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UV Treatment Effects on Disinfection By-Products in Swimming Pools: A Comprehensive Analysis

This master's thesis explores photolysis and secondary formation of disinfection by-products in swimming pool water via UV treatment. It covers the introduction, background, DBPs, UV irradiation, conflicting research, hypothesis, analytical conditions, and results. The study aims to determine the impact of medium-pressure UV radiation on water quality in chlorinated indoor pools and investigates mechanisms behind DBP formation.

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UV Treatment Effects on Disinfection By-Products in Swimming Pools: A Comprehensive Analysis

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  1. Photolysis and secondary formation of disinfection by-products by UV treatment of swimming pool water SpiliotopoulouAikaterini Master thesis 30 ECTS Supervisors: HenrikRasmus Andersen Kamilla Marie Speht Hansen

  2. Outline • Introduction • Disinfection by-products (DBPs) • Need for Swimming Pool research • Hypothesis • Background • Analytical conditions • Results & Discussion • Conclusions 1

  3. 1. Introduction and Background 2

  4. Need for swimming pool research • Common form of exercise • Safe swimming pools • Chlorine • Strong oxidant • Effective to pathogens and modified cells • Chloroform (TCM) • Bromodichloromethane (BDCM) • Dibromochloromethane (DBCM) • Dichloroacetonitrile (DCAN) • Trichloropropanone (TCprop) Combination: NOT well defined • BUT: Cl2 + Dirt  DBPs 3

  5. Disinfection by-products (DBPs) • Exposure: • Ingestion, inhalation, dermal absorption • Affect Human Health • Suspected for: • Eye and skin irritation, respiratory infection, cancers, stillbirths and other birth defects, genotoxicity Need for their limitation!!! 4

  6. UV irradiation • UV as secondary treatment • Bactericidal • Inactivate pathogens resistant to Cl2 • Inorganic chloramines reduction Combination: NOT well defined Figure 1: The electromagnetic spectrum. 5

  7. Swimming pool Figure 2: Schematic drawing of a swimming pool. 6

  8. Conflicting researches Enhancement of Thrihalomethane (THM) formation in presence of residual Cl 2 by UV was observed in: • Short term full scale experiments • Laboratory studies When: • Low pressure UV or • Medium pressure UV lamps Cl2 + UV = ? Suggestion of mechanisms which explain DBP formation!!! 7

  9. 2. Hypothesis & Objectives 8

  10. Breaking point Hypothesis • • DBPs are formed in UV reactor HOCl + hv + H+Cl+ •OH then •Cl + organic matter DBPs • UV and radicals change organic matter making it more reactive to Cl2 • •OH more reactive organic matter to Cl2 DPBs are formed after Cl2 addition •OH Cl2 Cl2 Figure 3: The mechanism of •OH contribution to a compound transformation. 9

  11. Question Does UV create more DBPs or speed up their formation Based on the mass balance all the carbon in the pool is oxidized by Cl2 10

  12. Objetives • Which are the effects of medium-pressure UV radiation on the water quality in chlorinated indoor swimming pools in presence of • chlorine? • hydrogen peroxide? • nitrate? • Which mechanisms explain DBP formation? • Which is the main DBP formed in pools? • Which process contributes more to their formation? • Could ABTS method be used for Cl2 determination in SW? 11

  13. 3. Experimental Approach 12

  14. Analytical conditions • 4 different indoor public pool locations in Copenhagen • Physicochemicalparameters: • Cl2 ABTS method at 405 nm • NO3- and NO2- kit • pH was adjusted to 7.5 • Chemical parameters: • TOC TOC meter • H2O2 TiO-oxalate method at 400 nm • Volatile DBPs P&T coupled with GC-MS Figure 4: Schematic drawing of experimental design. 13

  15. Experimental conditions Dark: Untreated water Dark, Cl2: chlorination Dark, HighCl2:long term retention time UV/Cl2, Cl2 : post UV Cl2 (20 min exposure) UV/Cl2, Cl2, Air: post UV Cl2 (20 min exposure), aeration after 24h UV/Cl2, Cl2, Air, High Cl2: post UV Cl2 (20 min exposure), High Cl2 UV/Cl2, High Cl2: post UV High Cl2 (20 min exposure) UV40/Cl2, Cl2: extent post UV Cl2 (40 min exposure) UV/Cl2: Cl2 not in the UV reactor UV, Cl2: Cl2 in the UV reactor UV20: 20 min exposure UV40: 40 min exposure UV/NO3-, Cl2: •NO2 effect, UV (exposure 20min), Cl2 UV/H2O2, Cl2: •OH effect, UV (exposure 40-70min), Cl2 14

