ABSTRACT
Staged, aerobic constructed wetlands offer an inexpensive, natural, low maintenance, and potentially long-term solution to treating acid drainage without chemical additives. Isolated deep pockets up to 2.0 m were included in many cells to provide for aquatic fauna refuge in drought events. The system treats acid seepage emanating from an earth dike impounding 16 ha of coal slurry at Tennessee Valley Authorities (TVA's) reclaimed Fabius Coal Preparation Plant in Jackson County, Alabama. TVA’s experience suggests that these numbers may represent an upper-limit sizing criteria for aerobic wetlands as they are currently designed and constructed. TVA’s encouraging results suggest that staged treatment wetlands systems are preferred designs potentially capable of treating poor-quality acid drainage. Such staged treatment may consist of: an initial anaerobic limestone trench at the source of the seepage to passively add alkalinity; a large, deep settling basin to accumulate oxidized and precipitated Fe sludges; and a two- or three-cell constructed wetlands for Mn and further Fe removal.
