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Issue link: http://wateronline.epubxp.com/i/597858
gravity flows to it, so self-priming (rather than submersible) pumps were selected, in large part because of the potentially corrosive equalization tank water. Submersible pumps would need to be constructed entirely of stainless steel to withstand the environment, which wasn't economically feasible. Flow control evaluations considered variable frequency drives (VFDs), motorized V-port discharge ball valves, and multiple pumps. VFDs were eliminated from consideration because of concerns about keeping the pumps primed at low motor speeds. Three pumps, along with a flow-controlled V-port ball valve on the common recycle line, were selected for the implementation. Disinfection. Another significant challenge for the project was how to disinfect the ZLD-treated water without exceeding disinfection byproduct (DBP) limitations. The city was providing 4-log virus treatment in accordance with the Ground Water Rule through free chlorine addition to the blended permeate and raw water bypass in the clearwell prior to chloramination. The project's original concept was to combine the ZLD-treated water with the permeate and the raw water bypass streams in the clearwell, but higher TOC concentrations in the ZLD-treated water were a concern. Because the lime and soda ash softening combined with membrane filtration can provide 2-log virus inactivation, the ZLD-treated water was disinfected separately with free chlorine to provide the remaining 2-log virus treatment before chloramination. Integrating With An Existing Facility The concentrate ZLD process is complex and needed to be fully integrated with its respective components as well as the existing plant so the facility could operate as a single entity. This operational approach complies with the operating permit that was issued to incorporate the concentrate ZLD process and increase the plant's overall capacity. Operational Considerations Instrumentation And Electrical. The existing instrumentation and SCADA system at WTP No. 2 consisted of a centralized plant control system providing monitoring and operating capability from a centralized computer system. Plant operations were directly wired into the control room's programmable logic control cabinet, and the system was expanded to incorporate and completely integrate all the ZLD processes into the modified SCADA system. These changes allow operators to monitor and control all the plant's operations and processes from a single location. Electrical And Standby Power. The electrical system for the existing facility was expanded and upgraded to accommodate the ZLD process. The existing emergency generator was rehabilitated and used for the concentrate ZLD process. A new emergency generator was installed to reinforce the plant's reliability. This approach was more cost-effective than replacing the existing emergency power system with a larger system to safeguard the expanded operations. The electrical system's design, including sequencing its two generators, minimized the need for plant shutdowns during construction. Yard Piping And Underground Utilities. The existing raw water bypass piping was relocated to accommodate the new UF building. A significant amount of piping and other underground utilities exist onsite. As a result, new piping and other underground utilities placement was challenging, which is a common issue when improving an existing facility. The keys to success were identifying existing piping and utilities early in the project through the use of record drawings, subsurface utilities excavations, and staff 's knowledge of previous plant improvements. Current Status Substantial completion of the concentrate ZLD project occurred on March 2, 2015. The team experienced a few challenges during startup, but these were overcome by close collaboration with the City of Palm Coast, the engineer of record (McKim & Creed, Inc.), the contractor (Wharton-Smith), and the original equipment manufacturer (Doosan Hydro Technology). Additionally, operational modifications are being tested and implemented to reduce DBP formation. In April, the team was awarded the David W. York Water Reuse Project of the Year award by the Florida Water Environment Association. n 16 wateronline.com n Water Innovations About The Authors Phillip Locke, PE, is a senior project manager with McKim & Creed, Inc. and served as project manager and lead process engineer of Palm Coast's ZLD project. He has more than 20 years of experience, including serving as engineer of record for five advanced water treatment projects. The instrumentation and SCADA system associated with the ZLD process was integrated into WTP No. 2's existing SCADA system. Fred Greiner is the chief operator of WTP No. 2 for the City of Palm Coast. Ryan Popko, PE, served as project engineer on the ZLD project while with McKim & Creed. Currently, Ryan is a process engineer with JEA. THICKENINGANDDEWATERING