Historically, Florida’s Tampa Bay region relied primarily on groundwater to meet its potable water needs. In the 1990s, population growth in the Tampa Bay area outpaced the development of new drinking water supplies. The demand for water, combined with drought and continued development, strained the environment’s long-producing wellfields. New water supplies were needed to offset groundwater pumping, reduce environmental stress, and meet the growing needs of the region. In 1998, a plan was developed to implement alternative sources of drinking water. One part of the plan was to build a desalination plant that could remove salt from seawater and send millions of gallons of treated drinking water to residents every day. That plan would eventually lead to what is now the largest seawater desalination plant in North America.
Designed for a maximum capacity of 28.75 MGD, the Tampa Bay Desalination Plant was originally designed and built by others to supply 10% of the region’s drinking water. Since the start-up in March 2003, the plant was only capable of working intermittently and, although it initially produced water to the required quality, it became impossible to maintain the production to comply with client requirements. In June 2005, Tampa Bay Water was forced to shut down the plant.
Desalination is no easy task. Although the original plant produced some water, the design was deficient, causing costly filters to clog too quickly. After Tampa Bay Water shut down the plant, ACCIONA Agua and its JV partner began to develop a solution that would remediate the facility.
Tampa Bay Water enacted a design-build-operate prequalifica- tion phase, after which short-listed teams offered proposals to remediate the original treatment plant.
This form of procurement, based on an extended performance test contract payment regime, rewarded the design-builder for proving that the remediation works designed and constructed by the ACCIONA Agua led team were reliable and robust solutions that proved capable of meeting quality and quantity objectives required by Tampa Bay Water whilst protecting Tampa Bay Water from technical and performance related risks.
ACCIONA Agua identified 40 deficiencies in the original facility and developed the following remediation strategies:
• Control bio-growth, both macro and microscopic
• Add a coagulation-flocculation stage upfront of the media filtration
• Improve mechanical and flow distribution to the sand filters
• Add an additional re-treatment stage: Diatomaceous Earth Pre-coat Filtration
• Modify the RO first pass membrane configuration (2 stages) • Modify the RO cleaning and control system
• Improve the re-hardening system to address high turbidity • Add a Waste Treatment System: Lamella clarifier and sludge processing effluent treatment
• Automation and control of the whole system
The ACCIONA Agua JV constructed and commissioned these new treatment process stages to treat source water with variable turbidity, organics, suspended solids, and temperatures to comply with the quantity and quality of drinking water required by Tampa Bay Water.
The plant has successfully dealt with shallow water, sharp temperature changes (depending on whether the power plant is working or not), spikes of raw water turbidity, and regular infestations of shellfish. Since its takeover test at the end of 2007, and over the past 11 years of operation, the plant has been producing potable water under contract specifications with no penalty events, including a four-month non-stop period at full production capacity test.
The desalination plant has been a successful drought-proof, alternative water supply for the Tampa Bay region, providing safe drinking water during the seasons with rain scarcity.
“In the Tampa Bay area, a drought such as this one used to mean pumping more water from the aquifer to replace the lack of rain. The result would be dried-up lakes and wetlands, sometimes causing permanent damage.
“No more, though. Now that Tampa Bay Water has built a desalination plant and a 15-billion-gallon reservoir, the region can handle a drought without damaging the environment. Having those facilities does impact how we can manage our way through a drought now. We can continue meeting the demand for water and not have the kind of environmental damage we had.”
—Alison Adams, TBW Chief Technical Officer
“We use the water from the bay, the seawater. We also have river water, the surface water, and we have groundwater, through our northern part of the region. The water is safe to drink and there’s no difference in taste from tap water.
“We relied 20 years ago on just one source, and it was groundwater. Having all your eggs in one basket was an issue, so now we have two more eggs in that basket. We can move and mix, and we have every base covered.”
—Chuck Carden, TBW Chief Operating Officer
“I like to refer to the Tampa Bay Seawater Desalination Plant as our secret weapon. It is there always. That should make us sleep quieter. In my case, it is like that, without any doubt.”
—Susan Latvala, Pinellas County Commissioner and Chair of the Board of Directors of Tampa Bay Water
“The remediation of the largest desalination plant in the United States has been an excellent exercise in applied engineering. Other companies had failed earlier with the original design. We have used all the capabilities of the company, from the R&D department to the construction and commissioning engineers, to provide alternatives and put them into practice, ensuring a stable and reliable operation for future years.”
—Julio Zorrilla, ACCIONA Agua USA and UK Construction Director
“The redesign and reconstruction project of the Tampa Bay Seawater Desalination Plant has been a technical and human challenge. Few facilities have such complex working conditions in terms of process, water quality, temperatures, salinity . . ..”
—Pedro Miranda, ACCIONA Agua International Desalination Production Manager