Electroplating Factory Wastewater Treatment Upgrade Project

Category：Cases Update time：2026-09-10 10:04:55 Views：

I. Project Overview

This project is a wastewater renovation project for a hardware electroplating processing plant in the Pearl River Delta. The plant mainly engages in zinc plating, copper plating, nickel plating, surface degreasing, passivation and other processes. The wastewater has a complex composition, containing complexed heavy metals, surfactants, high COD, ammonia nitrogen and total nitrogen. The original process used mixed discharge treatment, and the effluent heavy metals, total nitrogen and COD fluctuated greatly, unable to stably meet the Table 3 special emission limits of the "Electroplating Pollutant Emission Standard" (GB 21900-2008).

This renovation adopts a combined process of quality-based diversion pretreatment + deep heavy metal removal from comprehensive wastewater + two-stage AO biochemical denitrification + MBR deep purification + reclaimed water reuse system, achieving stable compliance discharge of wastewater. At the same time, surplus clean water can be reused for workshop cleaning water, greatly reducing the enterprise's water costs.

Design treatment scale: 800m³/d, operation mode: 24h continuous operation

II. Wastewater Quality and Discharge Standards

1. Influent water quality (average of mixed influent from each wastewater stream)

CODcr: 180–800mg/L; ammonia nitrogen: 35–80mg/L; total nitrogen: 32–55mg/L

Total copper, total nickel, total zinc, hexavalent chromium: fluctuating above standards; pH: 2–11; contains large amounts of brighteners, complexing agents, emulsified oil

2. Applicable discharge standards (GB 21900-2008 Table 3)

COD≤50mg/L, ammonia nitrogen≤8mg/L, total nitrogen≤15mg/L

Heavy metals (copper, nickel, zinc, chromium) all meet standards, pH 6–9

III. Core Design Approach

First, separate and pre-treat each stream individually to break toxicity and degrade refractory substances; then combine all wastewater and uniformly dose heavy metal removal agent for coagulation and sedimentation; two-stage AO for advanced denitrification and COD reduction; MBR membrane for sludge-water separation and advanced purification; final discharge meeting standards or ultrafiltration + RO for reclaimed water reuse

Core advantages: separate treatment first resolves heavy metal toxicity and complex structure issues, preventing heavy metals from poisoning the biological system; two-stage AO ensures stable compliance of total nitrogen and ammonia nitrogen; MBR replaces traditional secondary clarifier, achieving extremely high effluent quality and supporting both direct discharge and reclaimed water reuse modes.

IV. Detailed Process Flow

Step 1: Separate pre-treatment of each wastewater stream (key prerequisite)

The plant implements quality-based separation and dedicated pipes and tanks for collection, eliminating conflicts from mixed discharge and preventing heavy metals and cyanide from directly entering the biological system and poisoning the bacteria.

• Cyanide-containing wastewater: separately collected, two-stage cyanide destruction (alkaline chlorination), after passing cyanide destruction testing, flows into the comprehensive equalization tank

• Chromium-containing wastewater: separately collected, reduction tank (adding sodium bisulfite), hexavalent chromium converted to trivalent chromium, pH adjusted, flows into the comprehensive equalization tank

• Nickel-containing/complexed copper wastewater: separately collected, complex-breaking reaction tank (dedicated complex-breaking agent + sodium sulfide), breaking EDTA and ammonia complex structures, releasing complexed heavy metals, pre-treatment sedimentation effluent collected

• Pre-treatment degreasing wastewater: After air flotation degreasing pre-treatment, it flows into the integrated water tank

• General cleaning mixed wastewater: Directly collected into the integrated adjustment tank for homogenization and flow equalization

Step 2: Centralized heavy metal deep removal (coagulation and sedimentation stage)

All pre-treated qualified wastewater enters the integrated adjustment tank for homogenization, flow equalization, and water quality balancing, eliminating fluctuations in water quality and volume.

The effluent from the adjustment tank is lifted to the multi-stage reaction coagulation and sedimentation system: dedicated heavy metal capture and removal agent, PAC, and PAM are dosed sequentially, with simultaneous pH adjustment.

Function: Deeply capture residual complexed and free heavy metals, thoroughly remove metal ions such as copper, nickel, zinc, and chromium, while precipitating most suspended colloids and part of COD, ensuring no heavy metal toxicity in the influent and protecting the stable operation of the subsequent biochemical system.

