Impact of the UV Lamp Power on the Formation of Swimming pool Water Treatment By-Products
Published Online: Apr 04, 2019
Page range: 131 - 138
Received: Jan 03, 2018
Accepted: Apr 19, 2018
DOI: https://doi.org/10.21307/acee-2018-045
Keywords
© 2018 Edyta Kudlek et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
Swimming pools are a special kind of water reservoirs that need to be constantly disinfected to protect their users from infections caused by microbial pathogens. The disinfection process can be carried out by the use of [1, 2]:
chlorine based disinfectants such as: chlorine gas, calcium/sodium/lithium hypochlorite, dichloro isocyanurates and trichloro isocyanurates;
bromine based disinfectants – bromochlorodi-methylhydantoin and sodium bromide with an oxidizer;
new/emerging disinfectant combinations such as: magnesium salts or ozone with hydrogen peroxide;
other disinfection methods used in the combination with chlorine/bromie based methods – ozone, UV light, chlorine dioxide and potassium iodide.
Those processes beside the favorable elimination of pathogens can also cause the transformation of several chemical contaminants present in pool water [3].
Chemical contaminants of organic origin enter the swimming pool in the form of body excretions, lotions, cosmetics, pharmaceuticals and other products used by the swimmers [4, 5]. Cleaning agents used around the swimming pool may also contact the pool water. Moreover the source water may contain trace amounts of micropollutants [6]. Therefore the concentration of organic micropollutants is highly variable and depends both on the loading introduced into the pool by swimmers, the half-life of compounds and on the used pool water treatment technology.
Organic micropollutants during the contact with disinfection agents undergo several reactions [7]. They lead to both the complete decomposition of some chemical contaminants into water and carbon dioxide or to the generation of so called disinfection by-products (DBPs). In the group of well known DBPs trihalomethanes (THMs), haloacetic acids (HAAs), haloacids, halodiacids, iodo-THMs, halo-aldehydes, halo-nitriles, -ketones, -nitromethanes, -amides, -alcohols, bromate, nitrosamines, and 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) and its homologues can be listed [8]. However, all micropollutant transformations products generated during the contact of those compounds with disinfectants can also be called as DBPs. Bottoni et al [3] based on the analysis of test results carried out on pharmaceuticals and personal care products (PPCPs), indicated that the transformation by-products may be more harmful for swimming pool users than the unchanged compounds. PPCPs in contact which hypochlorite solutions were chlorinated, oxidized or undergo some other chemical modifications [9]. Furthermore, compounds containing in their structures amine groups could act as nitrosamine precursors during chloramine disinfection processes [10]. Therefore, before the implementation of a disinfection technology, it is necessary both to prove the efficiency in terms of emanation of pathogens and also to determine the possibility of DBPs generating.
The paper presents the effect of the implementation of UV irradiation on the decomposition and the generation of transformation products of organic compounds occurring in swimming pool water. The tests were performed under laboratory conditions by the use of two UV lamps with a different irradiation spectrum. To examine the effectiveness of the UV irradiation process, chromatographic analysis preceded by solid-phase extraction was used.
The subject of the study was swimming pool water collected from an indoor sport pool. The implemented water treatment system based on coagulation, filtration on multi-layer pressure filters and disinfection by NaOCl. The used disinfection method was not supported by UV irradiation. The parameters of the collected swimming poll water sample are summarized in Table 1. The water samples were stored in dark glass bottles in the temperature equal to 4±1°C.
Parameters of swimming poll water
| Parameter | Value |
|---|---|
| pH [-] | 7.34 |
| UV absorbance λ=254 nm [cm-1] | 0.041 |
| Conductivity [mS/cm] | 2.04 |
| Redox potential [mV] | 664 |
| TOC [mg/L] | 15.53 |
| Free chlorine [mg/L] | 0.42 |
| Combined chlorine [mg/L] | 0.46 |
The irradiation of the swimming pool water with UV was preformed in a laboratory bath reactor Heraeus (volume of 700 ml). The reactor was optionally equipped with an immersed medium-pressure UV lamp of power 150 W and a low-pressure UV lamp of 15 W. The radiation spectrum of the used UV lamps was given by the manufacturer and was equal to λexc = 254, 313, 365, 405, 436, 546, 578 nm for the medium-pressure lamp and λexc = 254 nm for the low-pressure lamp. In order to ensure a constant temperature of the reaction mixture of 20±1°C, the UV lamp was placed in a glass cooling jacket. The cooling agent was tap water. Additionally the reactor was placed on a magnetic stirrer.
