ETP for Electroplating & Surface Finishing
Chemical ETP systems for electroplating workshops, PCB manufacturers, and metal finishing units — cyanide destruction, Cr⁶⁺ reduction, heavy metal precipitation, and ZLD options for CPCB Red Category compliance in electroplating clusters across India
Industry Overview
ETP for Electroplating & Surface Finishing
Electroplating, PCB manufacturing, anodising, galvanising, and metal polishing units are classified as CPCB Red Category industries. Their wastewater contains cyanide (from copper, silver, and zinc cyanide plating baths), hexavalent chromium (from chrome plating and passivation), heavy metals (nickel, copper, zinc, lead, cadmium), and acids/alkalis from cleaning and rinsing. These compounds are acutely toxic and must be destroyed or removed before discharge. Standard discharge limits for cyanide (0.2 mg/L), Cr⁶⁺ (0.1 mg/L), and total heavy metals (2–5 mg/L per metal) are far below typical untreated effluent concentrations (cyanide 50–500 mg/L, Cr⁶⁺ 100–2,000 mg/L).
Electroplating ETPs use chemical treatment processes — not biological treatment. The standard treatment train involves stream segregation (cyanide stream, chrome stream, acid/alkali stream, rinse water), followed by cyanide destruction (alkaline chlorination, two-stage), hexavalent chrome reduction (acidic sodium bisulphite reduction, then alkali precipitation), and combined heavy metal removal (pH adjustment to 8.5–9.5, coagulation with lime or NaOH, plate/frame filter press for sludge). The treated effluent achieves metal removal of 95–99%.
Spans Envirotech designs and commissions chemical ETPs for standalone electroplating units (5–100 KLD) and contributes treatment technology to CETP schemes serving electroplating clusters (such as Kundli, Aligarh, Ludhiana hardware clusters). Our systems include automatic pH control, multi-stage reaction chambers, sludge dewatering, and SCADA monitoring for continuous compliance. For cluster-level CETP solutions see our CETP for Electroplating Clusters page.
Industry Challenges
Key Environmental Challenges
Cyanide Toxicity and Destruction
Free cyanide at even 0.5 mg/L is acutely lethal to aquatic life. Cyanide destruction by alkaline chlorination requires pH >10.5 and adequate NaOCl dose (two-stage: cyanate formation then complete oxidation to CO₂ + N₂). Inadequate reaction time, pH control, or chlorine dose results in discharge limit violations (CPCB limit: 0.2 mg/L free cyanide, 1.0 mg/L total cyanide).
Hexavalent Chrome Reduction
Cr⁶⁺ is a carcinogen and must be reduced to Cr³⁺ by acidic sodium bisulphite or sodium metabisulphite reduction (pH 2.5–3.0) before precipitation as Cr(OH)₃ at pH 8.5–9.0. Incomplete reduction at insufficient contact time or pH leaves Cr⁶⁺ above the 0.1 mg/L limit. Chrome sludge (classified as Hazardous Waste Schedule II) requires TSDF disposal.
Multiple Heavy Metals with Different Optimal Precipitation pH
Nickel precipitates optimally at pH 9–10; copper at pH 8–9; zinc at pH 9–10; cadmium at pH 10–11. A combined treatment at single pH may not achieve simultaneous limit compliance for all metals. Multi-stage precipitation or chelating agent dosing may be required for mixed-metal electroplating wastewater.
High Volume of Hazardous Sludge
Chemical precipitation generates 0.2–0.8 kg of mixed heavy metal hydroxide sludge per m³ of wastewater. This sludge is classified as Hazardous Waste (Schedule II) requiring TSDF disposal at ₹15,000–25,000/MT. Sludge minimisation through rinse water optimisation (drag-out recovery, counter-current rinsing) reduces both water use and sludge generation.
Stream Segregation and Chemical Compatibility
Mixing cyanide wastewater with acid stream generates toxic HCN gas — a life-safety hazard. Mixing chrome and cyanide streams creates insoluble Chrome-cyanide complexes that are difficult to treat. Strict stream segregation at source, with separate collection tanks, is non-negotiable. This requires plant-level repiping and operator training.
Our Solutions
Tailored Wastewater Treatment Solutions
Two-Stage Alkaline Cyanide Destruction
Stage 1: pH 10.5–11, NaOCl dose 6–7 mg NaOCl/mg CN, 30-minute contact time — converts cyanide to cyanate. Stage 2: pH 8.5, NaOCl dose 4–5 mg NaOCl/mg CN, 60-minute contact time — oxidises cyanate to CO₂ + N₂. Automatic pH and ORP (redox potential) control ensures reliable destruction to <0.2 mg/L free cyanide.
Cr⁶⁺ Reduction and Chrome Precipitation
Acidification to pH 2.5–3.0 with H₂SO₄, followed by sodium bisulphite dosing (ratio 3 mg bisulphite/mg Cr⁶⁺) at ORP -250 to -300 mV reduces Cr⁶⁺ to Cr³⁺. Alkali neutralisation to pH 8.5–9.0 then precipitates Cr(OH)₃. Plate-frame filter press dewatering produces chrome cake for TSDF disposal.
Combined Heavy Metal Precipitation
Combined wastewater (after cyanide and chrome streams treated) adjusted to pH 8.5–9.5 with lime or NaOH, with coagulant aid (polyelectrolyte). Lamella clarifier separates precipitated metal hydroxide sludge. Polishing sand filter achieves TSS <20 mg/L in treated effluent.
Automatic pH and ORP Control
Each reaction chamber equipped with pH electrode and ORP sensor linked to dosing pumps. PLC-based control maintains reaction conditions within ±0.2 pH units and ±20 mV ORP — critical for reliable cyanide destruction and chrome reduction. Alarm triggers automatic shutdown if parameters deviate.
ZLD Option with RO
For units under ZLD mandate, treated effluent after heavy metal removal is polished through pressure sand filter and UF, then fed to RO for 90–95% water recovery. RO permeate is recycled to rinse water, reducing freshwater consumption by 85–90%. RO concentrate with residual TDS goes to a small MEE for ZLD closure.
Technologies
Proven Technologies for Your Industry
Benefits
Why Choose Spans for Your Industry
- CPCB Red Category compliance — cyanide <0.2 mg/L, Cr⁶⁺ <0.1 mg/L, total metals within limits
- Automatic ORP control prevents cyanide and chrome discharge limit violations
- Hazardous sludge characterised and manifested under Hazardous Waste Rules
- Stream segregation system prevents toxic HCN gas formation on-site
- ZLD option available — 85–90% water recycling from rinse water recovery
- OCEMS-ready for Red Category continuous monitoring requirements
Success Stories
Case Studies
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