Push-pull tests for assessing in situ aerobic cometabolism

Area of Science:

• Environmental Science
• Microbiology
• Environmental Engineering

Background:

• Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants.
• In situ aerobic cometabolism offers a promising bioremediation strategy.
• Assessing the feasibility of this approach requires effective field methods.

Purpose of the Study:

• To develop and evaluate single-well push-pull tests for assessing in situ aerobic cometabolism of CAHs.
• To determine the feasibility of stimulating indigenous microbial populations for CAH degradation.
• To quantify substrate utilization rates and confirm cometabolic activity.

Main Methods:

• Three types of push-pull tests were employed: transport, biostimulation, and activity tests.
• Transport tests used conservative tracers, growth substrates (propane), CAH surrogates (ethylene, propylene), and electron acceptors (oxygen).
• Biostimulation and activity tests involved sequential injections to stimulate and quantify microbial degradation of substrates and CAH surrogates.

Main Results:

• Transport tests confirmed conservative movement of injected solutes prior to biostimulation.
• Biostimulation tests successfully increased rates of propane and oxygen utilization.
• Activity tests demonstrated the stimulation of monooxygenase enzyme activity, evidenced by the transformation of ethylene and propylene to their respective oxides.

Conclusions:

• The developed push-pull test series provides a rapid and cost-effective method for feasibility assessments of in situ aerobic cometabolism of CAHs.
• These tests effectively stimulate and quantify the microbial activity required for CAH degradation.
• The findings support the application of this approach for remediating CAH-contaminated sites.