The significance and role of ultraviolet disinfection in water treatment

The significance and role of ultraviolet disinfection in water treatment

With economic development and improved living standards, the government and the public are increasingly prioritizing drinking water safety. my country's drinking water quality standards have undergone several revisions in recent years. The latest "Standard for Drinking Water Quality" (GB 5749-2022) sets higher safety requirements for drinking water quality, particularly regarding disinfection byproducts and upper limits for residual chlorine, which pose certain challenges to traditional chlorine disinfection processes. Consequently, cities such as Shanghai, Shenzhen, Suzhou, and Fuzhou have also established more stringent targets or local standards for high-quality or premium drinking water. Ultraviolet disinfection, as a physical disinfection method, has become an important option for improving water supply safety under these new conditions due to its broad-spectrum bactericidal properties, the absence of chemical agents, and the generation of no disinfection byproducts.

Chlorine-resistant microorganisms may exist in drinking water. In addition to well-known chlorine-resistant microorganisms such as Giardia lamblia and Cryptosporidium, studies have shown that chlorine-resistant microorganisms such as Sphingomonas, Pseudomonas, Cereus, Acinetobacter haemolyticus, Bacillus fuscae, Bacillus alvei, Legionella, and Thiophages are commonly found in the outlet water and water supply networks of Chinese water plants. Some of these chlorine-resistant microorganisms are opportunistic pathogens. Effectively inactivating these chlorine-resistant microorganisms requires a significant increase in the CT value of chlorine, making chlorine disinfection uneconomical or even impossible to implement, and significantly increasing the risk of excessive disinfection byproducts. Strictly speaking, the traditional single-unit chlorine disinfection model presents a safety vulnerability. Once a chlorine disinfection unit fails, the water plant's microbial safety barrier is completely lost. Therefore, from the perspectives of biological and chemical safety, a multi-barrier disinfection strategy and concept is essential for improving water supply safety. This concept has now been widely accepted and practiced in urban water plants in North America and the European Union. Ultraviolet disinfection has become an indispensable and even a key part of the combined disinfection method because it can meet both biological and chemical safety requirements.

Current Application of Ultraviolet Disinfection in my country's Water Treatment

In recent years, the multi-barrier disinfection concept and ultraviolet disinfection technology have gradually gained recognition and promotion in my country's water supply sector, with initial application in urban water plants. According to incomplete statistics, over 60 large-scale water plants in China currently employ ultraviolet disinfection processes, with a treatment capacity of 10 million m³/day. Among them, the Tianjin TEDA Waterworks Phase III project, completed in 2009, and the Shanghai Linjiang Waterworks ultraviolet disinfection process became the first water plants in my country to implement ultraviolet disinfection as a primary disinfection process. The Beijing Guogongzhuang Waterworks, completed and operational in 2014, uses a combined ultraviolet and chlorine disinfection process, becoming a demonstration project for a major national project under the 12th Five-Year Plan. The ultraviolet disinfection process employed by the Lasanajin Waterworks, built in 2017, is the largest project to utilize domestically produced equipment.

Practice has shown that ultraviolet disinfection as a primary disinfection process can improve the microbiological safety of water quality, appropriately reduce the CT value of subsequent chlorine disinfection processes, and, to a certain extent, reduce the formation of disinfection byproducts and the toxic effects of water, playing a positive role in ensuring water quality safety. Related research has also shown that UV combined with chlorine disinfection improves water quality safety in pipe networks compared to traditional UV disinfection.

In practice, water supply plants place greater emphasis on the disinfection performance and quality of UV disinfection equipment than sewage treatment plants, as this is essential for ensuring water supply safety. When selecting and purchasing UV disinfection equipment, in addition to industry-standard biological testing and dosing verification, my country's water-related approval is also a key certification requirement. In some cities, local health and quarantine authorities explicitly require that water supply plants use equipment and materials with domestic approvals before they can begin supplying water. my country's newly revised "Outdoor Water Supply Design Standard" (GB 50013-2018) has also updated its standards by adding relevant content on UV disinfection processes, providing positive guidance and promoting the application of UV disinfection technology in my country's urban water supply plants. It is understood that an increasing number of cities are considering or designing UV disinfection processes for drinking water, and it is foreseeable that UV disinfection will play a more important role in improving the quality and safety of my country's urban water supply.