  16. Cl2 determination - colorimetric methods • DPD (N, N-diethyl-p-phenylenediamine sulfate) • Widely used • Measured at 520 nm • Drawback: the colored product of the reaction is not stable • ABTS (2.2-azino-bis (3-ethyl-benzothiazoline)-6sulfonic acid-diammonium salt) (Pinkernell et al., 2000). • Simple • Accurate • Measured at 405 nm • Reaction product: stable without causing any interference of chlorite • Able to distinguish: chlorine, chloramines and chlorine dioxide 15

  17. Collimated beam set up Figure 5: The schematic description of the quasi-collimated beam irradiation apparatus, to the right: picture of the commercial UV system from the public swimming pool. 16

  18. 4. Results & Discussion 17

  19. Results – ABTS method DL= 0.005 mg/L Cl2 Figure 6: ABTS calibration curve. 18

  20. Results - Chemical characterization of pool waters pH adjusted to ≈ 7.5 after chlorine addition Table 1: TOC, NO3- andNO2- concentration (mg/L) analysis for the four different swimming pools. 19

  21. Results- Chlorine consumption • Highest Cl2 consumption: • UV/Cl2, Cl2: Pool 1 &2 • Dark, High Cl2:Pool 3 &4 • H2O2: • Pool 1: no significant difference • Pool 2: precursors removal TOC Figure 7: Chlorine consumption in 24h. 20

  22. Results – Total Trihalomethane (TTHM): TCM + BDCM +DBCM • Proportional to Cl2 consumption • The main formed compound in TTHM: Chloroform • UV: Br2 removal • UV/Cl2, Cl2 • Highest DBP formation • Increase Br-DBPs Close to DL Figure 8: Total trihalomethaneformation in water samples treated by different procedures including the brominated species. 21

  23. Theory of Br-Cl-DBP formation UV Irradiation Further reaction Cl2 addition Figure 9: Schematicrepresentation of brominanted DBP formation. 22

  24. Results –Chloroform formation (TCM) • TCM formation is proportional to Cl2 consumption • Untreated SW: contain TCM • UV/Cl2, Cl2 • Highest TCM formation • Figure 10: TCMformation in pool water samples treated by different procedures. 23

  25. Results - Brominated THM formation • BDCM: highest formation than DBCM • More Br for DBCM • UV: removal rate of brominated compounds is proportional to the bromine substitution • Figure 11: DBCM and BDCM formation in pool water samples treated by different procedures. 24

  26. Results - DCAN and TCprop formation • Untreated SW: contain DCAN • Cl2 addition: higher decrease of DCAN • Figure 12: DCAN and TCprop formation in pool water samples treated by different procedures. • UV: no impact to DCAN • UV/Cl2, Cl2: highest DCAN & TCprop formation 25

  27. Results – Radical effects • UV + Cl2 •Cl2 +organic matter chloroform • UV/Cl2, Cl2: highest formation in all the studied compounds • UV • Dark,Cl2 • • NO2 – : significant increase of Cl2 consumption due to the reaction of NO3 – with Cl2 • No change in Cl2 consumption • TTHM and DCAN: decrease • TCprop: uncertainty • UV forms •OH which partially oxidize organic matter more reactive to Cl2 • TTHM and DCAN: no effect • TCprop: significant increase does not seem to affect significantly the chloroform formation 26

  28. 5. Conclusions-Perspectives 27

  29. Conclusions - Contribution • ABTS method: suitable for Cl2 determination in Swimming Pool water • UV/Cl2, Cl2 : high DBP formation • Chloroform: the main DBP in pools • Radicals do not affect significantly DBP formation • DBPs are NOT formed in UV reactor BUT after Cl2 addition • UV treatment amplified the fraction of brominated THM 28

  30. Hypothesis Evaluation DBPs are NOT formed in the UV BUT when Cl2 is added • DBPs are formed in UV reactor • UV changes carbon making it more reactive to Cl2 • Does UV create more DBPs or just speed up DBP formation: • UV speeds up DBP formation (Dark, High Cl2 vs. UV, Cl2) • Uncertainty about the concentration • more DBPs were formed from UV (UV, Cl2 vs.Dark, Cl2) • The increased concentration make the water more toxic 29

  31. Perspectives • Supplementary experiments (laboratory and full scale) to define: • the kinetics and mechanisms of DBP formation • the processes occurring during UV irradiation • Focus on: • Repetition for complete data set in all the pools for better understanding of the combined UV-Cl2 treatment 30

  32. Thank you for your attention!

  33. Table 2: WHO guideline values in μg/L.

  34. Table 2: AgenceRegionale de santé, guideline values in μg/L. Code de la santé publique Limites et références de qualité des eaux destinées à la consommation humaine (Arrêté du 11/01/2007relatif aux limites et références de qualité des eaux brutes et des eaux destinées à la consommation humaine mentionnées aux articles R. 1321-2, R. 1321-3, R. 1321-7 et R. 1321-38 du code de la santé publique)

  35. Table 3: Detection limits and SIM parameters.

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