Use of saltwater from a deep water aquifer at the MFEC
An aquifer is a body of saturated rock through which water can easily move. Saline well water from the Floridan aquifer, Lower Avon Park formation (LAP), 840 feet below ground will be used for aquaculture of sportfish at the Marine Fisheries Enhancement Center (MFEC) and invertebrates grown for restoration by partners at the Florida Conservation and Technology Center in Apollo Beach, FL (Figure 1). The saltwater from the LAP formation within the Floridan Aquifer is crystal-clear, free of parasites and pollutants, and the chemistry is like natural seawater except for dissolved calcium which is three times more than what is found in natural seawater. Dissolved calcium in seawater is essential for marine fish and invertebrates, but in the saline well water at MFEC, it is too high to grow marine fish and invertebrates. Therefore, a novel method was developed by FWC scientists to reduce the dissolved calcium concentration to be like natural seawater.
Figure 1. Saline well system, well head and pressure tanks at the Florida Conservation and Technology Center (left). Pumped saline well water (right).
Reduction of the dissolved calcium concentration to be like natural seawater occurs by adding sodium carbonate (soda ash), which is used commonly in swimming pools to maintain pH balance, to the saline well water. The carbonate part of the soda ash binds with dissolved calcium to form powdered calcium carbonate (limestone) which is then separated from the resulting “seawater.” Powdered limestone is used for industrial and agricultural applications. Perhaps the limestone produced at the MFEC could be used for those purposes, as well.
An automated computer process with a series of sensors, specialized valves, and pumps was developed by FWC to reduce the footprint of the calcium reduction process. Automation relies on computers and engineering software to develop Virtual Instruments that provide a nearly continuous supply of seawater and to minimize the need for hands-on attention by FWC staff persons. A Virtual instrument (VI) is a computerized simulation of a series of physical hardware that represents a real-life machine that can be monitored and controlled by the user.
The VI for reduction of calcium concentration in saline well water was written by FWC using LabVIEW coding software to communicate with commercial computer hardware and a variety of instruments and sensors (Figure 2). The VI to make seawater from saline well water monitors and controls the amount of useable seawater stored at the MFEC and automatically makes new seawater from the saline well water when supply is needed. The VI also alerts FWC staff if attention is needed through digital feedback from any of the control points sensors and instruments.
The process includes 28 sensors, in duplication as a fail-safe, and instruments operated by 60 control points and dozens of steps. The basics of the process are:
- Raw saline well water is pumped from the saltwater well to a raw saline well water storage tank.
- Sodium carbonate is mixed into a solution with purified water and is in stored until seawater is needed.
- Seawater supply sensors in storage tanks detect when more seawater is needed.
- Saline well water and soda ash storage pumps turn on, and valves are opened for saline well water and sodium carbonate to mix in an eductor pump.
- Calcium carbonate from the reaction of soda ash with saline well water is separated from the newly made seawater by a centrifuge.
- Clear seawater is pumped to large tanks with approximately 90,000 gallons of storage capacity.