(278e) A Pilot-Scale Study of Electrocoagulation for Phosphorus Separation in Liquid Animal Manure

Zhang, X., University of Minnesota
Lin, H., University of Minnesota
Hu, B., University of Minnesota
Pork production is one of the most important agricultural activities in the United States, and 75% of the swine operations are geographically located in the Upper-Midwest. There is 20.79 thousand m3/yr of flushed manure or 2.18 thousand m3/yr of deep-pit manure produced annually in a typical 2400-head barn. It is a big problem for farmers to handle such a large amount of manure. Swine manure contains a high level of phosphorus (P), ranging from 4.1 g/kg to 18.3 g/kg-dry matter for dairy manure and even higher (9.9 g/kg to 22.7 g/kg-dry matter) for swine manure. The fine particles in manure usually cannot be effectively removed through physical solid-liquid separation methods, such as natural sedimentation, centrifugation, or drum screen, resulting a substantial amount of P contained in these solid fine particles remaining in the liquid manure. Improper land application of manure will create P overload and accumulation in the soil, and eventually leaching to nearby water body, causing eutrophication. Our research group has evaluated electrocoagulation (EC) for P separation from both dairy and swine manure in lab scale, and reached the P removal efficiency of 99% and 85%, respectively. In this work, pilot-scale EC study was conducted with 20 L manure per run and 4-6 runs per day followed by natural sedimentation for 24 h. The results show that 70-90% of P could be concentrated in sludge with a volume of only 5% to 10% of the untreated manure volume. The resulting supernatant is more nitrogen concentrated with a N: P ratio between 10 and 40, compared with the initial ratio of around 2. The sludge has the P contents of between 5% and 10%. Based on these results, we predict that in a typical barn with 2400-head of pigs, operating EC in a deep-pit manure management system will add $0.97 per grown-finish pig. The pilot scale demonstration experiment provides strong evidence that EC has great potential for real application in both small and large barns.