Improving multi-soil-layer (MSL) system remediation of dairy effluent

Dairy effluent disposal is a serious problem in the Hawaiian Islands. Dairies often establish multiple settling lagoons to accumulate and store effluent. Occasionally, the overflow of lagoons leads to the transfer of nutrients, such as nitrogen (N) and phosphorus (P), and other contaminants, to hydrologically associated surface, subsurface, and coastal waters. This study was conducted to assess the removal of inorganic N and phosphate in dairy effluent using multi-soil-layer (MSL) systems. Four MSL systems were constructed with two replications of two treatments, which were Perlite and the Leilehua soil. Both materials were used separately for forming an aerobic layer in the MSL systems, whereas an anaerobic layer was formed from a mixture of charcoal, sawdust, iron filings and Honouliuli soil. The results of this study revealed that the removal of inorganic N was similar for the Leilehua and Perlite MSL system, which was 22–93% and 21–96%, respectively. Phosphate removal was higher in the Leilehua MSL system (64–99%) compared to the Perlite MSL system (9–97%). Additional aeration increased the removal of phosphate by the Leilehua MSL system. Sucrose application with a constant rate of aeration increased the removal of inorganic N both in the Leilehua and Perlite MSL systems and increased phosphate removal in the Perlite MSL system. The study demonstrated that MSL systems have the potential to remove high percentages of inorganic N and phosphate in dairy effluent enabling reuse of the water.