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Abstract
The International Association on Water Quality (IAWQ) Activated Sludge Model No. 1 was used to optimise a full-scale activated sludge plant, treating a high-strength pulp and paper mill effluent operating at a temperature of 38°C. The model was calibrated by determining the mixing characteristics of the reactor and the oxygenation capactity of the aeration system in situ. In addition batch tests were carried out to determine wastewater COD fractions together with the important kinetic parameters necessary to run the IAWQ Model. Steady-state simulations carried out using the calibrated model were in good agreement with average plant operational data. As a result of major modifications which were undertaken to the paper mill white water systems, the investigation was repeated and the results revealed that both the wastewater characteristics and process kinetic features had changed and this was mirrored by changes in plant performance. Again simulations carried out using the revised parameters showed good agreement with plant operating data. As a result the model was used to provide recommendations for optimising plant operation, namely that by reducing sludge age, there would be a reduced oxygen consumption together with an enhanced COD removal. The model proved to be a valuable tool for predicting the steady-state performance of this activated sludge system treating pulp and paper mill effluent at elevated temperatures.