Wiki Page, Community Fluoridation: Module 6 - Fluoridation System Design Part 1

Wiki Page
2017-07-06T15:19:29-06:00

Dry Feed System

Module 6 Part 1 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 dry feed system, sodium fluorosilicate is typically used. As shown in the images below, the dry powder is supplied to a solution tank to make a fluoride solution which is then fed into your water. The first image is of a feed screw system. The second image is belt feed system.

In order to performance process calculations you need to know the differences between your treatment facility capacities:

−Maximum hour capacity (2.0 million gallons per day, MGD)

−Maximum day capacity (1.4 MGD)

−Maximum month capacity (1.0 MGD)

−Annual average capacity (0.8 MGD)

−Actual capacity (could be any of the rates)

−Actual operating rate (measured)

−Minimum capacity (0.2 MGD)

Most groundwater wells deliver constant volume, often to a storage tank

Then you can determine the amount of fluoride that you need to add. Typically we follow the conversion wheel

...but because of the purity and AFI differences, we need to account for those in our calculations.

Now let's do a sample calculation.

Scenario:

Plant 2 has an average daily flow of 5.8 MGD and the source water has a natural fluoride level of 0.2 mg/L. The recommended level for oral health is 0.7 mg/L. The fluoride product is sodium fluorosilicate with 98.5% purity. What is the dosage required and how many pounds will be necessary?

What we know:

Average daily flow is 5.8 MGD

Recommended fluoride level is 0.7 mg/L

Natural fluoride level is 0.2 mg/L

Recommended minus natural is

0.7 – 0.2 = 0.5 mg/L = dosage

According to our AFI table, the AFI is 0.607

Purity is 0.985

So the feed rate should be 41 pounds per day or

1.7 pounds per hour (dividing by 24 hours)

0.78 kilograms per hour (divide pounds by 2.2 to get kg)

13 mg per minute (1000 mg in a Kg, and 60 minutes in an hour)

Now, it's time for a quiz! Click next at the bottom for Module 6 - Quiz 1.