A/0 retention time and assistance regarding the sludge thickening tank
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1. When designing, the effective tank capacity is determined based on the required time; does it need to take backflow into consideration? 2. When all tanks are designed to be entirely underground, how is the supernatant from the sludge thickening tank discharged?
1. When designing, the effective tank capacity is determined based on the required time; does it need to take backflow into consideration? There is no need to consider the backflow volume
2. When all tanks are designed to be entirely underground, how is the supernatant from the sludge thickening tank discharged? A buffer tank can be installed next to the concentration tank; the supernatant flows automatically into this buffer tank, and the wastewater in it is pumped away.
The A/O process features two types of recirculation: one internal recirculation for nitrogen removal, and one external recirculation to balance MLSS.
1. When designing, the effective tank capacity is determined based on the required time; does it need to take backflow into consideration? It is recommended to leave a somewhat larger margin, with a residence time of 30–40 hours, to provide more flexibility in operation.
The external return design features two outlets: one leads to the anoxic inlet and the other to the aerobic inlet, allowing for greater flexibility during operation.
For oxygen-deficient feedwater, a feedwater tank is designed, with a residence time of 5–10 hours; this tank functions as a biological selector and is very helpful for operation.
The water entering the secondary sedimentation tank should not be fed via overflow; an immersion method is used to prevent aerobic foam from entering the tank, thereby **reducing** the likelihood of foam and scum forming in it.
If the sulfate concentration in the wastewater exceeds 1000 ppm, it is recommended to provide partial aeration in the anoxic tank; this can prevent the formation of hydrogen sulfide due to anaerobic conditions that occur when the water stays there for too long. Hydrogen sulfide not only contaminates the environment but also hinders the growth and reproduction of aerobic bacteria.