Distribution System Considerations Associated with Chlorine Dioxide Hélène Baribeau, Nicola Bazzurro, and Giuliano Ziglio

Transcription

1 Distribution System Considerations Associated with Chlorine Dioxide Hélène Baribeau, Nicola Bazzurro, and Giuliano Ziglio AMGA Foundation Chlorine Dioxide for Drinking Water Utilities October 26, 2007 Genoa, Italy

2 Approaches 1. USA a. Regulations require a residual disinfectant all the way to the consumer tap 2. Europe ClO 2 as pre- or intermediate oxidant ClO 2 for small distribution systems a. In 6 countries, regulations limit ClO 2- to 0.05 mg/l (Denmark) to 0.7 mg/l (Italy), others at 0.2 mg/l ClO 2 as pre- or intermediate oxidant b. New Directive regulates ClO 2- at 0.7 mg/l ClO 2 as distribution system residual disinfectant?

3 Outline of Presentation 1. ClO 2 and its by-products in distribution systems a. Occurrence of ClO 2, ClO 2- and ClO 3 - b. Fate of ClO 2, ClO 2- and ClO 3-2. Effect of ClO 2 on water quality a. Tastes and odors b. NOM, biomass, and nitrification c. Corrosion 3. Summary and conclusions

4 ClO 2 and its By-Products in Distribution Systems 1. Use of chlorine dioxide in the USA (AWWA Disinfection Systems Committee) Disinfectant 1978 Survey 1989 Survey 1998 Survey Cl 2 gas 91% 87% 84% NH 2 Cl 20% 29% NaOCl 6% 7.1% 20% ClO 2 1% 4.5% 8.1% O 3 0.4% 5.6% Others 2% 0.8% 1.0%

5 ClO 2 and its By-Products in Distribution Systems 1. Occurrence of ClO 2, ClO 2- and ClO 3- in American distribution systems (ICR data, ) a. ClO 2, ClO 2- and ClO 3- not regulated at the time Plant effluent Distribution system Min Average Max Min Average Max ClO 2 - ND ND ClO 3 - ND ND

6 ClO 2 and its By-Products in Distribution Systems 1. Occurrence of ClO 2, ClO 2- and ClO 3- in Italian distribution systems (1995 CISPEL Survey) ClO 2- (µg/l) < 200 > 200 but < 500 > 500 but < 1,000 > 1,000 % Water Samples 24% 40% 24% 12%

7 Fate of Chlorine Dioxide and its By-Products in Distribution Systems

8 Fate of ClO 2 in Distrib. Systems 1. ClO 2 used as system residual disinfectant a. Decrease with water age Little to no residual detected Faster decay in the distribution system than in batch incubations (Bergeon et al., 1992) Very low concentrations in premise plumbing b. Fairly stable in a pilot system (Block et al., 1992) Dissipation kinetics: 1.34 mg/day ClO mg/day Cl 2 2. Cl 2 used as system residual disinfectant a. Reformation in the distribution system b. Decrease with increasing water age

9 Fate of ClO 2- in Distribution Systems 1. Either ClO 2 or Cl 2 as distribution system residual disinfectant a. No trend, variable b. Stable with water age c. Decrease with increasing water age d. Decrease in premise plumbing

10 Fate of ClO 3- in Distribution Systems 1. ClO 2 used as residual disinfectant a. No trend, variable b. Stable with water age c. Decrease slightly with increasing water age d. Increase in premise plumbing 2. ClO 2 used prior to free chlorination a. No trend, variable b. Increase with increasing water age c. Decreased with increasing water age

11 Fate of ClO 2 ; Used as Distribut. System Residual Disinfectant 1. Full scale ClO 2 residual ClO 2 - ClO 3 - Thompson et al., mg/l after 10 hours 0.12 mg/l after 70 hours 0.76 mg/l after 10 hours 0.67 mg/l after 70 hours Volk et al., mg/l average 0.20 mg/l at end 0.68 mg/l at plant eff mg/l in system mg/l at plant eff mg/l in system

12 Fate of ClO 2- in Distribution Systems (Francais et al., 1994)

13 Fate of ClO 3- in Distribution Systems (Francais et al., 1994)

14 Fate of ClO 2- in Distribution Systems Main pipes Small pipes Dead-end Batch incubation 0.7 Chlorite (mg/l) (Baribeau et al., 2002) Residence Time (hours)

15 Fate of ClO 3- in Distribution Main pipes Small pipes Dead-end Batch incubation Systems Main pipes Small pipes Dead-end Batch incubation Chlorite (mg/l) Chlorate (mg/l) Residence Time (hours) (Baribeau et al., 2002) Residence Time (hours)

16 ClO 2- and ClO 3- in Premise Plumbing (Baribeau, 1995)

17 ClO 2 and its By-Products 1. Free chlorine as distribution system residual disinfectant, full scale (Hoehn et al., 2003)

18 Fate of ClO 2 in Distribution Systems ClO2 residual (mg/l) Pertusillo Fortore Sinni Locone (AQP) Residence time (hours)

19 Fate of ClO 2- in Distribution Chlorite (mg/l) Systems Pertusillo Fortore Sinni Locone ClO2 residual (mg/l) Residence time (hours) Pertusillo Fortore Sinni Locone (AQP) Residence time (hours)

20 Chlorate (mg/l) Fate of ClO 3- in Distribution Systems (AQP) Pertusillo Fortore Sinni Locone ClO2 residual (mg/l) Chlorite (mg/l) Residence time (hours) Residence time (hours) Pertusillo Fortore Sinni Locone Pertusillo Fortore Sinni Locone

