Mechanism of UV Disinfection

UV light radiation is a widely accepted method for accomplishing disinfection of treated water. Its germicidal action is attributed to its ability to photochemically damage links in the DNA molecules of a cell, which prevents the future replication of the cell, effectively “inactivating” the microorganism.

UV radiation is most effective in the region of the electromagnetic spectrum between 230 nm and 280 nm (referred to as the UVC range); this corresponds to the UV absorbance spectrum of nucleic acids. The optimum germicidal wavelengths are in the range of 254-265 nm. 

We carefully look at dose delivery through bioassays with different surrogate tests of the dose delivery of the disinfection system under different combinations of source water and UV transmittance (UVT) at 254 nm. In addition, we are equally dedicated to the longevity of our products, paying special attention to: lamp irradiation, lamp driver optimization, and non fouling of lamp sleeve through proper maintenance (ie. keeping the quartz surface in a clean state thereby efficiently transmitting the UV energy to the liquid). We optimize system Reliability by using advanced monitors, alarms, and/or indicators which adjust delivered dose according to the change in the environmental conditions (fluid temperature and flow rate), quartz fouling (attenuation factor for quartz transmittance) and lamp aging. 

The key design consideration of UV systems is efficient delivery of the germicidal UV energy to the fluid and to the organisms. The total germicidal efficacy is quantified as the “UV dose”. 

The last component of the system is the UV reactor design. Theoretically; the delivery of UV radiation to the fluid can be computed mathematically  as  the product of the UV radiation intensity (I, W/cm 2 ) and the retention time (t, seconds) is equivalent to the UV dose which is experienced by a population of organisms. The geometry and hydraulic behaviour of the system must be well-characterized. 

Ideally, all elements entering the reactor should be exposed to all levels of radiation for the same amount of time. In fact, non-ideal conditions when there is a distribution of retention times in the reactor due to advection dispersion and to mixing in the reactor. The degree to which the reactor strays from ideal plug flow directly impacts the efficiency of dose delivery in the system.  

CFD modeling is an effective technique which is used to address the problem as long as it includes all submerged components of a real reactor, such as quartz-sleeve(s) mounting hardware, wiring, baffles, sensors, and cleaning systems that influence the flow path of the water parcels.