Samples for analyses were taken after 10, 30 and 60 minutes of constant UV irradiation.
For the identification of organic micropollutants present in swimming pool water before and after UV irradiation, gas chromatograph coupled to mass spectrometry (GC-MS) with electronic ionization preceded by solid phase extraction SPE was used. Supelclean™ ENVI-18 extraction tubes with C18 phase were conditioned with 5 ml of methanol and 5 ml of acetonitrile and next washed with the same volume of distilled water of pH 7. After the extraction of collected sample of a volume 100 ml the column bed was dried at vacuum. The analytes adsorbed on the tube bad were eluted with 1.5 ml of methanol and 1.5 ml of acetonitrile and subjected to chromatographic analysis. The GC-MS Model 7890B by Perlan Technologies was equipped with a SLBTM – 5 ms capillary column of Supelco with an internal diameter of 0.25 mm, a length of 30 m and a layer thickness of 0.25 µm.
The GC oven temperature programme was as follows: 80°C (6 min), 5°C/min up to 260°C, 20°C/min up to 300°C (2 min). The carrier gas was helium at a flow rate of 1.1 ml/min. The ion trap temperature was equal to 150°C, the ion source was heated to 230°C and the injector temperature was set at 250°C. The mass detector operated in the ion recording mode in the range from 50 to 400 m/z. The validation of the applied analytical procedure were made on the basis of results obtained for five extractions. The precision of determination between individual samples did not exceed 1%. Details of the developed analytical method are presented in a previous paper [11].
The identification of micropollutants was made based on their mass spectra, which were compared with the NIST 17 Mass Spectral Library.
The concentration o total carbon (TC), total organic carbon (TOC) and inorganic carbon (IC) was estimated by the use of the TOC-L total organic carbon analyzer by Shimadzu.
The organic solvents of GC grade used in this study were purchased from the Avantor Performance Materials Poland S.A.
The chromatographic analysis of swimming pool water not exposed to UV light indicated the presence of over 40 different organic compounds with a probability ranged from 65 of over 99%. The compounds identified with a probability higher than 85% are listed in Table 2. Those compounds belong to the group of pharmaceuticals, personal care product additives, food additives, phthalates and organic solvents. The obtained results correlate with data received for other swimming pools [12,13], which also confirm the presence of a significant number of compounds from the group of PPCPs.
Organic micropollutants identified in swimming pool water samples
| Group | Name | Abbreviation | Molar mass [g/mol] |
|---|---|---|---|
| Pharmaceuticals | caffeine | CAF | 194.19 |
| carbamazepine | CBZ | 236.30 | |
| batilol | BAT | 344.57 | |
| hydrochlorothiazide | HCT | 297.74 | |
| Personal Care Product additives | 2-phenoxyethanol | POE | 138.16 |
| benzophenone-3 | BP3 | 228.25 | |
| benzophenone-8 | BP8 | 244.24 | |
| hedione | HED | 226.32 | |
| levomenthol | LVM | 156.27 | |
| trichloroacetic acid | TCA | 163.39 | |
| oleic acid | OA | 282.47 | |
| Food additives | butylated hydroxytoluene | BHT | 220.35 |
| carvone | CRV | 150.22 | |
| Other | chloroform | CRF | 119.38 |
| dimethyl phthalate | DEP | 194.18 | |
| dibutyl phthalate | DBP | 278.34 |
The next part of the study was focused on the observation of changes in the composition of swimming pool water after the irradiation with UV light with different wavelength spectra. UV light indicated the generation of strongly oxidizing hydroxyl radicals (OH•) and other highly reactive oxygen species such as superoxide radical (O2 •-) or hydroperoxyl radical (HO2 •), which can act as free radicals able to decompose organic micropollutants [14]. During the exposition of pool water on both 15 W and 150 W UV lamp work some changes in the profile of the obtained GC-MS chromatogram were observed (Fig 1). The UV supported oxidation process lead to the decomposition of some compounds or generation of new compounds. The presence of decomposition byproducts was confirmed by the appearance of peaks (Fig 1b and 1c), which were not observed during the analysis of swimming pool water before UV irradiation (Fig 1a).
Figure 1.
Chromatograms obtained during the analysis of swimming pool water (a) before and after 60 min of UV irradiation with lamps of (b) 15 W and (c) 150 W
The conducted quantitative analysis show a decrease in the concentration of detected organic micropollutants. Figure 2 presents the changes in pharmaceuticals, personal care product additives, food additives and other compounds during the irradiation with the low-pressure 15 W UV lamp. The removal rate of all compound decreased with the increase of the irradiation time. The lowest concentration decrease, which not exceed 2% was noted for CAF (Fig 2a). This pharmaceutical compound is relative by hardly degradable also in other oxidation processes like H2O2, O3 or UV/TiO2 [15]. 60 min of the UV/TiO2 process of deionized water containing CAF in a concentration of 1mg/L allowed only for a 3% decrease in the compound concentration.
