A research paper published by the American Chemical Society indicates that biodiesel production from municipal sewage is tantalizingly close (within several pennies) of being profitable. Although kind of disgusting, few would argue there isn’t a tremendous, renewable supply of the stuff. Nor would they say that every municipality doesn’t already have its’ own sources.
One of the main issues with turning poop into fuel is simply how to make it cost effective. One might assume that with really what amounts to a surplus of raw material, that production costs shouldn’t be much of an issue. The paper cites $3.11 per gallon as the production cost for sewage to biodiesel conversion. To be competitive in the marketplace, the study authors say the cost must be the same as petroleum diesel. Their competitive diesel figure is $3 per gallon, so eleven cents isn’t a long way to go.
What makes sewage sludge so good for biodiesel production? Energy-containing lipids like monoglycerides, phospholipids, free fatty acids, triglycerides, and diglycerides are found in great quantities in it. Also, the microbes used in sewage treatment contain lipids that can yield from 7% to 36% oil. And it’s not just the quantity of lipids, it’s the type; the study authors say that the particular lipids found in sewage could produce a very high quality biodiesel.
The paper cites another study which found that if 50% of municipal wastewater treatment plants used lipid extraction, and chemical conversion, about 1.8 billion gallons of biodiesel could be produced annually.
However, there are many challenges. Specifically the chemistry involved, combined with reducing the production cycle to something reasonable by ‘cooking’ the sludge and using enzymes, sounds as if there is still a long way to go. Bioreactor design is a piece of the puzzle, and is a whole field unto itself. Finding the right microorganisms which increase oil yields, could boost biodiesel production from sludge up to 10 billion gallons per year, the study says.
The authors also say that a tax break could help spur sewage biodiesel production, as it did for biodiesel from other sources in 2005. Congress members would have to be aware of this type of technology though, and some of them must already have pressure from agribusiness lobbyists, if 90% or the oil currently used in biodiesel production comes from soybeans. Even if we get to the point where the complex chemistry is worked out, will politics stop the poop?
Image Credit: Chesapeake Bay Program