Dozens of cities in Sweden are using biogas: a fuel which comes from sewage. Vehicles which can run on compressed natural gas are able to utilize this fuel.
A big blow to this technology came when Volvo (owned by Ford) decided two years ago to stop producing vehicles which ran on the fuel. The company states not enough vehicles were sold, and it opted to focus on vehicles which can use ethanol.
Bo Ramborg left Volvo so he could create FordonsGas which is a company focused on the infrastructure needed for biogas. He sees the technology as delivering lower emissions than competing fuel sources. 4 other countries in Europe now use biogas.