Learn who determines the rules for UV system validation?
Who Determines the Rules for UV System Validation?
There are a number of different validation systems. The internationally recognised validation protocols for drinking water are:
- NSF (USA)
- USEPA(USA–as per the UVDisinfectionGuidance Manual – UVDGM)
(Interestingly, there is as yet no internationally recognised validation protocol for wastewater.)
Of these protocols, the USEPA and DVGW are the clear leaders. In general, Australian state health authorities will accept UV systems validated against an internationally accepted validation protocol, which includes either of these two protocols.
Currently, the only internationally recognised water reuse validation protocol is:
- USEPA – National Water Reuse Institute (NWRI)
This validation protocol is administered in a similar way to the UVDGM protocol for drinking water. The main difference is that the dose required to meet the validation standard is affected by the nature of the pre-treatment of the water upstream of the UV system. This introduces the concept of “log credits”.
This concept is best illustrated by way of the following example.
Let’s assume that a pathogen requires a 7-log reduction on its passage through a water reuse disinfection system. The filter system in use upstream of the UV system has been validated to provide a 3-log reduction in the pathogen (i.e. it provides a “3-log credit”), therefore the UV system is required to provide only a 4-log reduction to achieve the 7-log target. The filter system would have been validated in some way similar to the biodosimetric method described above.
Various filter media perform better than others when it comes to providing log credits. In general media filters are less efficient than membrane filters, which are in turn less efficient than, say Reverse Osmosis (RO).
So, in summary, to have a UV system work for you, you need to know the following:
1. The minimum UVT of the water.
2. The peak, instantaneous maximum flow rate of the water passing through the UV system.
3. The log reduction requirement with respect to the pathogen(s) of interest.
The consequence of overestimating the minimum UVT or underestimating the instantaneous maximum flow, while making the system cheaper, will be failed UV disinfection that is not the fault of the system. Therefore, don’t rush the specifications. Take the time to collect quality data and achieve a system that delivers that extra barrier to pathogens and reduced risk to public health.
Graham Smith. Fluidquip Australia Pty Ltd.