Reducing the Cost of Operational Water in Military Water Systems: A Data-Driven Modeling and Optimization Study

Reducing the Cost of Operational Water in Military Water Systems: A Data-Driven Modeling and Optimization Study

 

Corey James, Michael Webber and Thomas Edgar

Department of Chemical Engineering

The University of Texas at Austin, 1 University Station C0400, Austin, TX 78712

email: cmjames@utexas.edu

Military water systems are tasked to provide safe and clean water to support soldiers, their families and mission related activities.  Due to the historic low price and relative abundance of water, there has been little motivation to ensure that water systems minimize water waste after treatment.  Currently, water is treated for disinfection as needed to meet demand.  The concentrations of common disinfecting agents (chloramines or chlorine) begin to exponentially decay the moment they are placed in the water [1].  A system that treats water without rigorously considering unique demand data and the temperature dependent nature of chloramine decay will inevitably waste water.  Waste is created when excess water is treated and placed into the system that exceeds demand.  The volume that exceeds demand resides in the system long enough to run out of “lifetime”, where the concentration of chlorine in the treated water decays below the legal safe threshold.  This water must be flushed, or wasted, in order to ensure a safe water source.   Embedded in the water waste is the energy and cost required to pump and disinfect that volume of water.  A system that is not optimized to account for chlorine decay could cause thousands of gallons of water wasted on a monthly basis, not to mention the embedded energy and cost.   

Approximately 300 million gallons of potable water was wasted in 2013 due to routine maintenance in Texas’ 10 largest cities [2].  Water wasted due to decayed chlorine levels is unknown, but likely similar.  Lack of optimization of an appropriate objective function in water systems is the main cause of wasted water and energy related to lifetime.  Military installations have unique water requirements with regard to emergencies, base resiliency and fires.  Volume and pumping constraints within the model are vital to reducing the water and power consumed.  Awareness of water shortages, installation of water conserving fixtures/appliances and an increase in stewardship over the past decade created an overall reduction (~13%) in per capita and overall potable water consumption [3].  Unfortunately, the reduction in consumption creates a new unintended consequence for the water system.  Water systems are not optimized for the new reduced flow and further waste is created when excess treated water that reaches its disinfectant lifetime is purged.  A substantial amount of studies have examined optimizing both residential and commercial water consumption  networks, but rigorous studies optimizing water use and related power consumption on military installations are not available .

Results on the optimal production of treated water to minimize waste and energy consumption (pumping costs) while meeting demand and quality constraints utilize data from Fort Carson, Colorado and The Pecan Street Project.  The unique demand data and constraints of a typical military system are used to create a time-resolved water profile for an installation, which is then used to examine the fully burdened cost, energy consumption and waste of less than optimal water systems through rigorous multi-tiered optimization and control.  Financial, social, economic and environmental impacts are analyzed as part of the fully burdened cost. 

References

[1] Peter J. Vikesland, Kenan Ozekin and Richard L. Valentine (2001).  “Monochloramine Decay in Model and Distribution System Waters”.  Water Resources 35(7): 1766-1776. <>[2] Amarillo Globe-News, “Cities wasted nearly 300M gallons of water.” 4-July-2014.

[3] M.A. Maupin, J.F. Kenny, S.S. Hutson, J.K. Lovelace, N.L. Barber and K.S. Linsey (2014). “Estimated use of water in the United States in 2010”. U.S. Geological Survey Circular 1405(56).