CONSEQUENCES OF THE BEHAVIOUR OF ACTIVATED SLUDGE PLANTS WITH COMBINED SEWAGE INFLOWS

The paper deals with the dynamic behaviour of activated sludge plants resulting from combined sewage inflows. Implications for the planning and operation of activated sludge plants are inferred from this behaviour. On the basis of a measured rain event dynamic simulation is used as a tool to investigate the influences of combined sewage inflows. Following an increase in the water inflow rate due to rain, a significant increase in concentration of nitrogen is observable at the outflow of the activated sludge tank The reason for this is the total Kjeldahl nitrogen influent load peak generated by the combined sewage inflow, together with displacement of biomass to the secondary sedimentation tank. Since the effluent concentration peaks are caused by inflow load peaks, measures must be taken to buffer these load peaks in the inflow zone. Best results can be achieved with inflow storage. Given a sufficiently large storage tank and optimum load management, a relatively low ammonium effluent value could be maintained even at high inflow rates. Optimum inflow control is feasible if both the water volume and the nitrogen concentration can be measured at the inflow and can be influenced by means of storage tanks. Dynamic simulation continues to be useful during operation, and can support tank control.