Ammonia nitrogen increases instead of decreasing after entering the aerobic tank
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A medical and chemical company previously had a COD value in the range of 100–150 for wastewater treatment, with an ammonia nitrogen level of 1–3. To further enhance the activity of the bacteria in the aerobic tank, a biological enhancer named SD1 was used (the composition of which is unknown, as the manufacturer refused to disclose any information regarding its components). One pack (25 kg per pack) was added daily. Initially, the water quality parameters were satisfactory, with some improvement in COD levels. On the 13th day after the addition of this enhancer, ammonia nitrogen levels began to rise rapidly, and by the 15th day, they exceeded the acceptable limits. After aeration during that period, the color of the bubbles and sludge was normal; starting from day 13, the bubbles and slurry turned dark black, the bubble layer became thinner, the water quality deteriorated rapidly, and COD levels increased sharply. After aeration stopped, a layer of sludge floated on the surface of the water. I would like to ask if this is a case of poisoning? If it is poisoning, what measures should be taken to address the situation?
Blackening of sludge can be addressed by increasing aeration or boosting sludge return.
It is estimated that the main components of biological enhancers are small organic molecules; their addition increases the carbon source, leading to insufficient dissolved oxygen. The lack of oxygen in the water causes the sludge to float to the surface, ammonia levels to rise, and the quality of the effluent water to deteriorate. It is recommended to increase sludge discharge, raise dissolved oxygen levels, and reduce the return flow from the secondary sedimentation tank.
Blackish slurry indicates low DO; why reduce DO then?