Nanofiltration Stage — Continuous Ultrafiltration & NF Salt Fractionation Technology
Introduction
In the resource-recovery treatment of high-salinity organic wastewater, Plum Membrane deploys a combined scheme of continuous ultrafiltration (UF) + nanofiltration (NF) salt fractionation. The core objectives are precise retention of organics and color, and selective separation of monovalent and multivalent ions—achieving coordinated decolorization/purification and high-value salt recovery. The technology has been successfully applied across multiple industrial ZLD scenarios, featuring flexible configurations, stable operation, and superior economics.
Background & Challenges
High-salinity, high-organics wastewater often faces incomplete decolorization, low COD removal, and high mixed-salt content with conventional approaches. While evaporation–crystallization enables concentration and recovery, it is energy-intensive, yields low-value salts, and suffers from stability issues. Single-stage salt separation methods struggle to achieve high-purity crystallization, limiting resource-recovery efficiency.
Continuous Ultrafiltration Pretreatment Technology for COD Removal
Using antifouling, wide-channel spiral-wound UF membranes, the process efficiently removes macromolecular organics and color, lowering downstream loads without extra chemicals. Post-UF, the concentrate is predominantly organic with low salinity; organics can be concentrated to >10%, followed by either:
1. Co-treatment with organic wastewater via biological treatment and reuse of the treated water;
2. Evaporation of the concentrate and incineration, with distillate recovered. Alternatively, the UF permeate may undergo AOP/Fenton oxidation prior to NF treatment.
Two-Stage NF for Precise Salt Fractionation
Primary NF performs pre-concentration for initial salt split, while secondary NF refines separation, exploiting the Donnan effect to selectively split monovalent chlorides from divalent sulfates:
1. NF concentrate (divalent salts) → evaporation or freeze-crystallization to high-purity sulfates; distillate reused; a small mother-liquor bleed can recycle to UF decolorization or be treated separately.
2. NF permeate (monovalent salts) → evaporation–crystallization to high-purity chlorides; distillate reused; with minimal organics, mother liquor can be recycled, or directly dried if purity is met.
Process Flow
Ultrafiltration & nanofiltration membrane salt separation photos (stock solution, ultrafiltration membrane concentrate, ultrafiltration membrane clear solution, first-stage nanofiltration concentrate, second-stage nanofiltration clear solution)
Process Highlights
Applications
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