Which unit expresses a loading rate for a filter?

Which unit expresses a loading rate for a filter?

• A. gpm per ft²
• B. gpd per ft²
• C. mg/L per min
• D. liters per second per square meter

Answer: (A)

A filter loading rate is the amount of water passing through a square foot of filter media each minute, so the standard way to express it is gallons per minute per square foot. This directly shows how much flow the filter area is handling in a given time, which is exactly what operators need for sizing and backwashing. Using gallons per day per square foot would give a rate, but it’s per day and much too coarse for operational decisions. Concentration units like mg/L per minute mix amount with time in a way that isn’t about flow through the filter area. And liters per second per square meter describes a velocity-like measure rather than the practical loading rate in common US practice. So gpm per ft^2 best expresses the loading rate.

A filter loading rate is the amount of water passing through a square foot of filter media each minute, so the standard way to express it is gallons per minute per square foot. This directly shows how much flow the filter area is handling in a given time, which is exactly what operators need for sizing and backwashing. Using gallons per day per square foot would give a rate, but it’s per day and much too coarse for operational decisions. Concentration units like mg/L per minute mix amount with time in a way that isn’t about flow through the filter area. And liters per second per square meter describes a velocity-like measure rather than the practical loading rate in common US practice. So gpm per ft^2 best expresses the loading rate.