Dynamic evaluation of integrated control strategies for enhanced nitrogen removal in activated sludge processes

In this paper, six different strategies for integrated control of nitrate recirculation flow rate and external carbon addition in a pre-denitrifying biological wastewater treatment system are proposed and evaluated using the COST simulation benchmark. The proposed control strategies consist of two or three feedback control loops, which manipulate the nitrate recirculation and the carbon dosage flow rates in an integrated manner, such that the consumption of external carbon is minimized while the nitrate discharge limits are met. The control systems require measurements of nitrate concentrations at the end of both the anoxic and the aerobic zones. A number of simulations are performed and the results show that the control strategies can maintain the designated effluent quality in the presence of external disturbances, while obtaining excellent results in terms of consumption of external carbon, as well as meeting the general plant performance and controller criteria as defined by the benchmark group.