Chlorine Dioxide Application for Water Quality Challenges: Experience from Texas Systems
Last Modified: Nov 08, 2018
- Marc Santos, William Becker PhD, PE - Hazen and Sawyer
- Gabriel Ramirez, Crystal Ybanez, Rafael Martinez - City of Corpus Christi
- Logan Burton PE - LNV Inc.
Chlorine dioxide application in the water industry has increased over the past few decades to address a variety of treatment challenges. In Texas alone, 101 water systems across the state currently use chlorine dioxide for various treatment goals including disinfection, disinfection by-product (DBP) reduction, metals oxidation, taste and odor reduction, and nitrification prevention. Nitrification prevention, in particular, has become a rising challenge for Texas utilities, as they must maintain a 0.5 mg/L total chlorine residuals with high temperature surface waters and often long distribution system residence times.
The City of Corpus Christi experienced an increase in water quality excursions related to nitrification at the farthest locations within its distribution system which contributed to a boil water advisory in 2016. To deter future water quality challenges, the City began an aggressive program to upgrade treatment and distribution system, which included the installation of a new chlorine dioxide system. The new chlorine dioxide system has been successfully in operation for a year and has been a part of a treatment portfolio that has seen a marked improvement in water quality. Both WTP data and distribution system data have been closely monitored to identify key water quality parameters and persistence of chlorite in the distribution system.
Water quality considerations are a focus for the various types of chlorine dioxide generation system options. The different precursor chemicals and generation methods of chlorine dioxide may impact pH and other secondary water quality parameters. To establish the optimum application point of chlorine dioxide within a water treatment plant both the potential benefits and negative impacts on other treatment processes should be evaluated.
Chlorine dioxide has been successfully used for nitrification mitigation by maintaining a residual of chlorite in the distribution system; however, many Texas systems with chlorine dioxide system still struggle with nitrification challenges. This paper will provide an explanation of chlorine dioxide chemistry and applications of chlorine dioxide in Texas for nitrification prevention, including the successful City of Corpus Christi case study. In addition, the paper will highlight previous work investigating chlorine dioxide efficacy for treatment of distribution system biofilms.
Utilities that are currently using or considering the use of chloramines and/or chlorine dioxide will gain knowledge regarding the benefits and optimization of chlorine dioxide to prevent nitrification. Utilities will learn about water quality data trending and will learn how to use trending tools to track positive system performance or water quality degradation. Utilities should also understand the challenges and potential negative outcomes when operating chlorine dioxide and should consider all treatment barriers to find the right fit for the particular system.
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