PCB Circuit Board Production Wastewater Treatment Project - 600m³/d

1. Project Overview

This project is a wastewater treatment renovation and new construction project for a precision PCB circuit board manufacturing enterprise in Hunan. The company mainly produces double-sided and multilayer precision circuit boards, nickel-gold boards, immersion gold boards, and hot air solder leveling (HASL) boards. The production processes cover the full workflow including: brushing, acid washing, alkaline etching, micro-etching, electroless nickel, electroplating nickel, immersion gold, developing, stripping, and green solder mask removal.

Project wastewater characteristics: multiple types of pollutants, containing Class I heavy metal pollutants, highly toxic cyanide, high-COD ink wastewater, and refractory complexed copper. Strict source separation and diversion, separate pretreatment, no mixing of streams, and no dilution to meet standards are mandatory.

This project strictly implements: 7 independent wastewater diversion collection streams + segregated pretreatment + comprehensive physicochemical treatment + A/O biological treatment + advanced filtration + optional reclaimed water reuse process, fully matching the aforementioned process flow diagram scheme.

Design treatment capacity: 600 m³/d (24-hour continuous operation, hourly treatment capacity 25 m³/h)

Applicable standards: GB39731-2020 "Discharge Standard of Water Pollutants for Electronic Industry" + GB21900-2008 Workshop Class I Pollutant Discharge Standard

Construction mode: exposed pipe classified collection, independent pretreatment systems, fully automatic chemical dosing, online pH/ORP monitoring, emergency response system, sludge hazardous waste disposal system

II. Wastewater Quality and Quantity Classification

The workshop of this project strictly implements 7 independent pipeline diversion collection streams. Pipeline colors and inspection wells are fully zoned according to specifications, with no cross-contamination between streams.

III. Overall Process Flow (consistent with the flow chart)

Workshop drainage collected separately via 7 independent pipelines

├─Cyanide-containing wastewater → Cyanide regulating tank → Primary cyanide destruction → Secondary cyanide destruction → Sedimentation tank effluent → Comprehensive wastewater tank

├─Nickel-containing wastewater → Nickel regulating tank → Fenton complex-breaking tank → pH sedimentation reaction tank → Sedimentation tank effluent → Comprehensive wastewater tank

├─Complexed copper wastewater → Complex regulating tank → Complex-breaking reaction tank → Coagulation sedimentation effluent → Comprehensive wastewater tank

├─General copper-containing wastewater → Copper regulating tank → pH-coagulation sedimentation effluent → Comprehensive wastewater tank

├─High-concentration ink organic wastewater → Ink regulating tank → Acidification demulsification → Air flotation effluent → Comprehensive wastewater tank

├─Low-concentration organic wastewater → Organic regulating tank → Coagulation sedimentation effluent → Comprehensive wastewater tank

└─ Combined Acid-Alkali Wastewater Combined Wastewater Equalization Tank

Combined Wastewater Tank pH Adjustment Tank Coagulation (PAC) Flocculation (PAM) Inclined Tube Settler Neutralization Tank Hydrolysis Acidification Tank Contact Oxidation (A/O Biological) Secondary Clarifier Sand Filter Discharge Compliance Tank

(Optional Reuse Branch)

MBR+RO Membrane System Reuse Water Tank; RO Concentrate Return to Combined Tank

All Settler Sludge Sludge Thickening Tank Plate-and-Frame Filter Press Hazardous Waste Sludge Outsourced Disposal

IV. Core Process Operating Parameters for Each Unit (On-Site Commissioning Parameters)

1. Cyanide-Containing Wastewater Pretreatment System

Adopts Two-Stage Alkaline Chlorination Cyanide Destruction Process

First-Stage Cyanide Destruction: pH=10.5–11.5, dosing sodium hypochlorite, ORP≥300mV, reaction 35min

Second-Stage Cyanide Destruction: pH=7.5–8.0, additional sodium hypochlorite dosing, ORP≥600mV, reaction 35min

Treatment effect: Total cyanide at workshop outlet ≤0.3mg/L, discharged into the comprehensive pool after meeting standards

2. Nickel-containing wastewater pretreatment system (key difficulty)

Adopts Fenton complex-breaking + high pH precipitation

Complex breaking: pH=3–4, ferrous sulfate 800mg/L, 30% hydrogen peroxide 2mL/L, reaction 50min

Precipitation: Adjust pH to 10.5–11.0 with NaOH, PAC 100mg/L, PAM 2mg/L

Effluent indicators: Total nickel at workshop outlet ≤0.1mg/L (special discharge limit)

3. Complexed copper wastewater pretreatment

Adopts heavy metal removal agent + Fenton composite complex breaking to break ammonia complexes and EDTA-complexed copper

After complex breaking, adjust pH to 9.0–9.5 for coagulation and precipitation, effluent total copper stable at ≤0.3mg/L

4. Ink high-concentration organic wastewater pretreatment

Concentrated sulfuric acid acidification demulsification at pH=2–4, stirring for 30min, air flotation skimming to remove ink scum

COD reduced from 10000mg/L to within 1500mg/L, greatly reducing biochemical load

5. Integrated physicochemical + biochemical main system

Physicochemical stage: pH8.5–9.5, PAC150mg/L, PAM3mg/L, removing residual heavy metals and SS

Biochemical stage: hydrolysis acidification HRT=10h, contact oxidation HRT=16h, DO controlled at 2.5–3mg/L

Sand filtration after biochemical treatment as final safeguard to ensure clear and stable effluent

V. Main tank design parameters (per HJ2058-2018 standard)

VI. Final Effluent Water Quality (Acceptance Test Data)

VII. Reclaimed Water Reuse System

This project reserves an MBR+RO reclaimed water reuse system. After treatment, the produced water conductivity is ≤50μS/cm, which can be directly reused in the workshop cleaning process. RO concentrate is returned to the comprehensive adjustment tank for re-treatment, with no discharge of concentrate pollution, increasing the water resource utilization rate to over 75%.

VIII. Sludge and Hazardous Waste Disposal

Sludge from each sedimentation tank and scum from air flotation are all collected into the sludge thickening tank. After dewatering by plate-and-frame filter press, hazardous waste sludge with a moisture content of ≤60% is formed. A hazardous waste agreement is signed, and periodic outsourced disposal by qualified units is carried out, with complete and compliant records available for inspection.

IX. Project Operation Advantages and Compliance Highlights

• Fully compliant diversion: 7 wastewater streams are independently collected and independently pre-treated, with Class I pollutants meeting standards at the workshop level, satisfying the latest environmental compliance inspection requirements.

• Solving industry challenges: thoroughly resolving the problems of difficult sedimentation of complexed copper and complexed nickel, excessive cyanide, and high-COD impact from printing ink.

• Stable and impact-resistant system: multi-stage adjustment + emergency tank can cope with fluctuations in workshop water quality and quantity.

• High degree of automation: pH, ORP, and dosing systems are fully automatically controlled, making operation and maintenance simple.

• Reusable, water-saving and consumption-reducing: A complete reclaimed water reuse module is reserved, adapting to enterprise expansion and water-saving policies.

10. Project Acceptance Status

This project has successfully passed the environmental protection completion acceptance, online monitoring comparison, and routine inspections. The effluent has remained stable and compliant over the long term, with no exceedances, no complaints, and no environmental penalties, making it a standard, replicable benchmark case for full-process classified wastewater treatment of PCB circuit boards.