Optimisation of the operation strategy of N-removing activated sludge processes (ASPs) contributes to improved effluent quality and/or costs savings. This paper deals with the development of an aeration strategy yielding optimal N-removal in continuously mixed, continuously fed ASPs. First, optimal control theory is applied to the generally accepted ASM no. 1 model. This study reveals that, from an N-removal point of view, both alternating nitrification/denitrification and simultaneous nitrification/denitrification at limiting DO-levels might be optimal, depending on the uncertain oxygen half-saturation constants of autotrophic and heterotrophic biomass. Hence, taking into consideration the risk of sludge bulking at limiting DO-levels, an alternating anoxic/aerobic strategy is favoured. A Receding Horizon Optimal Control (RHOC) strategy using NH4 and NO3 measurements is developed, enabling feedback control of the alternation between anoxic and aerobic phases with the explicit objective of optimal N-removal. Simple rules are given for straightforward tuning of this controller. The controller successfully passed several tests both in simulation and in application to a pilot plant continuously fed with presettled domestic wastewater.

This content is only available as a PDF.
You do not currently have access to this content.