A Combined Abiotic- and Bio-Remediation Approach Saves Money while Improving Performance for In-Situ Anaerobic Remediation

Background/Objectives. The in-situ destruction of halogenated compounds is readily done by providing electrochemically reducing conditions.  The chemistry is straightforward: simply provide electrons.  However, the engineering and economics are a bit more challenging.

Approach/Activities. Many laboratory and field studies over the last decade have shown bio-remediation to be a valuable tool for chlorinated compound remediation, where the focus has been primarily on electron donor formulations that stimulate dehalogenating microorganisms.  More recently, the science has advanced beyond the electron donor to include the pH stability of microorganisms, such that bio-remediation sites are now being engineered to include pH control and acid-tolerant cultures.

Organic compounds are not the only electron source.  In fact, metals provide an effective electron source under corrosive conditions.  In-situ zero-valent metal (zvm) injections and permeable reactive barriers (PRB’s) are common tools in the remediation field.  The zvm sources vary in size and chemistry, including microscale and submicron options of iron, zinc, aluminum, and many alloys.  The interesting aspect about in-situ metal corrosion is that it complements bio-remediation.  The same process that provides the desired electrons for the chlorinated compound destruction also provides protons for bio-stimulation while generating counter ions for raising the aquifer pH.  Combining injectable metals into a bio-remediation design makes a cost-effective “combined approach” strategy for site-wide performance.

We will present injection strategies for the three general site zones: source areas, detached sources, and plumes.  Each zone has a different design approach that should reflect both the cleanup goals and budget priorities.  Adding a network of real-time monitoring points provides insight into the transformation to an active reductive treatment area.  Real-time physical parameter monitoring through time during and after a pilot study allows adjustment to injectate amendments, such as pH modifiers, electron donors, and metal powders in the full-scale design.

Results/Lessons Learned. A tailored approach to each of the remediation zones provides cost-savings by minimizing amendment costs and improving performance.  Biasing the chemistry to abiotic reactions in source areas has a greater bang for the buck than pure biological reaction.  Similarly, bio-remediation in the downgradient plume is cost-effective when enhanced by kick starting the chemistry with zvm addition.