Has anyone ever encountered this situation? How was it solved?
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Has anyone ever encountered this situation? How was it solved? The COD of the influent water increases instead of decreasing by 400–500 mg/L after treatment, while the removal rate of ammonia nitrogen is over 95%. . . The raw water is the biogas slurry obtained after anaerobic fermentation of kitchen waste and subsequent centrifugation.
It is theoretically impossible for the COD level of the effluent to be high, but this situation often occurs in actual operation. Why is that? 1. The issue of residence time is that, due to the effect of residence time, the relationship between the effluent and the influent cannot be reflected; in other words, the current effluent is the result of the influent from that same time plus the residence time. If the residence time is 1 day, then it is the influent from 1 day ago that has the greatest impact on the current effluent ； 2. The impact of biochemical processes is generally caused by undissolved microorganisms, i.e., SS; when the effluent contains mud or colloids, COD levels will definitely rise ； 3. Failures in the secondary sedimentation tank affect the quality of the effluent; issues such as surface load exceeding design values, short-circuiting, heavy-phase flow, anaerobic or partial anaerobic conditions, and denitrification can all result in the effluent containing sediment ； 4. There is short-circuiting occurring, with water flowing directly from the inlet to the outlet ； 5. The sampling is unrepresentative or incorrect.
Based on the situation you described, an ammonia nitrogen removal rate of over 95% indicates that the concentration of organic matter in the effluent is low and there is an adequate supply of oxygen. This condition is likely to be accompanied by excessive aeration, which leads to sludge aging and subsequent disintegration of the sludge flocs, ultimately causing problems in the biochemical treatment process and resulting in poorer water quality in the effluent.
On the assumption that water quality fluctuations, as well as sampling errors or testing issues, are excluded. This situation may be caused by excessive aeration or the aging and decomposition of sludge, which leads to the breakdown of bacteria and the release of large amounts of cytoplasm, thereby increasing COD. First, identify the cause and then address it accordingly
Excessive aeration, or aged sludge, leads to COD being affected by SS
When testing the COD of wastewater, the reproducibility of the results was poor due to the presence of suspended solids; however, filtering the samples using a needle filter improved the testing results.