Silver Buckshot - Tackling Nitrification with a Diverse Portfolio of Treatment Strategies
Last Modified: Nov 08, 2018
- Marc Santos PE, Jim DeWolfe PE, William Becker PhD, PE - Hazen and Sawyer
- Gabriel Ramirez, Daniel Grimsbo PE - City of Corpus Christi
- Logan Burton PE - LNV Inc
Nitrification can be a constant challenge for any utility that uses chloramines as a residual disinfectant in its distribution system. Once nitrification is established in the distribution system, water quality can degrade quickly, and recovering the system can be challenging. A single strategy is typically not enough for recovering from nitrification or preventing early onset Nitrification.
The City of Corpus Christi operates a 161.5 MGD water treatment plant and maintains over 9,750,000 linear feet of piping in its distribution system. In recent years, the City of Corpus Christi has 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. The City began an aggressive program to evaluate their treatment and distribution system, specifically for nitrification-related criteria and develop a comprehensive portfolio of strategies to address nitrification mitigation. In collaboration with Hazen/LNV, the City of Corpus Christi identified vulnerable areas in the distribution system and operational challenges at the water treatment plant. A list of short-term and long-term action items was developed to evaluate the source water characteristics, the treatment processes and operations at the water treatment plant, and the distribution system operations.
Strategies at the water treatment plant included improved chemical mixing, improved chemical injection, minimization of travel time and flow stabilization in the plant, pH optimization, adjustments to the chlorine-to-ammonia ratios, improved chemical flow-pacing, the installation of new residual analyzers, and improved data trending and analysis. In addition, a fast-tracked design and construction of a new chlorine dioxide system began carrying a chlorite residual throughout the distribution system for chloramine control.
Strategies in the distribution system included chloramine booster stations, improved tank mixing and turnover, new control strategies for tank level operations, and improved distribution system water quality monitoring and trending. The operations evaluation included improvements to the NAP, improved internal communications within the utility, and updated SOPs that incorporated recent successes and lessons learned.
This paper will discuss the “buck-shot” strategy enacted by the City of Corpus Christi for nitrification prevention. Water quality data from the WTP and across the distribution system will be provided to demonstrate marked improvements that were observed as a result of the strategies. Utilities that are currently using or considering the use of chloramines as a distribution system disinfection will gain knowledge regarding industry standards for treatment techniques and technologies used to prevent nitrification and learn from the successes in Corpus Christi.
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