21 Effects of Chlorine Dioxide on Distribution System Water Quality

22 Tastes and Odors in Distribution Systems 1. Odor threshold: 0.2 mg/l ClO 2 Descriptors: Chlorinous (diesel, kerosene) (Masschelein and Hoehn, 1995) 2. Taste threshold: mg/l ClO 2 3. Compared to Cl 2, ClO 2 does not contribute to the formation of T&O in distribution systems, but is not as efficient as Cl 2 for reducing unwanted tastes in distribution systems (Burlingame and Anselme, 1995)

23 Tastes and Odors in Distribution Systems 1. Kerosene and cat urine odors: Reaction between ClO 2 (gas) and organic substances in air a. 0.1 mg/l ClO 2 sufficient (Hoehn et al., 2003) b. Reformation of ClO 2 in distribution systems 2. No T&O (Bergeon et al, 1992, Volk et al., 2002) 3. 5 of the 21 utilities surveyed did not report offensive T&O (CISPEL, 1999)

24 Tastes and Odors in Distribution Systems (Burlingame and Anselme, 1995)

25 Effect of ClO 2 on BOM 1. ClO 2 increases AOC from 146 to 230 µg/l (Mofidi et al., 2004) 2. BDOC of 0.21 mg/l after Cl mg/l after ClO 2 (Block et al., 1992) 3. No significant differences in TOC after ClO 2, or Cl 2, or monochloramine (Gagnon et al., 2004)

26 Effect of ClO 2 on Biomass 1. No effect, no change (Bergeon et al., 1992; Volk et al., 2002; Gagnon et al., 2006; Block et al., 1992) 2. Improvement in microbial water quality a. Temporary increased in bacterial counts and change in microbial ecology. Bacterial counts resumed to original levels (Krasner et al., 2003) b. ClO 2 more effective than Cl 2 in controlling biofouling (bench scale; Andrews et al., 2005) ClO 2 : 1.6 log suspended, 3.3 log fixed HPCs Cl 2 : 0.5 log suspended and fixed HPCs

27 Effect of ClO 2 on Biomass 1. Improvement in microbial quality a. Biomass inactivation at bench scale (Gagnon et al., 2004) Pipe material Suspended HPC Biofilm HPC ClO 2 : Polycarbonate 4.0 log 2.2 log Cast iron 2.8 log 2.0 log Cl 2 : Polycarbonate 2.2 log 1.4 log Cast iron 1.5 log 0.9 log

28 Effect of ClO 2 on Biomass 1. Degradation in microbial water quality (Dyksen et al., 2006) a. Two utilities b. Long-term effect c. Higher HPC after switching to ClO 2

29 Effect of ClO 2- Nitrification 1. Bench scale (McGuire et al., 1999) a. 1 mg/l ClO 2- : 2 to 3 log AOB inactivation; 30 minutes b mg/l ClO 2- : 4 to 5 log; 24 hours c. 5NaClO 2 + 5HCl 4ClO 2 + 5NaCl + HCl + 2H 2 O 2. Pilot studies (McGuire et al., 2005 & 2006) a. Continuous application of 0.1 mg/l ClO 2 - b. Intermittent application of mg/l ClO 2 -

30 Effect of ClO 2- Nitrification 1. Successful use of ClO 2- to control nitrification at full scale (McGuire et al., 1999; McClelland et al., 2004; Loveland et al., 2005) 2. Non-successful use of ClO 2 - (McGuire et al., 2006) a. Intermittent application of 0.2 mg/l ClO 2- did not prevent nitrification from occurring b. Continuous application was necessary

31 Effect of ClO 2 on Corrosion 1. Pipe loops with cast iron pipes (Eisnor and Gagnon, 2004) Cl 2 NH 2 Cl ClO 2 ClO - 2 Corrosion rate 3.3 mpy 5.9 mpy 2.2 mpy 0.9 mpy Iron release 2.82 mg/l 1.36 mg/l 0.72 mg/l 0.03 mg/l 2. Corrosion products reduce ClO 2 into ClO 2-, then Cl -

32 Effect of ClO 2 on Corrosion 1. ORP: ClO 2 > Cl 2 > KMnO 4 > NH 2 Cl > O 2 (James et al., 2004)

33 Summary and Conclusions 1. Fate of ClO 2 in distributions systems a. Decrease with increasing water age when ClO 2 is used as residual disinfectant b. ClO 2 may reform in presence of Cl 2 2. Fate of ClO 2- in distributions systems a. Variable, no trends b. Decrease with increasing water age 3. Fate of ClO 3- in distributions systems a. Generally stable when ClO 2 is used as residual disinfectant b. Increase in presence of Cl 2

34 Summary and Conclusions 1. Formation of offensive odors at customers houses when ClO 2 is used as residual disinfectant a. Successful cases 2. Variable effects of ClO 2 on biomass a. May help control nitrification 3. Effects of ClO 2 on corrosion: a. May not promote corrosion anymore than Cl 2 or NH 2 Cl b. Corrosion by-products reduce ClO 2 into ClO 2-, then Cl -

35 Thank You! Grazie!

36 Contact Information 1. Hélène Baribeau, Ph.D., P.E. Carollo Engineers, P.C. 199 S. Los Robles Avenue, Suite 530 Pasadena, California, USA Phone: , ext.238 Fax:

37 Research Needs 1. Effect of pipe material and diameter on ClO 2, ClO 2- and ClO 3-, including premise plumbing 2. Effect of household water use on ClO 2, ClO 2- and ClO 3-3. Effect of biofilm on ClO 2- and ClO 3-4. Monitoring in the distribution system 5. Predictive models for ClO 2, ClO 2- and ClO 3-6. Fate of ClO 2 by-products other than ClO 2 - and ClO 3 -

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