Water Resources Research Act Program

Details for Project ID 2012OH250B

Microbial Modulation of Acidic Coal Mine Drainage Chemistry: Implications for Passive Treatment of Minewater

Institute: Ohio
Year Established: 2012 Start Date: 2012-03-01 End Date: 2013-08-31
Total Federal Funds: $22,754 Total Non-Federal Funds: $45,720

Principal Investigators: John Senko

Abstract: Acid mine drainage (AMD) emanating from abandoned and active coal mines represents the largest surface water pollution problem in the Appalachian coal mining regions of the United States. The most prominent feature of AMD-impacted streams is the appearance of an orange Fe(III) (hydr)oxide precipitate (known as �yellowboy�) which arises when Fe(II)-rich AMD enters oxic, circumneutral streams. There, the increased pH facilitates rapid oxidation of Fe(II) and subsequent hydrolysis of Fe3+. The resulting Fe(III) (hydr)oxide precipitate (referred to as �yellowboy�) coats streambeds and kills most large aquatic life. AMD treatment approaches aim to intercept AMD before it reaches streams, and alter AMD chemistry (notably precipitating Fe) such that its impacts on streams will be minimized. Currently utilized AMD treatment strategies suffer from unpredictable or poor performance, and/or high energy, labor, material, and maintenance requirements, so there is a desire for more effective and sustainable systems to remove dissolved Fe from AMD. Depending on hydrologic and landscape considerations, when AMD reaches the terrestrial surface, it may flow as a 0.5 � 1 cm sheet over the terrestrial surface, facilitating the aeration of AMD and enhancing the activities of aerobic Fe(II) oxidizing bacteria (FeOB). These bacterial activities lead to the oxidative precipitation of Fe from AMD and the accumulation of thick Fe(III) (hydr)oxide crusts (referred to as �iron mounds�) on top of formerly pristine soil (i.e. before AMD reached the system). A system has been identified in Mahoning County, OH in which dissolved Fe(II) (at an initial concentration of approximately 10 mM) is removed from AMD by FeOB activities as it flows a distance of approximately 30 m over an iron mound. The iron mound and associated Fe-removal capacity have developed in a formerly pristine setting with no human intervention, suggesting that iron mound systems may provide inexpensive and sustainable means for removal of dissolved Fe from AMD. These observations also suggest that microbial communities associated with the formerly pristine soil adapted to the harsh chemical conditions of AMD, culminating in a community structure well suited to facilitate efficient oxidative precipitation of Fe from AMD. As such the overarching goal of this proposal is to evaluate the changes in microbial activities and communities that occur when AMD infiltrates unimpacted soil. We will conduct microcosm experiments in which pristine soil will be incubated with AMD and the concurrent changes AMD chemistry, rates of microbial Fe(II) oxidation, and microbial community structure and composition will be evaluated. This work will elucidate the biogeochemical changes associated with the development of robust iron oxidizing microbial activities associated with iron mounds. This work will also provide information on the initial development of iron mounds so that �designed� iron mounds, mimicking the biogeochemical conditions associated the Mahoning County site, may be employed for efficient AMD treatment.