Methods to reduce sewage COD as soon as possible
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Some time ago, the COD value of the water discharged by our company increased from 1000 to 2000. The aerobic sludge was in a suspended state, with a sedimentation ratio of around 99%; the AO value was approximately 7, and the pH was between 6 and 7. I would like to ask the experts: are there any ways to reduce COD as quickly as possible?
It mainly focuses on the aerobic tank, where the dissolved oxygen level is around 7 and the pH is between 6 and 7
Is the sludge a bit aged? The pH also seems to be slightly lower.
Should the sludge discharge be increased then? What would be a suitable value for PH?
This post was last edited by zhaolijun on 2015-6-7 at 13:54. Based on your description: 1. The DO level is too high; excessive oxidation of the sludge leads to aging and decomposition, resulting in poor sedimentation properties of the sludge, an increase in SS in the effluent along with turbidity, and an increase in COD in the effluent； 2. Due to excessive aeration, ammonia nitrogen is completely oxidized into nitrate salts, resulting in a low pH level ； 3. After excessive oxidation of the sludge, MLSS decreases while the organic load in the influent increases, leading to an increase in F/M and thus an organic load shock. The increased sludge activity further deteriorates the sedimentation properties of the sludge. Suggestions: 1. Stop aeration in the aerobic tank; resume aeration only after the DO level drops below 0.5, or reduce the aeration volume ； 2. Keep the DO at 0.5–1.5; increase it to 2–3 once the sedimentation properties of the sludge have recovered ； 3. Increase the return flow to the secondary sedimentation tank appropriately; due to the impact of organic load, it should not be too high, and a return ratio of 100% is sufficient ； 4. Reduce water inflow and appropriately increase sludge discharge ； 5. Monitor ammonia nitrogen and phosphorus, and supplement as appropriate to keep C:N:P above 100:5:1 ； Add alkalinity (sodium hydroxide or sodium carbonate) to raise the pH value to >7 ； 6 Add an appropriate amount of PAC or PAM to assist in sludge flocculation. It is estimated that it will take 2–4 days to recover; feel free to reach out if you have any questions.
Thank you so much; the analysis is excellent. I will follow it and see how it works, and I’ll keep in touch with you if anything comes up
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The analysis on the fifth floor is very thorough. I have a small suggestion regarding point six: given the current situation, the flocs formed using polyaluminum and polyacrylamide are relatively light, which hinders the settlement of the flocs. If possible, polyferric flocculants or ferrous sulfate or ferric chloride can be used, as this will speed up the settlement process and allow normal production to resume as soon as possible.
Ferrous and ferric trichloride have strong acidity, which causes the pH level to drop; if used, an alkaline substance needs to be added to compensate.
That makes sense; I’ve learned something new, thank you
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