NF Membrane Treatment Process for Pesticide Wastewater Decolorization

Pretreatment Stage

• Adjust the wastewater pH to 6-8 (by adding H₂SO₄ or NaOH) to balance the fluctuation of water quality and avoid damage to the membrane caused by extreme pH.
• If the wastewater contains oil or lipophilic components, add a dissolved air flotation unit (with PAC/PAM added) to remove floating oil.

• Fenton Oxidation (Fe²⁺ + H₂O₂) or Ozone Oxidation: Degrade large molecular organic compounds (such as aromatic pesticides) and reduce color (decolorization rate of 40-60%).
• After oxidation, add NaHSO₃ to neutralize residual oxidants to prevent damage to the NF membrane.

• Use a 5μm security filter to remove small flocs and residual particulate matter generated after oxidation, ensuring the SDI15 of the feed water is ≤5.
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NF Membrane Decolorization Stage

• Choose an organic solvent-resistant NF membrane (such as polyamide composite membrane or sulfonated polyethersulfone membrane) with a molecular weight cut-off of 200-500 Da, which prioritizes the interception of pigment molecules (such as azo groups, anthraquinone types).
• Recommended models: NF270 (Dow), DL (GE), etc., suitable for high-color wastewater.

• Operating pressure: 0.8-1.5 MPa (adjusted according to the molecular weight of pollutants)
• Recovery rate: 60-70% (permeate meets discharge standards or is reused, concentrate is further treated)
• Temperature: 20-35℃ (to avoid membrane structural deformation caused by high temperature)

• Pore Size Sieving: Intercept pigment molecules with a molecular weight >200 Da (such as pesticide intermediates, dye by-products).
• Electrostatic Repulsion: The negative charge on the membrane surface repels negatively charged organic compounds (such as sulfonic acid group pigments).

Post-treatment and Resource Recovery

• If the permeate contains residual small molecular organic compounds (such as phenols), use activated carbon adsorption or biological filters for further purification.
• After meeting the standards, reuse for production or discharge (color ≤50 times, COD ≤100 mg/L).

• Evaporative Crystallization: Recover high-concentration organic compounds (such as pesticide mother liquor) or salts.
• Incineration Treatment: For highly toxic concentrates (such as those containing organochlorine pesticides), high-temperature decomposition of harmful substances.

System Maintenance

• Weekly cleaning with 0.1% NaOH + 0.5% EDTA solution for organic contamination;
• Monthly cleaning with 1% citric acid for inorganic scaling (such as CaSO₄).

Brief Scheme Design

Core Equipment Configuration

Expected Treatment Results

Technical Advantages and Considerations

• High-efficiency Decolorization: The interception rate for pigment molecules (molecular weight 200-1000 Da) is >90%.
• Selective Separation: It is possible to recover some useful intermediates (such as aromatic compounds).
• Modular Design: It adapts to the intermittent discharge characteristics of pesticide wastewater and allows flexible start and stop.

• Enhanced Pretreatment: It is necessary to reduce the toxicity of wastewater through oxidation or adsorption to avoid membrane pollution and biological toxicity.
• Membrane Material Compatibility: Avoid wastewater containing strong polar solvents (such as DMF), which may cause membrane swelling.
• Concentrate Disposal Cost: High-concentration organic concentrates require supporting incineration or advanced oxidation facilities, which have a higher investment.

Reference Cases

• Original water color 1200 times, COD 4500 mg/L;
• Using the "Fenton oxidation + NF (NF90 membrane)" process, the permeate color was reduced to 30 times, and the COD was 600 mg/L, which was reused in the cooling water system.

• The NF concentrate was recovered as NaCl through evaporative crystallization, reaching industrial grade purity.