Sludge bulking is a common and thorny problem in the operation of wastewater treatment systems. It will lead to deterioration of sludge settling performance, deterioration of effluent water quality, and even affect the normal operation of the entire treatment system in severe cases. Therefore, effective prevention and response to sludge bulking problems are crucial to ensure the stable operation of wastewater treatment systems.
First, the influent water quality of wastewater should be strictly controlled to avoid high concentrations of toxic and harmful substances entering the system, which may inhibit the normal growth of microorganisms and cause sludge bulking.
Second, ensure the balance of nutrients in wastewater. Generally speaking, BOD₅:N:P should be maintained at around 100:5:1. If nutrients such as nitrogen and phosphorus are insufficient, microorganisms will grow poorly due to lack of nutrients, which may easily lead to the proliferation of abnormal microorganisms such as filamentous bacteria, causing sludge bulking. Balance can be maintained by regularly monitoring water quality and adding appropriate amounts of nutrients according to actual conditions.
Control the appropriate sludge load. If the sludge load is too high, the microorganisms will be in the logarithmic growth period, the coagulation performance of the activated sludge will decrease, and sludge bulking will easily occur; if the sludge load is too low, the microorganisms will enter the endogenous respiration period, which may also cause the sludge structure to be loose. Generally, the sludge load of the activated sludge method should be controlled between 0.20.4kgBOD₅/(kgMLSS·d).
Reasonably adjust aeration. Excessive aeration will cause the microorganisms in the activated sludge to be in a peroxidized state, the cell structure will be damaged, and the sludge flocs will disintegrate; insufficient aeration will cause an anoxic environment, which is conducive to the growth of filamentous bacteria. According to the water quality, water volume and treatment process characteristics of the wastewater, the dissolved oxygen meter should be used to monitor and adjust the aeration volume in real time to keep the dissolved oxygen concentration at around 24mg/L.
Timely sludge discharge is one of the important measures to prevent sludge bulking. Too long sludge age will cause sludge aging, reduced activity, and easy to cause sludge bulking. The sludge discharge volume and discharge time should be reasonably determined according to the sludge settling performance and sludge concentration, and the sludge age should be kept within an appropriate range. Generally, the sludge age of the activated sludge method is controlled at 5-15 days.
At the same time, attention should be paid to the sludge return ratio. If the return ratio is too large, the sludge concentration in the aeration tank will be too high, increasing the difficulty of sludge settling; if the return ratio is too small, sludge loss will occur, affecting the treatment effect. Usually, the sludge return ratio is controlled between 20% and 50%.
Regularly test and analyze the activated sludge, including indicators such as sludge settling performance (such as sludge volume index SVI), microbial composition, and sludge concentration. When it is found that the SVI value continues to rise or the microbial composition changes abnormally, the cause should be found in time and corresponding measures should be taken.
In addition, the morphology and number of microorganisms in the sludge can be observed under a microscope to determine whether there are abnormal conditions such as the massive reproduction of filamentous bacteria. Once excessive growth of filamentous bacteria is found, targeted measures should be taken in time to control it.
When sludge swelling has already occurred, chemical regulation can be adopted. For example, adding an appropriate amount of flocculants, such as polyaluminium chloride (PAC) or polyacrylamide (PAM), to the aeration tank can enhance the coagulation performance of sludge and improve the sedimentation performance of sludge. However, attention should be paid to the dosage, as excessive dosage may inhibit microorganisms.
Bactericidal or antibacterial methods can also be used, such as adding an appropriate amount of chlorine, hydrogen peroxide and other oxidants to inhibit the growth of filamentous bacteria. However, this method needs to be used with caution to avoid damage to the normal microbial community.
The problem of sludge bulking needs to be given enough attention in the operation of the wastewater treatment system. Through comprehensive measures such as strict control of water quality and nutrient balance, optimization of operating parameters, strengthening sludge management, regular testing and analysis, and taking effective emergency measures, the problem of sludge bulking can be effectively prevented and dealt with, and the stable operation of the wastewater treatment system and the compliance of effluent water quality with discharge standards can be ensured.
