How do you determine the size of a recirculating sand filter?

To determine the size of a recirculating sand filter, it is essential to understand the hydraulic loading rates, which refer to the amount of wastewater that can be effectively processed per square foot of filter area. The correct choice indicates that the size of the filter should be calculated at a rate of 1 square foot of filter area for every 3 gallons per day (gpd) of wastewater.

This calculation is based on standard design criteria for recirculating sand filters, which are engineered to optimize performance while preventing issues like clogging or poor treatment efficiency. At this loading rate, the filter is sized to allow adequate contact time between the wastewater and the sand medium, facilitating effective treatment through biological and physical processes.

When the system is designed correctly, it mitigates problems related to overloading, which can lead to inadequate treatment or premature failure of the filter system. This understanding is crucial for ensuring compliance with environmental regulations and providing effective wastewater management.

The other options do not align with the established guidelines for recirculating sand filters, as they either under or overestimate the necessary filter area, potentially compromising the treatment performance of the system.