Wiki Page, Community Fluoridation: Module 6 - Fluoridation System Design Part 3

Wiki Page
2017-06-27T15:04:26-06:00

FSA feed system

Module 6 Part 3 from Enos C Inniss on Vimeo.

There are several chemical choices available for feeding fluoride to your system. Each comes with a certain chemical purity and available fluoride ion (AFI) percentage.

For the fluorosilicic acid feed systems, as shown in the images below, there are several iterations of the system. In each, however, you should find a bulk tank, a day tank, a transfer pump, and a feed pump.

Again, the required dose of fluoride that should be added to the water = (recommended level - natural level). Knowing plant capacity and information about the fluorosilicic acid allows us to determine the fluoride feed rate using the equation:

An example calculation could look like the following.

Scenario:

Plant G has an average daily flow of 1.4 MGD and the source water has a natural fluoride level of 0.1 mg/L. The recommended level for oral health is 0.7 mg/L. If the FSA has a concentration of 25%, what is the dosage required and how many gallons will be necessary?

So, we know that

Average daily flow is 1.4 MGD

Recommended fluoride level 0.7 mg/l

Natural fluoride level is 0.1 mg/l

Recommended minus natural is the dosage 0.7 – 0.1 = 0.6 mg/L

The fluorosilicic acid AFI is 0.792

The purity is 0.25

FSA at 25 percent purity weighs 10.1 pounds per gallon. So the feed rate of 35 lbs/day divided by 24 hours is 1.4 lbs per hour.

The total feed rate therefore can be expressed in several units:

3.4 gallons per day (35 lbs divided by 10.1 pounds per gallon)

0.14 gallons per hour (3.4 gal per day divided by 24 hours)

530 mL per hour (3.4 gal multiplied by 3.78 liters per gallon)

Now, it's time for a quiz! Click next at the bottom for Module 6 - Quiz 3.