Multilevel samplers as microcosms to assess microbial response to biostimulation

Area of Science:

• Environmental Microbiology
• Geochemistry
• Bioremediation

Background:

• Uranium (U(VI)) and Technetium (Tc(VII)) are common groundwater contaminants.
• Biostimulation is a promising strategy for promoting microbial reduction of these contaminants.
• Understanding microbial community dynamics is crucial for effective bioremediation.

Purpose of the Study:

• To investigate the spatial variability of microbial communities in an aquifer.
• To assess the effectiveness of biostimulation in promoting U(VI) and Tc(VII) reduction.
• To evaluate the use of passive multilevel samplers (MLS) as in situ microcosms.

Main Methods:

• Deployment of passive multilevel samplers (MLS) at various depths in wells.
• Push-pull biostimulation experiment using ethanol-amended groundwater.
• Real-time quantitative polymerase chain reaction (Q-PCR) for microbial community analysis (bacteria, denitrifiers, Geobacter sp., methanogens).

Main Results:

• Pre-biostimulation microbial populations were low, limited by carbon substrate and pH.
• Biostimulation led to significant increases (1-2 orders of magnitude) in bacterial, denitrifier, Geobacter sp., and methanogen populations.
• Concurrent reduction of NO(3)(-), Tc(VII), and U(VI) was observed following biostimulation.

Conclusions:

• Passive MLS serve as effective in situ microcosms for studying microbial responses to biostimulation.
• Push-pull tests combined with MLS provide an inexpensive and efficient method for aquifer characterization and monitoring.
• This approach facilitates the assessment of contaminant reduction and microbial community function in deep aquifers.