Seeking advice on high settlement ratio
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Our wastewater treatment plant uses the A/O process. The test results for today’s phenol-containing wastewater show an inlet COD of 580 and an outlet COD of 44. The inflow flow rate is 2,000 tons; the inlet ammonia nitrogen level is 13.1, while the outlet level is 4.2. The DO level in the aerobic tank is 6.7, and it is 0.19 in the anoxic tank. The pH value in the aerobic tank is 7. The sedimentation ratios are Sv5 at 96, Sv10 at 87, and Sv30 at 54. There are particles suspended in the supernatant fluid. The sludge concentration is 3,530, with an SVI of 153. Microscopic examination today revealed rotifers, which had not been observed before. The system has not been functioning properly; the outlet COD has always been around 120. It was not until a week after adding sludge for acclimatization that the COD dropped to around 80. The normal load for the system is around 3,000 tons, but it is still operating at a reduced load. Under normal operating conditions, the sludge concentration is around 3,000, with an SV30 of around 30. Currently, the sedimentation ratio remains between 52 and 54. How can this ratio be reduced? Should sludge be removed, or should the load be increased? Or perhaps the dissolved oxygen level should be lowered?
Based on your description, it seems that the organic load F/M is low; operation at a low load level combined with excessive aeration has led to a deterioration in the flocculation properties of the sludge. Suggestions: 1. Reduce the DO level promptly; if the water temperature is below 20°C, it can be lowered to around 4, while when the temperature is between 20–25°C, it should be reduced to around 3. After the SVI decreases, increase the DO level as appropriate depending on the level of ammonia removal ； 2. Increase the sludge discharge rate, raise the F/M ratio to above 0.05, and keep the MLSS at around 3 g/L ； 3. Under normal circumstances, noticeable results can be seen in 2 days.
A friendly reminder: it’s okay to increase the load at this time, but be sure not to do it too quickly, as this can easily lead to a surge in organic load, making things more complicated to handle and causing the system to take longer to recover.