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 effective treatment of swine waste in lagoons. It also provides a potential means of removing some nutrients from the farm through composting and sale of solids. A field scale test of a settling basin was undertaken to determine the effects of solids separation on nutrient distribution in the two fractions (solids and liquids) and also to determine what effect the addition of aluminum sulfate (alum) would have on this process. A settling basin with a skimmer was developed and demonstrated to be effective in removing a significant portion of solids from a solution of recirculated lagoon effluent and fresh swine waste. Waste was collected for one week 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 fraction to flow into the lagoon. The basin removed approximately 60% of the solids present in the effluent and when amended with alum at 0.5% by volume, the separation efficiency increased to approximately 70%. A significant amount of phosphorus was also removed (75% with alum, 38% without), while only small amounts of nitrogen (20%) and potassium (8%) were removed from the liquid fraction. As a result, the Nitrogen to Phosphorus ratio of the effluent entering the lagoon improved from 3.6 with no separation to 8 with separation and to 16.7 with separation and alum amendment. These results indicate that, unless lagoon digestion processes result in higher nitrogen loss from the separated liquid than from unseparated manure, removing solids would result in a more balanced fertilizer in the lagoon. The solids fractions were mixed with woody mulch and composted. The addition 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 phosphorus was enough to affect the formation of struvite in equipment used to recirculate lagoon effluent.