Process Solutions, Inc. (PSI)

Automated Residual Control Maintains Tank Chloramine Residual Levels and Eliminates Nitrite Issues in 3 Million Gallon Tank Case Study

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Courtesy of Process Solutions, Inc. (PSI)

Automated Residual Control Maintains Tank Chloramine Residual Levels and Eliminates Nitrite Issues in 3 Million GallonTankLoudoun Water in Northern Virginia has a history of embracing change and seizing opportunities to create a more robust and sustainable water system. Situated in the fast-growing suburbs of Washington DC, Loudoun Water provides chloraminated drinking water to over 65,000 households through a network of over 1,200 miles of pipes and 7 tanks. A key element of Loudoun Water’s mission to sustainably manage water resources has been their efforts to improve the operational efficiency of their drinking water system. For a chloraminated water system, that means getting control of nitrification.

Loudoun Water used to be a simple secondary system, receiving free chlorine drinking water from the City of Fairfax, then chloraminatedwater from neighboring Fairfax County for a blended system. However, with the growth in their community, Loudoun County continued to expand their capabilities, building additional transmission mains and storage capacity that culminated with the construction of the Dulles South tanks, a pair of 3-MG fluted composite tanks to serve the southern portion of its system (Figure 1).

When the Dulles South tanks went online in 2012, managers of the Loudoun Water system anticipated that the additional storage would introduce some new challenges in managing drinking water quality. Water Quality Manager Cathy Cogswell developed a nitrification sampling plan to cover areas that, historically, had shown indications of low residual and nitrification. Once implemented, however, the sampling plan revealed that nitrification in the southern part of the system was worse than previous surveys had revealed. As a result, operators took one of the two Dulles South tanks offline in October 2014 to reduce water age and nitrification.

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