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

Authors: 
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.