Formatted Title

Microbiological Processes in Biogeochemical Remediation

Background/Objectives

Biogeochemical remediation of contaminated groundwater is frequently viewed as an abiotic process driven by reactive iron and iron sulfide minerals; however, the important role of sulfate reducing bacteria in formation of heavy metal sulfides (Miller, 1950) and several iron sulfides (Rickard, 1969) was recognized more than 50 years ago. The removal of dissolved metals by coprecipitation with iron sulfides (Arakaki and Morse, 1993) and the ability of iron oxide to support abiotic degradation of carbon tetrachloride (Amonette et al., 2000) were also established long ago. More recently, the important role of bioavailable organic carbon in the formation and transformation of reactive minerals has become a well-recognized area receiving substantial focus (He et al., 2009). The role of microbial processes such as anaerobic carbon metabolism and iron and sulfate reduction, in biogeochemical remediation has received comparatively little attention. Since it is virtually impossible for any process in soil or groundwater to be truly abiotic (i.e., uninfluenced by microbial activity), we should look more carefully at the role of microbiology in biogeochemical remediation. The objective of this presentation is to survey the microbial processes involved in biogeochemical remediation and highlight their importance.

Approach/Activities

Major microbial processes that impact the formation, transformation, and effectiveness of reactive minerals will be identified. The mechanisms through which microbial processes can alter groundwater chemistry to promote or inhibit effective biogeochemical remediation will be reviewed. The ability of groundwater chemistry to stimulate or suppress microbial processes will be addressed. Results from laboratory and field-scale applications of soil and groundwater remediation will be used to illustrate the interplay between microbial processes and biogeochemical removal of contaminants.

Results/Lessons Learned

Several microbiological processes are involved in the formation of reactive minerals; however, the focus of remediation researchers and practitioners has been more on the kinetics of contaminant degradation by these minerals than on how microbial processes can be managed to promote their creation. Environmental variables including the supply of bioavailable organic carbon and sulfate/sulfide, Eh, and pH can regulate the growth and activity of microbial populations in soil and groundwater. Microbial activity can alter geochemical conditions in ways that promote or suppress the formation, transformation, reactivity, and stability of minerals important in biogeochemical remediation. Better understanding and management of relevant microbial processes can improve the quality and increase the quantity of reactive minerals and thereby enhance biogeochemical remediation.