<p>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.</p>
<p><a>Swimming pool water treatment processes can play significant roles
in governing water and air quality.</a> 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.</p>
<p>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.</p>
<p>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. </p>
<p>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. </p>
<p>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.</p><p>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.</p><p></p>
<br>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/16695223 |
| Date | 22 November 2021 |
| Creators | Lester Ting Chung Lee (11495881) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Dynamic_Behavior_Of_Water_And_Air_Chemistry_In_Indoor_Pool_Facilities/16695223 |
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