The effectiveness of reverse osmosis membrane biocides at low concentrations requires comprehensive analysis from multiple dimensions, including their mechanism of action, microbial characteristics, environmental conditions, and membrane system compatibility. As a core agent ensuring the stable operation of reverse osmosis systems, its core function is to achieve highly efficient antibacterial and bactericidal effects by disrupting microbial cell structure or interfering with metabolic processes. Under low concentration conditions, its effectiveness depends on the synergistic effect of agent type, microbial species, and system operating parameters.
Non-oxidizing reverse osmosis membrane biocides typically exhibit superior inhibitory effects at low concentrations. These agents penetrate the microbial cell membrane, undergoing irreversible reactions with internal proteins or enzymes, blocking metabolic chains, and leading to cell death. For example, isothiazolinone bactericides can bind to the sulfhydryl groups of bacterial cell membranes at extremely low concentrations, disrupting cell permeability and preventing microorganisms from synthesizing key enzymes or secreting adhesive substances, thereby inhibiting their reproduction. The advantage of these agents is their long-lasting effect and low likelihood of developing resistance; even at reduced concentrations, they can maintain their antibacterial effect through continuous adsorption to the microbial surface.
Microbial species exhibit significant differences in their sensitivity to low concentrations of disinfectants. Gram-positive bacteria, with their thicker cell walls, are more resistant to disinfectant penetration and require higher concentrations for complete inhibition. Fungi and algae, with their complex cell structures and active metabolism, may only experience growth inhibition rather than complete eradication at low concentrations. For example, at the inlet of a reverse osmosis system, if bacteria are the dominant microorganisms, low-concentration disinfectants can achieve effective control by extending the contact time; however, if a large number of fungal spores are present, higher concentrations or shock-feeding methods are necessary to ensure effectiveness.
Environmental conditions have a significant impact on the performance of low-concentration disinfectants. Water temperature, pH, and organic matter content all alter the chemical stability and microbial activity of the disinfectant. High temperatures accelerate disinfectant decomposition, reducing the concentration of active ingredients; while acidic or alkaline conditions may damage the molecular structure of the disinfectant, weakening its antibacterial ability. Furthermore, organic matter in the water (such as humic acid) competes with disinfectants for adsorption sites on microbial surfaces, forming a protective layer that hinders disinfectant penetration. Therefore, when applying low concentrations, it is necessary to reduce the organic load in the water through pretreatment and optimize the pH value to the optimal range for the agent to improve inhibition efficiency.
Membrane system compatibility is a key limiting factor for the application of low-concentration bactericides. While some bactericides are effective at inhibiting bacteria at low concentrations, they may react chemically with membrane materials, leading to a decline in membrane performance. For example, chlorine-containing oxidizing bactericides may still oxidize polyamide membranes at low concentrations, damaging their separation layer structure; while non-oxidizing agents such as isothiazolinones have better compatibility with membrane materials and will not cause membrane degradation even with long-term low-concentration use. Therefore, selecting a bactericide type that matches the membrane material is a prerequisite for ensuring the safety of low-concentration applications.
The method of adding low-concentration bactericides directly affects their inhibitory effect. Continuous addition can maintain a stable concentration of the agent in the system, achieving sustained antibacterial activity; while intermittent addition may cause microorganisms to regain activity during fluctuations in agent concentration. For example, continuously injecting low-concentration bactericides using a metering pump at the inlet of a reverse osmosis system ensures that microorganisms remain suppressed. If periodic shock injections are used, the concentration per injection needs to be increased to compensate for microbial growth during the intermittent periods, potentially increasing both the dosage and operating costs.
Prolonged use of low concentrations may induce adaptive changes in microorganisms. Although non-oxidizing bactericides have low resistance, some microorganisms may reduce their sensitivity to the agents through gene mutations or biofilm formation. For example, bacteria exposed to low concentrations of isothiazolinones for extended periods may generate efflux pumps to expel the agent from their cells; or they may form biofilms by secreting polysaccharides, hindering agent permeation. Therefore, it is necessary to regularly monitor changes in the system's microbial population and alternate the use of oxidizing bactericides to delay the development of resistance.
Whether reverse osmosis membrane biocides can effectively inhibit microbial growth at low concentrations depends on the combined effects of the agent type, microbial characteristics, environmental conditions, and membrane system compatibility. Non-oxidizing agents are more advantageous at low concentrations due to their long-lasting effect and low resistance; however, it is necessary to optimize the dosing method, control environmental parameters, and regularly assess microbial adaptability to ensure long-term antibacterial effects. In practical applications, it is recommended to determine the minimum effective concentration through small-scale experiments and dynamically adjust the dosing strategy based on system operation data to achieve a balance between efficient antibacterial activity and economical operation.
