There are many kinds of industrial sewage, and there is not a basic unified model like urban sewage.

Take printing and dyeing wastewater as an example:

Dye production wastewater contains acids, bases, salts, halogens, hydrocarbons, amines, nitro compounds, dyes and their intermediates, and some also contain pyridine, cyanide, phenol, benzidine and heavy metals such as mercury, cadmium and chromium. These wastewater are complex and toxic, so it is difficult to treat. Therefore, the treatment of dye production wastewater should be based on the characteristics of wastewater and its discharge requirements, and appropriate treatment methods should be selected. For example, coagulation and filtration can be used to remove solid impurities and inorganic substances; Chemical oxidation, biological method and reverse osmosis are mainly used to remove organic matter and toxic substances. Generally, decoloration can be carried out by coagulation and adsorption, and heavy metals can be removed by ion exchange.

Take food wastewater as an example:

The food industry has a wide range of raw materials and products, and the quantity and quality of discharged wastewater vary greatly. The main pollutants in wastewater are (1) solid substances floating in wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc. (2) The substances suspended in the waste water include grease, protein, starch, colloidal substances, etc. (3) Acid, alkali, salt, sugar, etc. dissolved in wastewater: (4) Mud, sand and other organic matters entrained in raw materials; (5) Pathogenic bacteria and viruses. The wastewater from food industry is characterized by high content of organic matter and suspended solids, easy to rot and generally non-toxic. Its harm is mainly to make the water body eutrophic, so as to cause the death of aquatic animals and fish, promote the odor of organic matter deposited at the bottom of the water, worsen the water quality and pollute the environment. In addition to proper pretreatment according to the characteristics of water quality, biological treatment is generally suitable for food industry wastewater treatment. If the effluent quality is very high or the organic matter content in wastewater is high, two-stage aeration tank or two-stage biofilter, or multi-stage biological turntable can be used, or two biological treatment devices can be used in combination, or an anaerobic-aerobic biological treatment system can be used in series.