At the Tennessee Valley Authority's Fabius Coal Mine, Alabama, manganese was more effectively removed from a pond containing an algae mat consortium and limestone substrate than from ponds containing only limestone or pea gravel substrates. The algae mat resulted from the integration of a microbial mat and volunteer filamentous green algae. The microbial mat consisted of blue-green algae (predominately Oscillatoria spp.) and bacteria isolated from the site, cultured in the laboratmy, and returned to the site. System operation ran from August 1992 through March 1993. Manganese and iron were consistently removed more efficiently in the algae mat pond (mean flow of 4.2 L/min) than through gravel-only ponds even as water temperatures dropped to less than 5° C in the winter.. Based on filtered water samples, during winter months, at 2 m from the influent point of each pond, the algae mat pond removed 2.59 g/d/m' manganese, compared with 0.80 in the limestone pond and 0.37 in the pea gravel pond. At 1 m from the influent pipe in the algae mat pond, 2.67 mg manganese and 34.25 mg iron were deposited in a gram of dried mat. In March 1993 two events likely caused the loss of much of the algae mat: (1) a 50-cm snowfall followed by a heavy runoff and (2) establishment of a snail population, as well as other possible invertebrate herbivores, which consumed the algae mat. The algae mat was reestablished in June 1993 and has persisted to date. A green algae and microbial mat consortium may be a cost-effective treatment technique for permanently removing metals from mine drainage.

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