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Constructed wetlands have been implemented as treatment systems for wastewater. Wetlands may remove nutrients and sediment through biogeochemical functions such as adsorption, nitrification, denitrification, and plant uptake. Studies have shown that constructed wetlands are able to attenuate substantial amounts of nitrogen and phosphorous from wastewater. Denitrification is the primary mechanism by which nitrogen is removed from wastewater in constructed wetlands. Research has shown that nitrification of ammonium nitrogen to nitrate may indirectly limit denitrification. One practice that may increase the nitrogen assimilation in a constructed wetland is the use of a nitrification pretreatment system such as a trickling filter.

This study evaluated a site where a swine lagoon had leaked into the surrounding groundwater. The swine lagoon was eventually closed-out and a plan to pump out the contaminated groundwater was initiated. The water was pumped into a constructed wetland where nutrients could be removed. After three years of pumping the contaminated groundwater, a trickling filter was implemented to nitrify the wastewater before it was discharged into the wetland.

Over the course of the study the constructed wetland assimilated greater than 76% of the total nitrogen and more than 22% of the total phosphorous that it received. The nitrification pretreatment system converted 20% of the NH4-N it received to NO3-N on a mass basis. Although the nitrification pretreatment system was functional, nitrogen concentrations entering the trickling filter were low and there was no identified increase in total nitrogen assimilation within the constructed wetland.