Effects of Flow Rate on Turbidity and Microbial Growth in Premise Plumbing Systems

Undergraduate #138
Discipline: Technology and Engineering
Subcategory: Water

Margaret E. Carolan - Virginia Polytechnic Institute and State University
Co-Author(s): William J. Rhoads, Marc Edwards, and Amy Pruden, Virginia Polytechnic Institute and State University, Blacksburg, VA

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Opportunistic pathogens (OPs) are the leading cause of waterborne disease in developed countries. Water- and energyconserving plumbing system designs with reduced flow rates can increase OP growth by fostering sediment accumulation, biofilm development, and disinfectant residual decay. A simulated water faucet experiment was constructed, testing four flow rates (1.6-6.5 L/min) in duplicate. Hot (50°C) and cold (<20°C) water was mixed, targeting 37°C at each faucet. The lowest flow rate had 22-28% more turbidity and 22-32% more bacterial cells than the highest flow rate, confirming that lower flow rate faucets have an increased potential to facilitate growth. In a parallel bench-scale plumbing rig operated at four flow rates (0.2-9.8 L/min), and flushed with a 50 NTU solution of natural organic matter, 3.5 times more turbidity accumulated in the lowest flow rate pipe than the highest flow rate pipe. Chlorine residual disappeared in the lowest flow rate pipe 7 times faster than a stable chlorine residual control and 5.5-6.3 times faster than the higher flow rate pipes when 5 mg/L free chlorine was introduced. This parallel work confirms that lower flow rates create favorable conditions for microorganism regrowth. Future work will investigate the effects of low flow on Ops.

Funder Acknowledgement(s): NSF/REU Site Grant EEC-1359051 (Interdisciplinary Water Sciences and Engineering)

Faculty Advisor: Marc Edwards,