Control of anaerobic-anoxic-aerobic (A²/O) processes in wastewater treatment: a detailed review

This review paper describes different control applications for the A2/O process in sewage wastewater treatment plants. The contents elucidate the research carried out in the literature related to the design of different types of controllers for controlling different variables such as dissolved oxygen, nitrate, total suspended solids, ammonia, etc. that are responsible for the simultaneous removal of both nitrogen and phosphorus. A comprehensive analysis is carried out based on the important factors for the implementation of the control systems with critical discussion and achievements. Control strategies range from simple controllers such as proportional–integral (PI) to the latest (advanced) control approaches such as model-based predictive, fuzzy logic, artificial neural network, and optimal controllers. A distributed control system applied to the A2/O pilot plant is also elucidated. A summary of comparisons between different control systems are assessed and reported in this review.