Image credit: Laura Christianson/University of IllinoisImage credit: Laura Christianson/University of Illinois

Phosphorus and nitrates are well-known agents of oxygen depletion and algal bloom formation in aquatic ecosystems. States bordering the Mississippi River have focused on point source controls to reduce such nutrient inputs to the Gulf of Mexico as well as lakes and ponds.

Technology to augment controls applied to industrial and wastewater system discharges is being demonstrated by University of Illinois researchers. Woodchip-filled trenches have proven effective in removing nitrate from tile drainage water in Illinois croplands and were recently tested for the removal of phosphorus.

The researchers sought to develop a special “P-filter” to trap the fertilizer-derived pollutant in agricultural runoff. Tests were performed with acid mine drainage treatment residual (MDR) and steel slag, two industrial waste products that contain phosphorous-binding elements such as iron, calcium and aluminum.

A separate P-filter was placed upstream or downstream of a lab-scale woodchip bioreactor, which then received wastewater from an aquaculture tank. Nitrate removal was consistent, regardless of P-filter type and whether the P-filter was upstream or downstream of the bioreactor. MDR proved to be the superior P-filter, removing 80-90 percent at a medium flow rate.

Steel slag only removed about 25 percent of the phosphorus. “But steel slag is a lot easier to find in the Midwest. And according to the Illinois Nutrient Loss Reduction Strategy, we’re only trying to remove 45 percent of the phosphorus we send downstream. Since agriculture is only responsible for half of that, 25 percent would be pretty good,” says Laura Christianson, assistant professor of water quality in the Department of Crop Sciences.

To contact the author of this article, email shimmelstein@globalspec.com