I want to know about the characteristics of tannery wastewater and the treatment method of tannery w

The main characteristics of leather wastewater are more suspended solids, more complex, darker color, high biodegradability, toxic substances and high oxygen consumption content, which is a kind of industrial wastewater with medium and upper treatment difficulty level, which threatens the ecological environment on which human beings depend all the time. From the analysis of Figures 1 and 2, it can be seen that the main pollutant of leather wastewater is COD, which is measured by chemical methods to measure the amount of redox substances in the water sample, which essentially refers to the important organic matter pollution parameters, that is, it reflects the degree of pollution of reducing substances in the water. Among them, the COD in leather wastewater is mainly due to the addition of a large number of reagents in the process of tanning, including tanning agents, acids, alkalis, sodium sulfide and ammonium salts and other reducing substances, resulting in a high aerobic content of leather pulmonary edema.

The ammonia nitrogen is mainly used in the ammonium salt added in the deliming and softening stage of the tanning process, and the grease and fat are mainly added to the leather.

Meat scrap or oil residue.

It is characterized by containing a large amount of suspended solids, COD, caustic alkali, heavy metal CR, etc., which is difficult to treat, and the general treatment methods are, grid, precipitation, neutralization, flocculation and precipitation, biochemical treatment and other processes.

Grille: except for larger solids, debris.

Primary sedimentation tank: remove particles with large specific gravity such as sand and gravel.

Coagulation and precipitation air flotation tank: remove various pollutants, especially macromolecules, refractory and toxic substances, colloidal substances and insoluble substances, such as SS, color, heavy metals, S2-, surfactants, etc.

Aerobic aeration tanks: organic matter.

Secondary sedimentation tank: slurry separation.

The production of tanning industry generally includes several stages such as degreasing, liming and hair removal, softening, tanning, dyeing and processing, drying, finishing, etc., and a variety of chemicals need to be added during the processing process [2], so that the wastewater contains oil, collagen, animal and plant fibers, organic and inorganic solids, sulfides, chromium, salts, surfactants, dyes and other pollutants and toxic substances. The water quality characteristics of comprehensive wastewater in tanning industry are as follows: (CODCR) is 3000-4000mg L, (BOD5) is 1000-2000mg L, (SS) is 2000-4000mg L, and the pH value is 8-11.

Wastewater is mainly used in pre-tanning preparation, tanning and other wet processing sections. The most polluted is degreasing wastewater, liming and hair removal wastewater, chrome tanning wastewater, these three kinds of wastewater account for about 50% of the total wastewater, but contain most of the pollutants, the mass fraction of various pollutants in the total is: CODCR 80%, BOD575%, SS70%, sulfide 93%, sodium chloride 50%, chromium compound 95%.

The characteristics of tannery wastewater are manifested in the following aspects:

The characteristics of tanning wastewater are complex composition, dark color, many suspended solids, high oxygen consumption and large water volume.

Suspended solids: a large amount of lime, broken skin, wool, oil residue, meat residue, etc.

CODCR: Most of the materials used in leather processing are additives, lime, sodium sulfide, ammonium salts, vegetable tanning agents, acids, alkalis, proteases, chrome tanning agents, neutralizing agents, etc., so the COD content is large.

BODs: soluble proteins, oils, blood and other organic matter.

Sulfur: Mainly sulfide produced by the use of sodium sulfide in the liming process.

Chromium: It is the chromatic acid wastewater liquid discharged during chrome tanning.

Tannery wastewater is the wastewater discharged during the tannery production process. Usually the animal skin is salted or soaked in water to make it swell, lime, defleshed, dealkalized, and then used denim or chromium to tann and fattened to soften the orange after a few years, and finally dyed and processed into potato leather.

The tannery wastewater discharge is large, the pH value is high, the color is high, the pollutants are varied, and the composition is complex. The main pollutants are heavy metals chromium, soluble proteins, dander, suspended solids, tannins, lignin, inorganic salts, oils, surfactants, additives, dyes and resins. According to the determination, although chrome tanning stock solution, hair removal stock solution and dyeing stock solution only account for 20% 30% of the total wastewater volume, the pollution load accounts for 70% 80%, so it is extremely important for the treatment of tannery wastewater stock solution and save money, which is a key step in the treatment of tannery wastewater.

Tannery wastewater is the wastewater discharged during the tannery production process. Usually animal skins are salted or soaked in water to make them puff, lime, defleshed, dealkalized, then tanned with tannins or chromium, fatted and softened, and finally dyed and processed into leather. The whole tanning process produces 600-700 liters of wastewater per kilogram of salted skins, and the water quality varies depending on the size of the factory, the type of hides and the tanning method.

Usually SS1500-2000 mg L, BOD700-3000 mg L. In the process of fur dyeing, 2-3 L of dyeing wastewater is produced per kilogram of leather, water quality: BOD 500-2000 mg L, total solids 4000-8000 mg L.

In addition, a large amount of leather rinsing water is continuously discharged, but the concentration is low. Water quality of China's tannery industry: pH 7-9, COD2000-3000 mg L, BOD52000 mg L, chloride 2000-3000 mg L, sulfate 1000 mg L, trivalent chromium 70-80 mg L, phenol 5-10 mg L.

Treatment method of tanning wastewater: use sieve filtration or natural precipitation to remove hair, skin meat, skin flakes and sediments, etc., and then mix into domestic sewage and use coagulation and sedimentation, biological filter or activated sludge and other biochemical methods for treatment.

According to the main preparation section and tanning section, the leather washing sewage treatment equipment includes raw leather washing water and acid water containing high concentration of chloride, strong alkaline depilatory liming sewage containing lime and sodium sulfide, blue chromium tanning sewage containing trivalent chromium, brown vegetable tanning sewage containing tannins and gallic acid, deesterification sewage containing grease and its saponification, grease dyeing sewage and flushing sewage of each section, etc., among which the pollution of degreasing sewage, dehairing and liming sewage and chrome tanning sewage is the most serious.

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The leather washing and tanning sewage is first removed from the solid matter such as skin residue, meat and cow hair in the leather washing and tanning sewage through the coarse and fine grid and grit tank, and then the pump is lifted to the coagulation and sedimentation tank to precipitate the intolerant sediment and other fine solids in the water, and the water quality, water quantity and pH are adjusted at the same time, and then the air flotation tank is carried out.

The treated supernatant enters the hydrolysis acidification tank to improve the biodegradability of the wastewater. The hydrolyzed and acidified sewage then enters the biological selector and cast tank, and is immediately fully mixed with the aerobic sludge in the pool, aerobic bacteria, protozoa, metazoans, etc., for adsorption and metabolic activities.

There are two parts of ammonia nitrogen** in leather washing and tanning sewage: one part comes from the inorganic nitrogen added in the neutralization process, such as ammonia bicarbonate, ammonia sulfate and ammonia water, and one part comes from the organic nitrogen released after the decomposition of organic matter in the leather washing and tanning sewage, which is the reason why the water outlet of the secondary treatment of leather washing and tanning sewage is higher than the ammonia nitrogen at the water inlet.

The ammonia nitrogen of the sewage treated by CAST still cannot meet the standard, so a o denitrification tank is set up after it, and the denitrification and nitrification are fully carried out through the anoxic section and the aerobic section alternately, and the effluent can be discharged up to the standard after the sedimentation of the secondary sedimentation tank.

All the sludge generated by this process is discharged to the sludge thickening tank for thickening, and then can be used as agricultural fertilizer or landfill through the decanter centrifugal separator.