Water treatment for powder coating and chemical pretreatment

High-performance water treatment is a key component of chemical pretreatment before powder coating. We supply modular solutions (pre-filtration, oil separation, reverse osmosis + polishing for demineralized water, batch wastewater treatment) to ensure adhesion, surface quality, and operating costs.

Why water treatment is important in pretreatment

• Adhesion & Surface: Dissolved salts, oil residues, or organic contaminants lead to adhesion defects, whitening, or optical flaws.
  

• Process Stability: Constant conductivity, pH, and temperature reduce rejects and rework.

• Membrane Protection: Pretreatment protects RO membranes from grease, oil, and particles.

• Costs & Compliance: Reduced freshwater consumption, lower wastewater costs, and compliance with local discharge limits.

Target quality: Deionized water for final rinsing (< 30 µS/cm)

• Target: For demanding final rinsing and the highest adhesion requirements, we recommend target conductivity values ​​< 30 µS/cm; values ​​< 10 µS/cm are possible depending on the project.
• Proven setup: Prefiltration → RO → Polishing (mixed bed or EDI) → Buffer tank with inline conductivity monitoring.
• Operating functions: Automatic switchover in case of permeate deviation, alarm and bypass logic, CIP for membranes.

Reverse osmosis (RO): Design and practical guidelines

• Function: RO reduces total dissolved solids (TDS) and organic substances; permeate serves as the basis for further polishing.
• Recommended pretreatment: Multimedia/sand filter + cartridge (≤ 5 µm), antiscalant dosing, and, if necessary, softening in cases of high water hardness.
• Key performance indicators (guideline): Typical system recovery 60–85%; permeate before polishing 50–500 µS/cm (source and system specific).
• Operating requirements: Pressure monitoring, differential pressure alarm, regular membrane CIP, and antiscalant dosing in cases of hard raw water.

Polishing: Mixed bed / EDI for deionized water production

• Purpose: To reduce the conductivity of RO permeate to demineralization levels (< 30 µS/cm).

• Options: Mixed-bed exchange/regeneration (chemical) or EDI (continuous, less chemicals).

• Operational aspects: Consider regeneration, disposal logistics (mixed-bed salt solutions), and EDI maintenance costs.

Oil separation: Protection against membrane fouling

• Sequence: Oil separator always installed upstream of RO and fine filters.
• Technologies:

1. Coalescer: efficient for free oil; low operating costs.
2. API/Gravity separator: suitable for high flow rates, simple technology.
3. DAF (Dissolved Air Flotation): suitable for emulsified oil and fine particles; usually combined with flocculation.

• Monitoring: Oil-in-water sensor (mg/L) for alarm/bypass.
• Practical recommendation: Coalescer + cartridge upstream of RO; for persistent emulsions, DAF + flocculation.

Batch reactor for wastewater treatment (flocculation / sedimentation)

• Application scenario: small to medium-sized lines, fluctuating loads, flexible treatment.
• Process steps: Equalization (buffer) → pH/chemical dosing (coagulant/flocculation) → stirring/flocculation phase → sedimentation → clear water discharge → sludge treatment (thickener/filter press).
• Chemicals: FeCl₃, polyaluminum chlorides (PAC), or inorganic coagulants + polymer flocculants (dosage-dependent).
• Advantages: flexible, low investment costs, easy maintenance; Disadvantages: sludge production, chemical consumption.
• Sludge management: thickening + filter press; documentation/disposal in accordance with waste disposal regulations.

Monitoring & Process Control

Recommended parameters for process control:

• pH, conductivity (µS/cm), TOC/COD, turbidity (NTU), oil-in-water (mg/L), differential pressure filter/diaphragm, temperature.

Typical plant specifications

• Pre-filter: Cartridge 1–5 µm
• RO module: 150–600 l/h 
• RO recovery: 60–85% (project-dependent)
• Polishing: EDI or mixed bed for conductivity reduction (< 30 µS/cm)
• Batch reactor: Volume depending on throughput (8–24 m³/d typical range)

Note: Design is always project-specific, based on raw water analysis and process requirements.

Example flowchart (typical process)

1. Degreasing → Coarse filtration → Coalescence separator (oil)
2. Intermediate rinse → Fine filtration (≤ 5 µm)
3. RO skid → Permeate → EDI/Mixed bed → DI buffer (final rinse)
4. RO concentrates + residual water → Batch reactor (flocculation/sedimentation)
5. Clear water → Recirculation or disposal; Sludge → Filter press → Disposal

Quality and safety aspects

• Residue monitoring: TOC, conductivity, oil-in-water.
• Membrane maintenance: regular CIP cycles, antiscalant strategy.
• Occupational safety: chemical safety during regeneration/dosing, safe handling of sludge.
• Compliance: check local discharge limits; retain complete documentation for authorities.