The use of a subsurface infiltration system in treating campus sewage under variable loading rates

Abstract

The treatment of domestic sewage from a university campus area with diurnally and seasonally variable loading rates was investigated using a pilot-scale subsurface wastewater infiltration (SWI) system operated from January to August 2010. Operating conditions including hydraulic loading rate (HLR) and pollutant loading rate (PLR) were varied during the operation to investigate their impacts on overall treatment performance. The variation values were 0.040, 0.065, 0.081 and 0.125 m 3/m 2 d for HLR, 6.71, 9.30, 16.80 and 20.00 g BOD/m 2 d for PLR. The results showed that although the influent loading rates were highly variable, including sudden sharp increases in organic matter concentrations, the SWI system performed well throughout its operation. Taking the hydraulic and treatment efficiencies into consideration, HLR of 0.081 m 3/m 2 d and PLR of 16.80 g BOD/m 2 d were recommended. Under this condition, purification processes in the SWI system were gradually established over three weeks, after which the removal efficiencies for chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ammonia nitrogen (NH 3–N) were 87.5 ± 1.6, 91.8 ± 0.7, 80.1 ± 1.1 and 86.9 ± 2.0%, respectively. Overall, eight months of pilot-scale tests indicated the robustness of SWI system in terms of achieving very high quality of treated water under HLR (0.040–0.081 m 3/m 2 d) and PLR (6.71–16.80 g BOD/m 2 d). This study will guide the decision on a full-scale SWI application in the campus area.