In high-salinity water treatment scenarios, reverse osmosis membrane biocides need to achieve a precise balance between efficiently killing microorganisms and protecting membrane materials. Achieving this goal relies on the synergistic optimization of the biocide's mechanism of action, formulation design, and process control. High-salinity environments exacerbate microbial metabolic activity, leading to the rapid proliferation of salt-tolerant bacteria such as sulfate-reducing bacteria and Vibrio vulnificus on the membrane surface, forming dense biofilms. These biofilms not only clog membrane pores and reduce permeate flux, but their metabolic products also corrode membrane materials. While traditional oxidizing biocides can quickly penetrate biofilms, their strong oxidizing properties can damage the amide bond structure of polyamide membranes, causing irreversible membrane performance degradation.
Non-oxidizing biocides, due to their milder mechanisms of action, have become the mainstream choice for high-salinity scenarios. These biocides achieve broad-spectrum sterilization by disrupting microbial cell membrane permeability, inhibiting key enzyme activity, or interfering with nucleic acid synthesis, without chemically reacting with the membrane material. For example, isothiazolinone bactericides can penetrate the slime layer of microorganisms in high-salt environments, exhibiting significant kill rates against sulfate-reducing bacteria. Simultaneously, their molecular structure is stable, maintaining activity across a wide pH range and avoiding chemical corrosion of membrane materials. Quaternary ammonium salt bactericides, through the interaction of their positive charge with the negative charge of microbial cell membranes, cause leakage of cell contents. Their non-oxidizing properties make them highly compatible with polyamide membranes, extending the lifespan of membrane modules in seawater desalination systems.
Optimizing the compatibility of the formulation design is crucial for balancing bactericidal efficiency and membrane protection. For high-salt environments, bactericides must possess salt resistance to prevent salt ions from binding with the active ingredients and causing inactivation. Some products introduce hydrophilic groups to improve dispersibility in brine, ensuring uniform coverage of the membrane surface by the bactericidal components. Simultaneously, membrane protection aids, such as biodegradable polymers like polyaspartic acid, are added to the formulation. These form a dynamic protective film on the membrane surface, reducing direct contact between the bactericide and the membrane and inhibiting scale formation through chelation. This composite formulation design ensures stable membrane flux even under shock dosing mode, preventing membrane damage caused by excessively high local concentrations.
Precise matching of process control parameters is crucial for achieving balance. In high-salt systems, the concentration of the bactericide needs to be dynamically adjusted based on the influent microbial load. For example, in the treatment of high-salt wastewater from coal chemical plants, a combination of intermittent high-concentration shock dosing and continuous low-concentration maintenance is used to combat salt-tolerant bacteria contamination. This approach rapidly removes existing biofilms while continuously inhibiting microbial regeneration through low concentrations. The dosing frequency must be coordinated with the membrane cleaning cycle, replenishing the bactericide immediately after chemical cleaning to prevent microbial recolonization at sites of membrane surface damage caused by cleaning. Furthermore, temperature control is critical; non-oxidizing bactericides may exhibit reduced activity at low temperatures, requiring heating of the influent or selection of low-temperature resistant bactericides to ensure effectiveness.
Membrane material compatibility is the underlying logic for bactericide selection. Different reverse osmosis membrane materials exhibit significantly different tolerances to bactericides. Cellulose acetate membranes can withstand weak oxidizing bactericides, while polyamide membranes require strict avoidance of contact with oxidizing substances. While novel thin-layer composite membranes (TFCs) offer high desalination rates, they are more sensitive to chemical environments, necessitating the selection of pH-neutral, halogen-free bactericides. Some high-end bactericides undergo compatibility testing for specific membrane materials, providing key indicators such as membrane flux decline rate and desalination rate changes, offering users precise selection guidance.
Long-term synergistic effect management can further enhance system stability. The synergistic use of reverse osmosis membrane biocides and scale inhibitors must avoid chemical conflicts. For example, scale inhibitors containing polyphosphates may form precipitates with certain bactericides, requiring the selection of products with anti-precipitation formulations. Simultaneously, the compatibility of bactericides with reducing agents must be considered to prevent the degradation of bactericide activity during residual chlorine removal. Establishing a chemical compatibility matrix can systematically mitigate potential risks and ensure synergistic effects of various agents in high-salt systems.
As reverse osmosis technology advances towards higher flux and lower energy consumption, research and development of reverse osmosis membrane biocides will focus more on green and intelligent technologies. Emerging solutions such as bio-based bactericides and photocatalytic sterilization technologies are being explored. These technologies, by mimicking natural antibacterial mechanisms or utilizing light energy to activate bactericidal activity, can further reduce the impact of chemical agents on membrane materials. Simultaneously, by combining online microbial monitoring and AI-based dosing control systems, dynamic optimization of bactericide concentrations can be achieved, ensuring sterilization efficiency while maximizing the protection of membrane elements, providing a more sustainable solution for high-salinity water treatment.
