Huang Ming1, Wei Caichun1, Zhao Meng2, Lu Yanqin1, Zhang Xuehong1, Wang Dunqiu1 Abstract: The electroplating wastewater is treated by chemical classification method, and the wastewater containing chromium, copper and nickel is classified and collected, and divided and treated. The design processing capacity is 800m3/d. After one year of actual operation, the effect is obviously better than the traditional chemical treatment method. The indicators for treating the effluent meet the national first-class standard of Integrated Wastewater Discharge Standard (GB8978-96), namely SS< 70; total Cr: <1.5 mg / L; total Ni: <1.0 mg / L; total Cu: 0.5 mg / L; total Zn: 2.0 mg / L; pH: 6 ~ 9. The project has an investment of about 700,000 yuan and a treatment cost of 4.0 yuan/m3. The management company is responsible for the operation and the environmental protection department conducts online monitoring with good results. Guangxi Zhangpu electroplating wastewater production area is located in the suburb of Zhangpu County. There are five enterprises engaged in small-scale electroplating production. The scale of electroplating products is 3600t/a, which produces a large amount of heavy metal elements such as chromium, nickel, copper and zinc. Toxic wastewater, if discharged directly without treatment, can cause serious pollution to the environment. Therefore, according to the relevant national environmental protection regulations, the electroplating wastewater will be treated to achieve the discharge standard. At present, there are many methods for electroplating wastewater treatment, such as chemical precipitation method [1, 2, 3], microbial method [4], electrolysis method and air flotation method [5]. Through the experimental research on the treatment of the wastewater and the process comparison, we adopt the chemical classification method suitable for the characteristics of the water quality and quantity change of the wastewater, that is, the wastewater generated by each manufacturer in the production area is uniformly collected, and the chromium-containing wastewater and copper-containing nickel are collected. The wastewater is treated separately. The wastewater treatment station was jointly funded by electroplating factories in the electroplating city. It was contracted and managed by a management company. The project was put into operation in 2001. From more than one year of actual operation, the water quality is good and stable, and some major pollutants are indicators. It is superior to the national first-class standard of Integrated Wastewater Discharge Standard (GB8978-96). The wastewater mainly comes from the plating parts cleaning in the electroplating production process, the plating liquid filtration waste plating liquid, and the "run, run, drip, and leak" caused by poor operation or management, as well as the ground flushing, ventilation and condensation wastewater. The amount of wastewater discharged from the production area is 800m3/d, including 165 m3/d of nickel-plated wastewater, 94m3/d of chrome-plated wastewater, 165 m3/d of copper-plated wastewater and 376m3/d of pickling wastewater for other cleaning plating parts. The water quality monitoring of the former copper-containing nickel wastewater and chromium-containing wastewater is shown in Table 1. Table 1 Wastewater quality monitoring results Numbering Suspended matter (mg/L) CODcr (mg/L) Hexavalent chromium (mg/L) Total chromium (mg/L) Total nickel (mg/L) Total copper (mg/L) Total lead (mg/L) Total cadm (mg/L) 1 Chromium Waste water 2.26 18 High chromium concentration cannot be determined 678 920 not detected not detected 0.05 0.05 2 2.20 12 578 790 0.05 0.05 3 2.28 16 650 799 0.05 0.05 average value 2.25 15 635 836 0.05 0.05 4 Copper nickel Waste water 1.60 twenty two 99 not detected not detected 200 173 0.30 0.02 5 1.50 60 105 167 122 2.21 0.02 6 1.42 37 203 137 558 0.70 0.06 average value 1.51 40 136 168 284 1.07 0.034 See Figure 1 for the entire wastewater treatment process. The wastewater treatment project has the following characteristics: The main components of the wastewater in this production area are chromium-containing wastewater and copper and nickel-containing wastewater. Since the pH range of Cr(OH)3 complete precipitation is about 8 and the pH range of complete precipitation of Ni(OH)2 is about 9.5 [2], in order to minimize the precipitation process of chromium and nickel, the pH of both precipitates completely precipitates. The range is different and there is mutual interference. In the process, two regulating tanks are arranged for storing chromium-containing wastewater and copper and nickel-containing wastewater. The chromium-containing wastewater enters the reduction tank through the adjustment tank 1, where FeSO4 is added by controlling the pH value to about 2.3, the hexavalent chromium is reduced to trivalent chromium, and Cr(OH)3 precipitate is formed by adding lime milk. The muddy water mixture formed after the reduction tank reaction is pumped to the sludge tank for precipitation concentration. On the other hand, the copper and nickel-containing wastewater flows from the conditioning tank 2 into the neutralization reaction tank, and the lime milk is added to adjust the pH value to about 9.5. After sufficient agitation, the sewage pump is lifted into the hydraulic clarification tank to separate the mud water, and the effluent is discharged. Adjust pH and filter to reach the standard efflux. The sludge in the