BIOREMEDIATION OF ARSENIC CONTAMINATED GROUNDWATER IN A NATURAL SITE IN MACON COUNTY, ALABAMA

Naturally occurring arsenic (As) is one of the most common metalloid contaminants in groundwater in alluvial aquifers that is limiting the availability of safe drinking water. Fe-reducing and Mn-reducing bacterial metabolism have been reported in several research as one of the major reasons that mobilize As in groundwater. On the other hand, sulfate-reducing bacterial (SRB) metabolism can remove As and other metal(loid) contaminants from groundwater through co-precipitation on the pyrite-biomineral surface. The affinity between As and iron-sulfide minerals starts the adsorption of As on the biomineral surface. As the biominerals continue to grow, the metal(loid)s get incorporated into the biomineral crystals. This research project in Macon County, Alabama has been focused on field-scale bioremediation of arsenic-contaminated groundwater where As occurred naturally. 4 wells have been drilled and developed so far along the bank of Choktafaula (Chewacla) creek in the study area. A confined unconsolidated sand and gravel aquifer has been identified at 13.5 ft depth from the ground surface. At a depth of 18 ft, a lignitized wood layer has been encountered that is exposed in the spring, and naturally occurring pyrite is found there that contains a significant amount of As. The confined aquifer is assumed to have As concentration more than the acceptable limit. The proposed bioremediation technology will be applied to stimulate the indigenous sulfate-reducing bacteria with a nutrient-rich slurry solution containing labile organic carbon, ferrous sulfate, and fertilizer. This induced sulfate-reducing conditions can cause the co-precipitation and adsorption of the dissolved As in biogenic pyrite. The wells will be monitored for five-to-six months to assess the spatial and temporal changes in groundwater chemistry during the research project. Precipitated solids will be analyzed using XRD, XRF, EMP, SEM to characterize biogenic pyrite microcrystal. This research project on bioremediation in the natural site aims to provide a sustainable method that is capable of reducing As concentration within the acceptable limit.