Significance of sewage treatment: After sewage is treated, it can be recycled to reduce the consumption of water resources for China's production. Water treatment technology uses relevant technical means to purify sewage so that it can continue to be used, so sewage treatment is extremely important.

according to the classification of sewage sources, sewage treatment is generally divided into production sewage treatment and domestic sewage treatment. Production sewage includes industrial sewage, agricultural sewage and medical sewage, while domestic sewage is the sewage produced in daily life, which refers to a complex mixture of various forms of inorganic substances and organic substances, including:

① floating and suspended solid particles;

② colloidal and gelatinous diffusions;

③ pure solution.

According to the quality of water pollution, there are two types of water pollution:

One is natural pollution; The other

is man-made pollution, which is harmful to water bodies at present.

Sewage treatment is widely used in construction, agriculture, transportation, energy, petrochemical, environmental protection, urban landscape, medical treatment, catering and other fields, and it has also entered the daily life of ordinary people more and more.

Extended information

Sewage treatment can be divided into physical method, biological method and chemical method according to its function.

① physical method: the insoluble substances in sewage are mainly separated by physical action, and the chemical properties are not changed during the treatment. Commonly used are gravity separation, centrifugal separation, reverse osmosis, air flotation and so on. Physical treatment of structures is simple and economical, and it is used in villages and towns with large water capacity, strong self-purification ability and low requirements for sewage treatment.

② biological method: using the metabolic function of microorganisms, the dissolved or colloidal organic matter in sewage is decomposed and oxidized into stable inorganic substances, so that the sewage can be purified. Activated sludge process and biofilm process are commonly used. The treatment degree of biological method is higher than that of physical method.

③ chemical method: it is a method to treat or recover dissolved or colloidal substances in sewage by chemical reaction, which is mostly used in industrial wastewater. Coagulation, neutralization, redox and ion exchange are commonly used. Chemical treatment has good treatment effect and high cost, and it is mostly used as effluent after biochemical treatment for further treatment to improve the effluent quality.

after primary treatment, the BOD removal rate of wastewater is only 21%, so it is still not suitable for discharge, and secondary treatment is needed. The main task of secondary treatment is to greatly remove colloid and dissolved organic matter from sewage, and the removal rate of BOD is 81% ~ 91%.

Generally, sewage after secondary treatment can meet the discharge standard, and activated sludge method and biofilm treatment method are commonly used. The purpose of tertiary treatment is to further remove some special pollutants, such as fluoride and phosphorus removal, which belongs to advanced treatment and is commonly used by chemical method.

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