Dynamic Behavior Of Water And Air Chemistry In Indoor Pool Facilities
Creators: name: Lee, Lester Ting Chung
Publisher: name: Purdue University Graduate School
Year: 2021
Subjects: Atmospheric composition, chemistry and processes
Environmental engineering not elsewhere classified

description: Swimming is the second most common form of recreational activity in the U.S. Swimming pool water and air quality should be maintained to allow swimmers, pool employees, and spectators to use the pool facility safely. One of the major concerns regarding the health of swimmers and other pool users is the formation of disinfection by-products (DBPs) in swimming pools. Previous research has shown that volatile DBPs can adversely affect the human respiratory system. DBPs are formed by reactions between chlorine and other compounds that are present in water, most of which are introduced by swimmers, including many that contain reduced nitrogen. Some of the DBPs formed in pools are volatile, and their transfer to the gas phase in pool facilities is promoted by mixing near the air/water interface, caused by swimming and pool features. Swimming pool water treatment processes can play significant roles in governing water and air quality. Thus, it is reasonable to hypothesize that water and air quality in a swimming pool facility can be improved by renewing or enhancing one or more components of water treatment. The first phase of the study was designed to identify and quantify changes in water and air quality that are associated with changes in water treatment at a chlorinated indoor pool facility. Reductions of aqueous NCl<sub>3 </sub>concentration were observed following the use of secondary oxidizer with its activator. This inclusion also resulted in significant decreases in the concentrations of cyanogen chloride (CNCl) and dichloroacetonitrile (CNCHCl<sub>2</sub>) in pool water. The concentration of urea, a compound that is common in swimming pools and that functions as an important precursor to NCl<sub>3</sub> formation, as well as a marker compound for introduction of contaminants by swimmers, was also reduced after the addition of activator. The second phase of this study involved field measurements to characterize and quantify the dynamic behavior of indoor air quality (IAQ) in indoor swimming pool facilities, particularly as related to volatile compounds that are transferred from swimming pool water to air. Measurements of water and air quality were conducted before, during, and after periods of heavy use at several indoor pool facilities. The results of a series of measurements at different swimming pool facilities allowed for examination of the effects of swimmers on liquid-phase DBPs and gas-phase NCl<sub>3</sub>. Liquid-phase NCl<sub>3</sub> concentrations were observed to gradually increase during periods of high swimmer numbers (<i>e.g.</i>, swimming meets), while liquid-phase CHCl<sub>3</sub> concentration was nearly constant in the same period. Concentrations of urea displayed a steady increase each day during these periods of intensive use. In general, the highest urea concentrations were measured near the end of each swimming meet. Measurements of IAQ dynamics during phase 2 of the study demonstrated the effects of swimmers on the concentrations of gas-phase NCl<sub>3 </sub>and CO<sub>2</sub>, especially during swimming meets. The measured gas-phase NCl<sub>3</sub> concentration often exceeded the suggested upper limits of 300 µg/m<sup>3</sup> or 500 µg/m<sup>3 </sup>during swimming meets, especially during and immediately after warm-up periods, when the largest numbers of swimmers were in the pool. Peak gas-phase NCl<sub>3</sub> concentrations were observed when large numbers of swimmers were present in the pools; measured gas-phase concentrations were as high as 1400 µg/m<sup>3</sup>.<sup> </sup>Concentrations of gas-phase NCl<sub>3</sub> rarely reached above 300 µg/m<sup>3</sup> during regular hours of operation. Furthermore, the types of swimmers were shown to affect the transfer of volatile compounds, such as NCl<sub>3</sub>, from water to air<sub> </sub>in pool facilities. In general, adult competition swimmers promoted more rapid transfer of these compounds than youth competition swimmers or adult recreational swimmers. The measured gas-phase CO<sub>2</sub> concentration often exceeded 1000 ppm<sub>v</sub> during swimming meets, whereas the gas-phase CO<sub>2</sub> concentration during periods of non-use of the pool tended to be close to the background (ambient) CO<sub>2</sub> concentration or slightly more than 400 ppm<sub>v</sub>. This phenomenon was largely attributed to the activity of swimmers (mixing of water and respiratory activity) and the normal respiratory activity of spectators. IAQ models for gas-phase NCl<sub>3</sub> and CO<sub>2</sub> were developed to relate the characteristics of the indoor pool environment to measurements of IAQ dynamics. Several assumptions were made to develop these models. Specifically, pool water and indoor air were assumed to be well-mixed. The reactions that were responsible for the formation and decay of the target compounds were neglected. Two-film theory was used to simulate the net mass-transfer rate of volatile compounds from the liquid phase to the gas phase. Advective transport into and out of the air space of the pool were accounted for. The IAQ model was able to simulate the dynamic behavior of gas-phase NCl<sub>3</sub> during regular operating hours. Predictions of gas-phase NCl<sub>3</sub> dynamics were generally less accurate during periods of intensive pool use; however, the model did yield predictions of behavior that were qualitatively correct. Strengths of the model include that it accounts for the factors that are believed to have the greatest influence on IAQ dynamics and is simple to use. Model weaknesses include that the model did not account liquid-phase reactions that are responsible for formation and decay of the target compounds. The IAQ model for NCl<sub>3</sub> dynamics could still be a useful tool to form the basis for recommendations regarding the design and operation of indoor pool facilities so as to optimize IAQ.Measurements of CO<sub>2</sub> dynamics indicated qualitatively similar dynamic behavior as NCl<sub>3</sub>. Because of this, it was hypothesized that CO<sub>2</sub> may represent a surrogate for NCl<sub>3</sub> for monitoring and control of IAQ dynamics. To examine this issue in more detail, a conceptually similar model of CO<sub>2 </sub>dynamics was developed and applied. The model was developed to allow for an assessment of the relative contributions of liquid®gas transfer and respiration by swimmers and spectators to CO<sub>2</sub> dynamics. The results of this modeling effort indicated that the similarity of CO<sub>2</sub> transfer behavior to NCl<sub>3</sub> may allow use of CO<sub>2</sub> as a surrogate during periods with few to no spectators in the pool; however, when large numbers of spectators are present, the behavior of CO<sub>2</sub> dynamics may not be representative of NCl<sub>3</sub> dynamics because of spectator respiration. <br>