Membrane antiscalants play multiple roles in reverse osmosis systems. Their core function is to inhibit the crystallization and deposition of inorganic salts on the membrane surface. However, their inhibitory effect on microbial growth requires comprehensive analysis considering both their composition and the system environment. Traditionally, scale inhibitors were considered primarily designed to target mineral scaling. However, modern composite membrane antiscalants, through formulation optimization, have gradually expanded their synergistic inhibitory capabilities against microorganisms, forming a dual protection mechanism of "scale inhibition-bacterial inhibition."
The basic components of membrane antiscalants determine their differences in antibacterial potential. Early products mainly used polyphosphates and organophosphates. These substances indirectly inhibit microbial reproduction by chelating calcium and magnesium ions, disrupting the mineral environment necessary for microbial survival. For example, polyphosphates can bind to iron and aluminum ions in water, reducing the nutrient sources available to microorganisms and thus lowering the likelihood of biofilm formation. With technological advancements, polycarboxylic acid and polyether polymers have gradually become mainstream. These substances not only possess stronger dispersing abilities but can also disrupt the microbial cell membrane structure through electrostatic interactions. Some novel scale inhibitors incorporate antimicrobial groups such as quaternary ammonium salts and organic bromine, actively releasing antimicrobial components while inhibiting scale growth, forming a chemical barrier.
The unique environment of reverse osmosis systems amplifies the antimicrobial effect of scale inhibitors. The high-salt, low-flow-rate region on the reverse osmosis membrane surface due to the concentration effect is inherently unfavorable for microbial growth, and the presence of scale inhibitors further alters these local conditions. For example, scale inhibitors reduce particle deposition through dispersion, preventing the formation of a substrate for microbial attachment; their ability to regulate pH (typically maintaining pH 5-10) also inhibits the activity of some microorganisms. More importantly, scale inhibitors create a synergistic effect with flocculants and bactericides added during the pretreatment stage. For instance, after flocculants remove large suspended solids, scale inhibitors prevent the aggregation of residual particles, reducing microbial hiding space, while residual oxidizing bactericides (such as chlorine) react with the reducing components in the scale inhibitor, potentially generating intermediate products with sustained antimicrobial capabilities.
In practical applications, the antimicrobial effect of membrane antiscalants needs to be comprehensively evaluated in conjunction with system design. In industries such as power generation and chemicals, reverse osmosis systems often employ a combination of scale inhibitors and non-oxidizing bactericides. Scale inhibitors reduce the risk of biofouling by maintaining membrane surface cleanliness, while non-oxidizing bactericides (such as isothiazolinones) periodically kill residual microorganisms. In fields with extremely high water quality requirements, such as food and medical industries, phosphorus-free and low-toxicity environmentally friendly scale inhibitors are preferred. These products enhance dirt-holding capacity through dendritic polymer technology while avoiding phosphorus-induced microbial growth. It is important to note that the antibacterial effect of scale inhibitors has a boundary condition; when the influent microbial content is too high or pretreatment is insufficient, specialized bactericides are still needed for advanced treatment.
Membrane antiscalants exhibit an "indirectly dominant, synergistically enhanced" inhibitory effect on microbial growth. They form a multi-layered protection system by altering the physicochemical environment of the membrane surface, disrupting microbial survival conditions, and synergizing with other water treatment agents. This characteristic not only extends membrane lifespan but also reduces the frequency of chemical cleaning, lowering system operating costs. In the future, with the integration of nanotechnology and bio-enzyme technology, membrane antiscalant is expected to achieve integrated functions of "scale inhibition, antibacterial and antifouling", providing more comprehensive protection for the stable operation of reverse osmosis systems.
