Nitrification and Denitrification in a Passive On-site Wastewater Treatment System with a Recirculation Filtration Tank

Groundwater contamination due to the failure of septic tank systems is a vital concern in environmental health. Active on-site wastewater treatment counts on the use of pumps to sustain the aerobic condition in the process and promote the nitrification which might not be sustainable in terms of energy saving. In current practice, passive on-site wastewater treatment processing is deemed a cost-effective option to improve the nutrient removal. The recirculation filtration tank (RFT) is an intermediate process installed to trigger or promote the proper nitrification/denitrification process between the septic tank and the drain field. However quantification of the nitrification remains difficult. To explore the structure and function of the microbiological community in the RFT, two types of sands—fine and coarse—were used in two consecutive phases for elucidating the nitrification and denitrification effects. With the aid of real-time PCR, the growth of nitrifiers and denitrifiers in sand was monitored in the RFT without adding any external carbon source to the sand. Further, phosphorus removal from the wastewater and the ability of limestone for phosphorus removal were also confirmed in the RFT. Fine sand with limestone mixture performed better in nutrient removal if clogging was overcome by using a grinder pump for dosing. On average, removal efficiencies of 60.54% ammonium, 49.48% total Kjeldahl nitrogen (TKN), 42.57% total nitrogen (TN), 92.06% soluble reactive phosphorus (SRP) and 87.16% total phosphorus (TP) were achieved by the RFT with fine sand. The E. Coli removal efficiency by the RFT was 99.9% in both phases.