82-84 UV:SPN Master pages 13/9/08 01:47 Page 4
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2 radiation from the medium-pressure
UV lamp induced TOC removal, which
may be the result from its partial
mineralisation This is correct says
Hanovia and also explains why UV
should lead to reduced THM’s
3 UV radiation increased the level of total
THMs, particularly CHCl3 and CHBrCl2, but
removed CHBr3 and CHBr2Cl. However,
TTHM levels were lower than those
allowed by the WHO for drinking water.
The additional formation of CHCl3 and
CHBrCl2 may be explained by the increase
in active chlorine and by radicalising
mechanisms initiated by UV radiation
Hanovia claims studies have also shown
that UV reduces THMs (see news
announcement from last year below). The
reality is that pool chemistry is complex
and THM formation is a combination of
bather load (i.e. organic load) and chlorine
levels. As UV reduces organics and allows
lower chlorine, it should mean lower
THMs. Any pool with high organics and
high chlorine will have THMs. This was
demonstrated clearly by the tests
mentioned in the announcement below –
when the chlorine dosing equipment products of chlorination, but is also an disinfection – and this is where some of
failed, the pool switched to manual effective disinfectant in its own right, which the problems arise with those who doubt
dosing – chlorine levels increased and means pool operators can drastically the full effect of the UV treatment.
THMs increased dramatically. reduce chlorine usage (commonly down to Chloramines are formed when free
The impact of the changes in France as little as 0.5ppm). chlorine reacts with sweat or urine in pool
come at a time when sales of ultra violet Virtually no microorganisms are immune water. Trichloramines in particular are
systems for the UK’s swimming pools are to UV, even chlorine-resistant pathogens. It powerful irritants which are responsible for
set for another record year. It’s now an also significantly reduces the need for eye and respiratory complaints and the
established and accepted method of water backwashing and dilution, saving unpleasant ‘chlorine smell’ commonly
treatment for the smallest to the largest considerable costs for pool operators. associated with indoor pools. Chloramines
indoor pools. Although the need for chlorine is are also corrosive and in time can lead to
UV system suppliers claim it not only greatly reduced with UV, small amounts damage to pool buildings and structures
destroys chloramines, the unpleasant by- are still needed to ensure residual such as ventilation ducts. spn
LEISURE CENTRE TESTS SUPPORTS THM REDUCTION
Independent tests carried out last year at pool water samples for TOC, THMs, transmission values. Chlorine reacts with
a UK leisure centre showed a dramatic active/free chlorine and TDS (total dissolved organic material to form combined
reduction in TOC (total organic carbon), solids) before and after the installation of a chlorine, so lower organics would result
THMs (trihalomethanes) and combined UV water treatment system. in less combined chlorine, lower
chlorine in pool water following the In all cases, there was a significant absorbance, and therefore higher
installation of a Hanovia medium reduction of TOCs, THMs, combined transmission.
pressure UV system. chlorine and TDS post-UV. Transmission “The results of the analysis indicate
The tests were carried out by WRK values were higher post-UV, indicating a that the medium pressure UV system at
Design and Services Limited, an reduction in suspended organic material Lightwaves Leisure Centre was
independent chemical engineering (with correspondingly lower absorbance) as beneficial in reducing the TOCs and
consultancy at the Lightwaves Leisure a result of UV. The lower combined THMs to very low levels (~ 25 µg/litre)
Centre in Wakefield. chlorine levels also indicated lower levels up to 14 days after installing the UV
The objectives were to analyse swimming of organic material, matching the higher system.”
“WHEN UV IS USED WITH CHLORINATED WATER, IT IS
EFFECTIVE IN BREAKING DOWN COMBINED CHLORINE,
AS WELL AS SOME FREE CHLORINE, BUT THAT CREATES
BY-PRODUCTS, INCLUDING THMS, WHICH ARE
RECOGNISED CARCINOGENS”
84 swimming pool news OCTOBER 08 Digital edition available at www.swimmingpoolnews.co.uk
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