| A private utility in Southern California received funding to fluoridate its raw water supply and adopted a dual-tank fluoride saturator and feed system designed to precisely feed sodium fluoride while minimizing maintenance. Photo courtesy of Integrity Municipal Systems, LLC. |
The dual-tank fluoride saturator and feed system is designed specifically for smaller plants (1 to 3 million gallons pumped per day per well). It uses a saturator tank and a secondary solution tank (in contrast to traditional systems that utilize a single tank in which a sodium fluoride bed is flooded with water to form the fluoride solution, which is then withdrawn to the injection point through a metering pump). The IMS system minimizes the chance of carryover of sodium fluoride solids from the saturator tank to the solution tank and into the metering pump.
In the saturator tank, soft water enters through the bottom and flows up through a bed of sodium fluoride crystals via a PVC pipe distribution system. Saturated sodium fluoride solution gradually flows into the secondary solution tank via an overflow pipe. The solution tank is fitted with an ultrasonic level switch that detects both high and low water levels. When the solution level in the solution tank hits the low level, a solenoid valve opens, and make-up water is added to the saturator tank.
The make-up water percolates through a bed of sodium fluoride placed in the saturator tank. A flow control valve (FCV) controls the flow of make-up water - a critical process because saturation is optimal at a specific water flow rate.
As water flows into the saturator tank, the saturated solution overflows into the solution tank until it reaches the high level. The level switch then closes the solenoid valve and stops the inflow of make-up water.
A pre-wired electrical panel powered by a 110-volt electrical supply controls the fluoride feed system. The metering pump receives an external 4-20 mA signal and draws saturated fluoride solution from the solution tank to the injection point at the main water line.
Both of the tanks are contained in a fiber-reinforced plastic (FRP) containment structure that contains any spillage from the system. If spillage does occur, an alarm is tripped to alert the operator of a required maintenance issue.
Tying the system into the utility's existing infrastructure was a reasonably simple process. The fluoridation system is tied into the supervisory control and data acquisition (SCADA) system. An auto-dialer alerts the staff in the event of an alarm, which is triggered following a system shutdown in the event of excessive fluoridation. An alarm further indicates the need for an adjustment if the water fluoridation level is below 0.70 mg/L, but the system does not shut down.
