The Recirculating Sand Filter (RSF) concept was introduced in the late 1960s and early 70s by public health engineers from Illinois who were experimenting with sand filter designs. An RSF system is a modified version of the single-pass open sand filter. It was designed to alleviate the odor problems associated with open sand filters. The odors were eliminated through recirculation, which increases the oxygen content in the effluent that is distributed on the filter bed.
Recirculating Sand Filters are a simple, compact method of providing a higher level of treatment of wastewater as compared to conventional septic systems. RSFs are especially attractive for large flows and/or high strength wastes.