Low-cost, reliable, and highly efficient removal of COD and total nitrogen from sewage using a sponge-filled trickling filter

Development of low-cost and reliable reactors that need minimal supervision is a need-of-the-hour for sewage treatment in rural areas. This study explores the performance of a multi-stage sponge-filled trickling filter (SPTF) for sewage treatment, employing polyethylene (PE) and polyurethane (PU) media. Chemical oxygen demand (COD) and nitrogen removal/transformation were evaluated at hydraulic loading rates (HLRs) ranging from 2 to 6 m/d using synthetic sewage as an influent. At influent COD of ∼350 mg/L, PU-SPTF and PE-SPTF achieved a COD removal of 97% across all HLRs with most of the COD removal occurring in the first segments. Operation of PE-SPTF at an HLR of 6 m/d resulted in a substantial wash-out of biomass, while PU-SPTF retained biomass and achieved effluent COD < 10 mg/L even at an HLR of 8–10 m/d. The maximum total nitrogen (TN) removal by PE-SPTF and PU-SPTF reactors was 93.56 ± 1.36 and 92.24 ± 0.66%, respectively, at an HLR of 6 m/d. Simultaneous removal of ammonia (NH4-N) and nitrate (NO3-N) was observed at all the HLRs in the first segment of both SPTFs indicating ANAMMOX activity. The COD removal data, packed media depth, and HLRs were fitted (R2 > 0.99) to a first-order kinetic relationship. For a comparable COD removal, CO2 emission by PU-SPTF was 3.5% of that of an activated sludge system.