Scum-to-biodiesel plant being piloted in Minnesota

Researchers from the University of Minnesota are piloting a new plant which can convert by-products of wastewater treatment into biodiesel.

A white, muddy substance produced during wastewater treatment, scum presents a significant waste disposal challenge. In general it is either sent to anaerobic digestion facilities to produce biogas, or disposed of in landfill.

The new process developed by Professor R. Roger Ruan and doctoral candidate Erik Anderson, both from the University of Minnesota’s College of Food, Agricultural and Natural Resource Sciences, converts scum to biodiesel that can be used to fuel utility vehicles on the site of the university.

According to a statement from the university, 68% of dried and filtered scum can be converted to biodiesel, equivalent to approximately 140,000 gallons of biodiesel and $500,000-600,000 in profit per year. Further boosting the project’s environmental credentials, the U of M process utilises available waste heat from a nearby water treatment facility.

For their pilot, Anderson, Ruan and their team have been using scum from the local St. Paul Wastewater Treatment facility, processing it at U of M’s Rosemount Station. According to the U of M statement, the scientists hope that the St. Paul facility will soon be ready to install the process once the pilot scale testing is complete.

The U of M statement claims that if there is a constant supply of scum material over a 365-day period, a yield of between 189,000-216,500 gallons (859,000-984,000 litres) of usable oil could be produced annually. At the conservatively estimated process efficiency of 68.8 percent, the scum oil could yield between 130,000 and 149,500 gallons of biodiesel each year.

“Using a free oil source combined with the lack of transportation and handling costs makes a scum to biodiesel process very attractive financially,” said Anderson in the U of M statement. “Scum oil is not only free, but is considered a waste material. By converting most of the scum to biodiesel, and part removed as either distillation bottoms or filtered solids, the process saves a majority of the liquid organic scum from a landfill. That’s an immediate savings of more than $150,000 per year in costs associated with landfilling scum at the St. Paul facility, in addition to the revenue generated.”