When electrical energy is delivered to an electrolytic cell, a reduction-oxidation reaction occurs, resulting in electroplating. Surface plating procedures generate electroplating wastewater by dipping metal, in an electroplating solution of various metals and then rinsing it. Brass, nickel, cadmium, zinc, silver, copper, and gold are common plating materials.
The wastewater from electroplating is typically from washing, rinsing, and batch dumping, has a pH of 3-5, and contains soluble forms of the different metals. To extract soluble metals from wastewater, it must first be rendered insoluble. Sedimentation is used to coagulate, flocculate, and clarify the insoluble metal.
Let’s understand CPCB guidelines for electroplating industry effluent treatment plants.
Effluent Characteristics
Any or all of the electroplating chemicals (such as acidic solutions, hazardous metals, solvents, and cyanides), can be discovered in wastewater, either through product rinsing or through spillage and dumping of process baths.
Hot plating bath solvents and vapours produce high amounts of volatile organic compounds (VOCs) and, in some situations, volatile metal compounds (when may contain chromates). When baths are not regenerated, around 30% of the solvents and degreasing chemicals employed, can be emitted as VOCs.
CPCB Guidelines for electroplating industry ETP Plants
(i) Compulsory Parameter
Parameter |
Value |
pH |
6.0 |
Suspended Solids |
100 |
Colour |
400 |
Total Metal |
10 |
Trichloroethane |
0.1 |
Trichloroethylene |
0.1 |
Oil and grease |
10.0 |
(ii) Specific Parameter as per process
a. Nickel and Chrome plating
· Bio-Chemical Oxygen Demand [3days at 27oC] = 30 · Temperature = shall not exceed 5 degree Celsius above the receiving water · Chemical Oxygen Demand (COD) = 250 · Sulfate = 1000 · Sulphide (as S) = 2.0 · Phenolic Compounds = 1.0 · Total Dissolved Solids, Inorganic (TDS) = 2100** · Ammonical Nitrogen (as N) = 50
|
· Mercury = 0.01 · Hexavalent Chromium = 0.1 · Total Chromium as (Cr) = 2.0 · Copper = 2.0 · Zinc = 5.0 · Nickel = 3.0 · Lead = 0.1 · Manganese = 2.0 · Cadmium = 0.2 · Chloride = 1000 · Sodium Absorption Ratio (SAR) = 26** · Iron = 30
|
(iii) Cadmium plating
Parameters |
Value |
Cyanides |
0.2 |
Ammonical Nitrogen |
50 |
Total Residual Chlorine |
1.0 |
Hexavalent Chromium |
0.1 |
Total Chromium |
2.0 |
Cadmium |
2.0 |
(iv) Anodizing
Parameters |
Value |
Fluoride |
15 |
Ammonical Nitrogen |
50 |
Total Residual Chlorine |
1.0 |
Sulphate |
400 |
Phosphate |
5.0 |
(v) Copper, Tin plating
Parameters |
Value |
Cyanide |
0.2 |
Copper |
3.0 |
Tin |
2.0 |
(vi) Precious Metal plating
Parameters |
Value |
Cyanide |
0.2 |
Total Residual Chlorine |
1.0 |
NOTES:
Use at least 5 m3 of water per day. These units must channel their emissions through a stack or chimney that is at least 0 meters above ground level, or 3 meters over the top of the unit's shed or building, whichever is greater.
** Existing units must meet asterisked pollution standards by January 1, 2013. However, new units must comply with the standards as of plant commissioning.
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