Problems of bromate formation when ozonating water containing small amounts of bromide are well known. Even concentrations of bromate as low as 10 millionths of a gram per litre can be considered carcinogenic. However, ozone is very efficient in killing unwanted microorganisms in water.
Alternatives are few and far between, but some new technology has appeared on the scene which may change this. UV has been used in the past, but still has shortcomings, particularly for destruction of spore-forming microorganisms in high solids water. However, the synergistic effect of combining UV with ultrasound opens up new possibilities.
The ultrasonic emitter, located directly in the UV radiation chamber, causes the formation of minute super-heated steam voids in the water under low pressure. These voids form around spores, bacteria and cysts. When the voids collapse, zones of extreme temperature and pressure are created destroying microorganisms in close proximity.
At the same time, free radicals, hydrogen peroxide and other active species are generated in the process. They provide a significantly enhanced disinfection and photochemical oxidation of microorganisms compared with conventional UV treatment. An added bonus is that the ultrasound action prevents any build up of inorganic deposits on quartz sleeves and chamber walls, thereby maintaining optimum UV intensity.
Bromates are not formed, therefore removing the dangers associated with ozonation techniques.