Renovation and maintenance of wastewater treatment equipment

variousRenovation and maintenance of wastewater treatment equipmentElectroplating wastewater treatment equipment

1、 Classification and collection of electroplating wastewater

Electroplating wastewater needs to be strictly separated according to the nature of pollutants to avoid the formation of more difficult to treat substances (such as complexes) after mixing different wastewater. Common categories:

Cyanide containing wastewater: from processes such as copper plating and zinc plating, containingCN⁻Ionic, highly toxic.

Chromium containing wastewater: containingCr⁶⁺(Highly toxic) orCr³⁺From the chrome plating process.

Nickel containing wastewater: containingNi²⁺From nickel plating process (some nickel is a type of pollutant that needs to be treated separately to meet standards).

Mixed acid wastewater: containing sulfuric acid, hydrochloric acid, nitric acid, etc,pHLow value, possibly mixed with heavy metal ions.

Oily wastewater: from the pre-treatment oil removal process, containing emulsified oil or grease.

Other heavy metal wastewater: such as wastewater containing copper, zinc, cadmium, lead, etc.

2、 Core processing technology and equipment

1. Cyanide containing wastewater treatment——Cyanide breaking process

Principle: Through oxidation reaction, highly toxic substances are eliminatedCN⁻Decompose into non-toxic substancesCO₂andN₂.

Two stage cyanide cracking method (commonly used):

First level cyanide breaking (alkaline conditions): add sodium hypochlorite（NaClO）Or hydrogen peroxide（H₂O₂）, inpH=10~11Under certain conditions,CN⁻Oxidation to cyanate salt（CNO inauspicious;Reduced toxicity90%）：\\(CN^- + ClO^- + H_2O \\rightarrow CNO^- + Cl^- + 2OH^-\\)

Secondary cyanide breaking (neutral conditions): regulationpH=8~9Further adding oxidants willCNO inauspicious;Oxidation toCO₂andN₂：\\(2CNO^- + 3ClO^- + H_2O \\rightarrow 2CO_2 \\uparrow + N_2 \\uparrow + 3Cl^- + 2OH^-\\)

Equipment: Cyanide cracking reaction tank (with stirring)pHAutomatic control system, dosing device (sodium hypochlorite)/Hydrogen peroxide storage tank).

Attention: Cyanide containing wastewater needs to be treated separately and must not be mixed with acidic wastewater as it can generate highly toxic substancesHCNGas).

2. Chromium containing wastewater treatment——restore+Precipitation method

Principle: To reduce high toxicityCr⁶⁺Reduced to low toxicityCr³⁺Then remove it through neutralization and precipitation.

Process steps:

Reduction reaction: under acidic conditions（pH=2~3）Next, add sodium bisulfite（NaHSO₃）Or sodium metabisulfite（Na₂S₂O₅）, willCr⁶⁺Restore toCr³⁺：\\(Cr_2O_7^{2-} + 3HSO_3^- + 5H^+ \\rightarrow 2Cr^{3+} + 3SO_4^{2-} + 4H_2O\\)

Neutralization precipitation: regulationpH=8~9Add lime milk（Ca (OH) ₂）Or sodium hydroxide（NaOH）, generateCr (OH) ₃Precipitation:\\(Cr^{3+} + 3OH^- \\rightarrow Cr(OH)_3 \\downarrow\\)

Equipment: Reduction reaction tank, neutralization sedimentation tank, sludge dewatering machine (treatment)Cr (OH) ₃Sludge needs to be disposed of as hazardous waste.

3. Nickel containing wastewater treatment——Chemical precipitation method/membrane method/Resin method

Chemical precipitation method (applicable to non complexed nickel):

inpH=10~11Under certain conditions, addNaOHOr lime milk, generatedNi (OH) ₂Precipitation:\\(Ni^{2+} + 2OH^- \\rightarrow Ni(OH)_2 \\downarrow\\)

If there is complexed nickel (such as with citric acid or ammonia), a chelating agent (such as Fenton reagent or sodium sulfide) needs to be added first to break the complex before precipitation.

Membrane method (reverse osmosis)/Nanofiltration: By intercepting nickel ions through a membrane, concentration and recovery can be achieved, and clean water can be reused.

Resin method: using chelating resin (such asD401Type) adsorptionNi²⁺After saturation, it is regenerated and suitable for low concentration nickel containing wastewater or deep treatment.

4. Mixed acid wastewater treatment——neutralization+Heavy metal precipitation

Neutralizing acidity: Add lime milk or sodium hydroxide to adjustpHTo neutral（pH=6~9）.

Heavy metal precipitation: If it contains heavy metals such as copper and zinc, sodium sulfide should be added simultaneously（Na₂S）Or polyaluminum chloride（PAC）Generate sulfide or hydroxide precipitates.

5. Oil containing wastewater treatment——Air flotation method

Process: By introducing air into the wastewater, tiny bubbles are generated to adsorb oil droplets and float them to the surface, which are then removed by a scraper.

Equipment: Air flotation tank (can use dissolved air flotation or vortex concave air flotation), demulsifier dosing device (such as dosing)PAC+PAM）.

6. deep processing——Heavy metal capture+membrane treatment+disinfect

Heavy metal capture agent（HMC-M1For low concentration heavy metal ions (such as residual nickel and chromium), specific chelating agents are added to generate insoluble precipitates and ensure compliance (such as nickel)≤0.1mg/LTotal chromium≤0.5mg/L）.

Membrane treatment（UF+RO）Filter and desalinate the effluent to achieve the reuse of reclaimed water (such as for cleaning processes).

Disinfection: If reused in production, ultraviolet or ozone disinfection can be used to kill microorganisms.

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