Abstract: Euglena mutabilis is an acidophilic, photosynthetic protozoan that forms benthic mats in acid mine drainage (AMD) channels. At the Green Valley mine, western Indiana, E. mutabilis resides in AMD measuring <4.2 pH, with high concentrations of dissolved constituents (up to 22.67 g/l). One of the main factors influencing E. mutabilis distribution is water temperature. The microbe forms thick (>1 mm), extensive mats during spring and fall, when water temperature is between 13 and 28 degrees C. During winter and summer, when temperatures are outside this range, benthic communities have a very patchy distribution and are restricted to areas protected from extreme temperature changes. E. mutabilis also responds to rapid increases in pH, which are associated with rainfall events. During these events pH can increase above 4.0, causing precipitation of Fe and Al oxy-hydroxides that cover the mats. The microbe responds by moving through the precipitates, due to phototaxis, and reestablishing the community at the sediment-water interface within 12 hours. The biological activities of E. mutabilis may have a beneficial effect on AMD systems by removing iron from effluent via oxygenic photosynthesis, and/or by internal sequestration. Photosynthesis by E. mutabilis contributes elevated concentrations of dissolved oxygen (DO), up to 17.25 mg/l in the field and up to 11.83 mg/l in the laboratory, driving oxidation and precipitation of reduced metal species, especially Fe (II), which are dissolved in the effluent. In addition, preliminary electro-microscopic and staining analyses of the reddish intracellular granules in E. mutabilis indicate that the granules contain iron, suggesting that E. mutabilis sequesters iron from AMD. Inductive coupled plasma analysis of iron concentration in AMD with and without E. mutabilis also shows that E. mutabilis accelerates the rate of Fe removal from the media. Whether iron removal is accelerated by internal sequestration of iron and/or by precipitation via oxygenic photosynthesis has yet to be determined. These biological activities may play an important role in the natural remediation of AMD systems.

Abstract: As a result of the collapse of a mine tailing dam in april 1998 about 40 km of the Agrio and Guadiamar valleys were covered with a layer of pyrite sludge. Although most of the sludge was removed, a small amount remains in the soil of the Agrio valley and the aquifer remains polluted with acid water (ph<4) and metals (10 mg/L Zn, 5 mg/L Cu and Al). A permeable reactive barrier was build across the aquifer to increase the alcalinity and retain the metals. The barrier is made up of three sections of 30 m longX1.4 m thickX5 m deep (average) containing different proportions of limestone gravel, organic compost and zero-valent iron. The residence time of the water in the barrier is about two days. Within the barrier, the pH values increase to near neutral mainly due to calcite dissolution. Metals co-precipitate as oxyhydroxides, and they are also adsorbed on the organic matter surface. Down-stream the barrier, the total pollution removal is around 60-90% for Zn and Cu, and from 50 to 90% for Al and acidity.