Bioremediation occurs when we intervene in the conditions of the subsurface to stimulate microorganisms with nutrients and other chemicals to enable them to destroy contaminants.
Bioremediation occurs by stimulation of native microorganisms to use contaminants as an energy source. There are two types of bioremediation: anaerobic and aerobic.
Anaerobic bioremediation modifies the environment to stimulate existing bacteria in the subsurface that are capable of reductively dechlorinating chlorinated solvents at low oxidation reduction potential (ORP) and dissolved oxygen (DO) levels. Anaerobic bioremediation involves adding electron donors, nutrients, and bioaugmentation cultures to provide for complete reduction to ethene.
Aerobic bioremediation involves the addition of oxygen into an aerobic aquifer, which provides an energy source for the bacteria in the subsurface that will destroy the contaminants. Oxygen can be delivered in multiple forms including calcium peroxide, hydrogen peroxide, and ambient air.
Bioremediation is often used for cost-effective remediation of dilute chlorinated solvent or petroleum source areas and plumes. This is a widely utilized approach in our industry, and can achieve comparable results as chemical oxidation technologies. Selection on either approach is usually based on one’s experience with these technologies at similar sites. Generally, if sites show anaerobic dechlorination already taking place, bioremediation will be selected as the preferred alternative; however, it has also been effectively implemented at sites with high DO and ORP.
Bioremediation provides longer in situ persistence than chemical oxidants. This allows for extended residence time for treatment of contaminant mass sorbed to soil, or sites with low seepage velocity, which are often the root cause of groundwater rebound.