Analysis of Future Development Trends in Leather Wastewater Treatment

The United Nations has designated June 5th of each year as World Environment Day, issuing a warning that "there is only one Earth" to raise awareness of global environmental issues and remind people to protect the environment and cherish the Earth. The protection of the environment and ecological balance has become a global social issue of close concern to governments and people around the world today, closely related to people's health, living standards, economic and social development, and the happiness of future generations.

Since the 1950s, with economic development, people have greatly expanded industrial production, and large factories have sprung up. Many regions in the world have experienced increasingly severe pollution and destruction of their production and living environments. According to statistics, in our country, for every ton of raw leather processed, approximately 50 to 150 tons of wastewater is generated. The leather industry discharges more than 8 million tons of wastewater into the environment each year, accounting for about 0.3% of the total industrial wastewater discharge in our country; the pollution discharge per ten thousand yuan of output value in the leather industry ranks third in the light industry sector, second only to the paper-making and brewing industries.

Nowadays, environmental pollution has become a serious social public hazard, with smoke filling the sky; inland waters being dirty and polluted; and vast oceans turning into garbage dumps, greatly threatening the health and lives of the general public. In this era where environmental issues have become extremely severe, the leather industry, known for its filth, disorder, odor, and fatigue, is facing unprecedented pressure.

The hazards of wastewater from the leather industry

1. During the processing of leather, animal hides need to be dyed, resulting in a large amount of dye in the leather wastewater, which has a high color intensity. If discharged directly without treatment, it can affect the quality of surface water.

2. The depilation process requires a large amount of depilatory liquid, which contains a lot of sulfides. Sulfur-containing wastewater can easily produce H2S gas when it encounters acid, and sulfur-containing sludge can also release H2S gas under anaerobic conditions, posing great harm to water bodies and humans.

3. A large amount of lime, caustic soda, and Na2S is used in the peeling process, which can lead to alkaline wastewater. High alkalinity without treatment can affect the pH value of surface water and the growth of crops.

4. Chlorides and sulfates are used in the preservation, acid soaking, and tanning processes of raw hides. When the sulfate content exceeds 100 mg/L, it can make the water taste bitter, leading to diarrhea after consumption.

5. Due to the high organic content, such as proteins, in leather wastewater, along with certain reducing substances, both COD and BOD are very high. If discharged directly without treatment, it can cause water pollution, promote bacterial growth, and consume dissolved oxygen in the water body. When the dissolved oxygen in the water body falls below 4 mg/L, the respiration of aquatic organisms such as fish will become difficult, even leading to death.

According to incomplete statistics, there are currently more than 500 industrial-scale leather factories in China, over 15,000 small leather factories, and countless small workshops that cannot be counted. The annual processing capacity is over 10 million cowhides, 75 million pigskins, and 10 million sheepskins. Currently, nearly 150 leather factories in the country have established environmental protection facilities, but very few meet national discharge standards and operate normally, mostly due to unreasonable treatment processes, high operating costs, and complicated management, which prevent normal operation. Most leather factories discharge wastewater directly into rivers or lakes without treatment or only after simple sedimentation, and some even discharge into seepage pits.

In light of the actual situation of enterprises in various regions, we need to carefully consider, study, and conduct sufficient demonstration. Based on the principles of low investment, small land occupation, and low operating costs, we propose a wastewater treatment plan for experts to evaluate.