I. Advantages of Ultraviolet Devices:

　　1The problem of the two parasites (Cryptosporidium and Giardia). Abroad, drinking water is generally used. The discovery of Cryptosporidium in water has become the main reason for the application of ultraviolet devices (ultraviolet light can kill cryptosporidium). Although drinking water habits have protected public health, improving the quality of water supply and providing direct drinking water will be a trend. Currently, the new water quality standards have included Cryptosporidium and Trichomonas.

　　2The problem of by-products of ultraviolet devices. At present, all water sources are polluted to varying degrees. By-products are a relatively common problem and pose a significant threat to human health. For instance, trihalomethanes and haloacetic acids are carcinogens. Haloacetic acid may concentrate after boiling due to its relatively high boiling point. Ozone has produced bromate this year1month4The new by-product law of Japan and the United States has been released, revising the target values and current values of indicators such as haloacetic acid, trihalomethanes, bromate, and chlorite. Trihalomethanes are80μg/lHaloacetic acid is60μg/lBromate is10μg/lChlorite is1.0mg/lBy-products such as ozone or oxidized bromate cannot be detected in the future. In fact, the actual by-products existing in water are much more than those stipulated in the standards.

　　3Liquid chlorine has certain risks due to its ultraviolet properties. There is a risk of leakage during transportation and use. Teacher Liu joked that a good tool for terrorist activities is liquid chlorine. A liquid chlorine tank can cause tens of thousands of casualties.

　　From these three aspects, ultraviolet light does not require the addition of chemical reagents and has a good effect, thus having certain advantages.

　　Ii. Potential Disadvantages of Ultraviolet Devices and Solutions:

　　1The continuous effect of the pipeline network. The water quality standards stipulate that the pipe network should maintain a continuous effect, which is a matter of great concern to everyone. Teacher Liu mentioned that the following measures can be taken to solve the problem: First, supplement with chloramine; Chloramine has a relatively long persistence and a small by-product chain, but its effect is worse than that of chlorine and ultraviolet devices. Chlorine is commonly used in China+Chloramine. Second, in some areas of Europe with better water quality, residual chlorine is not added. They believe that a lot of by-products will be produced after chlorination. Such asAOCThe indicator is lower than10～20μg/lAt that time, no chlorine needs to be added. whenAOCThe indicators are50～100μg/lChlorine is added only when necessary. Professor Liu's research group has done a great deal of research work in this area. Research has found that despite sufficient residual chlorine, a large number of microorganisms can still be detected. However, given the current situation (the biological stability of water quality is very poor, the urban pipe network is large, the pipe network system is aging and not strictly managed), it is not very realistic not to add chlorine. But in the future, it can be achieved in some small areas with shorter pipe networks.

　　2The issue of the ultraviolet device being revived. When asked by Teacher Liu about the common concern of whether ultraviolet radiation would bring back life, he said that the principle of ultraviolet radiation is merely polymerization, which disrupts genetic abilityDNAIt cannot be replicated. Under certain lighting conditions, it will also undergo depolymerization. However, the water in the pipeline network is basically in a closed state, so there is no need to worry so much about the problem of revival. He also mentioned that even chlorination might bring microorganisms back to life due to their self-function. Therefore, the key issue is to reduce organic matter.

　　3The trend of ultraviolet devices is opposite to that of chlorine. The priority of chlorine is viruses in that order>>Protozoa, while ultraviolet light is just the opposite: protozoa>>Virus. That is, the removal effect of ultraviolet rays on viruses is poor. Especially adenovirus and rotavirus: when200mJ/cm2At that time, there was only4logThe removal of adenovirus. The standard dose of ultraviolet rays for drinking water worldwide is only40mJ/cm2. Therefore, the ideal approach is to combine chlorine with ultraviolet light, which also conforms to the concept of multi-level barriers in water quality assurance.