Faced with continuing growth and redevelopment, an aging water treatment plant, and increasingly stringent environmental regulations, Dania Beach, Fla., Public Services Department sought to design-build a new nanofiltration/reverse osmosis membrane process expansion to the city's existing 3-mgd lime-softening plant. The new treatment facility will meet future demand while improving both water quality and color. By using energy-efficient equipment, construction materials with high recycled content, and less water via xeriscaping and low-flow fixtures, the project also reflects the city's desire to provide sustainable infrastructure services.
The project — a collaboration between the city's public services department, a local university, and consulting engineers — shows how intellectual capital can be harnessed to produce cost-effective and long-lasting operational enhancements.
I'm a Florida Atlantic University College of Engineering and Computer Science professor who had been serving as a de facto consultant to Public Services for 10 years. When the department began drawing water from a new county wellfield, operators noticed it had much higher color and more organics than the city's wells, which were threatened with saltwater intrusion. Public Services needed to remove color, organics, and trihalomethane (THM) precursors while also increasing treatment capacity.
Nanofiltration was deemed to be the best process for meeting these goals. However, the reverse osmosis process presents two potential challenges for water-limited areas like Dania Beach: waste concentrate that must be disposed in an environmentally safe manner, and up to 20% water loss.
I assigned two groups of civil, environmental, and geomatics students the task of reducing concentrate volumes as their senior design project. Their solution had to be flexible enough to treat variable-quality raw water, achieve high system recovery, reduce energy demands, and minimize raw water and concentrate disposal costs.
They came up with an affordable innovation that can serve up to twice the city's population of 16,000 without additional capital investment: a 2-mgd, two-stage nanofiltration membrane system with convertible third- and fourth-stage reverse osmosis units. The convertible third stage operates as a single stage, allowing 91% to 92% recovery to meet concentrate disposal restrictions; or reconfigures to a third- and fourth-stage (2:1 array) to maximize water recovery and further lower operating costs. Pilot testing confirms that recovering up to 95% of raw water is possible.
After analyzing the process, site, and design issues to reduce power and water use, the students also suggested building a facility that could be certified Gold according to the U.S. Green Building Council's LEED standards, in part by generating a significant amount of power onsite from wind and solar sources. The university administered the application process with their help.
Fast track to stimulus funding
Public Services had a $8,820,923 Clean Water Revolving Loan to design and build the nanofiltration facility when the Florida Department of Environmental Protection offered to provide $2.55 million of that amount as an American Recovery and Reinvestment Act of 2009 “principal-forgiveness loan” (the law's term for a grant).
Public Services had identified design-build as a potential bidding option because the project-delivery method would give managers firm pricing for all costs within roughly four months. Design-bid-build, on the other hand, would've taken approximately one year for completion of detailed design while adding at least $500,000 in fees. The tight deadline for awarding stimulus funds clinched the decision for design-build.
Design-build was pursued using a two-step process. The first part was qualification-based. The contractor, engineer, and membrane constructor were identified and evaluated by a five-person selection committee consisting of city employees and employees from two nearby utilities that had recently built a nanofiltration facility. Of the seven qualifications packages the committee received, the two top-ranked firms were asked for cost proposals.
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.