In the ongoing global quest to ensure safe and clean drinking water, the emergence and persistence of disinfection by-products (DBPs) in treated water supplies have posed a formidable challenge for water treatment professionals and public health officials alike. Disinfection processes, essential for eliminating pathogenic microorganisms, inadvertently generate these DBPs through reactions between disinfectants and natural organic matter. The presence of DBPs in drinking water has been linked to significant health risks, including carcinogenic and mutagenic effects observed in numerous epidemiological studies. Consequently, researchers and engineers have been intensifying efforts to optimize water treatment technologies that can effectively target and remove these harmful compounds, with nanofiltration (NF) and reverse osmosis (RO) membranes gaining renewed attention for their promising capabilities.
Nanofiltration and reverse osmosis, both pressure-driven membrane separations, have shown exceptional promise due to their ability to filter out contaminants at a molecular level. Unlike traditional treatment methods, these membranes operate by allowing water molecules to permeate while rejecting a broad spectrum of solutes based on size exclusion, electrostatic interactions, and other physicochemical phenomena. However, the exact mechanisms governing DBP removal via these membranes remain incompletely understood, with recent studies highlighting considerable variability in rejection efficiencies depending on membrane properties, feed water composition, and operational parameters. This complexity underscores the pressing need for a more comprehensive exploration of the interplay between membranes, DBPs, water matrix components, and system conditions to fully harness nanofiltration and reverse osmosis for effective DBP control.
Central to the rejection of DBPs via NF and RO membranes is the intricate relationship between membrane characteristics and the physicochemical properties of DBPs. Membrane pore size plays a pivotal role, where membranes with smaller effective pore diameters enhance size exclusion, effectively filtering out larger DBP molecules. For example, reverse osmosis membranes characteristically exhibit tighter pore structures than nanofiltration counterparts, resulting in superior rejection rates for a range of solutes. However, smaller pore size alone cannot explain all removal patterns, as many DBPs are minute and neutral, capable of passing through pores that would otherwise exclude larger molecules. Therefore, membrane surface properties, such as charge density and roughness, add additional layers of selectivity through electrostatic repulsion and adsorptive interactions. Adjusting these characteristics emerges as a critical strategy to optimize DBP removal.
Electrostatic interactions between charged membrane surfaces and ionizable DBPs represent one of the fundamental mechanisms of rejection in membrane filtration. Membranes exhibiting higher surface charge densities can repel charged DBP species, thereby reducing their permeation into the treated water. However, many DBPs, particularly those that are neutral or carry minimal net charge at typical drinking water pH values, evade this defense, creating significant challenges for treatment systems reliant on electrostatic exclusion. In this context, membrane roughness further influences interactions at the interface, altering local flow dynamics and contact time, which can affect the adsorption and subsequent rejection of certain DBP species. Advanced membrane engineering efforts focused on fine-tuning these surface properties are critical to overcoming limitations in conventional designs.
Water quality parameters, including ionic strength, pH, temperature, and the presence of natural organic matter, exert profound effects on the efficiency of NF and RO membranes in DBP removal. Variations in ionic strength can modulate the electrical double layer surrounding membrane surfaces, altering charge density and impacting electrostatic repulsion forces. Likewise, pH shifts influence the speciation of DBPs, particularly ionizable species, modifying their charge state and solubility, which directly affects their interaction with membranes. Temperature not only affects permeate flux rates but can also subtly change membrane polymer structures, influencing pore sizes and surface characteristics. Furthermore, natural organic matter in feed water can compete for adsorption sites or foul membranes, complicating the rejection dynamics and potentially facilitating DBP breakthrough.
Operational parameters such as pressure, recovery rates, and crossflow velocities are equally paramount in defining DBP rejection outcomes. Increasing operating pressure generally enhances permeate flux, pushing more water through the membrane matrix; however, higher pressures can also stress membrane integrity and potentially reduce selectivity over time. Recovery rates, which govern the proportion of feed water converted to permeate, influence solute concentrations near the membrane surface, leading to concentration polarization effects that may reduce effective rejection. Crossflow velocity mitigates fouling by sweeping away foulants but must be balanced against energy consumption and system wear. Optimizing these parameters demands a nuanced understanding of system hydraulics and membrane material science to maximize DBP removal without compromising operational viability.
Membrane ageing and fouling represent long-term challenges that alter the dynamics of DBP retention by NF and RO membranes. Over time, exposure to oxidants, temperature fluctuations, and varying feedwater composition can degrade membrane polymers, effectively modifying pore size distributions and surface chemistry. Intriguingly, such ageing processes may have divergent effects depending on DBP charge; while the removal of neutral DBPs may decline due to enlarged pores or reduced hydrophilicity, charged DBP rejection could conversely improve if membrane surfaces accumulate charges or acquire new functional groups. Fouling layers, often composed of biofilm, organic matter, or inorganic scales, add another layer of complexity, potentially blocking pores or creating additional rejection barriers. Managing membrane integrity through cleaning protocols, monitoring, and materials research is critical for sustained DBP mitigation.
