High rate simultaneous nutrients removal in a single air lift bioreactor with continuous feed and intermittent discharge regime: Process optimization and effect of feed characteristics

• CNP removal process was investigated in an air lift bioreactor with CFID regime.
• The system performance at different wastewater characteristics was assessed.
• The effect of two independent variables on the performance was assessed using RSM.
• The variation trends of 7 responses were monitored over optimum condition.

In this research, continuous feed and intermittent discharge air lift bioreactor (CFIDAB) was evaluated under two independent variables to treat milk processing wastewater (MPW). The effect of HRT (6–14 h) and air flow rate (1–3 l/min) on the performance of CFIDAB was studied in a laboratory scale of the bioreactor. The optimum values of HRT and air flow rate were 10 h and 3 l/min, reaching SCOD, TN, and TP removal efficiency around 98%, 85%, and 78%, respectively. The results showed that TP and TN removal were enhanced simultaneously with an increase in HRT and air flow rate. Oxidation–reduction potential (ORP) measurement at the optimal condition showed the successful occurrence of anaerobic, anoxic, and aerobic zones in the CFIDAB. Moreover, the effect of feed characteristics on the process performance for milk processing and soft drink wastewaters was investigated. Based on the obtained data, CFDIAB operated with soft drink wastewater (SDW) showed a better performance in removal of carbon and phosphorus compounds, while nitrogen content was removed more efficient for MPW. As a result, the performance of CFIDAB is sensitive to BOD5/COD ratio of wastewater. Overall, this single compartment air-lift bioreactor could act as an efficient biological nutrient removal system, providing the conditions for good carbon and nutrient removal. It showed an excellent reactor geometry as well as operating strategy to be used as a membrane bioreactor.