Sludge in the aeration tank turns black
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Wastewater type: scouring wastewater; inlet COD = 1700–2000 mg/L； The hydraulic retention time is about 3 days ； sv30=20% ； The aeration method involves the use of aeration hoses, with a gas-to-water ratio that is higher than the typical design value. The sludge is almost as black as that in anaerobic conditions, and the dissolved oxygen level remains at 0 throughout ； There is a hydrolysis-acidification tank at the front end, but the COD removal rate is almost 0. Apart from high organic load and insufficient dissolved oxygen, are there any other possible reasons for the discoloration? Please share your opinions freely; let’s pool our ideas. Thank you!
The main issue is insufficient dissolved oxygen; water supply can be stopped to allow for aeration, in order to increase the dissolved oxygen level as quickly as possible. It is also common for hydrolytic acidification to have no effect on removing COD; this is due either to improper operation or to bacteria breaking down large molecules into smaller organic compounds, which raises the COD level.
Are you in the debugging phase? Pay attention and see if there are any good solutions.
The air-water ratio should be set aside, and the aeration volume should be recalculated based on COD and ammonia nitrogen. The gas-to-water ratio is an empirical value, a quick estimate for those who are lazy, and is far less accurate than the calculated value.
It is caused by low dissolved oxygen; check the indicators related to aerobic conditions: 1. Is the fan functioning properly, and is the flow rate normal?； 2. Is aeration functioning properly, evenly, without any blockages or dead zones? ； 3. Is the water inflow volume highly variable? ； 4. Has there been a significant increase in the quality of the incoming water? ； 5. Is sludge discharge normal, and is the sludge concentration increasing? ； 6. Is the flow rate of mixed return water and secondary sedimentation tank return water too high? ； 7. Is the ammonia nitrogen level in the incoming water too high, and has the amount of reducing substances increased significantly? ； Identify the causes one by one and resolve them as soon as possible; an emergency solution can be to stop the water supply and allow the system to sit.