What causes there to be a lot of foam in the aeration tank?

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　　During the treatment of wastewater, it must go through many processing steps before it can be discharged once it meets the required standards. There is a process that involves intense contact between air and water, with the aim of dissolving oxygen from the air into the water, or removing unwanted gases and volatile substances from the water back into the air. 　　Sometimes, there is a lot of foam on the surface of the wastewater being treated in the aeration tank. Why does this foam appear? 　　The foam that is produced comes in two types. One is chemical foam, and the other is biological foam. 　　Chemical foam is formed due to detergents in wastewater as well as certain industrial surfactants, under the action of aeration, stirring, and stripping; it is produced in large quantities, and sometimes even \"foam mountains\" several meters high can form. However, compared to biological foam, the treatment method for chemical foam is quite simple – adding an appropriate amount of defoamer is sufficient. 　　Biofoams are formed by a type of filamentous fungus called Nocardia; these foams are brown in color, stable, persistent, and difficult to control, with higher concentrations of organic matter in the effluent and a strong odor. This type of foam can be treated by methods such as allowing water to flow over its surface, reducing the sludge age, adding defoamers, increasing sludge recirculation, introducing microorganisms, controlling dissolved oxygen levels, and adjusting the water inflow rate. 　　Both insufficient aeration and excessive aeration can lead to an increase in foam; therefore, it is essential to pay attention to the amount of aeration used.