In this study, a pilot-scale, two-stage cascade biological nutrient removal (TSC-BNR) process with a 10 m3.d-1 capacity was used in order to remove carbon and nutrient from municipal wastewater. The process was composed of screens, a primary sedimentation tank, a distribution tank, an anaerobic tank, anoxic1/aerobic1/anoxic2/aerobic2
tanks, and a final sedimentation tank. Real (Sewer system) wastewater was fed to the pilot plant and the inflow was fed to the anaerobic and anoxic2 tanks at the same rates to eliminate the need for external carbon source in the second stage anoxic tank. The mixed liquor suspended solids (MLSS) concentration was kept between 4500 and 5500 mg.L-1 during the study. The sludge retention time was 15 days and the hydraulic retention time was 16 hours.
The average concentrations of chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4+-N), total phosphorus (TP), phosphate phosphorus (PO43--P), suspended solids (SS), and volatile suspended solids (VSS) in the influent were 555 mg.L-1, 71.9 mg.L-1, 44.0 mg.L-1, 8.1 mg.L-1, 4.0 mg.L-1, 316 mg.L-1, and 230 mg.L-1, respectively, the average removal efficiencies were 86.7±10.4%, 80.3±11.0%, 92.5±10.1%, 89.5±6.8%, 87.5±8.8%, 94.8±3.2%, and 95.0±3.4%, respectively. The results indicated that TSC-BNR process can be confidently used for the removal of carbon and nutrients from medium-strength municipal wastewaters.