Abiotic Capture of Stormwater Nitrates with Granular Activated Carbon

Abstract

Stormwater runoff from urban and agricultural watersheds carries nitrate, which is difficult to remove because it is highly soluble and thought to be relatively inert in abiotic processes such as ion exchange and sorption. Thus, current practice relies on denitrification to capture nitrate in stormwater treatment practices, requiring storage of captured stormwater, anaerobic conditions, and enough residence time for the bacteria to convert nitrate to nitrogen gas. The purpose of this research was to (1) quantify abiotic nitrate removal and removal capacity of two granular activated carbons (GACs), and (2) illustrate use of GACs in stormwater treatment practices. Batch and upflow column experiments found that two commercially available GACs captured nitrate abiotically, although competition between (bi)carbonate and nitrate limited removal of nitrate. Compared with removal of nitrate by denitrification, abiotic capture of nitrate during storm events requires less stormwater storage volume and less residence time to remove nitrate because it accumulates on the media as stormwater passes through the filter. This suggests that nitrate can be removed from stormwater with less storage and smaller treatment practices.