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Removing the N and P in Dairy Effluent using Multi-Soil-Layer (MSL) Systems

The disposal of untreated dairy wastewater in Hawaii is a current concern because of possible contamination of surface, subsurface, and coastal water as well as increasing treatment costs resulting in the closure of many dairies. The objective of this study was to quantify the effectiveness of Multi-Soil-Layer (MSL) systems in removing nitrogen (N) and phosphorus (P) from the dairy effluent and to explore ways to increase MSL efficiency. Four MSL systems were constructed with replications of two treatments. Treatments were commercial Perlite or the Leilehua soil in the aerobic layer. A mixture of charcoal, sawdust, iron filings, and Honouliuli soil comprised the anaerobic layer in both treatments. Untreated dairy effluent was applied to each system at a flow rate of 505 L m-2 d-1 over a 4-month period. During the study, the removal of phosphate ranged 94% to 97% by the Leilehua MSL system in contrast to 47% to 97% by the Perlite MSL system. Effluent nitrogen (N) consisted of 98% ammonium and about 1% nitrate. Total inorganic N removal ranged 51% to 93% for the Leilehua and 46% to 96% for the Perlite MSL system. The results indicate that MSL systems can be effective in removing inorganic N and phosphate from dairy effluent. The MSL systems can be economical because of the nominal cost of the material used and the small amount of space needed.