Discussion on Dissolved Oxygen Control Methods in Stage A of the A/O Process
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In the A stage of the A/O process, the dissolved oxygen level is generally required to be no more than 0.5; however, the dissolved oxygen concentration in the wastewater from stage O due to internal recirculation is relatively high. Please share your experiences in controlling dissolved oxygen levels in stage A
1. I wonder if the original poster has measured the dissolved oxygen level in section A; generally, it isn’t too difficult to keep the dissolved oxygen in section A below 0.5. 2. Generally, for the recirculation rate in denitrification processes, it is equal to (4~6)Q; this is the value we have here. I’m curious to know what the experiences of other users are?
The flow rate of internal recirculation is controlled based on the efficiency required for nitrogen removal; the higher the efficiency, the greater the recirculation
In the A/O process, stage A can be used for ammonia removal or phosphorus removal. If it is used for nitrogen removal, a DO level of around 0.5 or lower is required, as this facilitates nitrogen removal. It is necessary to control the ratio of mixed liquor return; too high a return ratio may lead to an increase in DO levels. However, the mixed liquor return ratio is related to the efficiency of nitrogen removal – the higher the return ratio, the better the nitrogen removal efficiency. If phosphorus removal is required, stage A must be anaerobic, meaning the DO level is 0. In this process, sludge return is used to enable the phosphorus-removing bacteria present in the sludge to absorb phosphorus, which is then removed through sludge discharge.