Upgradation of conventional MBBR into Aerobic/Anoxic/Aerobic configuration: A case study of carbon and nitrogen removal based sewage treatment plant

Abstract

The thrust of this study was to assess the upgradation of an existing 3.5 million liters per day (MLD) full-scale conventional MBBR-based sewage treatment plant (STP) into Aerobic/Anoxic/Aerobic configuration. Initially, the plant was designed and constructed for achieving BOD and TSS to <30 mg/L and <50 mg/L, respectively. Recently, due to the advent of stringent effluent standards for BOD (Biological Oxygen Demand), TSS (Total Suspended Solids), and TN (Total Nitrogen) to <10 mg/L, with a strong emphasis on non-potable re-use of treated effluent, the existing system needed intensive upgradation. The upgraded STP was modified from two hours to five hours of hydraulic retention time (HRT). The upgraded plant was examined by removing organic carbon and nitrogen from municipal wastewater through both partial nitrification-denitrification (PND) by aerobic and anoxic reactors and simultaneous nitrification and denitrification (SND) process by PVA (Poly Vinyl Alcohol) gel aerobic reactor. After ten months of operation and monitoring, the plant has reached its upgraded effluent discharge standard. It was found that average BOD, COD, TSS, TN, and TP (Total Phosphorus) concentrations were 8 mg/L, 25 mg/L, 12 mg/L, 9 mg/L and 5 mg/L respectively, with 91 %, 90 %, 93 %, 84 %, and 64 %, removal efficiency. It was observed that PVA-gel beads are not only efficient for carbon removal (BOD & COD) but also achieve high SND rates.