Sequestration and Transformation in Chemically Enhanced Treatment Wetlands: DOC, DBPPs, and Nutrients

This paper examines the effectiveness of chemically enhanced treatment wetlands (CETWs), wetlands that received water treated with coagulants, to remove dissolved organic carbon (DOC), disinfection byproduct precursors (DBPPs), nutrients, and metals from agricultural drain water. Wetlands consisted of controls with no coagulant addition, ferric sulfate dosed, and polyaluminum chloride dosed treatments. CETWs were more effective in removing DOC, DBPPs, phosphate, dissolved organic nitrogen, and metals than control wetlands. Coagulation-treated wetlands removed 245-349 g/m2/year DOC, whereas control wetlands produced 51 g/m2/year. Wetland passage released DOC in the controls and dosed treatments; this release was directly correlated to temperature, suggesting thermally dependent mechanism(s) were partly responsible. A first-order plug flow reactor kinetic model that considered hydraulic retention time (HRT), temperature, and DOC concentration was tested for wetland DOC processing. Models indicate that operating CETWs at high coagulant dosing and low temperature can result in the lowest DOC release. Operating at the lowest HRT to meet discharge targets helps overcome wetland processes that increase DOC release and provide the smallest footprint needed for treatment.