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33
Swimming baths
The following is a report prepared by the Baths Superintendent
on the use of breakpoint chlorination at the Council's baths:—
The breakpoint process was first introduced at the Open Air Pool,
Bellingham, in the spring of 1948, and resulted in an immediate improvement
in the condition of the water. It was, however, soon realised
that an alteration to the circulating system would have to be made.
This pool, 140ft. long, is provided with two inlets at the shallow end.
Effluent at the inlets would contain 2 parts of chlorine per million, but
by the time the freshly chlorinated water reached the deep end of the
pool the chlorine content would have diminished to 0.5 parts per
million. This condition was remedied by providing an additional inlet
at the deep end. During the summers of 1949 and 1950, the standard
of water, physically, chemically, and bacteriologically, was first class.
The higher chlorine content affected the alkalinity (pH value)
of the water and it was necessary to inject more alkali to neutralise
the extra acidity created by the addition of the extra chlorine. It also
soon became apparent that the reagents previously used in determining
the amount of chlorine residual and the pH values did not adequately
fulfil the requirements with this new process of water conditioning.
Neutral ortho-tolidine used for determining the residual chlorine
in the marginal method was replaced by acid ortho-tolidine and sodium
arsenite, and instead of one test, three tests are taken to ascertain the
correct amount of free chlorine in the sample of water. The phenol
red solution used to indicate the pH value in the former treatment, did
not give an accurate reading in the higher values, and was replaced by
diphenol purple. It also became necessary to add sodium thiosulphate
to dechlorinate the sample before testing, to prevent the bleaching
effect the superchlorinated water would otherwise have had on the
indicator. A keener watch had to be kept on the pH value because if
this was allowed to fall below 7.2 irritation to bathers' eyes resulted.
At the Open Air Pool we have not been troubled with offensive odours.
Breakpoint chlorination was commenced in the covered Baths in
August, 1949. Full use was made of the experience gained at the Open
Air Pool, but the production of nitrogen trichloride, peculiar to covered
baths, giving rise to offensive odours, was soon manifested. A lower
water temperature and making the best use of the ventilation system did
much to keep the development of this trouble to tolerable limits. Whilst
low water temperature (72° to 74°F.) and adequate ventilation do
much to eliminate a concentration of nitrogen trichloride, an open mind
and watchful eye are being kept for any treatment that will neutralise
this odour trouble.
The additional alkali needed to maintain the correct pH value is
obtained by injecting sodium carbonate in the bath water circulating
pipeline near to the point where the chlorine solution is added, but in
spite of this arrangement there was a tendency on occasions for the water
in the pools to develop a milky opalescence. This was due to the
sodium carbonate acting as a softening agent resulting in a precipitation
of calcium carbonate.