Tampa —- Plagued by regular drought, this booming Florida community of 2.4 million now boasts what officials call their secret weapon: a plant that turns seawater from Tampa Bay into fresh water for residents.

Local officials cut the ribbon on the new $158 million desalination plant last month. Supplying 10 percent of the region's water needs, it is the largest such plant in the United States.

The plant's progress has been followed closely both in this country and abroad. Water experts say it could significantly accelerate construction of such facilities in areas that suffer chronic water shortages.

"It will be a model around the country," said Don Correll, president of American Water, the nation's oldest investor-owned water utility. "You are going to hear everyone talking about the Tampa Bay experience."

But Tampa's secret weapon also has been a public nightmare, and the plant's construction offers a cautionary tale for Georgia and other coastal states hoping to tap the oceans.

Initially conceived more than a decade ago, the plant opened five years behind schedule and $48 million over budget. While operating costs are low by desalination standards, they are double initial projections.

Tampa officials faced a slew of problems that threatened to scuttle the project altogether. The first contractor declared bankruptcy and abandoned the plant after repeatedly failing to make it run properly.

Engineers also underestimated the difficulty —- and expense —- of filtering raw seawater before routing it through the desalination process.

"I describe Tampa Bay water as primordial ooze," said General Manager Jerry Maxwell. "It's the seawater chemistry that's so tricky."

Last month's opening came after American Water and a Spanish company specializing in desalination were brought in to reconfigure the plant and salvage the project.

"Yes, it's expensive. Yes, it's complex," said Maxwell. "But it's good to know we have this [water] source that's safe and reliable."

Similar problems

Twelve years ago, Tampa-area residents faced problems now familiar to metro Atlanta. Explosive growth in the 1990s was forcing urban water utilities to venture into outlying counties for groundwater.

Water tables dipped drastically, drying up lakes and bogs. Coupled with a two-year drought, the region faced a major water supply shortage. The area also had its own version of the "water wars," as outlying counties objected to Tampa residents raiding their groundwater.

To settle the disputes, metro Tampa's three major counties and its three largest cities banded together under a single water authority in 1998. The new entity launched a 10-year plan to cut groundwater pumping from 181 million to 90 million gallons per day.

To meet the goals and plan for population growth, the region needed to increase water supplies by 85 million gallons per day.

Saltwater was only one part of the supply plan. The region also built a 15 billion-gallon reservoir on 1,100 acres southwest of the city.

"It's like financial planning," said Ken Herd, Tampa Bay Water's operations director. "You don't want to have all your eggs in one basket."

Electricity bills high

Desalination technology has evolved over the past 10 years, but the process can essentially be broken down into three phases.

Raw seawater is filtered and treated to remove particles and solids. Then it is pushed through ultrafine membranes under high pressure. The membranes, contained in long cylinders, capture the salt, forcing a stream of desalinated water to the middle of the filter. A salt concentrate flows out the back end. Then chemicals are added to stabilize the water because the membranes remove not only the salt, but all the minerals. Untreated, the desalinated water would literally rip the metals off the insides of pipes.

Engineers built the Tampa plant at Apollo Beach, 14 miles south of the city, next to Tampa Electric's Big Bend Power Station. The location is strategic for several reasons. The power plant provides a ready supply of water and electricity. Desalination requires huge amounts of electricity to drive seawater through the reverse osmosis membranes, so much, in fact, that the water plant has its own power substation.

The plant's electricity bills total $8 million to $10 million a year, Maxwell said, as much as 50 percent of the total cost of operation.

The plant also relies on Tampa Electric for water.

About 1.4 billion gallons of seawater passes through the power plant every day. Diverting some of it to the desalination plant avoided the expense of building a separate intake system.

The power utility also helps the plant dispose of the salt concentrate. It takes 44 million gallons of seawater a day to produce 25 million gallons of drinking water, leaving behind about 19 million gallons of salt concentrate.

The location next to the power plant enables the desalination plant to dilute the concentrate with the cooling water before it returns to the bay.

Membrane problems

The plant's initial design failed to remove all the particles, microorganisms and dissolved solids in the pretreatment stage, wreaking havoc on the filtering membranes. The repeated fouling led to numerous shutdowns and ruined the membranes, which were intended to last up to seven years. Separate backup filters that were supposed to last 60 days lasted less than a week.

Of the $48 million spent to correct the problems, $6 million went toward replacing most of the 10,000 membrane filters used in the plant.

The plant is operating near its maximum production of 25 million gallons a day, but still not at the cost initially promised.

The average operating cost of $3.38 per 1,000 gallons is roughly twice the $1.71 figure promised by the first contractor. In Tampa, that compares to roughly $1 per 1,000 gallons for treating groundwater and $2 per 1,000 for treating surface water.

Maxwell said the security of having a drought-proof water supply justifies the expense, a view echoed by much of the city's local leadership.

With the plant now running smoothly, Maxwell said he expects desalination to migrate to other regions of the country, including Georgia.

"I doubt the costs would be higher than they are here," he said.

 ELIZABETH LANDT / Staff 
HOW THE TAMPA BAY WATER DESALINATION PLANT WORKS 

Seawater or brackish water

Power plant

Filter process: Filters out everything but the salt and water —- from large particles like shells to microscopic materials. At the Tampa plant, this takes four steps.

Solids: The solids removed from the water are prepared for off-site disposal. 

High-pressure pumps: Water is pumped through the membrane assembly at 900 pounds per square inch  to remove most of the salt from the water.

Emergency filter: The water is filtered one more time to remove any contaminants.

Post-treatment: The desalinated water is highly unstable. Minerals are mixed back into the water before it is pumped to the regional water facility.

Fresh water: The desalinated water is mixed with treated fresh local water. 

Reverse-osmosis membranes

Concentrated saltwater (brine)

Energy recovery turbine: Recaptures about 30 percent of the energy used to pump the water through the membranes, which helps lower energy costs.

brine return: The brine is sent back to the power plant and mixed with a large amount of water used in the cooling system of the power plant. The mixed water is then returned to the bay by a discharge canal.  

Discharge canal

Flow chart illustrates the process with icons.

Source: Tampa Bay Water