Swine manure solids separation and composting using alum

Separation of solids from flushed swine manure and subsequent composting of the solids fraction is one way of reducing the size requirement for effect ive treatment of swine waste in lagoons. It also provides a potential means of removing some nutrients from the farm through composting and sale of so lids. A field scale rest of a settling basin was undertaken to determine th e effects of solids separation on nutrient distribution in the two fraction s (solids and liquids) and also to determine what effect the addition of al uminum sulfate (alum) would have on this process. A settling basin with a skimmer was developed and demonstrated to be effect ive in removing a significant portion of solids from a solution of recircul ated lagoon effluent and fresh swine waste. Waste was collected for one wee k in one of two 1,000-head swine finishing houses during the last two weeks of the growout cycle. The collected waste was then flushed into the basin and allowed to settle approximately one hour before allowing the liquid fra ction to flow into the lagoon. The basin removed approximately 60% of the s olids present in the effluent and when amended with alum at 0.5% by volume, the separation efficiency increased to approximately 70%. A significant am ount of phosphorus was also removed (75% with alum, 38% without), while onl y small amounts of nitrogen (20%) and potassium (8%) were removed from the liquid fraction, As a result, the Nitrogen to Phosphorus ratio of the efflu ent entering the lagoon improved from 3.6 with 170 separation to 8 with sep aration and to 16.7 with separation and alum amendment. These results indic ate that, unless lagoon digestion processes result in higher nitrogen loss from the separated liquid than from unseparated manure, removing solids wou ld result in a more balance fertilizer in the lagoon. The solids fractions were mixed with woody mulch and composted. The additio n of alum at the low levels studied had no effect on the composting process or the odors generated. A long-term study would be necessary to determine if the removal of phosphorous was enough to affect the formation of struvit e in equipment used to recirculate lagoon effluent.