Model-based evaluation of control strategies for phosphorus removal in a full-scale advanced phase isolation ditch process

A model-based evaluation of operation conditions and control strategies was conducted for phosphorus removal in a full-scale Advanced Phase Isolation Ditch (APID) process. The APID process is an alternating type and does not have a separated anaerobic reactor. We suggested that it would be a suitable operational option for robust phosphorus removal by having a different input point for the influent and return sludge flow at specific modes. For evaluation of control strategies, three cases of influent disturbance were assumed, and five manipulated variables were selected for controlling the cases of disturbance. In the case of an increased influent flow rate, a combination of four manipulated variables is proposed through our simulation results as the best control strategy. The optimal k(L)a value was found to be 250/d when pollutants loading kept increasing without variations in the flow rate. When both the pollutants loading and the influent flow rates were increased simultaneously, the robust control strategy is to combine the return sludge inflow point, the exclusive operation modes which have a relatively long hydraulic retention time (HRT), operation period of 30 minutes, and the increase of the return sludge flow rate in proportion to the influent flow rate added to 300/d of k(L)a value.