6 Applied Groundwater Microbiology

Groundwater microbiology is applied in a wide variety of processes that have been developed not only for in situ bioremediation of organic and inorganic contaminants but also for the control and management of groundwater flow. The success of these applications stems from the tremendous metabolic flexibility that exists among different microorganisms and their influence on groundwater geochemistry, including heterogenous solid phase adsorption and mineral precipitation reactions. Another important factor that is often taken for granted, but is worth reemphasizing, is the small size of microbial cells. This physical attribute is what allows microorganisms to gain access to, and reside within, subsurface habitats that are either suffering from contamination or are targets for management of groundwater flow.

A primary consideration for in situ bioremediation is oxidation state, which determines whether contaminants can be metabolized by microorganisms as an electron donor (reductant), an electron acceptor (oxidant), or not at all (as is the case with elements that lack multiple oxidation states such as strontium or cadmium). If a contaminant is subject to microbial metabolism, it can be removed from groundwater by transformation (oxidative or reductive degradation) into inert products. Options for contaminants that cannot be metabolized include capture and immobilization by adsorption or coprecipitation in minerals precipitated in response to microbial metabolic activity.