Constructed wetlands to remove nitrate

Free water surface treatment wetlands are finding increasing usage for nitrate reduction in waters. An extensive database now exists, in fragmented form, in many publications and operating reports. First order models are appropriate, if implemented with due regard to hydraulic efficiency and flow patterns. Annual average rate constants are distributed around 0.25 d(-1). Performance is better at higher water temperatures, with a modified Arrhenius temperature factor of 1.088. Values of the tanks-in-series parameter are centered around N = 4.5. Wetland performance for nitrate removal also increases with prevention of short-circuiting and better areal contacting. Higher nitrate removal efficiencies are associated with submergent and emergent soft tissue vegetation, and tower efficiencies with unvegetated open water and with forested wetlands. Carbon availability Limits denitrification at high nitrate loadings; however, wetlands produce carbon in sufficient quantities to support typical municipal and agricultural nitrate Loads. Significant ancillary benefits of ecological diversity and wildlife habitat are certain to accompany the project. Economic issues include land cost and water transport.