What is the typical backwashing flow rate for a manganese greensand filter bed, depending on water temperature?

• A. 5-7 gpm/ft²
• B. 10-12 gpm/ft²
• C. 15-18 gpm/ft²
• D. 20-25 gpm/ft²

Answer: (B)

When considering the backwashing flow rate for a manganese greensand filter bed, the correct flow rate typically ranges from 10 to 12 gallons per minute per square foot (gpm/ft²). This appropriate range is influenced by various factors, including the type of media used and the temperature of the water being treated.

Backwashing is an essential maintenance process for filter beds, as it helps to remove accumulated particulate matter and restores the media’s effectiveness. Manganese greensand specifically requires a substantial flow to ensure that the media is effectively fluidized during the backwashing process. This flow rate is sufficient to dislodge contaminants without damaging the filter bed itself, and it ensures optimal cleaning.

Lower backwashing flow rates, such as those found in the option that suggests 5-7 gpm/ft², may not provide enough force to properly clean the bed, while higher rates like 15-18 gpm/ft² or 20-25 gpm/ft² could potentially lead to issues such as media loss or compaction. As a result, the 10-12 gpm/ft² range is optimal for maintaining filter performance and longevity.