The purpose of wastewater treatment is to separate the pollutants in the wastewater in a certain way, or to decompose and convert them into harmless stable substances, so that the sewage can be purified. It is generally necessary to prevent the infection of poisons and germs; to avoid visible smells and odors to meet the requirements of different uses.
The choice of wastewater treatment method depends on the nature, composition, state and water quality requirements of the pollutants in the wastewater. The treatment methods of general wastewater can be roughly divided into three categories: physical method, chemical method and biological method.
Physical method: The physical action is used to treat, separate and recover pollutants in wastewater. For example, the particulate matter having a relative density of more than 1 is removed by precipitation to recover the particulate matter; the flotation method (or the air floatation method) can remove the emulsion oil droplets or the suspension having a relative density of nearly 1; the filtration method can remove the suspension in the water. Particles; evaporation method for concentrating non-volatile soluble substances in wastewater.
Chemical method: Recovering soluble waste or colloidal substances by chemical reaction or physicochemical action, for example, neutralization method for neutralizing acidic or alkaline wastewater; extraction method utilizing “distribution” of soluble waste in two phases with different solubility, recovering phenol Classes, heavy metals, etc.; redox method is used to remove reducing or oxidizing pollutants in wastewater, killing pathogenic bacteria in natural waters, etc.
Biological method: The biochemical action of microorganisms is used to treat organic matter in wastewater. For example, the biological filtration method and the activated sludge method are used to treat domestic sewage or organic production wastewater, and the organic matter is converted into an inorganic salt to be purified.