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

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

1. Introduction and Background 2

Need for swimming pool research 3  Common form of exercise  Safe swimming pools  Chlorine Strong oxidant Effective to pathogens and modified cells Combination: NOT well defined Chloroform (TCM) Bromodichloromethane (BDCM) Dibromochloromethane (DBCM) Dichloroacetonitrile (DCAN) Trichloropropanone (TCprop) BUT : Cl 2 + Dirt  DBPs

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 4 Need for their limitation!!!

UV irradiation  UV as secondary treatment  Bactericidal  Inactivate pathogens resistant to Cl 2  Inorganic chloramines reduction 5 Combination: NOT well defined Figure 1: The electromagnetic spectrum.

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

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 7 Cl 2 + UV = ? Suggestion of mechanisms which explain DBP formation!!!

2. Hypothesis & Objectives 8

Hypothesis 9 1. DBPs are formed in UV reactor HOCl + hv + H + Cl + OH then Cl + organic matter DBPs 2. UV and radicals change organic matter making it more reactive to Cl 2 OH more reactive organic matter to Cl 2 DPBs are formed after Cl 2 addition Breaking point OH Cl 2 Figure 3: The mechanism of OH contribution to a compound transformation.

Question 10 Does UV create more DBPs or speed up their formation Based on the mass balance all the carbon in the pool is oxidized by Cl 2

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 Cl 2 determination in SW? 11

3. Experimental Approach 12

Analytical conditions Figure 4: Schematic drawing of experimental design. 4 different indoor public pool locations in Copenhagen  Physicochemical parameters:  Cl 2 ABTS method at 405 nm  NO 3 - and NO 2 - kit  pH was adjusted to 7.5  Chemical parameters:  TOC TOC meter  H 2 O 2 TiO-oxalate method at 400 nm  Volatile DBPs P&T coupled with GC-MS 13

Experimental conditions 14 Dark: Untreated water Dark, Cl 2 : chlorination Dark, High Cl 2 : long term retention time UV/Cl 2, Cl 2 : post UV Cl 2 (20 min exposure) UV/Cl 2, Cl 2, Air: post UV Cl 2 (20 min exposure), aeration after 24h UV/Cl 2, Cl 2, Air, High Cl 2 : post UV Cl 2 (20 min exposure), High Cl 2 UV/Cl 2, High Cl 2 : post UV High Cl 2 (20 min exposure) UV40/Cl 2, Cl 2 : extent post UV Cl 2 (40 min exposure) UV/Cl 2 : Cl 2 not in the UV reactor UV, Cl 2 : Cl 2 in the UV reactor UV20: 20 min exposure UV40: 40 min exposure UV/NO 3 -, Cl 2 : NO 2 effect, UV (exposure 20min), Cl 2 UV/H 2 O 2, Cl 2 : OH effect, UV (exposure 40-70min), Cl 2

 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 Cl 2 determination - colorimetric methods 15

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

4. Results & Discussion 17

Results – ABTS method Figure 6: ABTS calibration curve. 18 DL= mg/L Cl 2

Results - Chemical characterization of pool waters pH adjusted to ≈ 7.5 after chlorine addition Swimming poolsTOC analysis Initial NO N concentration NO N concentration after UV/Cl 2 /NO 3 -, Cl 2 Pool Pool Pool Pool Table 1: TOC, NO 3 - and NO 2 - concentration (mg/L) analysis for the four different swimming pools. 19

TOC Results- Chlorine consumption Figure 7: Chlorine consumption in 24h. 20  Highest Cl 2 consumption:  UV/Cl 2, Cl 2 : Pool 1 &2  Dark, High Cl 2 :Pool 3 &4  H 2 O 2 :  Pool 1: no significant difference  Pool 2: precursors removal

Close to DL Results – Total Trihalomethane (TTHM): TCM + BDCM +DBCM Figure 8: Total trihalomethane formation in water samples treated by different procedures including the brominated species.  Proportional to Cl 2 consumption  The main formed compound in TTHM: Chloroform  UV: Br 2 removal  UV/Cl 2, Cl 2  Highest DBP formation  Increase Br- DBPs 21

Theory of Br-Cl-DBP formation UV Irradiation Cl 2 addition Figure 9: Schematic representation of brominanted DBP formation. Further reaction 22

Results – Chloroform formation (TCM)  TCM formation is proportional to Cl 2 consumption  Untreated SW: contain TCM  UV/Cl 2, Cl 2  Highest TCM formation Figure 10: TCM formation in pool water samples treated by different procedures. 23

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

 Untreated SW: contain DCAN  Cl 2 addition: higher decrease of DCAN Results - DCAN and TCprop formation Figure 12: DCAN and TCprop formation in pool water samples treated by different procedures. 25  UV: no impact to DCAN  UV/Cl 2, Cl 2 : highest DCAN & TCprop formation

 UV + Cl 2 Cl 2 + organic matter chloroform  UV/Cl 2, Cl 2 : highest formation in all the studied compounds UV Dark,Cl 2  NO 2 – : significant increase of Cl 2 consumption due to the reaction of NO 3 – with Cl 2  No change in Cl 2 consumption  TTHM and DCAN: decrease  TCprop: uncertainty  UV forms OH which partially oxidize organic matter more reactive to Cl 2  TTHM and DCAN: no effect  TCprop: significant increase Results – R adical effects does not seem to affect significantly the chloroform formation 26

5. Conclusions-Perspectives 27

Conclusions - Contribution  ABTS method: suitable for Cl 2 determination in Swimming Pool water  UV/Cl 2, Cl 2 : high DBP formation  Chloroform: the main DBP in pools  Radicals do not affect significantly DBP formation 28 DBPs are NOT formed in UV reactor BUT after Cl 2 addition UV treatment amplified the fraction of brominated THM

Hypothesis Evaluation 29 DBPs are NOT formed in the UV BUT when Cl 2 is added 1. DBPs are formed in UV reactor 2. UV changes carbon making it more reactive to Cl 2  Does UV create more DBPs or just speed up DBP formation:  UV speeds up DBP formation (Dark, High Cl 2 vs. UV, Cl 2 ) Uncertainty about the concentration  more DBPs were formed from UV (UV, Cl 2 vs. Dark, Cl 2 )  The increased concentration make the water more toxic

 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-Cl 2 treatment Perspectives 30

Thank you for your attention!

CompoundsGuidelines (μg/L) Chloroform200 Bromodichloromethane60 Dibromochloromethane100 Combined chlorine60 Monochloramine3000 Table 2: WHO guideline values in μg/L.

CompoundsGuidelines (μg/L) Total Thihalomethane100 Nitrate50000 Nitrite500 Chlorite200 TOC2000 Table 2: Agence Regionale 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 , R , R et R du code de la santé publique)

Start time (min) Quantifier Ions Detection Limit (μmol/L) Detection Limit (μg/L) TCM * BDCM * DBCM * DCAN * *10 -2 TCprop * *10 -2 Table 3: Detection limits and SIM parameters.