Downloaded from orbit.dtu.dk on: Jun 07, 2018 Laboratory studies on the effect of ozonation on THM formation in swimming pool water Kaarsholm, Kamilla Marie Speht; Spiliotopoulou, Aikaterini; Cheema, Waqas Akram; Andersen, Henrik Rasmus Publication date: 2015 Document Version Peer reviewed version Link back to DTU Orbit Citation (APA): Hansen, K. M. S., Spiliotopoulou, A., Cheema, W. A., & Andersen, H. R. (2015). Laboratory studies on the effect of ozonation on THM formation in swimming pool water [Sound/Visual production (digital)]. 6th International Conference Swimming Pool & Spa, Amsterdam, Netherlands, 17/03/2015 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Laboratory studies on the effect of ozonation on THM formation in swimming pool water K.M.S. Hansen, A. Spiliotopoulou, W.A. Cheema, H.R. Andersen 6 th International Conference Swimming Pool & Spa 17 20 March, 2015 Amsterdam, The Netherlands
Ozone chemistry t½, 20 C = 3 days t½, 20 C = 20 min Increased ph Contaminants High reactivity: Low reactivity: O 3 + R R ox double bond Urea Organo-chlorine
Ozone chemistry I. Organic matter reactive with ozone Direct oxidation by ozone Fast consumption of ozone Decrease chlorine reactivity of pollutants Low ozone life time no reaction with bromide II. Organic matter not reactive with ozone Slow consumption of ozone Ozone converts to hydroxyl radicals with time Radical attack of inactive carbon increased chlorine reactivity Long ozone life time oxidation of bromide to bromate
Systems: DIN (German standard) Equalization basin 0.2-0.3 mg/l free chlorine ph flocculant Filtration Chlorine addition Nominal ozone addition 0.8 mg/l Residence time > 3 min Activated carbon /sand filter
Systems: Slip-stream (USA) DEL Ozone proprietary drawing
Our aim Optimizing ozone treatment Contact time Required ozone dose to minimize chlorination DBPs Ozone kinetics not well described in swimming pools Effects of ph Effects of organic, repeated ozonation Effect of ozonation on DBP formation Pool water Filling water Fresh pollutants
Lab-scale experiments Stock solution of ozone
Effect of ph on ozone lifetime C/C0 (%) 100 ph 6.8 ph 7.0 75 ph 7.3 ph 7.8 50 25 0 0 10 20 30 40 time (min) Very little difference in the ph range swimming pools are operated
Repeated ozonation ozone lifetime C/C 0 (%) 50 Filling water 100 1st 2nd 75 3rd MilliQ C/C 0 (%) Swimming pool water 100 1st 2nd 75 3rd 4th 50 25 25 0 0 10 20 30 40 50 60 time (min) Fast removal of 1 st ozone dose ozone reactive material 2 nd and 3 rd no ozone reactive material 0 0 10 20 30 40 50 60 time (min) Little difference no ozone reactive material in the water
Chlorination of the ozonated samples Chlorine: 24 h at 25 C Chlorine residual + Purge & trap GC/MS
Chlorine consumption 2.0 Filling water Swimming pool water Cl 2 -consumption (mg/l) 1.5 1.0 0.5 I II II I. Direct oxidation by ozone II. Radical mechanism 0.0 0 1st 2nd 3rd 0 1st 2nd 3rd 4th 5th Ozone dose 2 mg/l Different chlorine consumption for tap water and swimming pool water
Formation of total trihalomethane TTHM formation (µmol/l) 1.0 0.5 Filling water I II 26 % 37 % 13 % 10 % Swimming pool water DOC II 6.2 % 4.3 % 3.3 % 3.6 % 4.2 % 4.2 % TTHM Incorporated Br I. Direct oxidation by ozone II. Radical mechanism 0.0 0 1st 2nd 3rd 0 1st 2nd 3rd 4th 5th Ozone dose 2 mg/l Ozonation of filling water decreased THM Ozonation of swimming pool water increased THM
Fresh pollutants Why do not we see an decrease in THM formation in pool water? + + Control 0.5 ppm O 3 1.0 ppm 1.5 ppm 3.0 ppm +100 ppm Artificial body fluid
Total organic carbon (TOC) and chlorine consumption TOC Chlorine consumption 3 25 2 1 20 15 10 5 TOC (mg/l) Cl2-consumption (mg/l) 0 Pool Mix Mix + 0.5 ppm O3 Mix + 1.0 ppm O3 Mix + 1.5 ppm O3 Mix + 3.0 ppm O3 Mix + 100 ppm O3 Pool Mix Mix + 0.5 ppm O3 Mix + 1.0 ppm O3 Mix + 1.5 ppm O3 Mix + 3.0 ppm O3 Mix + 100 ppm O3 Ozonation decrease TOC and decreased chlorine consumption 0
TTHM formation 0.4 0.3 0.2 0.1 I TTHM Bromine incorporation TTHM formation (µmol/l) 0.0 Mix Mix + 0.5 ppm O3 Mix + 1.0 ppm O3 Mix + 1.5 ppm O3 Mix + 3.0 ppm O3 Mix + 100 ppm O3 Fresh pollutant direct ozone reaction short ozone life time no decrease in formation of brominated THM
Conclusions Kinetic possible ph minimal effect TOC (ozone reactive vs non-reactive) Chlorinated pool water Reaction via hydroxyl radical, making the organic material more reactive and increased THM formation. Presence of fresh pollutants Direct oxidation by ozone decreased THM formation Still need some more information on ozone dose required
Thanks for your attention See you at the next pool conference with results from ozonation of full scale system