PERFORMANCE OF SUBMERGED AERATED BIOFILTER FOR THE POST TREATMENT OF UASB EFFLUENT

Abstract

The performance of a laboratory scale upflow submerged aerated biofilter (1.5 L) operated at an ambient temperature ranging from 10.5 — 35° C for the post treatment of UASB effluent was evaluated. Except for 3-4 weeks (when synthetic wastewater or sewage mixed with synthetic wastewater was used), UASB was fed with sewage collected from a sump well outside IIT-Roorkee campus. The entire operation was divided into three Stages comprising of operation in four Phases with Stage II had two runs operated simultaneously (i.e. Phase 2 & Phase 4). In each phase, a particular DO level was maintained ranging 0-2, 2-4, 4-6 and >6 mg/L. Hydraulic retention time and hydraulic loading rate was kept constant at 0.67 hrs i.e. 40 min (based on pore volume) & 0.1 m3/ m2.hr respectively in all the phases. The reactor was operated in continuous mode all the time. The pH, temperature & DO of the reactor were measured periodically. The performance of reactor was evaluated in terms of chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia (NH3), faecal coliform (FC), suspended solids (SS) and turbidity removal efficiencies. The reactor operated at DO > 6 mg/I (Phase 4) showed highest removal efficiencies for all parameters. Average COD and BUD removal efficiencies were found to be 34.4 and 40.1, 52.1 and 56.5, 55.1 and 59.5 and 62.7 and 67.5% for Phase 1, 2, 3 and 4 respectively. Removal efficiency increases with increase in DO concentration. The aim of this study was to bring anaerobically treated wastewater in compliance with effluent discharge standards. BOD and SS concentration in Phase 3 and 4 were met with the effluent discharge standards. Nearly 60% ammonia was removed. The removal was not solely through nitrification though it was principal removal mechanism in Phase 4. The removal of indicator of microbial pathogen (FC) was averaged 1.04, 1.46, 1.40 and 1.64 log units for phase 1, 2, 3 and 4 respectively. SAB was able to work better at low temperature and sustain shock load giving consistent performance in all the phases.