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Effect of ClO2 Pretreatment on Subsequent Water Treatment Processes |
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| Authors: | M. Zamir B. Alam Raymond E. Cantwell Ron Hofmann Robert C. Andrews Jennie L. Rand Graham A. Gagnon Monique VanderMarck Erin Moffat Susan A. Andrews |
| Affiliation: | 1Research Fellow, Dept. Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto ON, Canada M5S 1A4. 2Ph.D. Candidate, Dept. Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto ON, Canada M5S 1A4. 3Assistant Professor, Dept. Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto ON, Canada M5S 1A4 (corresponding author). E-mail: hofmann@ecf.utoronto.ca 4Professor, Dept. Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto ON, Canada M5S 1A4. 5Assistant Professor, Ivan Curry School of Engineering, Acadia Univ., Wolfville NS, Canada B4P 2R6. 6Associate Professor, Dept. Civil Engineering, Dalhousie University, 1360 Barrington St., Halifax, NS B3J 2X4. 7Water Treatment Superintendent, East Bay Municipal Utility District, Oakland, CA 94623. 8Research Assistant, Dept. Civil Engineering, Univ. of Waterloo, 200 University Ave. W., Waterloo ON, Canada N2L 3G1. 9Associate Professor, Dept. Civil Engineering, Univ. of Waterloo, 200 University Ave. W., Waterloo ON, Canada N2L 3G1. |
| Abstract: | The effect of chlorine dioxide (ClO2) pretreatment on subsequent treatment processes (coagulation, flocculation, sedimentation, filtration, and ozonation) was studied at pilot-scale at the Upper San Leandro Water Treatment Plant near Oakland, Calif. Potential impacts of ClO2 on the distribution system were also studied at bench scale using simulated distribution system (SDS) tests. Pilot trials were conducted with one train operating without ClO2 pretreatment (Train 1) and the other with a ClO2 dose of between 0.6 and 1.0?mg/L (Train 2). Comparison between Trains 1 and 2 showed that ClO2 pretreatment resulted in a 0.1–0.2 NTU decrease in settled water turbidity when compared to no pretreatment. ClO2 pretreatment also resulted in a small (0.01?cm?1) decrease in ultraviolet absorbance at 254?nm. Following sedimentation, about 60% of the applied ClO2 formed chlorite (ClO2?), with 10–20% forming chlorate (ClO3?). Ozonation immediately converted all residual ClO2 and ClO2? to ClO3?. There was no significant difference in the performance of the filters between the two trains in terms of headloss, particle count, and turbidity. Bench-scale SDS tests indicated that chlorine dioxide preoxidation did not affect subsequent chloramine stability or concentrations of trihalomethanes, haloacetic acids, or adsorbable organic halides in the distribution system. |
| Keywords: | Potable water Chlorine Disinfection Chlorides Oxidation Water treatment |