Course: BFM 203 Water Treatment and Control

Lecture

(7/8)

Clarification Mathematics

Operators may be required to calculate loading rates and detention times for various reasons, including troubleshooting ineffective operation. The following information is a summary of the definitions and calculations with which you must be familiar in order to perform necessary clarification mathematics. In order to perform these calculations, you will need to know the following values:

- Flow (cu. ft./second)
- Surface Area (ft^2)
- Depth (ft)

Surface Loading Rates - Also referred to as "surface settling rate" or "surface overflow rate," this is a hydraulic loading factor expressed in terms of flow per surface area. Typical values of surface loading rates for primary clarifiers are 600 - 1000 gallons per day per square foot.

Detention Time - As noted previously, detention time is the theoretical time over which water is held in a clarifier based on the flow and volume if the tank. Most primary clarifiers are sized to have detention times in the range of 1 1/2 - 2 1/2 hours at average flow.