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What are the methods for defoaming wastewater?

There is a phenomenon of foam in sewage treatment. These foams include dense small foams and large and brittle foams. The existence of these foams will block oxygen from entering the water, seriously affecting the growth of aquatic organisms, the operation and operation of the treatment process, and the quality of the effluent water. So, under what circumstances will the sewage foam? What are the methods for defoaming wastewater?

Chemical foam
Active agent foam: When there are detergents, colloidal organics and other surfactants or other foaming substances in the sewage, under the conditions of water flow speed, drop, aeration, blow-off, etc., a large number of small and light white water will appear on the water surface. Brown unstable foam. This kind of wastewater is a polymer synthetic substance with poor biodegradability, which is a problem in sewage treatment.

Oily and suspended substance foam: This is a physical and chemical foam produced by the action of tiny bubbles in high SS and high oily wastewater.
Treatment method: In the pretreatment of sewage, such foam can be added with polymerized ferric sulfate, etc. for coagulation treatment, adsorb the surfactant and change the specific hydrophilicity of the surfactant, and then perform catalytic oxidation such as Fenton or strengthening oxidant. The process oxidizes large molecules into small molecules or carbon dioxide and water, and then dilutes them into biochemical treatment.

Biological foam
Biofoam is generally brown or taupe. There are many reasons for this type of foam. For example, the soil brown foam caused by too low dissolved gas in common biochemical tanks, the gray brown foam caused by too low MLSS, or caused by microbial factors such as microbial abnormalities. Filamentous bacteria grow abnormally and accumulate with air bubbles and floc particles. This foam is relatively difficult to handle.
Treatment method: This type of foam can be treated by adjusting DO and MLSS in water, and sludge reflux. Or you need to adjust the balance by adding vegetative bacteria and increase the DO concentration.