In the first stage aerobic tank for wastewater treatment, the water in that tank cannot have its color adjusted and remains black – how should this be dealt with?
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Our wastewater mainly contains starch, with a small amount of oil (from equipment cleaning). It goes through processes such as screening, purification, aerobic treatment, secondary sedimentation, and sand filtration before being discharged. At present, the color of the water in the first and second aerobic tanks cannot be adjusted; the water in the other tanks is clear. During this process, substances such as dipotassium hydrogen phosphate and urea are continuously added to strengthen the sludge. The aeration period consists of 2 hours of aeration followed by 1 hour of rest. The pH value is within normal ranges. What should be done in this situation?
The water quality in the aerobic zone suddenly turns dark, which is usually caused by insufficient DO, along with an increase in the substrate level. If there is scum in the system’s primary sedimentation tank, it indicates that the raw water has not undergone proper hydrolysis and acidification; the large molecular organic compounds have not been broken down. This may lead to shock conditions, resulting in a decrease in the removal efficiency during the anaerobic stage. As a consequence, the COD concentration of the incoming water increases, the load on the system rises, and short-term DO shortages may occur. After the DO-deficient phase, some of the microorganisms within the biofilm are internally consumed or even die, causing the effluent to turn dark and increasing the suspended solids level. After some of the sludge dies, the existing aeration rate becomes excessive, and the DO returns to the level before the shock or even higher. The removal efficiency in the aerobic stage continued to decline, the effluent levels exceeded the limits by many times (several to dozens of times), and ultimately the entire microbial community collapsed.
Isn’t aeration carried out continuously?
In the AO activated sludge process, this is a normal phenomenon; increasing the aerobic retention time will result in normal effluent quality
Based on the description, it is likely caused by insufficient aeration and low dissolved oxygen levels; increasing aeration continuously will help improve the dissolved oxygen level.
What was said above makes some sense; it is recommended that the original poster try adjusting according to the listed possible causes and observe for a few days