Solid-liquid Separation of Swine Manure with Polymer Treatment and Sand Filtration

Small particles typical of liquid swine manure often clog sand filter beds and fine filters. We evaluated the effectiveness of polymer flocculants to improve drainage and filtration performance of sand filter beds by increasing the particle size of manure. A pilot separation unit was evaluated at the Swine Unit of the NCSU Lake Wheeler Road Laboratory in Raleigh, North Carolina, in 40 consecutive cycles during a 20-month period. The unit consisted of a homogenization tank that mixed the flushed swine manure, an in-line polymer mixer, and two sand filter beds (29.7 m2) designed to receive 30.5 cm (1 ft) depth of the polymer-treated effluent. Flocculation treatment using polyacrylamide (PAM) polymer improved drainage characteristics of the sand filter by preventing clogging and surface sealing. The combination of flocculation and filtration treatment removed 97% of total suspended solids (TSS) and volatile suspended solids (VSS), 85% of biochemical oxygen demand (BOD5), and 83% of chemical oxygen demand (COD) from the flushed manure. Along with the solids, treatment resulted in capture of 61% total Kjeldahl nitrogen (TKN) and 72% total phosphorus (TP). Most of the nutrients removed in the solids were organic forms. Drying time to produce removable cakes varied significantly with the loading rate of solids applied to the sand filter bed. A load of <2 kg TSS m−2 per drying cycle allowed completion of the drying cycle in about 8 days, which is desirable to reduce potential fly problems. Our results indicate that PAM flocculation enhances performance of dewatering sand filter beds for swine manure applications.