Determining nitrogen removal in US sewage treatment

Lia R. Cattaneo1, Robert Bastian2, Lisa M. Colosi1, Allison M. Leach3, James N. Galloway1

 1University of Virginia, 291 McCormick Road, Charlottesville, VA, 22904 USA, [email protected]

2United States Environmental Protection Agency, 1200 Pennsylvania Ave., NW, Washington, D.C. 20460

3University of New Hampshire, 131 Main Street, 107 Nesmith Hall, Durham, NH, 03824 USA

Abstract

Most of the nitrogen (N) in food passes through the human body, is excreted, and enters the wastewater stream. This sewage N is an important component of the food consumption N footprint. The US N-Calculator (a per capita nitrogen footprint tool) calculates N removal from sewage by estimating the proportion of homes connected to wastewater treatment plants (WWTPs) with tertiary treatment N removal technologies. However, this assumes that no N is removed in WWTPs with primary or secondary treatment or in WWTPs with tertiary treatment processes other than nitrogen removal. This paper uses a mass balance approach to revise the factor used in the US N-Calculator to better represent the N removal from sewage treatment in the US. N in wastewater can have several fates: release to the environment through septic systems, release to the environment through WWTPs, release to the environment in disposed sludge, conversion to N2 in WWTPs, and beneficial use as land-applied sludge. The national average N removal factor (55%) represents N converted to N2 or used as beneficial sludge compared with the N in wastewater. The removal from just WWTPs was 73%. The new total removal reduces the average US per capita food consumption N footprint by 2.63 kg N, resulting in a total footprint decrease of 6.7%.