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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 effective particle size. A pilot unit was evaluated at the Swine Unit of the NCSU Lake Wheeler Rd. Laboratory in Raleigh, N.C., in 35 consecutive cycles during a 19-month period. The unit consisted of a homogenization tank that mixed the flushed manure, an inline polymer mixer, and two sand filter beds (29.7 m2) for dewatering designed to receive 30.5 cm (1- ft) depth of the polymer treated liquid.

Flocculation improved drainage characteristics of the sand filter and prevented clogging and surface sealing. The treatment removed 98% of total suspended solids (TSS) and volatile suspended solids (VSS), 87% of BOD, and 84% of COD from the flushed manure. Along with the solids, there was a capture of 62% TKN and 76%TP. Most of the nutrients removed in the solids were organic forms. Drying time to produce removable cakes varied with the loading rate of solids applied to the sand filter bed. A load of 2 kg TSS/m2 per drying cycle provides a balance between bed size and drying time.