Organic Carbon and Ammonium Nitrogen Removal in a Laboratory Sand Percolation Filter

Abstract

The on-site treatment of wastewaters from single dwellings requires simple, low maintenance systems that reduce the chemical and biochemical oxygen demand (COD and BOD respectively), ammonium-nitrogen (NH₄-N), orthophosphate (PO₄-P), phosphorus (P), and microorganisms to acceptable concentrations. Sand filters have the potential to achieve these reductions. In this study, a sand tank model of a percolation trench and filter was constructed in the laboratory, loaded with wastewater, and monitored for a period of 293 days. The silty sand filter was seeded for 153 days with effluent from an aerobic biofilm treatment unit. The filter was then loaded with synthetic wastewater of domestic strength for 193 days, when the average organic and hydraulic loading rates on the percolation trench were 13.33 g BOD/m² d and 75 L/m² d respectively. Removal rates of 90% for total COD, 99.3% for BOD₅, >99% for total NH₄-N, 89% for total PO₄-P, and 96% for total suspended solids (TSS) were recorded during the study. No excessive clogging of the sand filter was observed. During the study very good dispersion of the wastewater over the sand filter by the percolation trench was recorded. The sand filter was simple to construct and operate and achieved excellent results.

Keywords:

• Sand filter
• Nitrification
• Phosphorus
• Coliform
• Carbon

Acknowledgments

This work was supported by the Irish EPA. Thanks are due to Ms. Mary O’ Brien, Mr. Gerry Hynes, and Mr. Mike Rathaille, Department of Civil Engineering, NUI, Galway and Mr. Michael Coughlan, Microbiology Department, NUI, Galway.