FIELD-SCALE BIOREMEDIATION OF NATURALLY OCCURRING ARSENIC CONTAMINATED GROUNDWATER USING SULFATE REDUCING BACTERIA IN MACON COUNTY, ALABAMA

Arsenic (As) is one of the most common naturally occurring metalloid contaminants found in groundwater. Presence of arsenic (from both natural and anthropogenic sources) represents a severe threat to the availability of safe drinking water in many parts of the world. Fe-reducing and Mn-reducing bacterial metabolism are reported in different research as the major cause of arsenic to be released in alluvial aquifers. Other research suggests that indigenous sulfate-reducing bacteria (SBR) can immobilize arsenic under sulfate-reducing conditions. SRB can remove arsenic from groundwater through co-precipitation and adsorption on arsenian pyrite biominerals. This process involves sorption of metal(loid)s on the biominerals surface, as the minerals continue to grow and evolve during bacterial metabolism, the sorbed elements get incorporated into the enlarging crystal structure.

This research has been focused on field scale bioremediation of naturally occurring arsenic-contaminated groundwater at a natural site along the bank of the Choktafaula creek in Macon County, Alabama. A confined unconsolidated sand and gravel aquifer has been identified there at 13 ft depth from the surface where arsenic concentration in groundwater is assumed to be more than the acceptable limit. For this research, a solution (a mixture of organic carbon molasses, ferrous sulfate, and agriculture grade fertilizer) will be injected into the aquifer to develop a reducing condition to stimulate sulfate-reducing bacterial growth. This artificial reducing condition will be maintained up to several months to observe the changes in the concentration of cations, anions and trace elements (mainly As and Fe) in the groundwater. ICP-MS will be used for chemical analysis. XRD, XRF will be used for the identification of arsenian pyrite microcrystal from the precipitated sediments. This ongoing research is focusing on arsenic sequestration in iron sulfide biominerals and also the possibility of removing arsenic from groundwater even after the bacterial activity is stopped or slowed down.