In the field of environmental protection, magnesium sulfate is used directly as a sewage treatment agent or as a raw material for the production of sewage treatment agents. It is used in industrial sewage treatment, which condenses and settles waste liquid sewage, making it quickly reach sewage discharge standards.

The pollutants in printing and dyeing wastewater are mainly dirt, salts, oils and lipids on textile fibers such as cotton wool, as well as various slurries, dyes, surfactants, additives, acids, alkalis, etc. attached to the processing process. These are a class of industrial sewage that is extremely harmful to the environment. The discharge volume is large, the color is high, and the organic matter is difficult to degrade. It has brought great difficulties to wastewater treatment, and it is difficult to meet the standards using conventional treatment methods. Liu Gong of North Sichuan Chemical Industry carried out scientific and technological research for this purpose and pioneered the magnesium salt method to treat printing and dyeing wastewater.First of all, Liu Gong analyzed the characteristics of printing and dyeing wastewater in detail：

1. The amount of wastewater is large. The wastewater for printing and dyeing of pure cotton and blended fabrics is 2.5-3.5m3/100m fabric, polyester-cotton fabrics are 2-2.4m3/100m fabric, silk fabrics are 4-6m3/100m fabric, and fine wool textiles are 12-15m3/100 fabric. The amount of wastewater is quite large.

2. The water quality is complex, and the wastewater contains residual dyes, pastes, additives, fiber impurities and inorganic salts.The nitro and amine compounds and heavy metals such as copper, chromium, zinc, and arsenic in the dye structure have greater biological toxicity.

3. The organic matter content of printing and dyeing wastewater is high. The total adjusted COD is 800-1200mg/L. The composition of COD is residual dyes, additives, slurries, etc., and the amount of lye wastewater COD is as high as 100g/L.

4. The biochemical properties are poor, and the BOD/COD value of wastewater is very low, generally around 0.2. Therefore, measures need to be taken to increase the B/C value in order to facilitate biochemical treatment.

5. Wastewater contains a large number of additives and surfactants. In addition to being difficult to biodegradable and polluting water bodies, it produces foam during biological treatment and aeration, which hinders oxygenation.