Alum Settling and Filtration Treatment of Liquid Swine Manure

Abstract

A physical/chemical treatment train, which involved preliminary settling for 24 h followed by coagulation/flocculation of supernatant, and filtration, was applied to raw flushed swine manure in bench- and pilot-scale experiments to investigate the effectiveness of the treatment train against the removal of total suspended solids (TSS) and total phosphorus (TP). Alum was used as a coagulant at an average dose of 1600 mg L-1. In the bench-scale experiments, alum treatment was performed using a jar test apparatus, and filtration was achieved by using polycarbonate track-etched membrane filters of pore sizes of 10 and 20 m. At the pilot plant, coagulation, flocculation, and clarification were achieved in a custom-designed sludge blanket clarifier equipped with inclined plate settlers, followed by media filtration in a set of three patented Martin filter columns containing glass beads of different void sizes ranging from 5 to 25 m. Overall percent reductions in TSS and TP were 85% (from 9944 to 1470 mg L-1) and 64% (from 449 to 163 mg L-1) in the bench-scale experiments and were 76% (from 3945 to 936 mg L-1) and 75% (from 164 to 40 mg L-1) in the pilot plant treatment, respectively. Preliminary settling was found to be a very effective step, which removed 53% to 56% and 22% to 28% of TSS and TP, respectively, from the raw liquid swine manure. Moderate reduction in chemical oxygen demand was also observed, while the treatment train had little effect on total Kjeldahl nitrogen and dissolved solids. Particle size distribution analysis showed that most of the phosphorus in the liquid manure was associated with particles <10 m in size and that coagulation and flocculation could enhance the phosphorus removal considerably. At the end of the pilot-scale experiment, approximately 70% and 50% of the initial mass of TSS and TP was removed from the liquid swine manure, respectively, as preliminary settling sludge, whose volume was accounted for approximately 36% of the volume of initial raw manure.