Treatment & Purification
- J. Robert Dean Water Treatment Facility
- Kermit H. Lewin Reverse Osmosis & Marathon Reverse Osmosis Water Treatment Facilities
J. Robert Dean Water Treatment Facility [Public Water System Identification (PWS ID) Number: FL4134357]
The water treatment plant is an integrated source facility staffed by state-licensed personnel. Groundwater extracted from the Biscayne Aquifer is the primary source water for this facility. A secondary groundwater source, the Floridan Aquifer, is utilized to a much lesser extent.
The Biscayne source water is classified as very hard due to the high concentration of calcium in the water. A process called lime softening is used to reduce calcium hardness.
Lime softening is achieved by the addition of excess calcium under high pH conditions. This allows the water to become supersaturated with calcium, causing the calcium to sink to the bottom of the lime softening treatment unit, leaving less hard (softened) water for use by Florida Keys Aqueduct Authority (FKAA). The FKAA finished product water is considered moderately hard.
The softened water is then piped to dual media filters, which are made up of layers of anthracite and fine sand, for additional removal of particles (calcium) and further purification. Chlorine and ammonia are injected into the water to form chloramines, which provide long-lasting disinfectant protection without the objectionable taste and odor of regular chlorine. Fluoride, which is recommended for drinking water by the American Dental Association to prevent cavities, is also added.
Low-Pressure Reverse Osmosis (LPRO)
In order to comply with Biscayne Aquifer withdrawal limitations, a Floridan wellfield and LPRO water treatment plant were constructed. Operational since the summer of 2009, the LPRO water treatment plant treats the brackish water of the Floridan Aquifer. The Floridan raw water contains approximately 4,000 to 5,000 parts per million (ppm) of salt.
This concentration is significantly lower than the 35,000 ppm typically found in seawater, but higher than the 200 ppm found in the Biscayne Aquifer. This LPRO system utilizes very fine membrane elements. The water is pressurized to approximately 250 pounds per square inch (psi), rejecting the salt while allowing the passage of the pure finished water. The LPRO water is disinfected in the same manner as the Biscayne lime-softened water.
Finished water from the LPRO Water Treatment Plant (WTP) is blended with water treated from the Biscayne Aquifer. The FKAA treated water is pumped 130 miles from Florida City to Key West, supplying water to the entire Florida Keys. The water provided to customers in the Florida Keys is continuously monitored and tested to ensure the water quality is consistent, safe, and meets all federal and state drinking water standards. The FKAA operates two treatment plants.
Kermit H. Lewin Reverse Osmosis & Marathon Reverse Osmosis Water Treatment Facilities (PWS ID Number: FL5444047)
Through a process called Reverse Osmosis (RO), the Kermit H. Lewin and Marathon RO water treatment facilities desalinate saltwater, producing potable water. The saltwater from seawater wells first enters the cartridge filter to remove particulate matter. From the filters, the water is pressurized up to 900 pounds per square inch.
These pressures are significantly higher than those required at the Florida City LPRO due to the significantly higher salt content of the seawater. The high pressure forces some of the water in through the RO membranes and is commonly referred to as permeate; the remainder of water is rejected as brine and disposed in an underground injection well. The permeate flows into a degasifier and clear well, where hydrogen sulfide and carbon dioxide are removed.
Next, sodium hydroxide is added to raise the pH, and a corrosion inhibitor may be added to provide corrosion control. In the final treatment stage, the permeate is disinfected with chloramines, and the finished product is transferred to the storage tank for distribution.