Simulation of respirometry-based detection and mitigation of activated sludge toxicity

This paper presents the results of an evaluation of a toxicity mitigation control strategy using the IWA simulation benchmark (Respirometry in control of the activated sludge process: benchmarking control strategies, IWA Scientific and Technical Report #11, IWA, London, England, 2002; The COST simulation benchmark: description and simulator manual, Office for Official Publications of the European Community, Luxembourg, 2001, 154pp). The aim of the proposed strategy is to minimise the impact of a toxic influent shock load on process performance. To do this, the strategy depends on a respiration rate measurement to detect toxic events and uses an equalisation tank to store toxic influent. A defined control algorithm specific for the benchmark plant was developed and controls the reintroduction of the stored influent back into the process stream once the influent is deemed non-toxic. Implemented into the benchmark-defined nitrifying configuration, the evaluation required several alterations to the simulation benchmark including three model changes, the addition of a soluble unbiodegradable toxic state variable and the development of two toxic influent files: The results of the simulations indicate that the impact of the toxicant can be significantly mitigated through the use of off-line storage and reintroduction of suspected influent. (C) 2003 Elsevier Science Ltd. All rights reserved.