The effluent from the SBR tank has high COD levels and is turbid
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Recently, the COD level in the effluent has been high, ranging from 70 to 120. When SV30 testing is performed, there is a large amount of suspended solids in the supernatant, making it very turbid; microscopic examination reveals only a small number of rotifers. The ammonia nitrogen in the incoming water ranges from 120 to 240, COD ranges from 350 to 550, and total phosphorus is between 4 and 5. The ammonia nitrogen in the effluent is very low, generally below 1; COD is on the higher side, ranging from 70 to 120; and total phosphorus is between 3 and 4. In terms of operating mode, it involves four stages of aeration. During the first two stages, the DO level is very low; in the latter two stages, it can reach 6. Another anomaly is the pH level: during the last two aeration stages, the pH rises and ultimately reaches around 7.8. Please help analyze it, thanks
It’s similar to our operating method: the pH should decrease. The high COD level indicates that the anoxic phase lasted too short, resulting in incomplete denitrification. In the latter two phases, the dissolved oxygen level is too high, which inevitably leads to low ammonia levels. You can measure TN and TP; they cannot be removed in your system
How long was this period of hypoxia for you? You can give it a try – increase the period of oxygen deprivation!
After stopping aeration in the first two stages, the DO is basically 0; anaerobic conditions should last for about 60 minutes.
There is a problem with the aeration and mixing time you use; why does the final settling time need to be so long? 30 minutes is sufficient. Adjust according to this timing: first exposure 70 min, first mixing 70; second exposure 60, second mixing 50; third exposure 50, third mixing 40; fourth exposure 30. Let it settle for 50 minutes (30 minutes is actually enough), then decant the liquid after 60 minutes. I wonder if you have any requirements for TN? If it is available, add it during the mixing stage; after adding it, the DO level must be kept below 0.5 during the second aeration phase. If this level is exceeded, adjust the timing or the fan flow rate accordingly. Ammonia nitrogen removal must take place during the aerobic stage; the more thorough the aerobic conditions, the better the removal of ammonia nitrogen. However, if there is a lack of oxygen, COD and TN certainly cannot be removed. I hope you will review the mechanisms of nitrification and denitrification again. It should be noted that this system will not go after TP
Typing on a phone is too tiring. I forgot to mention it – methanol or other simple organic molecules can be added; methanol is the most ideal choice