Ultraviolet light-emitting diode technologies in water disinfection

Waterborne pathogens and chemical contaminants continue to pose a major global public health challenge, underscoring the need for effective and environmentally sustainable disinfection technologies. Conventional mercury-based ultraviolet (UV) systems, although widely applied, are associated with environmental and operational drawbacks. Ultraviolet light-emitting diodes (UV-LEDs) have recently been emerged as a promising alternative, offering tunable wavelengths, low energy consumption, operational flexibility, a cost-effective solution, and mercury-free design. This review critically examines recent advances in UV-LED-based water disinfection technologies, evaluating mechanisms of microbial inactivation, innovations in reactor design, and synergistic integration with advanced oxidation processes (AOPs). Special emphasis is given on wavelength-specific disinfection efficiency, hybrid treatment systems, and validation across diverse water matrices, including drinking water, wastewater, and industrial effluents. Challenges such as the formation of disinfection by-products (DBPs), turbidity effects, and techno-economic limitations are analyzed in detail. Furthermore, emerging directions, including smart UV-LED reactors, hybrid photonic systems, and decentralized water treatment units, are discussed in the context of global sustainability goals. Overall, UV-LED-based disinfection technologies demonstrate substantial potential to achieve high microbial inactivation while minimizing environmental impacts. Future opportunities lie in enhancing energy efficiency, integrating renewable energy sources, and developing multifunctional reactors to improve treatment efficacy against a broader spectrum of contaminants.