The city of Seattle has temporarily stopped buying biodiesel fuel for its fleet of vehicles because of concerns that the soy-based mix it was using was more harmful to the environment than regular diesel.
"Not all biodiesels are the same," Bauer said.
She said Mayor Greg Nickels directed her department to stop buying soy-based biodiesel fuel about a month ago. That was after the Environmental Protection Agency released a report that said ethanol production was potentially worse for the environment than gasoline.
Increasingly, critics say the production of crop-based alternative fuels -- ethanol made from corn and biodiesel made from soy -- is detrimental because of the amount of land needed to grow crops and greenhouse gas emissions.
So the city is testing waste grease-based biodiesel to see whether it meets local and national standards.
"Fuels are really complex," Bauer said. "We are trying to stay ahead of the curve in terms of finding fuels that are responsible fuels that will help us reduce our petroleum consumption. We're looking for a fuel source that has a good greenhouse-gas profile -- ultimately it's not going to be petroleum."
She said the city had been buying about 73,000 gallons a month of biodiesel for its hundreds of vehicles such as fire engines and pickup trucks that use diesel fuel. Whether it was cheaper to use the biofuel mix or regular diesel varied, she said, with the fluctuating prices of fuels.
King County Metro stopped using canola-based biofuel in May of 2008 because of cost concerns.
Most recently Seattle had been using a blend of 40 percent biodiesel and 60 percent ultra-low diesel fuel.
Using locally produced waste grease-biodiesel could be more environmentally friendly than other options, Bauer said.
"It's definitely something that would otherwise go in a landfill," she said.