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AWWA MTC69728
- Ft. Lauderdale 12-MGD Water Treatment Plant: Double Hybrid RO and NF Design
- Conference Proceeding by American Water Works Association, 11/01/2009
- Publisher: AWWA
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The City of Ft. Lauderdale Peele-Dixie Water Treatment Plant is a 12 MGD (1,893 M<sup>3</sup>/day)facility with four membrane system trains producing 3 MGD (473 M<sup>3</sup>/day) capacity per train. Thisplant required a significant review of the optimal dosing of sulfuric acid in lowering feed pH andthe use of antiscalant to control the precipitation of hardness while maintaining sufficient levelsof alkalinity to meet permeate quality goals and chemical costs. The plant used a low TDS wellwater supply from the Biscayne Aquifer ranging from 350 to 500 ppm, feed iron up to 2 ppm,total hardness up to 270 ppm as CaCO<sub>3</sub>, alkalinity before acidification up 270 ppm as CaCO<sub>3</sub>,TOC as high as 11 ppm, and color as high as 90 Color Units. Thepermeate quality goals of this potable water treatment facility were very stringent and requiredextensive pilot testing to develop an optimal spiral wound membrane design configuration usingboth RO (reverse osmosis) and NF (nanofilter) membranes. A minimum level of permeate alkalinity was desired to make thefinished water less corrosive in the city's distribution piping.The system configuration by train is a 53 pressure vessel 1st stage by 24 pressure vessel 2ndstage pyramidal two-stage array with seven element long pressure vessels. The designincorporated the use of seven ultra-low pressure reverse osmosis (RO) membrane elements per pressure vesselin the 1st stage. This is followed by a 2nd stage containing 4 ultra-low pressure RO membraneelements and then 3 high-flow/low-rejection nanofiltration (NF) membrane elements in the same pressurevessel.This unique design, referred to as a Double Hybrid RO/NF design, produced the client'srequired stringent permeate water quality at a very low operating pressure of about 100 psi.Pilot testing was required to develop and confirm a design basis and rejection criteria for eachtype of RO and NF membrane employed. The position of each RO and NF membrane in thesystem has an impact on the specific water quality that the train can produce. Includes tables, figures.
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