The optimal design conditions of the multi-staged aeration tank and final sedimentation vessel of activated sludge process have been studied, with the assumption that the flow pattern of the each aeration tank is of perfect mixing.
The objective function was taken as the total volume and/or total construction cost of the aeration tank and the final sedimentation vessel. The volume of each vessel and the inflow rates of the feed and the return sludge to the each stage were considered as the decision variables.
In this work the method of approximation to the solution by the discrete maximum principle has been employed as the optimization technique. The optimal operation policy of a model plant of activated sludge process system has been also studied by the same method, taking the BOD concentration of the exit water from the final sedimentation vessel as the objective function,
The computational results has been revealed as follows ;
1. The distributions of the fresh feed and the return sludge are not recommendable, but feeding both inflows only to the first stage is found to be preferable.
2. The total volume of aeration tanks and the final sedimentation vessel can be reduced to 68 %, 59 %, 55 %, 48 % in the case of two, three, four and ten-staged aeration process, respectively, compared with that of single-stage aeration process.
3. The construction cost can be reduced to 75 %, 70 %, 70 %, 71 %, in the case of two, three, four and five aeration process, respectively, compared with that of single-stage aeration process. The construction cost is of minimum when the aeration process is 3 or 4 staged.