City buses turn to sewage for 'clean' fuel

Can the key to "clean" energy be found down in the sewer? That's the idea in Oslo, where city officials soon plan to introduce buses that run on biofuels extracted from human waste.

As of next year, the new buses are due to start plying the streets of the Norwegian capital.

"It's a win-win situation: It's carbon neutral, it hardly pollutes the environment, it's less noisy and its endlessly renewable," says Ole Jakob Johansen, one of the people in charge of the project at Oslo city hall.

The biofuel, which is methane generated by fermenting sludge, will come from the Bekkelaget sewage treatment plant which handles waste from 250,000 city dwellers.

"By going to the bathroom, a person produces the equivalent of eight litres of diesel per year. That may not seem like a lot, but multiplied by 250,000 people, that is enough to operate 80 buses for 100,000 kilometres each," said Mr Johansen.

Compared to diesel, biomethane is a giant green step forward.

In addition to being carbon neutral, it emits 78 per cent less nitrogen oxide and 98 per cent fewer fine particles - two causes of respiratory illnesses -and is 92 per cent less noisy.

Even the price is advantageous, remarked Mr Johansen.

All included, the cost of producing biofuel equivalent to one litre of diesel comes to €0.72, while diesel at the pump in Norway currently costs more than €1.

"The fuel is less expensive but the cost of the new buses and their maintenance is higher. In total, it's about 15 per cent more expensive," notes Anne-Merete Andersen of Ruter, the operator of Oslo's public transport system.

Contrary to first generation bio-ethanol, made from grains and plants, biomethane has the added advantage of not impacting food supplies, nor does it require fertilisation or deplete precious water resources.