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Wastewater Treatment System's Normal Question
- Mar 16, 2018 -

Wastewater treatment system's normal question 


10. We are a two-stage biochemical treatment of petrochemical wastewater. The first stage is a circular fully-mixed aeration tank, and the second stage is a push-flow aeration tank. The first-grade DO is 0.2 mg/L and the second-grade DO is 5.0 mg/L. During this time, biochemical influent PH 8.0, effluent 6.5, pH 5.78 after secondary biochemistry, beyond the scope of indicator 6-9, how is this going?


Answer: The low level of DO is normal, because the sludge load is high, and the primary pH drop may be due to the acidification of the load being too high. The pH drop of the secondary effluent may be caused by the alkalinity consumption of the nitration reaction. Because you introduced it too simply, I can only analyze and infer


11. In addition to the removal of ammonia nitrogen, in addition to having sufficient carbon source and a sufficiently long sludge age and ensuring adequate reflux, is the reflux flow back to the aerobic tank or the bottom of the secondary settling tank? I am now debugging spandex waste water, originally designed to return to the aerobic pool water, but in fact, if the return flow rate doubles, it cannot guarantee the anaerobic environment of the anoxic tank in front, and my master said that the aerobic tank dissolved oxygen is controlled at 1mg. /L or so will be better, is this correct?


Answer: According to your introduction, it should be pre-denitrification, and you need to return the effluent from the aerobic tank and the sludge in the second settling tank. You said that if the return flow rate is doubled, there is no guarantee that the anaerobic environment of the anoxic tank in front is not appropriate. The anoxic area is not equal to anaerobic, and the DO is less than 0.5 mg/L. Your master said that the aerobic tank dissolved oxygen control at 1mg/L is also justified, so as to prevent the anoxic area DO greater than 0.5mg/L.


If the DO is about 1 in the aerobic zone and the flow rate of the effluent is doubled, the DO in the anoxic zone is still greater than 0.5 mg/L. Do not reduce the dissolved oxygen in the aerobic zone, and do not arbitrarily reduce the effluent flow (entering the hypoxia). There will be less nitric acid and nitrogen in the area. At this time, the amount of mud in the secondary settling pond can be reduced without affecting the sedimentation effect of the second settling pond. The sludge layer in the pond can be raised to make the residence time of the sludge in the second settling pond. Increasing it to a defective oxygen or oxygen-free state also helps to prevent DO from rising in the anoxic zone.


The reduction of mud volume in the secondary sedimentation tank will not affect the amount of sludge flowing back to the reaction tank, because the concentration time of the sludge in the mud layer is long under the condition that the sediment layer in the secondary sedimentation tank is increased. The amount has decreased but the mud concentration has increased. If it is a contact oxidation process, the effluent should be returned and the sludge should not be returned. I do not support the use of pre-denitrification. Because of the large energy consumption of the return flow of the effluent, the large return flow requires a large volume of the reaction tank. It's not a good idea to remove nitrifying bacteria, but understand what you mean