When treating wastewater containing organic matter, reverse osmosis water purification equipment must address the core challenge of membrane fouling. Organic matter easily adsorbs and deposits on the membrane surface, forming a gel layer or clogging the membrane pores, leading to decreased flux, reduced desalination rate, and even shortened membrane lifespan. To overcome this bottleneck, the synergistic application of oxidative pretreatment and membrane surface modification has become a key technological approach, achieving the dual goals of pollution control and performance improvement through a combination of physical and chemical processes.
The core of oxidative pretreatment lies in using strong oxidants to break down the molecular structure of organic matter, reducing its fouling potential. In wastewater containing organic matter, large-molecule natural organic matter (such as humic acid and fulvic acid) and small-molecule synthetic organic matter (such as surfactants and solvents) are the main sources of pollution. Oxidants break down long chains of organic matter, oxidize functional groups, or introduce polar groups, converting them into small molecules or hydrophilic substances, thereby reducing the tendency for adsorption on the membrane surface. For example, ozone oxidation can open the aromatic ring structure of organic matter, reducing its hydrophobicity; hydrogen peroxide oxidation can introduce hydrophilic groups such as hydroxyl groups, enhancing the water solubility of organic matter. Furthermore, the oxidation process can decompose microbial cell walls, inhibit biofilm formation, and create low-fouling feedwater conditions for subsequent reverse osmosis treatment.
Membrane surface modification constructs an antifouling barrier at the material level, optimizing membrane surface properties through physical or chemical means. Physical modification often employs surface coating technology to form a functional pre-coating on the membrane surface, such as hydrophilic polymers like polyvinyl alcohol and polyethylene glycol, which prevent organic matter from approaching the membrane surface through steric hindrance. Chemical modification introduces specific functional groups onto the membrane surface through graft polymerization, plasma treatment, or redox reactions. For example, grafting zwitterionic polymers can simultaneously enhance the membrane's hydrophilicity and charge neutralization, reducing electrostatic adsorption and hydrophobic interactions; plasma treatment can introduce oxygen- or nitrogen-containing polar groups, increasing the membrane surface energy and making it difficult for organic matter to adhere. The modified membrane surface has reduced roughness and a more uniform pore size distribution, further weakening the physical basis for organic matter deposition.
The synergistic effect of oxidation pretreatment and membrane surface modification is reflected in a multi-stage fouling control mechanism. First, oxidation pretreatment significantly reduces the concentration of pollutant precursors in the influent by degrading macromolecular organic matter and disrupting microbial structures, thus alleviating membrane fouling pressure at the source. Second, the modified membrane surface, with its excellent hydrophilicity and anti-adsorption properties, forms a dynamic repulsion layer against residual trace organic matter, making it difficult for any organic matter to form a stable fouling layer even if some reaches the membrane surface. Furthermore, active species such as hydroxyl radicals generated during the oxidation process can continuously act on the membrane surface, decomposing adsorbed organic matter and achieving an "online cleaning" effect, extending the chemical cleaning cycle. This synergistic model of "front-end reduction + end-end blocking + process purification" enables the reverse osmosis system to maintain efficient and stable operation when treating wastewater with high organic matter content.
During implementation, attention must be paid to the compatibility between the oxidant selection and the modification method. For example, while chlorine-containing oxidants (such as sodium hypochlorite) can effectively oxidize organic matter, they may cause chlorine damage to polyamide reverse osmosis membranes. In such cases, it is necessary to combine them with a reducing agent for dechlorination or use chlorine-resistant modification technology. Ozone oxidation, on the other hand, requires control of the reaction time to avoid over-oxidation leading to membrane material degradation. In terms of membrane surface modification, graft polymerization requires optimization of monomer concentration and reaction conditions to ensure a uniform and dense graft layer; plasma treatment requires control of power and gas atmosphere to avoid excessive etching of the membrane surface. Through precise control of process parameters, the optimal synergistic effect of oxidation pretreatment and membrane modification can be achieved.
Practical application cases show that synergistic technologies can significantly improve the ability of reverse osmosis water purification equipment to treat wastewater containing organic matter. In a pharmaceutical wastewater treatment project, using ozone oxidation pretreatment combined with a polyethylene glycol graft-modified membrane, the membrane flux remained above 90% of its initial value after six months of system operation, while the flux of the unmodified system decreased by more than 40%. In a dyeing and printing wastewater reuse project, the combination of hydrogen peroxide oxidation and zwitterionic modified membranes reduced membrane cleaning frequency by 60%, and the product water quality consistently met industrial water standards. These cases verify the significant advantages of synergistic technologies in extending membrane life, reducing operation and maintenance costs, and ensuring product water quality.
In the future, with advancements in materials science and oxidation technology, the synergy between oxidation pretreatment and membrane surface modification will develop towards intelligent and green directions. For example, developing photocatalytic oxidation pretreatment technology utilizes solar energy to drive the degradation of organic matter, reducing the use of chemical agents; designing stimulus-responsive smart membrane surfaces that switch antifouling properties triggered by pH, temperature, or light exposure, achieving dynamic pollution control. These innovations will further expand the application boundaries of reverse osmosis water purification equipment in the treatment of wastewater containing organic matter, driving the water treatment industry towards higher efficiency and sustainability.
