What are the benefits of activated sludge?

When air is continuously introduced (aerated) into wastewater rich in organic matter and bacteria, suspended flocculent mud particles will appear after a certain period of time. This mud particle is actually an aggregate composed of aerobic bacteria (and facultative bacteria), organic matter adsorbed by aerobic bacteria and products metabolized by aerobic bacteria, which has a strong ability to decompose organic matter and is called "activated sludge". Activated sludge is easy to precipitate and separate, so that wastewater can be clarified. This biological treatment method with activated sludge as the main body is called "activated sludge method". The purification of wastewater by activated sludge process is completed in two steps: adsorption stage: polysaccharide mucus secreted by aerobic bacteria has strong adsorption effect, and after contacting with wastewater, a large amount of organic matter will be adsorbed by sludge in a short time (10 ~ 30 min); Oxidation stage: aerobic bacteria decompose and metabolize the adsorbed and absorbed organic matter, so that some organic matter can be transformed into stable inorganic matter, and the other part can synthesize new cytoplasm. At the same time, through oxidative decomposition, the sludge that has reached adsorption saturation reproduces its activity and restores its adsorption and catabolism capabilities. This stage is very slow. Biofilm method When wastewater flows over the surface of solid filter material for a long time, microorganisms grow and multiply on the surface of medium "filter material", forming slime-film biological sludge, which is called "biofilm". A water treatment method using a large number of microorganisms on biofilm to adsorb and degrade organic pollutants in water is called "biofilm method". The difference between activated sludge process and activated sludge process is that microorganisms are fixed on the surface of medium filter material, so it is also called "fixed growth process", and activated sludge process is also called "suspended growth process". Biofilm has a large surface area. A thin and slow-flowing water layer is attached to the membrane, which is called attached water layer. Inside and outside the biofilm, many substances are transferred between the biofilm and the water layer. Organic matter in wastewater is transferred from flowing water layer to attached water layer, and then absorbed by biofilm. Oxygen in the air is dissolved in the flowing water layer and transferred to the biofilm through the attached water layer for microorganisms to breathe. Under this condition, aerobic bacteria decompose and assimilate organic matter, and some metabolites such as CO2 are dissolved in the attached water layer, and some of them are released into the air (that is, they are discharged into the air from the biofilm through the water layer in the opposite direction). In this way, the organic matter in the wastewater is continuously reduced, thus purifying the wastewater.