The sludge concentration is low, with SV30=30 (1000 ML). How can the sludge be cultivated properly?

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In a leather processing plant, the quality parameters of the wastewater are as follows: COD in the inlet water is 2300 mg/L, ammonia nitrogen is 90 mg/L, and pH is 5.2; COD in the outlet water is 700 mg/L, ammonia nitrogen is 80 mg/L, and pH is 8.2. The process used is coagulation sedimentation – hydrolysis acidification – aerobic treatment – aerobic treatment – secondary sedimentation – intermediate tank – effluent discharge. At present, the removal efficiency in the aerobic tanks is not very good due to the low sludge concentration, and ammonia nitrogen levels fail to decrease. Flour and phosphate fertilizer are added daily to cultivate microorganisms; microscopic examination of the sludge from the secondary sedimentation tank reveals only a small number of rotifers, nematodes, and cladocerans, while there are almost no insects in the aerobic tanks. The dissolved oxygen levels in these tanks are relatively high: around 4.0 in the first aerobic tank and around 7.5 in the second one. Currently, water is introduced into the system for 6 hours per day at a flow rate of 100 tons/h. I would like to ask experts how to improve aeration and accelerate the development of suitable sludge!