Nitrogen removal for on-site sewage disposal. Field evaluation of buried sand filter/greywater systems

The nitrogen removal associated with buried sand filter/greywater systems, patterned after RUCK system designs, was assessed in a field laboratory and two fullscale systems in Rhode Island. Specifically, the study tested the ability of buried sand filters to support nitrification and the suitability of household greywater as a carbon source for denitrification. The buried sand filter/greywater systems removed approximately 50% of the total nitrogen in household wastewater before the wastewater entered the soil absorption field. Nitrification within the buried sand filters was a major limiting factor to complete nitrogen removal, with filters generally providing 50-80% nitrification. Denitrification rates of 100% were routinely observed using greywater as a carbon source and a rock tank with a three day retention period as an anaerobic environment. Rock-free tanks with a one day retention period were also assessed as an anaerobic environment, providing an average of 74% denitrification. Buried sand filter/greywater systems show promise as a nitrogen removal system for on-site sewage disposal.