Enhancing treated wastewater effluent characteristics using hybrid biofilm/activated sludge process – a case study

This paper documents the results of 12 months of monitoring of an upgraded hybrid moving bed biofilm reactor-conventional activated sludge wastewater treatment plant (MBBR-CAS WWTP). It also targets the assessment of the increment of the hydraulic load on existing treatment units with a zero construction and land cost. The influent flow to the plant was increased from 21,000 m 3 d -1 o 30,000 m 3 d -1 , 40% of the existing CAS reactor volume was used for the MBBR zone with a carrier fill fraction of 47.62% and with Headworks Bio ActiveCell™ 515 used as media; no modifications were made for the primary and secondary tanks. The hybrid reactor showed high removal efficiencies for biochemical oxygen demand (BOD 5 ), chemical oxygen demand (COD) and total suspended solids (TSS), with average effluent values recording 33.00 ± 8.87 mg L -1 , 52.90 ± 9.65 mg L -1 and 29.50 ± 6.64 mg L -1 respectively. Nutrient removals in the hybrid modified biological reactor were moderate compared with carbon removal despite the high C/N ratio of 12.33. Findings in this study favor the application of MBBR in the upgrading of existing CAS plants with the plant BOD 5 removal efficiency recording an increase of about 5% compared with the plant before upgrade and effluent values well within the legal requirements.