Introduction The ultraviolet (UV) disinfection industry has experienced rapid growth over the past 20 years. During this period, the development of UV technology has become a perfect example of industrial investment meeting market demands for efficient, low-cost, and environmentally friendly disinfection technologies. With the application of UV disinfection technology in water treatment plants, treating over three billion liters of water worldwide daily, it proves that UV technology is no longer an "emerging" technology, but a widely adopted technology by engineers to protect human health. UV technology continues to evolve and grow, with new products and applications constantly being discovered. This article briefly introduces the development trends of UV technology. Industry Maturity Almost all leading UV technology companies, such as Berson, Hanovaia, Trojan, and Wedeco, belong to diversified industrial and financial groups such as Halma, Danaher, and ITT. These groups, while stabilizing the market, can provide specialized product lines, meaning that these subsidiaries must generate or maintain profits, thus validating the earlier acquisitions. The establishment of corresponding UV standards and certification standards for new UV reactor designs indicate that this technology will become a mainstream application. Over the past 20 years, UV disinfection equipment has achieved double-digit sales growth, and the total annual sales of UV disinfection products worldwide will soon exceed 4 billion RMB (approximately 550 million USD). New Technologies The use of fluid dynamics software modeling methods has greatly improved manufacturers' predictability of the treatment levels and capabilities of their products, giving them greater confidence. System selection is no longer magic, as manufacturers can collaborate with design engineers to more accurately predict treatment levels and capabilities under different water quality and flow rate conditions. UV equipment manufacturers will soon be able to use this tool to optimize UV ​​dosage within reactors and reduce energy consumption. After manufacturers develop and improve reactors, they adopt a series of certification protocols to validate the design, such as the European DVGW and NORM certifications (drinking water), and the NWRI certification (wastewater), and the USEPA certification. In the coming years, more optimized reactors will be produced and deployed. Traditional UV technology will also be further improved. Medium-voltage lamps will see improvements in energy efficiency, lifespan, and power density, and their integration with quartz sleeves can extend lamp life to over 12,000 hours. This technology is compact and requires little floor space, making it particularly attractive to designers and users, especially when renovations or automatic cleaning of the sleeves is required. The output power of low-voltage, high-intensity lamps will also be further increased, perhaps reaching 1kW, significantly reducing system footprint and simplifying maintenance. Lamp arrangement is also a crucial issue for low-voltage UV equipment, as a single system can use thousands of low-voltage UV lamps. New UV light sources, such as light-emitting diodes (LEDs), are considered the technology of the future. LEDs offer the advantage of concentrating all electrical energy within a narrow wavelength range of 260nm-262nm, and possess high efficiency and a long lifespan (reportedly exceeding 100,000 hours). Because they are point light sources, they are not limited by traditional cylindrical designs. This promising technology also suffers from limitations in lamp power driving, thus remaining largely conceptual. Other lamp types, such as excited-state molecular lamps, offer advantages such as mercury-free operation and no preheating required, but are currently limited by low efficiency and high rectifier costs. Furthermore, excited-state molecular lamps are often more toxic than the products they replace. UV intensity sensors have also seen significant improvements over the past decade, with stable, reliable, and accurate germicidal sensors now available, along with a well-established certification system. Additionally, data from sensors, flow meters, and other monitoring devices can help manufacturers improve control systems and optimize equipment performance. They can also communicate with operators at the control center via an operating platform. Increasing amounts of microbial D10 values* are being understood, and this list is constantly being updated. Most notably, research has confirmed that very low doses of UV light can kill Cryptosporidium and Giardia, but several viruses with extremely high D10 values ​​have also been discovered. With the advancement of ultraviolet (UV) technology, more microorganisms will be added to the existing D10 value list. Reactivation is a key focus in UV technology—some microorganisms, after their DNA is exposed to UV light, exhibit a remarkable characteristic: they can act on damaged areas and complete repair processes. DNA repair can occur in closed (dark) systems or in open systems