Ammonia nitrogen issue in domestic wastewater
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For domestic wastewater, MBR integrated systems are used. The COD level of the inlet water is 280, while the ammonia nitrogen level is 55; the COD level in the outlet water is below 10, and the ammonia nitrogen level there is 48. The originally designed value for ammonia nitrogen in the inlet water was 25 (but we’re just the equipment supplier, so that’s not relevant here). After some problems arose, the pH was measured to be around 7-8. The total alkalinity was 500 in the inlet water, 450 in the anoxic tank, and 400 in the membrane tank. The residence time in the anoxic tank was 3.2 hours, and that in the membrane tank was 2.3 hours. The inflow rate of water is currently controlled at around 15 cubic meters per hour, with the DO level kept around 3. Is the aeration time too short? Nitration had no effect ； Or the nitrifying bacteria simply didn’t grow at all; aerobic bacteria are dominant. How should this be adjusted? Thank you
This post was last edited by zhaolijun on 2016-5-5 at 16:44. The ammonia nitrogen level is 55, while the designed value for the incoming water was 25; this issue needs to be addressed, as the actual level is nearly twice the designed value, making it difficult to meet the requirements. Moreover, high ammonia nitrogen levels can act as toxins and inhibit the proper progression of the nitrification process. It is necessary to take a look at the design parameters, such as MLSS, nitrification rate, and water inflow volume. Under the current conditions, DO=3, the COD of the effluent is 10, and PH is 7-8; these are favorable conditions for nitrification. Under normal circumstances, it is possible to reduce ammonia nitrogen levels below 10 without any problems ； However, the ammonia nitrogen level in the effluent being 48 indicates three problems: 1. There are no nitrifying bacteria; 2. The residence time is too short, or in other words, the sludge age is too short, which is not conducive to the growth and reproduction of nitrifying bacteria; 3. Large fluctuations in the system or the presence of toxic substances make it difficult for nitrifying bacteria to survive, as these bacteria have a slow growth rate and are sensitive to changes in the environment. Suggestions: 1. Increase MLSS; values of 5–6 g/L are acceptable. Increase the sludge age to promote the growth of nitrifying bacteria ； 2. Stable operation, with all parameters remaining steady ； 3. Increase DO to around 5 or higher to accelerate ammonia oxidation ； 4. Ensure that the water temperature remains between 20° and 35°C, as this temperature is conducive to the progression of the nitrification process ； 5. Compared to the original design, if the load exceeds 120% of the designed capacity, it is necessary to reduce the processing volume or expand the processing facilities.