It is interesting how many industrial and academic facilities continue to
use UV as their prime source of water "sanitization". Having been
involved in manufacturing plant audits for a number of years, I've
observed several things in water systems used for chemical and biological
systems, to wit:
1) Despite the use of UV or the use of periodic maintenance programs,
many water systems still use polyvinyl chloride as the piping due to its
inexpensive nature. This material harbors sanitization-resistant
biofilms, which, even after sanitization and flushing, still will shed
plenty of CFUs into the water.
2) As Dr Jensen noted, poor maintenance of the UV chamber does indeed
allow post-filter biofilms to form. These films, usually well past the
sanitizer, reverse osmosis unit and the ion exchange beds, are difficult
to eradicate and can only be removed by replacing the piping with fresh
material. Success of remedial efforts are mixed but usually fail.
3) Most critical water systems that work are constructed of stainless
steel (which requires some maintenance). Some new systems are being
constructed of PFA Teflon, which appears to be easier to maintain.
Stainless steel constructs are expensive, and still require some downtime
4) The effectiveness of UV appears to be dependent upon the intensity of
UV light, the cleanliness of the UV chamber, and the flow of the water
through the cuvette (residence time).
I have been evaluating biofilm removal for a client company for over a
year, testing several novel materials for ease of film removal under
relatively gentle sanitation conditions, in comparison whth the standard
plastics and stainless steel. We're still gathering data but several
materials do have some promise in critical applications.