Removal of Nitrogen Pollutant during River Bank Filtration System Recharged by Reclaimed Water

Abstract:

Nitrogen contained in reclaimed water could be removed by River Bank Filtration (RBF). A field experiment at the Qingyang River replenished by reclaimed water was carried out to investigate the capability of nitrogen removal rate of RBF. Water samples from the river, the riverbed sediment, the unsaturated zone, and groundwater sampling points along a monitoring section were analyzed for NO₃-N and NH₄-N in this study. The migration and attenuation of NO₃-N and NH₄-N during river bank filtration were investigated. The quality of river water in the monitoring section showed a seasonal variation, with the highest NO₃-N concentration 18.7 mg/L during autumn season. The results also indicated that NO₃-N removal mainly occurred in the riverbed sediment during river filtration into the saturated zone, with a removal rate approximately 73%. While an evident NH₄-N accumulation was found in the riverbed sediment pore water. The average NO₃-N concentration decreased to 1.2 mg/L in the saturated aquifer, and the removal rate was approximately 88%. It showed that NO₃-N in the reclaimed water can be effectively removed by denitrification during the filtration process. While, NH₄-N concentration in river bank filtration was found to slightly increase from 0.18 mg/L to 0.31mg/L, thus showed a potential threat to groundwater pollution. Temperature played an important role in performance of RBF. Temperature of higher than 25℃ in river water improved NO₃-N removal.