Effect of ozonation of swimming pool water on formation of volatile disinfection by-products – A laboratory study

Abstract

Ozonation experiments were performed using unchlorinated tap water used for filling municipal swimming pools, actual pool water and pool water polluted by addition of fresh tap water and artificial body fluid to evaluate ozone kinetics and water quality effects on formation of volatile disinfection byproducts during subsequent chlorination. The ozone reaction was observed to behave according to first order kinetics. For tap water half-life was 4 min whilst polluted and unpolluted pool water exhibited half-life of 8 and 11 min, respectively. When ozonation dosage was repeated half-life of ozone was approximated 17-19 min in all samples. Subsequent chlorination revealed ozone removed reactivity of dissolved organic carbon toward chlorine for tap and polluted pool water, decreasing formation rate of trihalomethanes (TTHM). In pool water higher rates of TTHM formation was observed after the initial ozone dosage, however this decreased with subsequent treatments. For tap and polluted pool water, ozone reacted directly with the pollutants resulting in a short ozone half-life, removing reactivity towards chlorine oxidation and preventing TTHM production. Conversely for pool water samples, due to the long half-life of ozone, the molecule decomposed to hydroxyl radicals. These in turn reacted with aqueous organic matter increasing chlorine reactivity and rates of TTHM formation. Formation of other non-regulated volatile byproducts (e.g. dichloracetonitrile, trichlorpropanone and trichloronitromethane) was observed to increase in pool water with ozone treatment. Thus, ozonation dosage regimes should be designed such that ozone mostly oxidizes fresh pollutants before chlorine is able to react with it.

Disinfection Methods for Swimming Pool Water: Byproduct Formation and Control

“…The radical oxidation of that fraction of DOC enhances its reactivity to chlorine, and consequently the formation of TCM. The decrease in the concentration of TCM with a fourth and fifth dose is due to mineralization of that fraction of DOC with increasing oxidation [14]. Cheema et al [19] observed a similar trend in the formation of THMs with different doses of O 3 , as reported by Hansen et al [14] (Table A3).…”

“…In the study of different doses of O 3 in clean pool water (TOC 1.5 mg·L −1 ) , the formation of TCM increased from 25 to 60 µg·L −1 with the first three subsequent doses (2 mg·L −1 of O 3 each) and then with further addition decreased to 45 µg·L −1 , but still remained higher compared with chlorination (25 µg·L −1 ) [14] (Table A3) The increase in the formation of TCM with initial dose of O 3 in the clean pool water is likely due to decomposition of O 3 to OH • and radical oxidation of fraction of DOC present in the pool water, which has low reactivity towards chlorine. The radical oxidation of that fraction of DOC enhances its reactivity to chlorine, and consequently the formation of TCM.…”

“…In some other studies, it is reported that the concentration of different categories of DBPs in swimming pool water disinfected with O 3 /chlorine was lower than the pool disinfected with chlorine. This indicates the efficacy of O 3 /chlorine due to its high oxidation potential compared with chlorination (Table 2); thus the degradation of persistent organic substances is possible [14,15]. For instance, Hang et al [15] reported a higher concentration of TCM, BDCM and DBCM (220, 202 and 3.8 µg·L −1 , respectively) with chlorination compared with 141, 106 and 2.0 µg·L −1 , respectively in the case of O 3 /chlorine (Table A3).…”

“…Although the comparative analysis of different disinfection methods within studies is available, it has not been done between the studies. For instance, a comparison between chlorination, EGMO and O 3 /chlorine [3,6]; between chlorination and EGMO [5,7,8]; between chlorination, UV irradiation and UV/chlorine [10,37]; between chlorination and UV/chlorine [9,11,12]; between chlorination, UV irradiation, UV/chlorine, UV/H 2 O 2 and UV/H 2 O 2 /chlorine [13]; between chlorination and O 3 /chlorine [14][15][16]38]; between UV irradiation and O 3 /UV [18]; between chlorination, O 3 /chlorine, O 3 /H 2 O 2 /chlorine and O 3 /UV/chlorine [17]; and between chlorination, UV/chlorine, O 3 /chlorine, O 3 /UV and O 3 /UV/chlorine [19]. A comprehensive and critical review of performance and a comparison of all the disinfection methods is lacking.…”

“…With this awareness, the demand for alternatives to chlorine disinfection has increased. The alternative methods aimed at improving the quality of swimming pool water are: electrochemically generated mixed oxidants (EGMO) [3,[5][6][7][8], ultraviolet (UV) irradiation [9][10][11][12], UV-based advanced oxidation processes (UV-based AOPs) such as UV/H 2 O 2 [13], ozone (O 3 ) [14][15][16], and ozone-based AOPs such as O 3 /H 2 O 2 and O 3 /UV [17][18][19]. The use of O 3 and UV irradiation for the disinfection of swimming pool water has been adopted in some cases, though together with chlorine for the provision of a residual disinfectant [20].…”