Nitrogen and phosphorus removal from secondary effluent using drinking water treatment residuals fixed-bed column with intermittent operation

This work aims to explore a novel intermittently operated fixed-bed column with drinking water treatment residuals (WTR) as main medium to remove nitrogen (N) and phosphorus (P) from secondary effluent under different hydraulic loading rates (HLRs). The results showed that the WTR was beneficial for N removal and the average removal efficiency reached 59%. The denitrification was the primary pathway for N removal and the denitrification rate (2.19 g N/m³ d) was higher than the theoretical value based on the organic matter removal rate (7.35 g COD_cr/m³ d). The P removal was excellent and the efficiency still remained 98% after 260-day operation. The lifetime of the WTR fixed-bed column regarding P saturation was estimated to be 7.9 years under the highest HLR of 0.45 m³/m³ d. Moreover, the efficiency and stability of the nutrients removal further increased with the reduction of HLR. Based on regulations, the system holds great promise as a technology for water environment restoration and WTR recycling.