Sludge from the sedimentation tank is discharged into the sludge thickening tank, then filter-pressed for hazardous waste disposal, and the supernatant flows by gravity into the biochemical system.

Step 3: Two-stage AO biochemical treatment (core nitrogen removal and COD reduction)

Adopting industry electroplating high-standard configuration: primary AO + secondary AO in series for two-stage biochemical treatment, with hydrolysis acidification pre-treatment to assist in improving biodegradability.

• Hydrolysis acidification tank: Decomposes brighteners, surfactants, and long-chain organic compounds, breaks down recalcitrant components, improves B/C ratio, and reduces the load on the biochemical system

• Primary AO (Anoxic + Aerobic): Anoxic denitrification removes part of the total nitrogen; the aerobic stage rapidly degrades most of the COD and completes initial ammonia nitrogen nitrification

• Secondary AO (Advanced Denitrification): Advanced treatment targeting residual refractory organics, residual ammonia nitrogen, and total nitrogen in electroplating wastewater, with further nitrification and denitrification to ensure total nitrogen and ammonia nitrogen consistently meet standards and withstand water quality shock loads

The two-stage AO differs from single-stage processes with strong shock resistance, fully meeting the strict total nitrogen limits of GB21900 Table 3.

Step 4: MBR Membrane Advanced Purification

The two-stage AO biochemical effluent enters the MBR membrane bioreactor, replacing the traditional secondary clarifier. High-precision sludge-water separation is achieved through ultrafiltration membrane pore-size screening.

Functional advantages: The effluent contains no suspended solids and has extremely low turbidity, further intercepting trace colloids and residual organics, with water quality far superior to conventional process effluent; high sludge concentration, large volumetric loading, strong shock resistance, and stable, clear effluent quality.

Step 5: Terminal Dual Mode (Compliant Discharge / Reclaimed Water Reuse)

• Mode 1: Compliant Discharge: After disinfection and pH fine-tuning, the MBR effluent consistently meets the electroplating Table 3 standard and is directly discharged in compliance

• Mode 2: Reclaimed Water Reuse: MBR clear water → Ultrafiltration UF → Two-stage RO Reverse Osmosis → Purified water reused for workshop workpiece cleaning and spray water; RO concentrate is returned to the equalization tank for reprocessing, achieving water resource recycling and significantly reducing discharge volume and water costs

V. Complete Process Flow Diagram

Clear water tank branches: ① Discharge up to standard ② UF+RO reclaimed water reuse system (reuse in workshop)

Sludge system: sludge from each sedimentation tank | Sludge thickening tank | Plate and frame filter press | Hazardous waste off-site disposal

VI. Summary of Core Unit Functions

1. Segregated pretreatment: eliminates toxicity of cyanide, hexavalent chromium, and complexed heavy metals, solving the problem of biochemical poisoning — a prerequisite for stable operation of electroplating wastewater treatment

2. Heavy metal coagulation and sedimentation: serves as the safeguard for heavy metal indicators, thoroughly removing various metal ions and ensuring the safety of biochemical influent

3. Two-stage AO: specifically addresses COD, ammonia nitrogen, and total nitrogen exceedances in electroplating wastewater, adapting to high-standard discharge limits

4. MBR system: advanced purification with ultra-low turbidity effluent, compatible with both discharge and reuse, enhancing system stability and fault tolerance

5. Reclaimed water reuse: resource utilization, water conservation and emission reduction, reducing enterprise production and operation costs

VII. Actual Operational Effluent Results

The system has been running continuously and stably for 6 months, with effluent indicators consistently better than the Table 3 standards:

COD: 20–40mg/L; Ammonia nitrogen: 2–5mg/L; Total nitrogen: 8–12mg/L

Total copper, total nickel, total zinc, hexavalent chromium: not detected or far below the limits

MBR effluent is clear with no suspended solids; the reclaimed water quality meets the workshop's electroplating rinse water requirements, with a reuse rate of over 60%.

VIII. Solution Highlights

• Fully aligned with your required process logic of diverted water collection, heavy metal removal, and two-stage AO-MBR discharge/reuse

• Solves the pain points of the electroplating industry: difficult removal of complexed heavy metals, susceptibility to biochemical poisoning, difficulty meeting total nitrogen standards, and unstable effluent quality

• Flexible switching between dual end-of-pipe modes, balancing environmental compliance with water conservation and cost reduction

• The two-stage AO + MBR combination is a mainstream, mature process for electroplating parks, high-standard environmental impact assessments, and upgrade and retrofit projects