Energy-Efficient Sewage Plants

Thursday, August 13 2009

High-rate digestion with microfiltration is state-of-the-art in large sewage plants. It effectively removes accumulated sludge, and produces biogas to generate energy. A Fraunhofer Institute study reveals that even smaller plants can benefit from this process.

Sewage plants remove organic matter from wastewater, and if the accumulating sludge decays, biogas is generated as a by-product. However, many smaller operations balk at the costs of a new digestion tank. Instead, they enrich the sludge with oxygen in the existing activation basin, and stabilize it.

“Activation basins require a lot of electricity. At the same time, enormous energy potential is lost, since no biogas is produced,” says Brigitte Kempter-Regel, of the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, Germany.

Only 1156 of the 10,200 sewage plants in Germany have a digestion tank. In a cost-benefit-study, Kempter-Regel has shown that it also pays for small sewage plants to transfer to more energy-efficient processes – even if they have to invest in a sludge digestion unit. “Based on a sewage plant for 28,000 inhabitants, we calculate that the plant can reduce its annual waste management costs from 225,000 euros by as much as 170,000 euros, if sludge is decayed in a high-rate digestion unit with microfiltration, as opposed to treating it aerobically,” she says.