Figure 2.
Influence of irradiation time on the decrease of the concentration of (a) pharmaceutical compounds, (b) personal care product additives, (c) food additives and (d) other compounds (15 W UV lamp)
Other detected pharmaceuticals were removed after 60 min of UV exposure respectively by 23% for CBZ, 26% for BAT and 31% for HCT. The removal degree of BHT was also at low level and ranged from 18% after 10 min of irradiation to 21% after 60 min of UV exposure. More favorable decomposition effects ware observed for the personal care product additive TCA and OA. The concentration of those compounds decreased after 60 min of UV irradiation by more than 86%. It was also noted, that the phthalate DEP is characterized by a higher susceptibility to photochemical composition (an over 83% reduction in the compound concentration) than DBP, whose removal degree did not exceed 57%.
In samples exposed to the irradiation emitted by the medium-pressure 150 W UV lamp an increase in the removal rate of all tested organic micropollutants was observed (Fig 3). Four compounds: BAT, BP3, TCA and OA were completely removed after the first 10 min of UV irradiation. Whereas after 30 min of UV exposure an entire removal of CRV and CRF was noted. Also the removal rate of the hardly degradable compound CAF increased to 11%. Other pharmaceuticals were decomposed by more than 33% for HCT and 37% for CBZ (Fig 3a). Among personal care product additives the lowest removal was observed for BP8 (Fig 3b). The concentration of this UV filter decreased by 76%, while the concentration of both HED was reduced by over 80%, POE by 17% and LVM by more than 14%. Only in the case of the phthalate compound DEP (Fig 3d) a decrease of its removal rate compared to the results obtained for the 15 W UV lamp was observed.
Figure 3.
The decrease of the concentration of (a) pharmaceutical compounds, (b) personal care product additives, (c) food additives and (b) other compounds during the irradiation with the 150 W UV lamp
The decrease of micropollutants concentration after the implementation of UV light was also proved by the results obtained during the measurement of the TC and TOC concentration. Figure 4a presents the decrease of the concentration of the carbon forms during the irradiation wit UV light with a power of 15 W, while figure 4b shows the same results obtained during the exposure of swimming pool water of UV light with a power of 150 W. The highest decrease of TOC concentration was observed during the first 10 min of irradiation with both UV lamps. After 60 min of light exposure the TOC, concentration decreased in samples subjected to 15 W UV light by 23%. The use of the 150 W UV lamp allowed for an over 32% reduction of TOC concentration. A decrease of organic matter was also reported by other investigation focused on the use of UV light [16].
Figure 4.
Decrease of carbon amount during the irradiation of swimming pool water with the (a) 15 W and (b) 150 W UV lamp
According to high removal degrees of most of the tested micropollutants it was expected, that the concentration of TOC also decreases by more than 50%. Therefore it can be assumed, that the only 32% reduction of the TOC is associated with the generation of DBPs. The presence of new compounds was already mentioned by the analysis of the obtained chromatograms. An in-depth analysis of mass spectra of those new compounds allowed for their unequivocal identification and the designation of their parent substances. Reactions from (1) to (4) show compounds identified after 30 min of UV irradiation with the medium-pressure 150W UV lamp and their parent compounds. For example during the UV supported oxidation of CBZ 9-acridinecarboxylic acid was generated, which oxidize to acridine (1). The decomposition of BHT leads to the formation of methyl-1, 4-benzoquinone (3) and the degradation of DBP and DBE resulted in the generation of phthalic acid (4).
(1)
(2)
(3)
(4)
The conducted research show that swimming pool water contains several organic micropollutants, which are not only generated during the used disinfection methods but are also introduced into the water by the pool users. Those compounds can undergo different reactions leading to the formation of more complex compound. UV irradiation can be used as a part of the disinfection system and in addition, it can be implemented as a supplementary separate water treatment process for the decomposition of a wide range of micropollutants. The 150 W UV lamps, emitting the radiation with different wavelengths was more effective during the removal of micropollutants than the 15 W UV lamp. The pharmaceutical removal degrees, with the exception of CBZ, exceeded 33%, while the concentration of other compound decreased by over 76%. It should by noted that during the oxidation of organic compounds a large number of decomposition by-product can by formed, which can have a negative impact on the swimming pool users.