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Collier County's North County Regional Water Treatment Plant (NCRWTP) is a combinednanofiltration (NF)/reverse osmosis (RO) treatment facility, with design production capacity of20-mgd (12-mgd NF, 8-mgd RO). The RO portion of the NCRWTP treats brackish water from 11wells in the Lower Hawthorne Aquifer. Since their construction in 1998, 4 of the 11 wells haveexperienced increased total dissolved solids (TDS). The chloride concentrations in these fourwells increased from a range of 2,000-3,000 mg/L to 6,000-10,000 mg/L by 2002, renderingthem useless to the existing low pressure RO system.The production loss from these wells allows the NCRWTP to marginally meet the 11-mgd rawwater required for the RO portion of the treatment system by eliminating available redundancy.Additional wells are planned for the future to improve the raw water supply capability; however,the prospect of abandoning four highly productive, permitted, and relatively new wells is notfavorable. Instead, the concept of independently treating the raw water from the high salinitywells was investigated.Treating high salinity groundwater using seawater RO (SWRO) technology is a new concept inFlorida. In theory, this scenario presents an ideal application for SWRO technology because ofthe high quality of the groundwater with respect to silt density index (SDI) and turbidity and thehistory of successful treatment of water from the Lower Hawthorne Aquifer by RO. However, theabsence of past experience with SWRO technology and the potential for unforeseeabletreatment challenges warranted demonstration testing.The objectives for this RO demonstration study were three-fold:verify treatability of high salinity Lower Hawthorne groundwater with SWRO technologyand minimal pretreatment (5-micron filtration and scale inhibitor only);develop energy use, chemical consumption, and cleaning interval data to estimateoperational costs and establish full-scale design criteria; and,familiarize Collier County operations staff with isobaric energy recovery technology.This paper discusses the application of the latest seawater technology for the treatment ofhighly brackish groundwater in Florida. Included is information on the development of thedemonstration testing protocol, establishment of the most economical design recovery and fluxrates, and the performance of the low energy seawater membranes and isobaric energyrecovery devices. Operational data from the demonstration study is presented, including operating pressures, water quality, and energy usage. This paper serves as a roadmap to otherutilities who are suffering from a reduction in potable water supply due to salt water intrusionand provides concrete evidence that the latest seawater technology and design conceptssignificantly lower the cost of treating high salinity water. Includes tables, figures.

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Edition: Vol. - No. Published: 03/01/2007 Number of Pages: 15File Size: 1 file , 380 KB