Case study: Abattoir waste fuels public transport
SINCE 1992, the public transport fleet serving the city of Lipkoping in Sweden has run on natural gas produced from abattoir waste.
Animal carcasses are put into tanks and decomposed before being converted into cheap -- and green -- biogas.
What's left over is turned into fertiliser and sold to farmers who spread it on their land.
Bertil Carlson, a project engineer with Svensk Biogas, which runs the city's plant, says the process used to turn animal waste into gas is the same that would apply to using grass or crops.
"We process the gas from waste, mostly slaughterhouse waste, but there are other plants in Sweden producing from grass and crops," he says. "It's the same process. The only difference is the material.
"The waste is put into a big tank. You decompose it with bacteria and micro-organisms. The raw gas is between 50pc and 70pc methane, and the rest is carbon dioxide. Before we can use it for cars, buses and trucks, we remove most of the carbon dioxide.
"The gas is pumped into tanks. We have a local pipeline system to the bus depot for public refuelling stations for cars and trucks. It goes directly from the production plant to the refuelling stations.
"The buses are 100pc biogas and the market is growing for cars. We have a problem with producing enough gas."
The gas is produced in sealed buildings where extractors and air collection systems ensure any smell produced does not extend beyond the plant.
The biogas can also be used to heat homes and for cooking. The end product is an odourless, natural gas.
Although it is costly to produce the fuel, running a bus is between 10pc to 20pc cheaper than using petrol or diesel.