Two-stage soil infiltration treatment system for treating ammonium wastewaters of low COD/TN ratios

Soil infiltration treatment (SIT) is ineffective to treat ammonium wastewaters of total nitrogen (TN) > 100 mg l−1. This study applied a novel two-stage SIT process for effective TN removal from wastewaters of TN > 100 mg l−1 and of chemical oxygen demand (COD)/TN ratio of 3.2–8.6. The wastewater was first fed into the soil column (stage 1) at hydraulic loading rate (HLR) of 0.06 m3 m−2 d−1 for COD removal and total phosphorus (TP) immobilization. Then the effluent from stage 1 was fed individually into four soil columns (stage 2) at 0.02 m3 m−2 d−1 of HLR with different proportions of raw wastewater as additional carbon source. Over the one-year field test, balanced nitrification and denitrification in the two-stage SIT revealed excellent TN removal (>90%) from the tested wastewaters.