Treatment by using a combination of UV radiation and ozone for water purification has attracted attention. UV radiation/ozone treatment equipment is marketed by Sen Lights Corporation with the trade name 'UZON'. Its special feature is that it does not require a separate ozone generator, because it generates ozone by passing air through the UV light source and aerifying the ozone in water.
UV radiation treatment has been developed as a technique for sterilization and disinfection of various substances. Its scope of application spreads throughout the industrial fields. Recently, its application has not been restricted only to disinfection, but it has also been extended to cleaning of parts in the semiconductor and electronic industries and improving quality. In the 1950s, it was introduced in water supply disinfection in many countries in Europe, and from 2000, its usage has widely spread mainly in North America for large-scale waterworks facilities which have the capacity to supply 1 million m3 of water a day.
Disinfection (sterilization) by UV radiation takes place by stopping the growth activity by directly acting on the genes (DNA) of living things. The method of treatment involves only passing water through the equipment. The treatment time is as short as a few seconds, without generating any waste water as in the case of filtration. Thus, it is a compact piece of equipment with the main feature being that there are no residual additives or any secondary matter. Especially, the main advantage is that it does not generate toxic side products like trihalomethane, haloacetic acid or bromic acid. However, since the treated water can easily get re-polluted, the simultaneous use of disinfectant becomes essential for maintaining the sterilized condition.
In Japan, the technique of UV treatment was first introduced in water purification facilities when chlorine resistant disease-causing germs like cryptosporidium were detected. In 1996, tap water-borne cryptosporidium infectious disease occurred for the first time in Japan and with this, the Ministry of Health and Welfare (the former Ministry of Health, Labour and Welfare) mapped out its guidelines for 'Provisional measures for cryptosporidium disinfection from tap water', and the guidelines were revised in 1998 and 2001. In 2003, the Ministry enacted 'Ministerial Ordinance for Establishing Technical Standards for Water Works', in which the installation of equipment, like filtering, etc, is stipulated for water works.
However, because the water works facilities were very slow to conform to the guideline, the 'Guidelines for countermeasures against cryptosporidium from tap water' was settled afresh in 2007, incorporating the UV radiation treatment technique. This was decided based on a scientific finding that oocyst of cryptosporidium gets deactivated with a relatively low exposure dose of UV radiation. Additionally, the equipment is less expensive and simpler than filtration equipment.
External view of UZON
The performance of UV treatment equipment is denoted as the UV radiation exposure dose (mJ/cm2) expressed as the product of strength (mW/cm2) and irradiation time (sec).
According to the standard (regulation) set for UV treatment equipment in 'Guidelines for countermeasures against cryptosporidium from tap water', at least 95% of the passing water should be exposed all the time to a UV radiation exposure dose of 10mJ/cm2, which causes inactivation of 3log (99.9%) of cryptosporidium.
Against this, outside Japan, the standard value of a UV radiation exposure dose is higher. It is 40mJ/cm2 for Austria and DVGW (Germany). For USEPA (USA) it is 36 mJ/cm2, and 25 mJ/cm2 in France and the Netherlands. The reason for the variation in the provision of UV exposure doses in different regions is due to the unavailability of a uniform standard, uncertainty regarding techniques for measurement of a UV exposure dose and a difference in the point of views regarding hygiene.
Further, among the domestic manufacturers of UV treatment equipment, some have introduced foreign-made equipment following foreign standards and thus different values of a UV exposure dose have been indicated. In the future, we expect that the Japan Water Research Center or Japan UV Water Treatment Technology Association will set appropriate guidelines.
As for water purification using UV radiation, a combination of UV radiation and ozone is attracting attention. This technique generates radical seeds of higher acidity to contribute to the decomposition of hazardous trace substances in addition to disinfection. In August 2007, the International Ozone Association (IOA) and International UV Association (IUVA) organized the worldfs first international joint convention in California. The main theme was fusion of ozone and UV radiation techniques. This means that a combination of UV radiation and ozone is attracting attention as a future water treatment technique.
Further, there are reports that combined UV radiation/ozone treatment is the most effective against cryptosporidium.
We are marketing UV radiation/ozone treatment equipment under the name 'UZON'. Its special feature is that it can generate ozone by passing air through a UV light source and aerifying the ozone in water. Thus a separate ozone generator is not required. Actual application examples are scenic areas of water such as ponds or brooks, and pools. The equipment, of course, disinfects, and also decomposes (de-colorizes) organic matter generated by living things (including humans). Combined UV/ozone treatment equipment, including 'UZON', is expected to be recognized as a novel technique for water purification.