From Poop to Pump

Biodiesel can be produced from everything from soybean oil to algae. But how about sewage sludge?

One of the biggest costs associated with biodiesel production is the “feedstock,” or raw material. Using refined oils can be expensive, so scientists are on the lookout for cheaper options. Sewage sludge might be promising “because of the remarkably high yield of oil and low cost,” a team of Korean researchers writes in Environmental Science & Technology.

Korea’s wastewater treatment plants produce roughly four million tons of sewage sludge per year. Historically, much of this waste has been dumped in the ocean. But transforming the sludge into biodiesel could potentially meet about 40 percent of the country’s biodiesel needs, the study authors say.

The team estimates that sewage sludge yields about 980,000 liters of oil per hectare annually, or about 82 times more than microalgae and 2,200 times more than soybeans. The oil would cost only 3 cents per liter, compared to 80 cents for soybean oil.

The researchers extracted lipids from sewage sludge and, using a new production method, converted the material into biodiesel. The conversion efficiency was 98.5 percent, they report. The work shows that sewage sludge has the potential to bring down biodiesel costs, “owing to its simplicity and technical advantages, as well as environmental benefits,” the team writes. Roberta Kwok | 28 August 2012

Source: Kwon, E.E. et al. 2012. Biodiesel production from sewage sludge: New paradigm for mining energy from municipal hazardous material. Environmental Science & Technology doi: 10.1021/es3019435.

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