In SBR plants for nutrient removal it is often necessary to add supplementary rbCOD during the anoxic phase to obtain complete nitrogen removal. In addition to the aeration, this supply of high-quality BOD is a non-negligible part in the operating costs. Because of the complexity of the bighly interconnected biological processes a heuristic approach for process optimization is hardly possible. Therefore the Nitrification Denitrification Biological Excess Phosphorus Removal (NDBEPR) model of Wentzel et al. and a numerical optimization a1goritbm were used to optimize SBR time scheduling, i.e. minimize both effluent concentrations and operating costs. It was found that a sequence of short aerobic/anoxic phases appears to be better than the usual sequence (one aerobic phase followed by one anoxic phase). This result was validated on a 500 I scale SBR. The optimized process saves up to 50% on extra BOD supply and up to 30% on aeration time. Moreover, it was shown that these cost savings were not at the expense of the phosphorus removal efficiency or the nitrification rate. From an additional numerical optimization it was seen that the ideal SBR time scheduling may depend on the loading. Therefore. a control strategy hased on OUR and ORP measurements is proposed.
