Improved water quality
through education and experience By Tom Lachocki and Rose Lyda
Trichloramine is irritating in the water and is the primary contributor to the noxious “chlorinelike” odour we smell around swimming pools
54 SPLASH! June/July 2018
L
ike a good relationship, education and experience go hand in hand. Education can be improved when it is based on data and applied science, which then equals experience. Experience in aquatic water chemistry is no different— applied science enhances aquatic education. The advantage of utilising education and experience in tandem is illustrated by one of the most commonly taught pool and spa water chemistry topics: combined chlorine and breakpoint chlorination. Field experience has proven that industry education on these topics is inadequate and can be improved. Fortunately, new science has helped advance education that more reasonably explains our experiences. To understand where chemistry education can be improved by the application of experience, this article will briefly review the two principles of combined chlorine and break-point chlorination.
Combined chlorine
Education and experience have established the importance of testing for free chlorine and total chlorine, and calculating combined chlorine. Measuring the free chlorine level serves to indicate the amount of active disinfectant in the water, and satisfies the product label requirement for free chlorine residuals. Free chlorine is commonly defined as the amount of hypochlorous acid (HOCl) and hypochlorite ion (OCl-) present in the water. When nitrogen-containing molecules like ammonia (NH3) is present in the water, free chlorine will quickly break the hydrogen-tonitrogen bond (H-N) and form a chlorine-tonitrogen bond (Cl-N). For example, ammonia (NH3) will react with free chlorine to form monochloramine (Cl-NH2). Chloramine is the term used for chemicals with this nitrogen-chlorine bond.