By Thomas M. Lachocki, PhD and Rose M. Lyda, MPA
Like a good relationship, education and experience go hand in hand. Education is based on data, and applied science, which equals experience, informs education. Experience in the water chemistry of aquatics is no different—applied science enhances aquatic education.
Combined chlorine and break-point chlorination
The advantage of utilizing education and experience in tandem is illustrated by one of the most commonly taught pool and spa water chemistry topics: combined chlorine and break-point 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 briefly reviews the two principles of combined chlorine and break-point chlorination. 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) are present in the water, free chlorine will quickly break the hydrogen-to-nitrogen (H–N) bond and form a chlorine-to-nitrogen (Cl–N) bond. 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.
The characteristics of chloramines are significant: they do not react as well as free chlorine, do not serve as disinfectants and do not appear in a free-chlorine test, commonly called the DPD1 test. What raises concern about these characteristics is that trichloramine is irritating in the water and is the primary contributor to the noxious, chlorine-like odor we smell by swimming pools. Chloramines are detected, however, when another reagent is added in a DPD3 test that measures total chlorine. Combined chlorine is then calculated by subtracting free chlorine from total chlorine: total chlorine – free chlorine = combined chlorine
It is commonly taught that chloramines, or combined chlorine, are destroyed through break-point chlorination, increasing the free-chlorine level to 10 times the combined chlorine level. The chemical reaction associated with break-point chlorination is the chlorination of ammonia to form monochloramine, dichloramine and then trichloramine. Trichloramine further breaks down to form harmless nitrogen gas and chloride ion:
Advancing education through experience
Experience and education concur on the practice that total chlorine and free chlorine can be tested, and that chloramines in swimming pools are irritants and ineffective disinfectants; science supports the ability of break-point chlorination to destroy ammonia-based chloramines. There is a common experience, however, that indicates a flaw in combined chlorine and break-point education. Water, which time after time has received adequate free chlorine to achieve break-point chlorination, should be free of combined chlorine; but, when the water is tested, combined chlorine remains. If education was correct, after break-point chlorination, the combined chlorine would be undetectable. Actual experience, on the other hand, indicates users continue to sense and smell nitrogen trichloride in the air above the pool.
The scientific method directs that in the presence of contradictory evidence, a hypothesis must be abandoned or modified to support the available evidence. In the example of chloramines, if break-point chlorination is performed and combined chlorine is still detected, ammonia cannot be the sole contributor to the formation of combined chlorine. Subsequently, the hypothesis has been modified to address another factor contributing to the presence of combined chlorine and the production of nitrogen trichloride: organic chloramines.
Understanding organic chloramines
Organic chloramines have been identified as negatively impacting the swimming-pool water and surrounding air. The most common organic chloramine comes from urea. Free chlorine will break urea’s nitrogen to hydrogen (N–H) bond and form a nitrogen to chlorine (N–Cl) bond, similar to free chlorine’s reaction with ammonia:
The difference between ammonia and urea’s chemical reaction to free chlorine is based on urea’s unique structure. Urea has nitrogen-to-carbon (N–C) bonds; ammonia has only nitrogen-to-hydrogen (N–H) bonds. The N–C bond takes days or even weeks to break down, depending on the free-chlorine concentration. Consequently, urea breaks down more slowly, producing ammonia at low levels over time. The subsequent chlorination of ammonia produces trichloramine, which irritates swimmers’ eyes and membranes and evaporates to create an offensive odor in the area nearby.
Combining education and experience to address combined chlorine
Education leading to prevention is key. Although perspiration cannot be prevented, water contamination from perspiration, skin cells and cosmetics can be reduced by showering before entering the water. With urine being the primary source of urea in pools, collaborative consumer education can continue to prevent pee in the pool. In addition to prevention, while not the most environmentally friendly solution to reducing and eliminating chloramines, water replacement guarantees the reduction of contaminants. Even partial water replacement is part of the European DIN standards. Other oxidization systems, such as UV, ozone or monopersulfate may also provide some benefits.
The hypothesis that organic chloramines contribute to the presence of combined chlorine in air and water has been substantiated by National Swimming Pool Foundation-funded research, which is published in scholarly journals and presented at the annual World Aquatic Health™ Conference (WAHC). The WAHC 2018 will feature Purdue University’s Professor Ernest ‘Chip’ Blatchley III, PhD, further exploring the chemistry between water contaminants, such as urea and the reduction of noxious organic chloramines.
The WAHC will be held October 10-12, in Charleston, SC and will be broadcast to six additional WAHCity locations throughout the US and Canada. Visit wahc.org for more information.
NSPF training and materials reinforce that both experience and education are vehicles for the industry to utilize in solving the problem of organic chloramines. Certified Pool & Spa Operator® (CPO®) certification equips pool operators with knowledge to address the issue. Advanced Service Technician™ training enables service technicians to identify and treat water for chloramines, as well. Visit nspf.org for more course information.
Education and experience have limits when applied in isolation; the combination of the two can advance industry practices. Experience has taught that poor water and air quality are not explained by common beliefs in the industry. Education, based on good science, has taught that new approaches must be taken to address the issue. The better the industry understands combined chlorine, the more likely solutions will be created for water quality.
About the authors
Tom Lachocki, PhD, proudly serves as CEO of the National Swimming Pool Foundation® (NSPF®), a position he has held since 2003. Prior to that, he held positions in research and business development in recreational water treatment, surfactants, lubricants, catalysts and solvents. Lachocki has also held leadership positions in various trade association committees and membership on boards of directors. An inventor on eight patents, he earned his PhD in chemistry from Louisiana State University and his BS Degree from Lock Haven University. Rose M. Lyda, MPA, is Director of Marketing for the foundation. An elementary school teacher by education, she has taught in Oregon, Oklahoma and Moscow, Russia. She earned a Master of Public Administration Degree and is engaged civically in her local community in the non-profit, private and public sectors. The combination of her education and experience gets put to daily use in directing NSPF’s marketing and product development.
About the organization
NSPF believes everything it does helps people live happier and healthier lives. Whether encouraging more aquatic activity, making pools safer or keeping pools open, the organization believes it makes a difference. Founded in 1965 as a 501(c)(3) non-profit and located in Colorado Springs, CO, NSPF proceeds go to fund education, research and to help create swimmers. For a full listing of the NSPF family of products, programs and services, visit nspf.org.