GROUNDWATER TREATMENT USING A CONSTRUCTED TERRACED WETLAND

An engineered treatment wetland in Mahoning County, Ohio was examined for its effectiveness in the removal of NH₃, total Fe, and total Mn from groundwater impacted by municipal solid waste and acid mine drainage. Groundwater that seeps to a mine pond is fed by gravity through a 5 cm PVC pipe into the terraced wetland. Upon entering the wetland, the water is diverted across a riprap area to produce sheet flow. The water then runs through six terraced treatment channels before exiting through an outlet. The elevation drop between inlet and outlet is 1.2 m. The terraced channels are connected through U turns and weirs. The channel is underlain by a clay liner to inhibit infiltration of partially treated water and then planted with phragmites, cattails, and swamp grass.

Four weekly samples were collected and analyzed at various points within the treatment wetland for the evaluation of Fe and Mn. Historical records from 1994 to 1996 were evaluated to determine the effects of seasonal variation including temperature and precipitation on the removal of NH₃. Ammonia removal is effective during warmer months and effectiveness increased with temperature. Ammonia data indicated that the constructed wetland is oversized. Mass loading removal efficiencies for Fe ranged from 32% to 77% between the inlet and outlet, while Mn ranged from 19% to 98%. The removal of Fe and Mn was accomplished by oxidation and hydroxylation with possibly the aid of catalyzing bacteria.