Treatment Technology Of Tannery Wastewater

Present situation of Industry and characteristics of Tannery Wastewater.

In daily life, bags, leather shoes, leather clothes, leather sofas and other leather products are everywhere. In recent years, with the rapid development of leather industry, the discharge of tannery wastewater has gradually become one of the important industrial pollution sources.

Leather making generally includes three stages: preparation, tanning and finishing. In the pre-tanning preparation section, the sewage mainly comes from washing, soaking, depilation, liming, deashing, softening, degreasing; the main pollutants include organic waste, inorganic waste and organic compounds. The wastewater in the tanning section mainly comes from washing, pickling and tanning, and the main pollutants are inorganic salts and heavy metal chromium. The waste water in the finishing section mainly comes from washing, squeezing, dyeing, fatliquoring and dedusting sewage, and the pollutants are dyes, oils and organic compounds. Therefore, tannery wastewater has the characteristics of large amount of water, large fluctuation of water quality and quantity, high pollution load, high alkalinity, high chromaticity, high content of suspended solids, good biodegradability and so on.

Sulfur-containing wastewater: refers to the ash leaching waste liquid produced by ash-alkali depilation in the tannery process and the corresponding wastewater from the washing process.

Degreasing wastewater: refers to the waste liquid formed by the treatment of rawhide oil with surfactant and the corresponding wastewater from washing process in the process of leather making and fur processing.

Chromium-containing wastewater: refers to the waste chromium liquid produced in the process of chrome tanning and chrome retanning and the corresponding wastewater from the washing process.

Comprehensive wastewater: refers to all kinds of wastewater produced by tannery and fur processing enterprises or centralized processing areas and directly or indirectly discharged into comprehensive wastewater treatment projects (such as production process wastewater, factory domestic sewage).

Common treatment methods of Tannery Wastewater.

The basic method of wastewater treatment is to use a variety of technical means to separate, remove, recycle and reuse the pollutants contained in the wastewater, or convert them into harmless substances to purify the water.

There are many methods to treat sewage, which can be divided into four categories, namely, biological treatment, physical treatment, chemical treatment and natural treatment.

1. Biological treatment.

Through the metabolism of microorganisms, the solution, colloid and micro-suspended organic pollutants in the wastewater can be transformed into stable and harmless substances. According to the difference of acting microorganisms, biological treatment can be divided into two types: aerobic biological treatment and anaerobic biological treatment.

Aerobic biological treatment is widely used in wastewater biological treatment. According to its different process methods, aerobic biological treatment can be divided into activated sludge process and biofilm process. Activated sludge process itself is a kind of treatment unit, it has a variety of operation modes. The treatment equipment of biofilm process includes biological filter, biological turntable, biological contact oxidation tank, biological fluidized bed and so on. Biological oxidation pond method is also called natural biological treatment method. Anaerobic biological treatment, also known as biological reduction treatment, is mainly used to treat high concentration organic wastewater and sludge.

two。. Physical treatment method.

The methods of physical separation and recovery of insoluble suspended pollutants (including oil film and oil droplets) in wastewater can be divided into gravity separation method, centrifugal separation method and sieving interception method. The treatment units of gravity separation are sedimentation, floatation (air floatation), etc., and the corresponding treatment equipment are sand settling tank, sedimentation tank, oil separation tank, air flotation tank and its ancillary devices. Centrifugal separation itself is a kind of treatment unit. the treatment devices used are centrifuge and hydrocyclone, etc. The sieve interception method has two processing units: grid interception and filtration. The former uses grille and screen, while the latter uses sand filter and microporous filter. The treatment method based on the heat exchange principle also belongs to the physical treatment method, and its treatment units include evaporation, crystallization and so on.

3. Chemical treatment method.

The treatment of wastewater by chemical reaction and mass transfer to separate and remove dissolved or colloidal pollutants or to convert them into harmless substances. In chemical treatment, the treatment units based on chemical reactions produced by adding chemicals are coagulation, neutralization, redox, etc., while the treatment units based on mass transfer are extraction, stripping, stripping, adsorption, ion exchange, electrodialysis and reverse osmosis. The latter two treatment units are also called membrane separation technology. Among them, the treatment unit using mass transfer has both chemical and related physical functions, so it can also be separated from the chemical treatment method and become another kind of treatment method, which is called physical and chemical method.