High-rate CNP removal from wastewater in a single jet loop air lift bioreactor: Process modeling and optimization with four process and operating factors

The present study investigates a jet loop-air lift bioreactor employed as a single cost-effective system with anaerobic, aerobic and anoxic zones in order to achieve high-rate simultaneous CNP removal from soft drink wastewater. The reactor was operated at continuous regime while different conditions were designed using central composite design (CCD) under response surface methodology. Four independent variables including hydraulic retention time (HRT), anaerobic volume to total working volume ratio (VAn/VT), air flow rate (AFR), and influent nitrogen concentration in the range of 8−16 h, 0.04−0.12, 3.5–5.5 l/min, and 150−300 mg/l, respectively, were evaluated in terms of their impacts on several responses. With regards to the results obtained, HRT and AFR directly enhanced the biological CNP removal while a decreasing effect for VAn/VT was observed. COD and TP removal efficiencies were not affected by influent nitrogen concentration while TN removal efficiency was negatively affected. Overall, chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) removal efficiencies obtained at optimum conditions (HRT: 14 h, VAn/VT: 0.06, AFR: 5.5 L/min, and influent nitrogen: 225 mg/l) were 97 %, 63 %, and 81 %, respectively, proving the reactor’s potential to remove CNP efficiently. The maximum COD, TN, TP removal efficiencies were 97, 99.9, 81 %, respectively.