EVALUATION OF WASTEWATER TREATMENT TO REDUCE NUTRIENT TRANSPORT

Excess amounts of phosphorus and nitrogen flowing into Lake Erie from agricultural fields in northwest Ohio has led to several harmful algal blooms (HABs). One potential source of those nutrients is manure applied to fields for fertilizer. Manure from confined animal feeding operations (CAFOs) is 95 to 98% water with only ~3% solids and nutrients, thus physical transportation is expensive relative to the value of the agricultural nutrients. Furthermore, once manure nutrients are applied to agricultural fields, they are relatively easily mobilized to waterways by precipitation. More than 700 lab-scale tests have been used to optimize the treatment of CAFO manure with cationic polymers and coagulant, which are commonly used in wastewater treatment plants, to sequester the nutrients as solids separated from water, thus reducing the weight by a factor of 20 and binding the nutrients in a form that greatly reduces its mobility in soils. A pilot test is underway on 8 small plots growing corn: 2 control, 3 with raw manure, and 3 with treated manure. As corn requires more nutrients than other crops, this would test the effectiveness of the treated manure as a fertilizer. Surface and subsurface runoff is collected from each plot separately after a rain event, using automated water samplers, and analyzed for nutrient concentrations of dissolved phosphate, nitrite+nitrite and ammonia and total phosphorous and nitrogen. Loads are calculated for all nutrients based on concentration measures in the runoff and total volume coming off the plots. Preliminary results are promising, showing that the runoff from the fields with the treated manure have significantly lower phosphate levels compared to plots with untreated manure. Work is still being done for improving the results of the other nutrients. Data collection is continuing to determine the ability of the treated manure to promote crop growth relative to untreated manure and to reduce nutrient migration to waterways over the entire growing season, which is the original goal of this research.