AWWA WQTC69469

This powerpoint presentation begins by providing a brief overview of Aurora (Colorado) Water's supply system, and process overview. A comparison of two treatment facilities, Wemlinger and Griswold, is presented, along with treatment plant upgrades, and the simultaneous addition of chlorine and chlorine dioxide. Observations following chlorine dioxide conversion are presented, along with optimization studies and the objectives for a follow-up study that include expanding the previous optimization study to answer the following questions: can results be replicated, does source water impact the findings, and does seasonal variability impact the findings? Other follow-up study objectives include: develop practical guidance for plant optimization of Cl₂ and ClO₂; and, develop test procedures and protocols. Experimental approach included jar tests lasting 1 year, test conditions consisting of initial Cl₂ and Cl₂ dose range: 0 - 1 mg/L, based on acceptable operating conditions at Wemlinger and Griswold WTFs, and 12 dose conditions evaluated per test. Summary of study includes the following: full scale data shows that the co-application of chlorine and chlorine dioxide had several advantages such as achieves adequate CT at lower ClO₂ dose, reduction in chlorite formation (compared to ClO₂ alone), reduction in TTHMs (compared to chlorine alone), and dampens the effect of TOC/UV spikes on TTHM formation. Preliminary optimization study findings include the following: the Cl₂:ClO₂ dose ratio does not have an "optimal" condition (contrary to our previous study); chlorite formation impacted by source water and seasonal variability; and, TTHM concentrations reduced by limiting chlorine dose. Includes tables, figures.