Brothers and sisters, let's talk about the long-standing problem of WWTP today - low sludge load leads to floating sludge in the secondary sedimentation tank! This scene gives everyone a headache: layers of sludge flocs float on the surface of the secondary sedimentation tank, which not only fails to meet the effluent quality standards, but may also block subsequent equipment, making it a ticking time bomb in the "sewage industry". Don't panic! Today, I will teach you step by step how to quickly handle this troublesome matter!
1, First, understand why this is happening? Knowing oneself and one's enemy is the key to prescribing the right medicine
We need to first clarify what the relationship between low sludge load and floating sludge in the secondary sedimentation tank is? Simply put, the sludge load is like the "flow of people" at the dining window in a cafeteria, where sludge is the people queuing up to serve, and the pollutants in the sewage are the food. Under normal circumstances, sludge can "dry and wipe away" pollutants. But once the sludge load is low, it's like suddenly there aren't many people coming to eat in the cafeteria, the sludge becomes too hungry, lazy, the activity decreases, and the settling performance also decreases. At this moment, the secondary sedimentation tank is like a chaotic parking lot, where the sludge flocs cannot stop and float directly onto the water surface, forming the phenomenon of floating sludge that we see.
In addition to the situation where the sludge is too hungry, there are several other situations that can make things worse. For example, if there is excessive aeration, the sludge that is already "not enough to eat" will be wildly stirred by the air, and the flocs will be completely dispersed; Or if the amount of returned sludge is not well controlled and the sludge stays in the tank for the wrong amount of time, it is also easy to "get angry" and not settle; Even sudden changes in water quality that sludge cannot adapt to can lead to floating sludge. So, in order to quickly solve the problem, we must first identify the root cause!
2, Quickly deal with the "three board axe" and achieve immediate results
1. Adjust the sludge reflux to make the sludge "move"
After discovering floating mud, the first step is to quickly check the sludge return system! If the sludge reflux ratio is too low, it is equivalent to removing all the workers, and the secondary sedimentation tank will definitely be in chaos. At this point, you can first try increasing the sludge return ratio by 10% -20% to allow more sludge to return to the aeration tank for work. For example, if the reflux ratio was originally 50%, we can first mention 60% -70%. It's like sending workers to a construction site, where the sludge has some work to do and its activity can slowly recover.
However, the reflux ratio should not be too strong, and the situation of the secondary sedimentation tank should be observed while adjusting. If the pressure of the sludge return pipe increases or the sludge layer at the bottom of the secondary sedimentation tank thickens, it is necessary to slightly adjust it to avoid excessive sludge accumulation in the secondary sedimentation tank, which may worsen the floating sludge.
2. Control aeration to prevent the sludge from becoming "breathless"
As mentioned earlier, excessive aeration can break up sludge flocs, so if you notice floating sludge, go to the aeration tank and take a look! If the bubbles on the water surface are small and dense, and keep churning, it is highly likely that the aeration is too strong. At this point, you can first reduce the air volume of the aeration equipment by 15% -20%. For example, the blower was originally fully turned on, but now it is adjusted to 80% -85% power.
After reducing the gas volume, check the dissolved oxygen (DO) value in the aeration tank every half hour. Under normal circumstances, the DO at the end of the aeration tank should be controlled at 2-4mg/L. If the DO decreases too quickly, it means that the amount of air lowered is not enough, continue to adjust slowly; If it cannot be lowered, then adjust it back a bit until DO stabilizes within the appropriate range and the sludge can settle quietly.
3. Add coagulants to help the sludge
If the floating mud still does not improve after adjusting the reflux and aeration, then we need to invite external assistance - coagulant aid to come on stage! Common coagulants include polyaluminum chloride (PAC) and polyacrylamide (PAM). PAC is like "glue" that can stick small sludge particles together; PAM is more powerful, like a "fishing net", which wraps the sticky particles into large flocs to accelerate the settling speed.
When adding, first conduct a small experiment in the laboratory. Take a cup of mud water mixture from the secondary sedimentation tank and add different concentrations of PAC and PAM respectively to see which ratio has the best effect. Generally speaking, the dosage of PAC is 10-30mg/L, and the dosage of PAM is 1-3mg/L. After determining the dosage, prepare the coagulant aid into a solution and slowly add it to the inlet of the secondary sedimentation tank or the return sludge pipeline through a dosing pump. After adding, keep an eye on the changes in the secondary sedimentation tank. If you see a significant increase in the size of the sludge flocs and start to sink within half an hour, it means this trick is effective!
3, Subsequent "maintenance" should not be neglected to prevent problems from recurring
The floating mud problem has been temporarily solved, don't think everything is fine! At this point, it is necessary to conduct follow-up monitoring and adjustments to prevent the recurrence of old problems.
Continuous monitoring of key indicators: In the next few days, key data such as sludge load, sludge concentration (MLSS), sludge settling ratio (SV30), and dissolved oxygen (DO) will be measured daily. If you find that the sludge load still cannot be increased, you can try reducing the amount of sludge discharged and allowing the sludge to "nourish" more in the tank; If the SV30 value remains low, it indicates that the sludge settling performance has not recovered, and it may be necessary to continue adjusting aeration or adding coagulants.
Optimize operating parameters: Based on the experience of floating mud this time, re evaluate the operating parameters of the sewage treatment system. For example, is the sludge age set too long, leading to sludge aging? Or is the inflow water quality fluctuating greatly, but the process has not been adjusted in a timely manner? Sort out all these issues and quickly adjust the parameters that need to be changed to avoid falling into the trap again next time.
Regular cleaning of equipment: During the process of floating sludge, some sludge flocs may stick to equipment such as the scraper and effluent weir in the secondary sedimentation tank. After the problem is solved, take some time to clean these devices and ensure their normal operation. Otherwise, if the equipment gets blocked, the next time the mud may come faster!
In short, although it is troublesome for the sludge to float in the secondary sedimentation tank due to low sludge load, as long as the cause is identified, these steps are taken quickly to deal with it, and subsequent maintenance is done well, this "thorn head" can be cleaned up obediently! I hope today's sharing can be helpful to everyone. If you encounter similar problems in the future, you will have peace of mind!
