Industrial wastewater refers to the waste water, sewage and waste liquid produced in the industrial production process, which contains industrial production 

materials, intermediates and products lost with water and pollutants produced in the production process.

There are usually three classification methods:

The first is classified according to the chemical properties of the main pollutants contained in the industrial wastewater, the inorganic pollutants are mainly 

inorganic wastewater, and the organic pollutants are mainly organic wastewater. For example, electroplating wastewater and mineral processing wastewater 

are inorganic wastewater; Wastewater from food or petroleum processing is organic wastewater.

The second is classified according to the products and processing objects of industrial enterprises, such as metallurgical wastewater, papermaking wastewater, 

coking gas wastewater, metal pickling wastewater, chemical fertilizer wastewater, textile printing and dyeing wastewater, dye wastewater, tannery wastewater, 

pesticide wastewater, power station wastewater, etc.

The third is classified according to the main components of the pollutants contained in the wastewater, such as acidic wastewater, alkaline wastewater,

 cyanide-containing wastewater, chromium-containing wastewater, cadmium-containing wastewater, mercury-containing wastewater, phenol-containing 

wastewater, aldehyde-containing wastewater, oil-containing wastewater, sulfur-containing wastewater, organophosphorus containing wastewater and 

radioactive wastewater.

The first two classifications do not involve the main components of the pollutants contained in the wastewater, nor can they indicate the harmfulness of the 

wastewater. The third classification method clearly indicates the composition of the main pollutants in the wastewater, which can indicate the harm of the 

wastewater.

In addition, starting from the difficulty of wastewater treatment and the harm of wastewater, the main pollutants in wastewater are summarized into three 

categories: the first type is waste heat, mainly from cooling water, cooling water can be reused; The second category is conventional pollutants, that is, 

substances without obvious toxicity and easy to biodegrade, including biodegradable organic matter, compounds that can be used as biological nutrients, 

and suspended solids. The third category is toxic pollutants, that is, substances that contain toxicity and are not easy to biodegrade, including heavy metals, 

toxic compounds and organic compounds that are not easy to biodegrade.

In fact, an industry can discharge several different nature of wastewater, and a wastewater will have different pollutants and different pollution effects. For 

example, dye factories discharge both acidic wastewater and alkaline wastewater. Textile printing and dyeing wastewater, due to the difference of fabrics and 

dyes, the pollutants and pollution effects will be very different. Even the wastewater from a production plant may contain several pollutants at the same time. 

Such as distillation, cracking, coking, polymerization and other units of the tower top oil vapor condensation water, containing phenol, oil, sulfide. In different 

industrial enterprises, although the products, raw materials and processing processes are very different, they may also discharge wastewater with similar 

properties. For example, oil refineries, chemical plants and coking gas plants may have oily and phenolic wastewater discharge.

Treatment method

Industrial wastewater treatment methods can be divided into four categories according to their principle of action, namely, physical treatment, chemical 

treatment, physical chemical treatment and biological treatment.

Physical treatment

Through physical action, to separate and recover the insoluble suspended pollutants in the wastewater (including oil film and oil beads), commonly used 

gravity separation method, centrifugal separation method, filtration method and so on.

Chemical treatment

Adding a chemical substance to the sewage, the use of chemical reactions to separate and recover the pollutants in the sewage, commonly used chemical 

precipitation, coagulation, neutralization, REDOX (including electrolysis) method. Chemical method can be used - polyaluminum chloride flocculant, as an 

inorganic polymer flocculant, through the compression of double electric layer, adsorption and neutralization, adsorption bridge, precipitation mesh and 

other mechanisms, so that fine suspended particles and colloids in water are destabilized, aggregated, flocculated, coagulated, precipitated, to achieve 

purification treatment effect, due to its wide pH value and good adaptability. The application of industrial wastewater treatment is also very extensive.

Physicochemical treatment

Physical and chemical processes are used to remove pollutants from wastewater, including adsorption, ion exchange, membrane separation and extraction.

Biological treatment

Through the metabolic action of microorganisms, the organic pollutants in the wastewater that are in solution, colloids and fine suspension state are 

transformed into stable and harmless substances, which can be divided into aerobic biological treatment and anaerobic biological treatment.