NITROGEN REMOVAL AND OTHER PERFORMANCE FACTORS IN RECIRCULATING SAND FILTERS

Abstract

Recirculating sand filters (RSFs) are used to provide advanced wastewater treatment for systems as small as for individual homes and small commercial flows up through systems for small communities. They are most often used for clusters of homes or small communities and are known to be robust and to provide consistent effluent quality. This paper presents performance data from over 40 different RSFS. These units differ in design, strength of the input wastewater and media used. Data showing both input and output water quality are presented for 15 systems and effluent quality only for another 28 systems. All RSFs are preceded by septic tanks for pretreatment. Systems operating in five states having different climatic conditions are producing similar effluent qualities with low BOD and TSS. Nitrogen removal rates for systems treating domestic strength wastewater ranged from 25% to 76% with all but one over 40%. Systems treating higher strength commercial wastewater showed nitrogen removal rates as high as 84% without any special intervention to bring nitrified effluent into contact with a carbon source other than that provided by septic tank effluent in the recirculation tank.