The Biocos strategy as a cyclical time controlled activated sludge system shows a great variability in operation and control. One topic such a type of treatment plant has to deal with is the optimum relation between aerobic and anoxic conditions. The aeration control has to adapt the length of the nitrification phases to the current constraints in order to save operational costs and maximise nitrogen elimination. Since wastewater treatment plants up to a certain size are usually not equipped with on-line nitrogen probes, influent flow and temperature can be taken as control parameters for the aeration system. The defined relation between influent flow and ammonia load is based on measurements and the relation between ammonia load and required aeration time is model based.

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