The electroplating industry discharges huge amounts of pollutants, which are highly toxic and difficult to treat, and can easily cause great environmental damage. Electroplating wastewater contains a large amount of heavy metals, which tend to accumulate in living organisms and are not biodegradable. Many heavy metal elements are toxic or carcinogenic and must be effectively treated before they can be discharged.
The production water for a certain electroplating wastewater treatment project that Shanqing Environment is responsible for includes water for electroplating, anodizing (including sulfuric acid anodizing, hard anodizing, and chromic acid anodizing), oxidation, chromate process, acid mist absorption treatment, and cleaning. The project water consumption is approximately 65m3 / d (4.06m3 /h), 19,500m3 / a.
According to the company, the discharge volume of chromium-containing wastewater (including acid mist absorption treatment wastewater) generated on the production line of this project is 200t/d, the discharge volume of heavy metal-containing wastewater (containing nickel and copper wastewater) is 160t/d, the discharge volume of acid-base wastewater is 150t/d, and the discharge volume of oil-containing wastewater is 100t/d.
After treatment by the sewage treatment facilities, 347t/d of chromium-containing wastewater (including acid mist absorption treatment wastewater) and heavy metal-containing wastewater (nickel and copper-containing wastewater) were reused, of which 3t/d was lost due to evaporation and crystallization during the treatment process. 185t/d of acid-base wastewater and oil-containing wastewater were reused and 65t/d were discharged.
Table 1.1 Water balance summary
| / |
Chromium-containing wastewater (including acid
Mist absorption wastewater treatment)
|
Wastewater containing heavy metals
(Wastewater containing nickel and copper)
|
Acid and alkaline wastewater |
Oily wastewater |
Domestic sewage |
Catering wastewater |
| Water consumption m3 / d |
1.6 |
1.4 |
20 |
45 |
8 |
5 |
| Production volume m 3 /d |
200 |
160 |
150 |
100 |
6.4 |
4 |
| Recycling amount m 3 /d |
198.4 |
158.6 |
130 |
55 |
/ |
/ |
| Loss m 3 /d |
1.6 |
1.4 |
/ |
/ |
/ |
/ |
| Emissions m3 / d |
0 |
0 |
20 |
45 |
6.4 |
4 |
Chapter 1 Design Conditions
2.1. Design scale
| Wastewater name |
Processing capacity (tons/day) |
| Chromium-containing wastewater |
200 |
| Heavy metal wastewater |
160 |
| Acid and alkaline wastewater |
150 |
| Oily wastewater |
100 |
| Domestic sewage |
6.4 |
| Catering wastewater |
4 |
2.2. Emission standards
The treated electroplating wastewater is discharged into the factory sewage network after being monitored and qualified at the workshop discharge port. The water quality of the discharged water should meet the standards in Table 2 of the "Electroplating Pollutant Emission Standard" GB21900-2008, as shown in Table 1-2.
| serial number |
Pollutants |
Standard limit |
Pollutant emission monitoring location |
| 1 |
Total chromium (mg/l) |
1.0 |
Wastewater discharge outlet of workshop or production facility |
| 2 |
Hexavalent chromium (mg/l) |
0.2 |
Wastewater discharge outlet of workshop or production facility |
| 3 |
Total Nickel (mg/l) |
0.5 |
Wastewater discharge outlet of workshop or production facility |
| 4 |
Total Silver (mg/l) |
0.3 |
Wastewater discharge outlet of workshop or production facility |
| 5 |
Total copper (mg/l) |
0.5 |
Total discharge outlet of enterprise wastewater |
| 6 |
Total zinc (mg/l) |
1.5 |
Total discharge outlet of enterprise wastewater |
| 7 |
pH |
6-9 |
Total discharge outlet of enterprise wastewater |
| 8 |
Suspended matter (mg/L) |
50 |
Total discharge outlet of enterprise wastewater |
| 9 |
Chemical oxygen demand (CODcr, mg/L) |
80 |
Total discharge outlet of enterprise wastewater |
| 10 |
Total cyanide (mg/L) |
0.3 |
Total discharge outlet of enterprise wastewater |
| 11 |
Ammonia nitrogen (mg/L) |
15 |
Total discharge outlet of enterprise wastewater |
| 12 |
Total phosphorus (mg/l) |
1.0 |
Total discharge outlet of enterprise wastewater |
| 13 |
Fluoride (mg/l) |
10 |
Total discharge outlet of enterprise wastewater |
Chapter 2 Process Design
3.1. Wastewater classification and water volume
Discharged wastewater is collected and treated according to its quality. There are five types of wastewater, including chromium-containing wastewater, heavy metal-containing wastewater, acid-base wastewater, oil-containing wastewater , and domestic and catering wastewater . Specifically:
| Wastewater name |
Classification Number |
Processing capacity
(tons/day)
|
Design processing scale
(tons/ hour )
|
| Chromium-containing wastewater |
W1 |
200 |
10 |
| Heavy metal wastewater |
W2 |
160 |
8 |
| Acid and alkaline wastewater |
W3 |
150 |
7.5 |
| Oily wastewater |
W4 |
100 |
5 |
| Domestic sewage + catering wastewater |
W 5 |
10.6 |
1 |
3.2. Treatment process determination
According to the classification of discharged wastewater, the wastewater treatment system of the comprehensive wastewater treatment station is determined to be composed of the following subsystems, and classified treatment of wastewater is implemented.
