Treatment of Leather Wastewater with Polyaluminum Chloride

The following is a detailed introduction to the causes and characteristics of leather wastewater, as well as the principles and advantages of using polyaluminium chloride to treat leather wastewater:

Generation of leather wastewater

Leather wastewater mainly comes from various stages of the leather making process. The leather making process usually includes three major stages: preparation, tanning, and finishing. In the pre-tanning preparation section, the sewage mainly comes from washing, soaking, dehairing, liming, deashing, softening, degreasing and other processes. The main pollutants include organic waste, inorganic waste and organic compounds. The wastewater in the tanning section mainly comes from the water washing, acid leaching, and tanning processes, with the main pollutants being inorganic salts and heavy metal chromium. The wastewater from the finishing section mainly comes from water washing, squeezing, dyeing, fatliquoring, and dust removal sewage, with pollutants including dyes, oils, and organic compounds.

Characteristics of leather wastewater

Leather wastewater has the characteristics of large water volume, large fluctuations in water quality and quantity, high pollution load, high alkalinity, high colority, high suspended solids content, good biodegradability, and certain toxicity. Leather wastewater is a high-concentration organic wastewater with high levels of COD (chemical oxygen demand) and BOD (biological oxygen demand). The chromaticity pollution in wastewater mainly comes from dyes and tanning agents, with a chromaticity of about 600-3000 times. The wastewater is slightly alkaline, mainly due to the use of lime, caustic soda, sodium sulfate, etc. in the production process. The suspended solids (SS) content in the wastewater is as high as 3000mg/L.

Principle of Polyaluminium Chloride in Treating Leather Wastewater

Polyaluminium chloride is a commonly used flocculant, whose molecules contain a large number of hydrogen bonds and electrical attractions, which can aggregate suspended particles and form larger precipitates during water treatment. This kind of sediment has strong sedimentation, which can quickly settle down from the water, thus effectively removing suspended particles in the sewage. At the same time, some mixtures of polyaluminium chloride can also remove the remaining suspended particles by forming ultrafine particles, making the sewage treatment effect more significant.

The principle of treating leather wastewater with polyaluminium chloride mainly includes charge neutralization and compression of double electric layer. Through the effects of charge neutralization and compressed electric double layer, polyaluminium chloride destabilizes suspended particles in wastewater, causing colloidal particles to coagulate and grow larger, forming large alum flowers that facilitate subsequent gravity sedimentation treatment.

Advantages of Polyaluminium Chloride in Treating Leather Wastewater

High purification effect: Polyaluminium chloride, especially products with a content of 28% or 30%, can form large alum flowers with less insoluble matter and significant purification effect. It can effectively remove suspended solids and colloidal substances in leather wastewater, with a removal rate of up to 80% to 95%.

Heavy metal removal ability: Polyaluminium chloride can not only remove suspended solids and colloidal substances, but also take away some heavy metals such as chromium from the wastewater, with excellent removal effect.

Efficient and rapid: Using polyaluminium chloride to treat leather wastewater has low investment and fast results, making it a cost-effective choice.

Reduce the risk of eutrophication in water bodies: Polyaluminium chloride can also reduce the content of ammonia nitrogen and phosphate in sewage, reducing the risk of eutrophication in water bodies.

In summary, polyaluminium chloride is one of the indispensable and important agents in the treatment of leather wastewater, and has been widely used in the field of leather wastewater treatment. At the same time, it is also necessary to pay attention to water quality monitoring, dosage control, and experimental verification during use to ensure optimal treatment results.