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Spiliotopoulou Aikaterini Master thesis 30 ECTS

Photolysis and secondary formation of disinfection by-products by UV treatment of swimming pool water. Spiliotopoulou Aikaterini Master thesis 30 ECTS. Supervisors: Henrik Rasmus Andersen Kamilla Marie Speht Hansen. Outline. Introduction Disinfection by-products (DBPs)

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Spiliotopoulou Aikaterini Master thesis 30 ECTS

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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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