RO DESALINATION PROCESS

Reverse Osmosis is used to extract fresh water from Tampa Bay's salt water.

Tampa Bay Seawater Desalination uses a process called reverse osmosis (RO) to produce drinking water from seawater. RO has been successfully used in nearly 200 water and wastewater treatment plants throughout Florida and produces some of the highest quality drinking water in the world.

Tampa Electric’s Big Bend Power Station already withdraws and discharges up to 1.4 billion gallons a day of seawater from Tampa Bay, using it as cooling water for the power plant. The Tampa Bay Seawater Desalination plant “catches” approximately 44 million gallons (mgd) of that warm seawater a day, separates it into drinking water and concentrated seawater.

The unused concentrated seawater is returned to TECO's cooling water where it is diluted with up to 1.4 billion gallons of water before it is discharged to the bay.

Desalination Process

There are basically three main treatment elements in the desalination process: pretreatment, reverse osmosis, and post-treatment.

Pretreatment

Pretreatment must be rigorous to remove sediment, organic matter and other microscopic particles to ensure efficient reverse osmosis operations.

Seawater entering the plant is first treated with chemicals to allow eventual settling of particles. It then goes through traveling screens that filter out shells and other larger debris. The screened water then goes through settling chambers. Similar to a traditional surface water treatment process, particles in the conditioned water clump together and settle out.

The next step in pretreatment is sand filtration, where smaller particles are filtered from the water. Next, diatomaceous earth filters eliminate microscopic materials before the water passes through cartridge filters, the last barrier before the RO process.

Reverse Osmosis

Reverse osmosis is what distinguishes a desalination plant from a traditional surface water treatment plant. During RO, high pressure forces the pretreated water through semi-permeable membranes, separating saltwater from freshwater and leaving salt and other minerals behind in a salty solution.

The size of each RO membrane pore is about .001 microns, which is about 1/100,000th the diameter of a human hair.

Post-treatment

The Tampa Bay Seawater Desalination Plant produces up to 25 million gallons per day of desalinated drinking water. Before that water is delivered to Tampa Bay Water, chemicals are added to stabilize the water. The water is then pumped to the regional facilities site, where the desalinated seawater is blended with treated drinking water from other supply sources before being delivered to Tampa Bay Water’s member governments.