor is it difficult: Simply pipe human and cow excreta (the cows’ add necessary volume) into underground tanks, where it ferments like a human stomach. Pipe the resulting gas to your stoves, light a match and cook. The gas doesn’t smell, but the mixing tanks do. In the dry season, prisoners stir the cow and human mixture with poles, as there is less water available. They claim not to mind. Juvenal, one of the prison’s 6,763 génocidaires, in his last year of a 15-year sentence, only shrugs. “I chose this because it’s an easy job.”
In the kitchen, the cauldrons are bubbling. The menu doesn’t change – prisoners get two meals a day of maize and beans – but the method has. “Biogas makes the food less soggy,” says one of the cooks. “You can regulate the temperature better than with firewood.” It is also less painful. The kitchen next door still uses firewood. The smoke stings eyes within minutes, and they stay stinging long after you leave.
Ten out of Rwanda’s 14 prisons now get up to 75 percent of their cooking fuel from biogas. It saves money and trees; Rwanda is fighting deforestation. Installing biogas digesters has saved the National Prison Service US$1 million a year in firewood costs. Unlike trees, biogas is an infinite resource. Economical, eye-sparing, inexhaustible, and it’s still called “waste.”
For Butare’s 8,364 inmates, the menu never changes: one bowl of beans, maize and vegetables, served daily at around 7am and 3pm, depending on the kitchens.
The waste of all Butare’s prisoners – including its 33 children born to inmates – is sent to seven digesters to become biogas; 6,763 prisoners are serving sentences for crimes committed during the 1994 genocide.
In the oxygen-free environment of the digesters, bacteria consume human and animal shit (from the prison’s 30 cows). A new digester takes two months to get going; after that, biogas can be produced in a week.
Every 100m3 of waste can produce 50m3 of fuel for cooking more bowls of beans, maize and vegetables. Biogas has cut Butare’s fuel costs by 85 percent, saving RWF200,000 (US$334) over the past six months.