Activated sludge is a floc with strong adsorption and decomposition capabilities. The core of activated sludge lies in the word "living". As we all know, natural rivers have self-purification functions. This is because a group of microorganisms live in the water. The microorganisms eat the pollutants, so the water body will return to cleanliness. Therefore, "living" is reflected in the group of microorganisms.
Microorganisms are part of activated sludge. In addition, activated sludge also includes residues produced by microbial metabolism, organic matter and inorganic matter adsorbed on microorganisms. The mixed liquid you usually see in the aeration tank is the form of activated sludge in water.