Issues related to the upgrading of sewage treatment plants

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I was tasked with a project to upgrade a wastewater treatment plant; the design capacity was 30,000 tons per day, but the actual capacity is 20,000 tons per day. The inlet water parameters are as follows: COD of 500–600, BOD of around 200, and ammonia nitrogen of 60–80. The A/O process was originally used, with the main treatment sequence being: screen – lifting – hydrocyclone sedimentation – A/O – sedimentation – coagulation filtration – disinfection. The original secondary effluent standard does not involve internal recirculation. It is now necessary to carry out modifications so that the water quality of the effluent meets Class A-A standards. The total volume of the A/O tank is 15,000 cubic meters. I am considering dividing this A/O tank into AAO tanks and adding internal recirculation – is this feasible? Is the tank volume sufficient for this? According to the AAO design specifications, the anoxic tank turns out to be larger than the aerobic tank! Moreover, with the high level of ammonia nitrogen in the wastewater, what should be the internal recirculation ratio? Can the effluent meet the standards? I would also like to ask for the calculation criteria for the AAO method. The current sludge return ratio is about 70%. (50% of the wastewater entering the treatment plant is industrial wastewater, mainly from pipe casting factories); I need experts’ help. . . .