Alum Amended Solids Separation and Composting of Swine Waste
Many swine farms, especially in the South, produce more nutrients in swine manure than can be effectively used on the producer’s land. If excess nutrients are applied to crop land over time, nutrient levels (especially phosphorus) will build up in the soil and then run off into surrounding bodies of surface water and/or leach into ground water, eventually causing eutrophication of lakes and streams. In addition, odors are a constant threat to good relations with neighbors. Anything that can potentially reduce odors would be a positive step toward the sustainability of a swine operation.
If a significant fraction of swine waste nutrients can be removed from the farm in an efficient, economical method, a more sustainable operation of these farms would be possible. One method of removal is through marketing of compost. A solids separation process would provide feedstock for compost and simultaneously make lagoon management more efficient.
One of the problems with solids separation is that phosphorus tends to stay with the liquid fraction, and thus stay on the farm instead of being removed with the compost. In this project, the producer added alum before solids separation. Research has shown that the addition of alum tends to (1) improve the efficiency of the solids separator by causing solids to coagulate, (2) cause much of the phosphorus to remain in the solids fraction, and (3) reduce odors in the composting phase.
An additional advantage is that by removing much of the phosphorus from the liquid fraction (lagoon), the buildup of struvite in pipes and pumps would be reduced or eliminated. Struvite (magnesium ammonium phosphate hexahyudrate) is a salt that builds up in equipment used for pumping waste water for recirculation, flushing buildings, or irrigation onto fields. This is an expensive problem on some farms, and the elimination of this problem would help make the total system (alum addition, solids separation, composting) more economically feasible.
The goals of the project were met. Alum (aluminum sulfate) was used to treat the swine effluent in a settling basin prior to discharge into the treatment lagoon. The alum acted as a dispersing agent to separate the solids from the effluent and also to keep the phosphorus with the solids. The solids were composted and the effluent was applied to land.
The system was successful at removing solids from the effluent. In addition, twice the amount of phosphorus was removed with alum treatment than without it. This resulted in less land needed for effluent application.