Optimal control of N-removal in ASPs

摘要

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 (Henze et al., 1987). This study reveals that, from an 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 NH, and NO, 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. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 9]