ASABE Technical Library - Abstract
Member and Access Notice
IMPROVING THE NITROGEN REMOVAL EFFICIENCY OF RECIRCULATING SAND FILTERS
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 701P0104, . (doi: 10.13031/2013.15787)Authors: E. E. Richardson, A. T. Hanson, R. P. Richardson
Keywords: Recirculating sand filters, nitrogen removal, on-site systems
Recirculating Sand Filters (RSFs) are commonly used to treat septic tank effluent from individual
homes and small communities. It is generally accepted that the RSFs can provide partially
nitrified effluent, with nitrogen removal efficiencies up to 40 percent. However, for applications
such as schools and restaurants, where the influent total nitrogen concentrations can be as high as
70 to 80 mg/L, RSFs can fail to achieve sufficient nitrogen removal to comply with the permit
requirements.
The RSF system that will be described in this paper is located in Chaparral, New Mexico. The
RSF unit currently serves one elementary school and the middle school of the community. After
the installation of the RSF unit, the Biochemical Oxygen Demand (BOD5) and Total Suspended
Solids (TSS) removal efficiencies were about 98 and 90 percent, respectively. However, the
nitrogen removal efficiency was sporadic, with an average of about 20 percent. In order to
enhance nitrogen removal and to comply with the 27 mg/L effluent nitrogen requirements of the
discharge permit, we applied simple process modifications to the 25,000 gallon per day RSF
treatment facility. The process modification included installation of a pump and a recycle line to
return the nitrified RSF effluent to the septic tank. The described process modification is a lowcost
and effective method of enhancing nitrogen removal, especially on existing systems without
changing major design components of a treatment facility. With the improvement, the nitrogen
removal efficiency observed at the plant increased to 54 percent.