It’s Time to Convert Disinfectants - Is Your System Prepared?

Authors:

  • Marc Santos PE, Jim Dewolfe PE - Hazen and Sawyer
  • Rafael Martinez, Gabriel Ramirez, Crystal Ybanez - City of Corpus Christi
  • Logan Burton PE - LNV, Inc.

The City of Corpus Christi operates a 167 mgd water treatment plant and maintains over 9,750,000 linear feet of piping in its distribution system. Over the past few years, the City has performed temporary free chlorine conversions to control nitrification in the distribution system. Free chlorine conversions had not been required in prior years; therefore, Corpus Christi Staff developed a new set of procedures and protocols for converting to free chlorine and back to chloramines.

A key component of the conversion process is communication - both internally to City staff and externally to the public. The City partnered with Hazen and Sawyer to develop a series of brochures detailing the treatment process, water regulations, and boil water notices.

As part of the communication strategy, maps were sent to media outlets showing the progression of free chlorine.

Tracking the chloramine/chlorine front in the distribution system provides de facto water age analysis.

Background and Problem Statement
For utilities using chloramine as a distribution system disinfectant, the prevention of nitrification is a constant concern. Utilities employ a variety of techniques to mitigate nitrification including booster chlorination or chloramination, distribution system flushing, and other water age reducing strategies. If these strategies are insufficient to mitigate nitrifying bacteria, a short-term conversion to free chlorine may be necessary to inactivate nitrifying bacteria in the distribution system. Some utilities perform a free chlorine disinfectant conversion annually as a preventative measure.

The City of Corpus Christi operates a 167 MGD water treatment plant and maintains over 9,750,000 linear feet of piping in its distribution system. Over the past few years, the City has performed temporary free chlorine conversions to control nitrification in the distribution system. Free chlorine conversions had not been required in prior years; therefore, Corpus Christi Staff developed a new set of procedures and protocols for converting to free chlorine and back to chloramines.

Approach
The City of Corpus Christi recently updated their standard operating procedures (SOPs) to prepare for converting their system from chloramines to free chlorine. The conversion efforts required significant coordination between the water treatment plant, water quality team, and maintenance of lines staff to ensure a smooth and rapid transition. The City has developed a plan that addresses the water treatment plant, distribution system, and communication with staff and the community. The conversion preparation at the water treatment plant includes reducing oxidant demand, converting analyzers, increased monitoring, and minimizing travel time through the process trains. Distribution system actions include minimizing water age through tank operations and flushing and increased monitoring to identify the path of converted water or “front”. A key component of the conversion process is communication – both internally to City staff and externally to the public. Understanding the travel time of the disinfectant or “front” is critical for understanding which areas of the distribution system have been converted. The City of Corpus Christi utilizes media coverage and system maps to provide daily updates for customers and educate residents on the facts about the water conversion. The City staff performs after action meetings and documents successes, lessons learned, and required actions to continuously improve and streamline the conversion process.

Recommendations
It is recommended that Texas utilities using chloramines perform a regular assessment to evaluate their SOPs for free chlorine or chloramine conversions. Utilities that have not performed a disinfectant conversion recently may communicate with other Texas utilities to understand the challenges and best practices for successfully converting their distribution system.

With 50% of Texas systems utilizing chloramines, and upcoming Stage 3 DBP regulations on the horizon, it is more critical than ever that utilities prepare for and understand the ramifications of the conversion process.

For more information, please contact the author at msantos@hazenandsawyer.com.

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