Development and verification of design and operation criteria for the stepfeed process with nitrogen removal

The step feed process with three stages of denitrification-nitrification re actors has been studied using simulations in order to develop criteria for the optimum selection of the design parameters and to propose efficient ope rational strategies. To verify the simulation results experimental studies in a pilot plant of 1100 litres were carried out. The simulation studies showed that the optimum influent flow distribution t o the three anoxic reactors is in the range of 40-40-20% and 33-33-34% depe nding on the wastewater characteristics and effluent requirements. These tw o latter conditions and in turn the influent flow distribution determine th e anoxic and aerobic reactor volumes. The reduction of the dissolved oxygen in the two first aerobic reactors and the use of facultative zones in the final D-N stage are proposed as operational strategy. The experimental resu lts proved the validity of the criteria developed for design and operation. A high capacity of the IAWQ activated sludge model No. 1 to predict the pe rformance of the step feed process was observed.