ST. PAUL, Minn. - Wastewater treatment plants keep our waterways clean.

In the process of cleaning dirty water, scum -- a white, muddy byproduct -- is produced. Normally the scum has no use and ends up in a landfill. But Professor Roger Raun and his team at the University of Minnesota found a better use for it.

"This is a very valuable product. It contains a lot of free fatty acids so that's very high value and high energy content in it. Now it simply goes to waste," said Dr. Ruan.

Locally, the St. Paul Wastewater Treatment Plant produces roughly 3.5 tons of scum a day. Over the course of a year, they say that could yield close to 200,000 gallons of bio diesel annually.

In the lab, Professor Ruan and doctoral candidate Erik Anderson have discovered that the process of converting scum to fuel is very efficient.

"The actual waste oil itself conversion is very very high, you are talking about complete utilization of the free fatty acids inside. That's the difference between this technology and some other traditional technique," said Ruan.

Right now, the process is close to 90 percent efficient and there are plans to expand it for use in large-scale wastewater treatment plants in the future.