Modelling and control strategy testing of biological and chemical phosphorus removal at Avedøre WWTP.

The biological phosphorus removal process is often implemented at plants by the construction of an anaerobic bio-p tank in front of the traditional N removing plant configuration. However, biological phosphorus removal is also observed in plant configurations constructed only for nitrogen removal and simultaneous or post-precipitation. The operational experience with this "accidental" biological phosphorus removal is often mixed with quite a lot of frustration, as the process seems to come and go and hence behaves quite uncontrollably. The aim of this work is to develop ways of intentionally exploiting the biological phosphorus process by the use of instrumentation, control and automation to reduce the consumption of precipitants. Means to this end are first to calibrate a modified ASM2d model to a full-scale wastewater treatment plant (WWTP), including both biological and chemical phosphorus removal and a model of the sedimentation process. Second, based on the calibrated model a benchmark model is developed and various control strategies for biological phosphorus removal are tested. Experiences and knowledge gained from the strategies presented and discussed in this paper are vital inputs for the full-scale implementation of a control strategy for biological phosphorus removal at Avedøre WWTP, which is described in another paper. The two papers hence show a way to bridge the gap from model to full implementation.