Hmm… have we been selling sewage short? Rob noted the other day that small-scale biogas digesters—which convert human and animal waste into methane that an be used for cooking fuel—can do a lot for the developing world. But now here's Flint, Michigan, thinking even bigger, looking to create a new biogas system that would turn municipal sewage into fuel for the city's bus fleet:

In the 1960s, Flint built digesters to turn sewage into methane to power its sludge incinerator, but the unpurified gas corroded pipes, and the operation was shut down in the 1980s. The new biogas plant will be housed in the same buildings at the city's wastewater treatment plant. And the city is banking on Swedish technology and expertise for a better result this time.

In Sweden—where high gasoline taxes forced investment in alternative fuels years ago—buses, trains and 6 percent of private vehicles run on biogas made from sewage, restaurant and slaughterhouse waste, and other organic sources.

Kettering Provost Michael Harris said biogas will cost significantly more to produce per gallon than gasoline, though it is still a viable undertaking for Flint because the city will eliminate the cost of burning sewage sludge, the solid waste left behind after water is extracted. But Swedish Biogas President Peter Unden believes the Flint plant can produce biogas that is 20 percent less expensive than gasoline.

Whether this could ever work on a broader scale depends, obviously, on the price of gas. Among other things, you'd have to build or convert car engines so that they could burn natural gas or biogas, a feature that's becoming common in Sweden, but not so much here. That's something T. Boone Pickens wants to change, though, as a number of critics argued when Pickens unveiled his big energy plan (in which we would get a big chunk of our electricity from wind and then use the natural gas we save to run our cars), plug-in hybrids and electric vehicles still look like the best bet for weaning the transportation sector off oil.

Also, Sweden's biogas experience hasn't worked out all that well, with companies like Volvo pulling out of the market—here's a longer piece on those efforts. Key quote: "When you're in the bathroom in the morning and you can see something good come out of that, it's easy to be taken in by the idea." Uh huh.

--Bradford Plumer