Among the myriad of DBP species, small, hydrophilic, and mostly neutral compounds present the greatest hurdles for membrane-based removal. Their diminutive size enables passage through fine membrane pores, while their lack of charge negates electrostatic repulsion mechanisms. Conventional size exclusion and surface interactions become insufficient defenses against these molecules, underscoring the necessity for innovative membrane designs or hybrid treatment approaches. Such stubborn DBPs warrant prioritization in research and development as they often include highly toxic substances that significantly jeopardize human health even at trace levels. Advancements in material science aimed at incorporating specific functional groups or nanoscale structures may offer pathways to enhanced targeting of these elusive molecules.
The intricate coupling between membrane characteristics, DBP diversity, and feed water conditions necessitates a systemic and multidisciplinary approach to optimize removal strategies. Researchers advocate for integrated modeling frameworks that combine physicochemical analyses, membrane transport theory, and empirical performance data to unravel the complex rejection phenomena. Such comprehensive understanding enables the design of membranes with tailored pore structures, surface chemistries, and mechanical properties tuned to specific source water profiles and target DBP contaminants. Moreover, adaptive operational schemes informed by real-time water quality monitoring can dynamically modulate membrane system parameters to maintain high removal efficiency under variable conditions, embodying the next frontier in DBP control technology.
Advancements in nanotechnology and polymer chemistry bring unprecedented opportunities to fabricate membranes with precisely engineered architectures. Incorporating nanomaterials such as graphene oxide, carbon nanotubes, or metal-organic frameworks into membrane matrices can enhance selectivity, permeability, and fouling resistance simultaneously. These innovative composites can offer multifunctional surfaces exhibiting tailored charge distributions, hydrophilicity, and even catalytic capabilities that degrade DBPs in situ. Despite promising laboratory results, challenges remain in scaling up these materials to commercial production while ensuring long-term stability and regulatory compliance. Continued collaboration between material scientists, engineers, and industry stakeholders is vital to translate these breakthroughs into practical solutions.
Energy consumption and operational costs associated with NF and RO systems also factor heavily into their widespread adoption for DBP removal. RO, in particular, requires higher pressures and energy inputs, which can be a barrier for smaller utilities and low-income regions. Strategies to optimize energy use encompass not only membrane material improvements but also system-wide innovations such as energy recovery devices, process integration, and renewable energy sources. Life cycle assessments underline the importance of balancing removal efficacy against environmental footprints to achieve truly sustainable solutions. As the water sector evolves, cost-effective and energy-efficient membrane technologies will be pivotal in safeguarding drinking water quality while minimizing resource burdens.
Regulatory frameworks and public awareness are also critical drivers shaping the trajectory of DBP mitigation approaches. Stringent water quality standards for DBPs have motivated utilities to explore advanced treatment methods, including NF and RO, while also encouraging source water protection efforts. Transparent dissemination of research findings and operational experiences can foster public trust and stimulate investments into cutting-edge treatment infrastructure. Interdisciplinary dialogues involving scientists, policymakers, and communities are essential to align technological capabilities with societal needs and to prioritize research on the most threatening DBP species based on epidemiological evidence.
The integration of real-time sensing and artificial intelligence offers transformative potential in monitoring and controlling DBP removal systems. Advanced sensors capable of detecting DBP precursors and speciation changes coupled with AI-driven process controls can optimize membrane operation dynamically, anticipating shifts in feed water quality and adjusting parameters accordingly. This smart approach not only enhances removal performance but also extends membrane lifespan by minimizing fouling and ageing effects. Deployment of such intelligent treatment platforms represents a paradigm shift aligned with the broader Industry 4.0 and water digitalization trends, promising safer drinking water with minimal human intervention.
Looking ahead, multidisciplinary research focused on the interplay between membrane science, toxicology, environmental chemistry, and engineering will be indispensable for closing knowledge gaps in DBP management. Collaborative efforts that combine fundamental studies with pilot-scale demonstrations and field implementations will accelerate the adoption of NF and RO technologies tailored for maximal DBP rejection. Enhanced understanding of emerging DBP species, evolving disinfection practices, and climate-induced water quality changes will inform adaptive treatment solutions, ensuring resilience and protection of public health as water quality challenges intensify globally.
In summary, the removal of disinfection by-products from drinking water through nanofiltration and reverse osmosis membranes embodies a technically complex but highly impactful frontier in water treatment science. Achieving comprehensive DBP control requires synergistic optimization of membrane properties, operating conditions, and feed water management informed by a deep mechanistic understanding. Innovations in membrane materials, process monitoring, and system integration are converging to address persistent removal challenges, particularly for small, hydrophilic, neutral DBPs. As this field progresses, the promise of delivering safer drinking water worldwide through advanced membrane technologies becomes increasingly attainable, heralding a new era of public health protection and environmental sustainability.
Subject of Research: Nanofiltration and reverse osmosis technologies for the removal of disinfection by-products (DBPs) in drinking water.
Article Title: Nanofiltration and reverse osmosis technologies for disinfection by-product removal.
Article References:
Wang, L., Tang, C.Y., Hu, Y. et al. Nanofiltration and reverse osmosis technologies for disinfection by-product removal. Nat Water 3, 388–414 (2025). https://doi.org/10.1038/s44221-025-00413-y
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