What is the collected treated effluent from an intermittent sand filter discharged by?

The collected treated effluent from an intermittent sand filter is discharged by a gravity discharge underdrain or a pump discharge underdrain. This method is integral to the design of the septic system, where the effluent, after being treated by the filtering action of the sand, needs a reliable removal mechanism to prevent ponding and ensure continued operation.

Gravity discharge utilizes the natural slope of the land to allow treated effluent to flow away from the filter, relying on gravity to move the water into the next phase of treatment or disposal. This system is often preferred for its low operational cost and minimal energy requirement. In cases where the landscape does not allow for gravity flow, a pump discharge underdrain can be employed. This system actively removes the effluent by using mechanical pumps to convey it to a designated area, ensuring proper drainage regardless of the site conditions.

The other options presented do not accurately describe how effluent is discharged from an intermittent sand filter. Direct evaporation, surface-level outlets, and engine-driven pressure discharges are not standard methods for discharging treated effluent from these systems, as they do not effectively manage the volume of effluent produced or may lead to inadequate treatment outcomes.