with light (photoreactivation). The UV dose and type of UV lamp determine whether a reactivation reaction can occur; low-pressure (single-wavelength) UV lamps are more likely to produce photoreactivation than medium-pressure (multi-wavelength) UV lamps. More research efforts are needed in the field of photoreactivation, and new advancements are likely in the next 5 years. Extensive research is also underway on UV disinfection, particularly on how to remove common substances in water, such as chlorine, bromides, nitrates, ozone, NOM**, and iron. Ordinary UV disinfection doses are insufficient to significantly remove these substances. Research on other foreign elements in water is also ongoing. Emerging Markets The largest potential market for UV disinfection technology is in the drinking water sector. Ultraviolet (UV) technology has been recognized as a suitable disinfection method for killing Cryptosporidium and Giardia, particularly for surface water and other susceptible water sources. Since 1997, market growth has slowed slightly due to several factors, including uncertainty regarding the UV sensitivity of Cryptosporidium and Giardia, the lack of a standardized framework for UV disinfection technologies, a lack of guidelines and instructions, a lack of case studies and engineering knowledge regarding UV disinfection in drinking water plants, the overall conservatism of the water industry, and the uncertain outcomes of several lawsuits concerning the use of UV technology to kill Cryptosporidium and Giardia. All these issues, whether resolved or underway, will pave the way for rapid market growth. Another promising market for UV technology is the application of recycled water and grey water in irrigation. Wastewater reuse technology is already common in the southwestern United States and other regions facing severe freshwater shortages, such as northern China, southern Europe, the Middle East, and North Africa. For this market, UV technology has proven effective when using higher UV doses than those used in drinking water systems. Strict co-occurrence standards similar to drinking water standards will be crucial for evaluating these critical applications. Preventing photoreactivation reactions will also be a key factor in treatment and evaluation. Another emerging market for UV technology is the application of UV-disinfected water to aquifer restoration and groundwater storage. This application includes injecting deeply treated wastewater into aquifers to supplement drinking water supplies. The states of California, Texas, and Florida in the United States are beginning to consider this technology, and interest in this application is growing in other parts of the world. UV technology can also act as an oxidant; using UV technology alone, or in combination with hydroxyl radicals, can destroy contaminants in water. This technology has been successfully applied in groundwater replenishment, industrial wastewater treatment, and drinking water treatment. It is worth mentioning that several large-scale strong oxidation projects in the United States have adopted ultraviolet (UV) technology for the oxidation treatment of NDMA**, MTBE**, pesticides, odor compounds, and chlorinated solvents. In summary, the UV technology industry has matured considerably over the past decade and is now being standardized and promoted by mainstream water treatment companies. Traditional UV technology has been field-tested and has achieved excellent results in widespread applications. With the reduction of uncertainties in standards, royalties, processes, and engineering, the acceptance of UV technology is expected to increase rapidly over the next 20 years. While the design of traditional UV products relies heavily on fluid dynamics (CFD) software, it will be used as a routine calibration tool in future designs. Improvements to traditional lamps, UV intensity sensors, and controllers will continue over the next decade. New technologies such as LED lamps and microwave lamps, with their advantages in efficiency, footprint, and energy consumption, will provide significant room for future technological innovation. Currently, especially with new technologies offering higher efficiency and lower energy consumption, the demand in the drinking water market is expected to grow rapidly. Other applications, such as wastewater reuse and aquifer storage and replenishment, have a smaller market and slower growth rate compared to drinking water, but remain attractive. The application of UV technology in strong oxidation projects is still in its early stages and is largely constrained by energy consumption. This field will experience rapid growth if new, more energy-efficient technologies emerge. Microbial D10 value*: The UV dose required to reduce the population of a microorganism to 99% after treatment. UV dose is logarithmically related to the kill rate. For example, if a kill rate of 99.99% is required for a specific microorganism, the required dose is the D10 value multiplied by 4. NOM**: Natural organic compound; NDMA**: Nitrosaminoglycans; MTBE**: Methyl tert-butyl ether.