hydraulic clarifier is concentrated by gravity flow into the sludge tank. Since there is still a certain amount of chromium, nickel, etc. in the supernatant of the sludge tank, it must be returned to the neutralization reaction tank for the next treatment. The concentrated sludge is filtered and discharged into the sludge drying field for drying. The filtrate of the pressure filtration water and the drying field must also be refluxed into the neutralization reaction tank. The dried sludge contains a large amount of pollutants such as chromium, nickel, iron and lead. Due to the high cost of extracting these metal elements in the sludge, it is not in line with the local reality, so we will eventually dewater the sludge. Shipped to the brick kiln factory, burned into bricks for storage and solidified pollutants. The main structures and equipment of the treatment station are shown in Table 2 and Table 3. Table 2: Main treatment structures Table 3: Main equipment The project was completed and put into operation in June 2001. The whole process was stable and the effluent quality was good. The results of the latest sampling are shown in Table 4. Table 4: Monitoring of main pollution indicators for treated effluent It can be seen from Table 4 that the effluent water quality monitoring indicators have reached the first-class standard of Integrated Wastewater Discharge Standard (GB8978-96), and the main pollutants of wastewater are efficiently removed, and the removal rates of total chromium, total nickel and total copper are all removed. More than 99%. (1) The electroplating wastewater is treated by chemical classification method, and the complete precipitation environment of copper, nickel and chromium is separately controlled, thereby avoiding mutual interference with each other. It effectively solves the shortcomings of poor water quality in traditional chemical methods, and the effluent quality is significantly better than that of mixed electroplating wastewater. (2) The whole process is intermittent operation, and the purpose of reaching the standard discharge is truly achieved, which avoids the situation that the continuous operation process affects the effluent water quality due to unacceptable errors and changes in water quality and quantity. (3) The treatment process has good adaptability to the change of water quality and quantity of the influent water. Since the sudden change of water quality and water quantity has no influence on the effluent, the process is more suitable for the treatment of electroplating wastewater with periodic production. (4) The practice of process operation shows that the whole project has low investment, simple process, stable operation, good operability, moderate operating cost, and basic control at 4.0 yuan/m3. (5) Since the treated wastewater is discharged into the pond, it may be used as irrigation water, and the treated water is required to meet the standard strictly. Therefore, the project is managed by the management company and is monitored online by the environmental protection department. It is proved by practice that the method is suitable for the local actual situation. Happening. references [1] Jia Zhusheng. Chemical treatment of chromium-containing electroplating wastewater. Material Protection, 2001, 34 (11): 53.
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(1. Department of Resources and Environmental Engineering, Guilin Institute of Technology; 2. Guilin Environmental Sanitation Management Office)
Key words: chemical classification, electroplating wastewater treatment
1. The wastewater from the metal electroplating plant is collected centrally. The wastewater is mainly concentrated in the working hours of 8 hours during the day. There is basically no wastewater outflow at night, and the water quality and quantity of wastewater vary greatly.
2. The water content of copper and nickel-containing wastewater is relatively large, and the content of copper and nickel is relatively high, and chromium is not contained. The amount of chromium-containing wastewater is relatively small, accounting for only 12% of the total water, and copper and nickel are lower than the main treatment items.
3. The entire wastewater treatment station occupies less land and has a compact layout. The self-flow form is used as much as possible between the structures to maximize energy savings.
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(6) Due to the requirement of expanding production, the electroplating city is undergoing the second phase of construction and will increase the electroplating wastewater by 800m3/d. Therefore, this project is a good reference for the construction of wastewater treatment stations with relatively concentrated electroplating enterprises.
[2] Tang Kunxian, Chen Miner et al. The role of pH regulation in the treatment of electroplating wastewater. Fujian Environmental Protection, 2002 19(2): 34-35.
[3] Peng Changsheng. Chemical treatment of mixed electroplating wastewater in Datong Gear Factory under alkaline conditions. Environmental Engineering, 2001, 19(6): 24-25.
[4] Li Fufu, Li Wei, Wu Ganqi, et al. New technology for the treatment of electroplating wastewater by microbial method. Industrial Water Supply and Drainage, 1997 23(6): 25-29.
[5] Chen Huiguo. On the development of electroplating wastewater treatment technology. Electroplating and environmental protection, 2001, 21 (3): 32-35.
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