Benchmarking combined biological phosphorus and nitrogen removal wastewater treatment processes

This paper describes the implementation of a simulation benchmark for studying the influence of control strategy implementations on combined nitrogen and phosphorus removal processes in a biological wastewater treatment plant. The presented simulation benchmark plant and its performance criteria are to a large extent based on the already existing nitrogen removal simulation benchmark. The paper illustrates and motivates the selection of the treatment plant lay-out, the selection of the biological process model, the development of realistic influent disturbance scenarios for dry, rain and storm weather conditions respectively, the definition of performance indexes that include the phosphorus removal processes, and the selection of a suitable operating point for the plant. Two control loops were implemented: one for dissolved oxygen control using the oxygen transfer coefficient K(L)a as manipulated variable, the second one for nitrate control in the anoxic zone using the internal recirculation flow rate as manipulated variable. Dynamic simulations for different dissolved oxygen set points illustrate the complex interactions in this plant, and the necessity for a continuous trade off between supplying sufficient oxygen to promote nitrification on the one hand, and the need for low dissolved oxygen concentrations on the other hand to allow sufficient development of phosphorus accumulating organisms. The potential for aeration energy savings in the plant is highlighted based on the dissolved oxygen profiles resulting from open loop simulations with a dynamic dry weather influent scenario. The influence of the dissolved oxygen set point selection on the nitrate control loop performance observed in the simulations further illustrates the need for a plant-wide optimization approach to reach optimal plant performance. (C) 2003 Elsevier Ltd. All rights reserved.