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Application to determine whether the energy savings gained by including a retrofitted ERD would outweigh the installed capital cost. While taking the payback period into consideration is important, ERD selection should be based on the present worth of equipment cost and energy, not on payback period or ERD efficiency alone. The tool calculates both presentFigure 2: The "Cost Summary" page presents capital cost and life-cycle cost for various ERDs, allowing users to compare worth RO system projand contrast the options. ect costs and payback Today, the majority of modern seawater RO systems period. The ERD providing the lowest present worth of (SWROs) have installed ERDs, with great success and a typiRO equipment and energy will have the lowest cost to cal payback period of less than three years. The high salinity desalt water, regardless of the ERD efficiency or payback of seawater increases the residual energy in RO concentrate period. and increases the value of the ERD. With an ERD, approxiTherefore, when planning to update or build a new mately 50 percent of the initial pumping energy in the RO plant, engineers and operators will find exceptional value treatment step can be recaptured and recycled, reducing the in this tool for determining the optimal RO design. overall energy consumption used by SWROs. The ERD tool and the related full report, funded However, for source waters with lower salinity, such by the WateReuse Research Foundation, the as wastewater or brackish waters, the new tool becomes California Energy Commission, and the United States especially useful because the residual energy in the conBureau of Reclamation, are available for free at centrate is significantly lower. Plants treating lower salinity http://www.watereuse.org/product/08-14-1. waters have less residual energy to recover, and, therefore, ERDs are not always cost effective regarding payback period. Using the tool to evaluate the costs and benefits of Steve Alt, a chemical engineer and membrane and desalination including an ERD becomes especially important. technologist with CH2M HILL's Water Business Group, has more than 16 years of membrane technology experience on a variety of environmental water and wastewater projects. He was the process lead and technical expert for WRF-08-14. Evaluates Payback Period And Capital Costs For Optimal RO System Design The decision on whether including an ERD in an RO system is economically feasible is based on the payback period. If the payback period is less than the projected ERD and associated equipment life, then ERD inclusion will save money over the duration of the equipment life. Using ERD product information and RO system parameters to perform a series of calculations, the tool calculates the payback period and capital costs associated with including an ERD into both new and existing RO systems. Displaying results in a simple summary table, the tool makes it easy for users to identify the optimal RO system design by comparing the present cost of desalting water and the payback period. As existing plants seek ways to conserve energy, the tool can also help engineers evaluate ERD retrofit options. However, the existing RO system must be closely evaluated wateronline.com Jim Lozier is one of only five Technology Fellows within the CH2M HILL Water Business Group's global technology organization and works on a worldwide basis on the application of desalination technologies for the production of drinking and high-quality industrial water. Tyler Nading is a process engineer with four years of experience in water treatment with CH2M HILL. Tyler's experience includes design, pilot plant operation, construction, and start-up for water and wastewater treatment plants. He served as the project manager and lead programmer for WRF-08-14. ■ Water Online The Magazine 13