The Gulf Coast seawater desalination project will likely use a process called reverse osmosis (RO) to produce high quality drinking water. RO uses pressure to force water through a series of membranes to separate the salt water from the fresh water.
Seawater desalination using RO produces some of the highest quality drinking water in the world. RO is a proven technology that has numerous applications. There are 30 known seawater reverse osmosis plants in the world that use technologies that are similar to those being considered for the Gulf Coast Seawater Desalination Project. Over the past few years, technology advancements and manufacturing improvements have made the cost of producing desalinated drinking water more affordable.
Here’s How It Works.
An RO plant has four main components: 1) the source water intake and concentrate discharge systems, 2) the pretreatment process, 3) the RO membrane treatment, and 4) the resulting fresh water storage, pumping and stabilization processes.
Intake & Pretreatment
It takes between 45 and 50 million gallons of seawater to make 25 million gallons of drinking water. Seawater or source water is pumped to the pretreatment facility. There it is screened to remove debris and to prevent plants and marine life from entering the system. The water then goes through filters to remove any large particles still in the water. The flow stream then receives water treatment additives before going through an even finer cartridge filter.
RO Membranes
After pretreatment, the water moves through the RO membranes where -- under high pressure -- it is forced through the membranes to separate fresh water from salty.
Product Water Storage, Treatment and Distribution
The finished water is piped to a storage tank. Before entering the finished water delivery pipelines, the water receives chemicals to adjust pH and provide disinfection. The desalinated water from the Gulf Coast facility will be blended with Tampa Bay Water’s other water supplies before being distributed throughout the region.
Discharge
The left over salt water is twice as salty as it was before desalination. This concentrated salt water is diluted and blended with out seawater sources through an environmentally acceptable disposal method. When the concentrate is sufficiently diluted, adverse environmental effects are minimized. The disposal methods being considered are: a) blending concentrate with a power plant’s cooling water, and b) piping discharge up to 13 miles into the Gulf of Mexico, where the Gulf floor is 30 feet deep. Permitting agencies feel this is a safe depth to ensure adequate mixing.
Safeguarding the Environment
The project will face extensive scrutiny from environmental and other regulatory organizations all during the development phase. Agencies that will be involved in the review process include the Florida Department of Environmental Protection, Southwest Florida Water Management District, and the United States Environmental Protection Agency, as well as Pasco and/or Pinellas County. These reviews are necessary to ensure the plant’s operations are environmentally safe and comply with all regulations.
Once the plant is up and running, a long-term monitoring program will be implemented to ensure that no adverse environmental effects occur. The monitoring requirements will be conditions of the facility permit. Tampa Bay Water will review and evaluate the monitoring results to assess any impacts to the sensitive marine life in this region.
