Once foam in the aeration tank spills over the tank wall, it not only pollutes the surroundings but also interferes with readings of online instruments, bringing real trouble to wastewater plants. The activated sludge process aerates continuously, and surface-active substances from microbial metabolism make foaming likely to begin with; when the influent also carries detergents, grease or industrial surfactants, the foam is even harder to control. Dosing a defoamer is a common measure, but in a biological system there is more to choosing and dosing than one might imagine.
Pass the Microbial Safety Gate First
The microbial community in activated sludge is very sensitive to chemicals; some defoamers contain inhibitory components that affect organic degradation efficiency and may even cause effluent indicators to fluctuate. For defoamers used in biological tanks, low toxicity and easy degradation are hard thresholds, and their impact on oxygen transfer and sludge settling must also be assessed. This is why polyether defoamers are increasingly recognized in water treatment: their effect on activated sludge microbial activity is relatively mild, with better biocompatibility.
Special Requirements of Membrane Systems
As membrane technologies such as MBR membrane bioreactors and reverse osmosis spread, the requirements on defoamers are raised another notch. If foam enters membrane modules with the water flow, it affects permeate flux and salt rejection, and oily residue may cause membrane fouling. Defoamers used ahead of the membrane must be highly water-soluble, low-residue and unlikely to deposit on the membrane surface; the advantages of polyether products, low COD and low tendency to clog membrane modules, exactly fit such demanding scenarios.
Anaerobic and Desulfurization Scenarios Are No Easier
Beyond aerobic aeration, anaerobic tanks, power-plant wet flue gas desulfurization slurry and landfill leachate treatment also foam frequently. Foam in anaerobic tanks often traps biogas, posing a safety risk if mishandled; desulfurization slurry foam may affect desulfurization efficiency. These scenarios differ greatly in working conditions, so products used in the aerobic stage cannot simply be copied; assessment must be made separately according to temperature, pH and medium characteristics.
Dosing Calls for Balance
Defoamers can be dosed for emergencies or added continuously in small amounts by metering pump. An overdose not only raises cost but may cause secondary pollution or interfere with downstream membrane units; too little fails to hold the foam down. In practice, one usually starts with a small trial dose and then adjusts gradually according to foam changes, finding the balance point that neither harms effluent quality nor fails to control foam.
As zero liquid discharge of industrial wastewater and water reuse advance, high-demand membrane scenarios will only increase, and the role of defoamers in the whole water treatment chain is becoming more critical. Our technical team has developed dedicated products and technical support for water treatment defoamers around biological compatibility and membrane compatibility, helping wastewater plants account for biological activity, membrane compatibility and dosing cost together and find the balance point between foam control and stable effluent.