The SV30 value is very low, and the total phosphorus content in the effluent exceeds the standard
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In the improved cartridge-type oxidation ditch, the SV30 value is only 7%; sedimentation occurs quickly, and the supernatant is clear (with only minor particles suspended). The sludge flocs are quite fine. By the next day, some of the sludge in the measuring cylinder floats to the surface, and filamentous substances appear. The total phosphorus content in the effluent is high at noon (lower in the morning and evening), reaching 1.4, while the total phosphorus in the influent is only 1.7. Removing more sludge would help, but I wonder if the frequency of sludge removal isn’t too high (about 10 hours per day). The COD level is between 80 and 100, the flow rate is 7,000–8,500, the ammonia nitrogen level in the influent is around 20, while it’s about 3 in the effluent. A friend told me that over-aeration is causing poor treatment of total phosphorus, suggesting that I keep the DO level around 1. (Our plant has few employees, so it operates for about 12 hours during the day; it shuts down at night.) Please help me figure out how to adjust the settings appropriately. It’s not possible to measure the MLSS because the equipment is broken.
Based on your description, the performance of the activated sludge is poor; there is excessive aeration, the sludge has aged, and the inorganic content in it is relatively high. Is the pH value of the effluent also a bit low? Suggestions: 1. Reduce the dissolved oxygen level to DO=1, or intermittent aeration can be used; since the ammonia nitrogen level is low, there is no need to focus much on its removal. Moreover, denitrifying bacteria will compete with polyphosphate-accumulating bacteria for carbon sources, thereby inhibiting the release of phosphorus by these bacteria ； 2. Reduce the sludge discharge volume; an SV of around 15% is preferable ； 3. Since there is a limited amount of carbon source, can some additional carbon source be added? ； 4. When starting up the system each day, it is possible to avoid aeration and instead run the water inflow, recirculation, and mixing functions for 1–2 hours; after that, some carbon source can be added, which will help with phosphorus removal ； 5. Controlling the pH of the effluent at 7–8 is more conducive to phosphorus removal.