Launch Slideshow

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Power to the pupils

Power to the pupils

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    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

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    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

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    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

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    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

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    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

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    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

After evaluating the proposals and interviewing both firms, Public Services awarded the project to the lower of the two pre-qualified bidders: CDM Smith. The firm was to integrate the existing lime-softening electrical system into the new facility while maintaining complete operational service during construction.

Had the department awarded the project via design-bid-build, the project would've taken 178 weeks to move from 30% design to completion. Design-build shaved 74 weeks — a 42% reduction — from the process. The project, including migrating the existing lime-softening electrical system to the new facility, was completed within 24 months of contract award.

LEED-certifying an energy-intensive process

Public Services and CDM Smith used the student designs to fully develop the plant concepts, including their ideas for LEED certification, a voluntary system that encourages architects and engineers to design and build more energy efficiently. The program evaluates projects in five categories.

1. Sustainable Sites. LEED wants applicants to use using existing disturbed sites as opposed to virgin sites and increase green space on the site. Dania Beach's new nanofiltration facility is on the same site as the current lime softening plant, which is refurbished and available to supplement the nano-filtered water.

The design increases the volume of pervious surface by reducing the amount of asphalt on the premises, using pervious pavement, and removing unused structures. To encourage employees to use alternative transportation, parking spaces are provided for carpoolers and those who drive alternative fuel vehicles. A bus stop is located at the site boundary. Showers and a bike rack also were added.

2. Water Efficiency. The building expects to use half the water of a similar structure, roughly 100,000 gallons annually; treatment process improvements are expected to save an additional 36 million gallons annually.

The new treatment process recovers a minimum 90% water, more than most membrane systems. When running at 95% recovery, the plant is 10% more efficient.

The city altered an ordinance to preclude the need to irrigate when Florida-friendly species are planted, and rain is being captured and stored to irrigate the rest. In addition, the administrative space has low-flow toilet fixtures, waterless urinals, and low-flow faucets and showerheads.

3. Energy & Atmosphere. By definition, nanofiltration would increase power needs. To compensate, our goal was to reduce energy use by 30% over a similar building while deploying energy-saving treatment technology.

White roofs lower attic temperatures by 30° F; insulation keeps cooled air inside. A high-SEER (seasonal energy-efficiency ratio) HVAC system automatically adjusts temperature depending on internal conditions and occupancy as well as external temperature. To lower lighting costs, almost all of the building — 95% — receives sunlight. Lights that weren't eliminated were changed to compact fluorescent bulbs and automatically turn on and off. Combined, these changes are expected to reduce interior electricity use by 2 kW hours/day.

On the treatment side of the equation, variable-frequency drives, efficient motors, and controls counter nanofiltration's energy requirements. The system operates at 100 psi, well below the 120 to 150 psi that similar facilities require.

The city also buys green power credits from the Carbon Solutions Group.

4. Materials & Resources. The contractor recovered and recycled 95% of asphalt, concrete, and steel and bought additional recycled material from sources within 500 miles. This reduced transportation costs, earning two points toward certification.

5. Indoor Environmental Air Quality. Since the goal here is to reduce air pollution, smoking is prohibited in both offices and the treatment plant.

In addition, the operator workspace was built using no VOC materials, paints, and finishes; low-VOC materials were used on the rugs, floor glue, paint, and cabinetry.

The facility has won a U.S. EPA award for sustainable infrastructure and a Florida Institute of Consulting Engineers design award.

— Bloetscher (h2o_man@bellsouth. net) is associate professor in Florida Atlantic University's College of Engineering and Computer Science and president of Public Utility Management and Planning Services Inc.