The purification of the water of swimming baths.

  • Great Britain. Ministry of Health
Date:
1929
Catalogue details

Licence: Public Domain Mark

Credit: The purification of the water of swimming baths. Source: Wellcome Collection.

    41/72 (page 31)
    Water drawn from a swimming bath which has been used by bathers, generally contains bacteria in large numbers, and it is useless to hope that they can be eliminated, or even reduced to reasonably safe limits by filtration alone, under conditions which are possible at a bath establishment. Continuous and effective chlorination has to be relied on to destroy these bacteria, and, if the chlorination breaks down, the risk of infection to bathers (which has been fully considered in the early part of this note) is present. The fact that chlorine treatment has, in any case, to be relied on to destroy the bacteria which the filters, designed for baths on lines now considered prac- ticable, cannot eliminate, has led to high speeds of filtration up to 450 gallons per square foot per hour being used. It would appear that the limit of speed (in the absence of definite knowledge on the subject) should be such as to yield a clear water having a definite standard of clarity at all times, and under all conditions of bathing. It may be of interest to state that the American Water Works Association, in their standard specification (1925), for pressure filters using a coagulant, lay down filtration rates for swimming pools of 2 to 4 U.S. gallons per square foot of sand area per minute. These rates are practically equivalent to speeds of 100 to 200 Imperial gallons per square foot of sand area per hour. In this country the majority of makers favour a rate of 200 gallons per square foot per hour or less, but competition is having the effect of increasing rates above 200, and it is not yet clear what is the maximum rate permissible. It is unfortunate that this question has not been settled by practical research because it is evident that economy of working (1.e., In power, chemicals, washwater and attendance) and speed of filtration must be related, while the important question of the maintenance of a standard of clarity in the filter effluent at all times has hitherto received scant attention. This subject is discussed later under the heading of Guarantees. Re -heating. The best method of re-heating is by the use of a calorifier, though it is sometimes done by the injection of steam. In the latter case, if exhaust steam from an engine be used in direct contact with the water, perfect elimination of oil is essential. From the point of view of economy it is one of the great virtues of the continuous. purification method that the loss of heat involved is comparatively small, so that re-heating is inexpensive compared with the cost of the large quantity of fuel which is required, when operating a bath on the fill-and-empty system, to heat the whole volume of the fresh water from the temperature (about 50° F.) at which it enters the bath from the mains to the desired temperature of about V7 phe aa