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Distribution System Simulators

Distribution System Simulators (DSSs) help us evaluate and understand what happens within distribution pipelines. The DSS units imitate water flowing through pipes. The DDS pipes are located above ground to provide easy access to the entire pipe network. Scientists can study the physical, chemical, and biological activities that occur within pipelines. (See Table 2)

DSS-1

Image: DSS 1

DSS-1 replicates continuous flow conditions. It has six 75-foot (25-meter) lengths of 6-inch (15-centimeter) diameter ductile iron pipe. These pipes are arranged in “pipe loop” designs. DSS-1 has two 1,500-gallon reservoir tanks. This unique engineering design allows operating any combination and configuration of the six loops, such as individual loops, collectively as a unit, or in various configurations according to EPA’s experimental research needs. Each loop is insulated and fitted with a heat exchanger to maintain constant temperature during operation. The distribution system simulator is interfaced with a Supervisory Control and Data Acquisition (SCADA) system, which is used to continuously monitor, control, and record operating conditions and collect data.

Scientists are using DSS­1 to study factors that influence biofilm growth and what can be done to control it. Biofilms form when bacteria adhere to pipe surfaces. The trouble with biofilm is that it is highly resistant to many disinfection methods and techniques.

Biofilm samples are collected on “coupons.” Coupons are metal devices that enable scientists to collect samples from the interior surface of a pipe without disrupting water flow. You might say coupons are harvesting devices. They are removed from the distribution pipe. The biofilm sample is scraped off the coupon. The coupons are put back into the distribution pipe. (See Table 1)

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DSS-2

Image: DSS 2

DSS-2 is more than 300 feet long. It is a once-through system composed of 6-inch (15-centimeter) diameter PVC pipe. DSS-2 is being used to evaluate water quality in a dead-end branch of a distribution system.

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DSS Research Goals

    • Understand what happens in drinking water distribution systems
    • Determine what physical, chemical, and biological factors promote biofilm growth in pipes
    • Develop and test mechanisms to control biofilm growth in a DSS
    • Conduct real-time monitoring, data collection, and archiving of water quality using remote telemetry within water distribution systems. These research results will be used to provide guidance on how to use remote monitoring of water quality to detect changes in water quality within distribution systems.

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    Table 1. Operating Parameters of the Distribution System Simulator
    Parameter Normal Operation Experimental Test Conditions
    Distribution System Simulator Parallel (six individual distribution system simulators) Parallel or series in groups of 6, 3, 2, or 1
    Housing Ductile iron (non-lined) Ductile iron (non-lined)
    Flow 88 gpma or 1 ft/secb No flow to 140 gpm or 0 to 1.6 ft/sec
    Temperature 60 oF (15.5 oC) 35 oF (1.6 oC) to ambient temperature
    Chemical Control Free chlorine 1.0 ppmc Chemical control as needed
    pH 7.0 to 7.5 Control/monitor as needed
    Turbidity <0.5 NTUd Control/monitor as needed
    Water Supply Cincinnati tap water (chlorinated) Dechlorinated, deionized, tanked, surface water (e.g., river water)

    agallons per minute
    bfeet per second
    cparts per million
    dnephelometric turbidity units

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    Table 2. DSS Studies
    No. Study Title
    1 Preliminary Studies of Biofilm Formation in Pilot-Scale Distribution Systems
    2 Opportunistic Pathogens in Biofilms
    3 Effects of a Pollution Event on a Simulated Water Distribution System
    4 Impact of Nutrient Removal on Growth Potential for Bacteria
    5 Impact of Alternative Treatment on Biofilm Growth
    6 Real-Time Monitoring and Control of Distribution Systems
    7 Effects of pH Changes on Biofilm Growth in a Distribution System
    8 Bacterial Growth in Distribution Systems

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