a. Chromium-containing wastewater pretreatment system to treat W1 wastewater.
b. Heavy metal wastewater pretreatment system to treat W2 wastewater.
c. Acid and alkaline wastewater pretreatment system to treat W3 wastewater.
d. Oily wastewater pretreatment system, to treat W4 wastewater.
e. Domestic sewage pretreatment system, to treat W 5 wastewater.
f. High-quality reused water and zero-discharge treatment system, which can reuse and treat the pre-treated wastewater of W1, W2, W3, W4 and W5 with high quality and zero-discharge.
3.3. Process flow chart
3.4. Treatment process description
3.4.1. Chromium-containing wastewater treatment system
The chromium-containing wastewater treatment system treats wastewater discharged from the production line. The specific treatment methods are:
a.Pre-treat W1, collect wastewater into regulating tank , pump it to integrated pre-treatment equipment, adjust pH value, acidic conditions, add FeSO 4 /NaHSO 3 for reduction reaction; adjust pH value, add limestone and sodium hydroxide for alkaline precipitation reaction.
b.Add heavy metal remover for enhanced sedimentation treatment; add composite flocculant for flocculation treatment; carry out solid-liquid separation treatment through inclined plate sedimentation tank; solid-liquid separation treatment water enters intermediate water tank for subsequent treatment.
c.The inclined plate sedimentation tank separates the sludge into the sludge thickening tank, and the filter press is used to dewater the sludge, and the dehydrated sludge is transported out as hazardous waste.
3.4.2. Heavy metal wastewater treatment system
The heavy metal wastewater treatment system treats the wastewater discharged from the production line. The specific treatment methods are:
a.W2 is treated. Wastewater is collected in a regulating tank and pumped to an integrated pretreatment device to adjust the pH value for alkaline precipitation treatment;
b.Add heavy metal remover for enhanced removal treatment; add composite flocculant for flocculation treatment; carry out solid-liquid separation treatment through inclined plate sedimentation tank; the solid-liquid separation treatment water enters the intermediate water tank for subsequent treatment.
c.The inclined plate sedimentation tank separates the sludge into the sludge thickening tank, and the filter press is used to dewater the sludge, and the dewatered sludge is transported out for hazardous waste treatment.
3.4.3. Acid and alkali wastewater treatment system
The acid and alkali wastewater treatment system treats the wastewater discharged from the production line. The specific treatment methods are:
a.W3 is treated. Wastewater is collected in a regulating tank and pumped to an integrated pretreatment device to adjust the pH value for alkaline precipitation treatment;
b.Add heavy metal remover for enhanced removal treatment; add composite flocculant for flocculation treatment; carry out solid-liquid separation treatment through inclined plate sedimentation tank; the solid-liquid separation treatment water enters the intermediate water tank for subsequent treatment.
c.The inclined plate sedimentation tank separates the sludge into the sludge thickening tank, and the filter press is used to dewater the sludge, and the dewatered sludge is transported out for hazardous waste treatment.
3.4.4. Oily wastewater treatment system
a.The oily wastewater treatment system treats the wastewater discharged from the production line. The specific treatment methods are:
W4 is treated. Wastewater is collected in a regulating tank and pumped to an integrated pretreatment device to adjust the pH value; demulsifier is added to the flotation system for oil removal.
b.Add composite flocculant for flocculation treatment; carry out solid-liquid separation treatment through inclined plate sedimentation tank; solid-liquid separation treated water enters the intermediate water tank for subsequent treatment.
c.The inclined plate sedimentation tank separates the sludge into the sludge thickening tank, and the filter press is used to dewater the sludge, and the dewatered sludge is transported out for hazardous waste treatment.
3.4.5. High-quality recycled water treatment system
After pretreatment, the wastewaters of W1, W2, W3, W4 and W5 enter the intermediate water pool for water quality and water volume adjustment. After four physical filtrations of quartz sand, activated carbon, self-cleaning filter and ultrafiltration, suspended solids, colloids, viruses, etc. in the wastewater are removed, and the SDI of the effluent water quality is less than 5, which meets the reverse osmosis inlet water quality requirements. After two-stage filtration of reverse osmosis and concentrated water reverse osmosis, the inorganic salts in the water are removed, the produced water is directly reused, a small amount of concentrated water enters the triple-effect evaporation for evaporation and concentration, the distillate is reused, and a small amount of solid wastewater is transported for treatment.
There are many types of electroplating wastewater treatment technologies, but because of various problems in the management level and production process of the electroplating industry, the quality of wastewater treatment is also very different. It is difficult to meet the wastewater treatment standards by relying on only one wastewater treatment method. According to the results of sewage monitoring, it is necessary to combine multiple treatment technologies to treat sewage in order to achieve the most significant treatment effect. If you have relevant project requirements, please leave a message or send me a private message at any time.
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