Introduction to Tannery Wastewater

       Tannery wastewater refers to the wastewater generated during the preparation and tanning stage of tanning production, that is, during the wet operation process [1]. The tannery has a large amount of wastewater discharge, high pH value, high color, various pollutants, and complex components. The main pollutants are heavy metal chromium, soluble protein, dander, suspended matter, tannin, lignin, inorganic salts, oils, surfactants, dyes and resins.

Wastewater hazards

  1、The leather wastewater has a large color. If it is directly discharged without treatment, it will give the ground water an abnormal color and affect the water quality.

  2、Leather wastewater is generally alkaline, and if it is not treated, it will affect the pH value of the surface water and the growth of crops.

  3、The suspended solids are high in content and are directly discharged without treatment. These suspended solids may block the pumps, drainage pipes and drains. In addition, a large amount of organic matter and grease will also increase the oxygen consumption of surface water, causing water pollution and endangering the survival of aquatic organisms.

  4、Sulfur-containing waste liquid is prone to produce H2S gas when it encounters acid, and sulfur-containing sludge will also release H2S gas under anaerobic conditions, which is extremely harmful to water bodies and people.

  5、High chloride content will cause harm to human body. When the sulfate content exceeds 100 mg/L, the water taste will become bitter, and diarrhea will easily occur after drinking.

  6、 Chromium ions in leather wastewater mainly exist in the form of Cr3+. Although it is less harmful to the human body than Cr6+, it can accumulate in the environment, animals and plants, and will have a long-term impact on human health.

  7、Due to the high content of protein and other organic matter in leather wastewater and a certain amount of reducing substances, both COD and BOD are high. Dissolved oxygen in the water body will be consumed after sewage is discharged into the water body.

Source of wastewater

       Tannery wastewater mainly comes from the wet preparation section and tanning section of tanning production. It mainly consists of five parts: degreasing wastewater, liming and dehairing wastewater, chrome tanning wastewater, fatliquoring and dyeing wastewater, and washing wastewater from various processes. Although ash dehairing wastewater and chrome tanning wastewater only account for about 50% of the total wastewater volume, they contain most of the pollutants in the wastewater, including 80% COD and 75% BOD of the total wastewater pollutants. , 70% SS, 93% sulfide, 50% sodium chloride, 95% chromium compound.

Wastewater characteristics

    1、Tannery wastewater is high-concentration organic wastewater, and the concentration of COD and BOD in the wastewater is very high.

    2、The toxicity of tanning wastewater comes from high concentration of sulfide and trivalent chromium. Sodium sulfide is used for hair removal and chromium salt is used for tanning. The content of chromium and sulfide in waste chromium solution can reach thousands of milligrams per liter. The smell of tanning wastewater is The taste is mainly caused by protein breakdown and added sodium sulfide.

    3、 The SS in the tannery wastewater is as high as 3000 mg/L or more.

    4、The chromaticity of tannery wastewater is mainly caused by dyes and tanning agents, and the chromaticity of wastewater is 600-3000 times.

    5、Tannery wastewater is generally alkaline, mainly from lime, caustic soda, and sodium sulfate used in dehairing and other processes, and the pH value is often 9-10.

    6、The chloride and sulfate concentration of tannery wastewater is 2000～3000 mg/L, mainly from raw hide preservation, pickling and tanning processes.