How to treat wastewater from electroplating
Author: Robby
The main methods of electroplating wastewater treatment include chemical, physical and biological methods.
Chemical method
Chemical method is to decompose harmful substances into harmless substances through redox reaction or neutralisation and precipitation reaction, or to remove heavy metals through precipitation and air flotation. Specific methods include:
- Neutralisation and precipitation method: adding alkali to the wastewater to carry out neutralisation reaction, so that the heavy metals can be separated in the form of hydroxide precipitate which is insoluble in water.
- Chemical reduction method: add reducing agent such as NaHSO3, FeSO4, etc. in chromium-containing wastewater to reduce Cr(Ⅵ) to Cr(Ⅲ), and then separate it by precipitation.
- Oxidation of cyanide: add chlorine oxidant under alkaline condition to destroy cyanide and transform it into harmless products.
- Chemical precipitation method: add lime, NaOH and other agents to the wastewater, so that heavy metal ions react with hydroxide ions to produce water-insoluble precipitates.
Physical method
Physical methods remove pollutants from wastewater by physical means without changing their chemical properties. The main methods include:
- Evaporation concentration method: through evaporation to make the wastewater concentration, applicable to heavy metal wastewater containing chromium, copper, silver, nickel, etc., usually as an auxiliary means.
- Reverse osmosis method: using semi-permeable membrane technology to remove heavy metal ions and organic matter in wastewater.
- Activated carbon adsorption method: the use of activated carbon adsorption of heavy metals and organic matter in wastewater, applicable to chromium-containing, cyanide-containing wastewater, but regeneration is complex and costly.
- Electrolysis: Remove heavy metals through electrolysis, applicable to wastewater with high content of precious metals.
- Ion exchange method: use ion exchange resin to remove heavy metal ions in wastewater, simple operation and recycling of heavy metals.
Biological method
Biological method uses microorganisms or plants to purify the wastewater, applicable to low concentration electroplating wastewater. The main methods include:
- Bio-flocculation method: using microorganisms or their metabolites for flocculation and precipitation.
- Biological adsorption method: using microorganisms or plants to adsorb heavy metals in wastewater.
- Biochemical method: degradation of organic matter by microorganisms.
- Phytoremediation: using plants to absorb heavy metals in wastewater.
Treatment process and equipment
The treatment process of electroplating wastewater usually includes steps such as classification and collection, pretreatment (e.g., oil removal, pH adjustment), heavy metal treatment (chemical precipitation, ion exchange, membrane separation), cyanide treatment (alkaline chlorination), and deep treatment (activated carbon adsorption, disinfection). Commonly used equipment include grease traps, air flotation tanks, neutralisation tanks, sedimentation tanks, reverse osmosis membrane units, etc.5
Cost and benefit analysis
The cost of electroplating wastewater treatment varies depending on the method. Chemical and physical methods have relatively low treatment costs, but may have sludge disposal problems; biological methods have lower operating costs, but are suitable for low concentration wastewater. Overall, the selection of a suitable method needs to be based on the composition, concentration and discharge standard of the wastewater in order to achieve the best economic and environmental benefits.