Existing technology can produce biodiesel fuel from municipal sewage sludge that is within a few cents a gallon of being competitive with conventional diesel refined from petroleum, according to an article in ACS' Energy & Fuels. Sludge is the solid material left behind from the treatment of sewage at wastewater treatment plants.
David M. Kargbo points out in the article that demand for biodiesel has led to the search for cost-effective biodiesel feedstocks, or raw materials. Soybeans, sunflower seeds and other food crops have been used as raw materials but are expensive. Sewage sludge is an attractive alternative feedstock -- the United States alone produces about seven million tons of it each year. Sludge is a good source of raw materials for biodiesel. To boost biodiesel production, sewage treatment plants could use microorganisms that produce higher amounts of oil, Kargbo says. That step alone could increase biodiesel production to the 10 billion gallon mark, which is more than triple the nation's current biodiesel production capacity, the report indicates.
The report, however, cautions that to realize these commercial opportunities, huge challenges still exist, including challenges from collecting the sludge, separation of the biodiesel from other materials, maintaining biodiesel quality, soap formation during production, and regulatory concerns.
With the challenges addressed, "Biodiesel production from sludge could be very profitable in the long run," the report states. "Currently the estimated cost of production is $3.11 per gallon of biodiesel. To be competitive, this cost should be reduced to levels that are at or below [recent] petro diesel costs of $3.00 per gallon."
- Kargbo et al. Biodiesel Production from Municipal Sewage Sludges. Energy & Fuels, 2010; 24 (5): 2791 DOI: 10.1021/ef1001106
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