Power to the pupils

Dania Beach Public Services and partners celebrate the March 27 dedication of their award-winning water treatment plant. The facility earned LEED Gold certification by skillfully compensating for the energy requirements of nanofiltration. For example, the white overhang (far left) blocks direct sunlight but lets in enough natural light to illuminate 95% of the building. On the treatment side, variable-frequency drives were used with high-efficiency pump motors to lower power demands. Photo: CDM Smith

COMPENSATING FOR CONCENTRATE Broward County water has a high organics content — thus the decision by Dania Beach Public Services Department to pursue nanofiltration in parallel with the city's existing lime-softening system. Just one problem: Membrane processes retain 15% to 20% water, leaving behind high levels of waste concentrate. The solution is a three- or four-stage membrane system that uses concentrate from one stage as feed water for the next. Up to 95% of water can be recovered depending on plant configuration. Next challenge: Nanofiltered water is basically distilled water, so hardness and alkalinity must be returned before distribution. Mixing the permeate with lime-softened water, which has an excess of both, saves chemical costs. The concentrate that exits the plant is discharged to the sanitary sewer system. Operating at lower concentrate volumes reduces the need to buy water from the county, saving $100,000 annually. Diagram: CDM Smith

A LAKOS Separators and Filtration Solutions Model JPX-0650-L/FLG/S6 separator keeps sand from migrating into the cartridge filters and damaging the membranes. Photo: Frederick Bloetscher

GE Water & Process Technologies' Muni.Z 5-micron polypropylene filters elements in Fil-Trek Corp. Model S6GLH30-087-4-10F-E-E5 cartridge housings remove sand and particulates from source water before membrane filtration. Photo: Frederick Bloetscher

The consulting firm Biwater designed and built the membrane skid testing bank instrumentation. All electrical systems in the old lime-softening plant were replaced with higher-efficiency systems and all instrumentation was moved to one central control center in the new operations building. Photo: Frederick Bloetscher

A new chemical feed system was required to feed sulfuric acid and anti-scalant to raw water to reduce pH before nanofiltration. A custom-designed Indusco Environmental Services Inc. degasifier removes the carbon dioxide that nanofiltration produces to restore pH. After leaving the degasifier tower, the membrane permeate is mixed with the lime-softened water in a 50:50 ratio. Photo: Frederick Bloetscher

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