Sewage treatment is purification process that in order to achieve the sewage drain or meet water quality requirements which can be used again. Sewage treatment is widely used in construction, agriculture, transportation, energy, petrochemical, environmental protection, urban landscape, medical, food and other fields, but also more and more into the daily lives of ordinary people.
Classification according to sources of wastewater, sewage treatment is generally divided into the production of sewage treatment and domestic sewage treatment. Production sewage including industrial sewage, agricultural runoff and medical sewage, and domestic sewage is generated everyday life, refers to a complex mixture of various forms of inorganic and organic, including: ①floating and suspended solids; ② gum and diffusion-like gelatinous substance; ③ pure solution.
According to the nature of sewage, water pollution has two types: one is natural pollution; the other is man-made pollution. Currently, man-made pollution is greater harm to the water. Depending on the contamination of water pollution can be divided into chemical pollution, physical pollution and biological pollution. The main pollutants are: ⑴ The discharge of untreated industrial wastewater; ⑵ discharged untreated sewage; ⑶ heavy use of agricultural waste water of chemical fertilizers, pesticides, herbicides; ⑷ stacked in the river industrial waste and garbage ; ⑸ soil erosion; ⑹ mine wastewater.