Bioremediation uses microorganisms to break down or transform contaminants in soil and groundwater. It may occur under aerobic or anaerobic conditions and can be supported through biostimulation, bioaugmentation, or both.
How Bioremediation Works
Microorganisms naturally use available compounds as sources of food and energy. During bioremediation, those biological processes are directed toward contaminants or toward conditions that make contaminants easier to treat. Depending on the treatment pathway, microorganisms may break contaminants into less harmful compounds, transform them into a different chemical form, or help immobilize them.
Bioremediation can be performed in situ, where contaminated soil or groundwater is treated in place, or ex situ, after contaminated material has been removed. In situ treatment can reduce excavation, transportation, and disposal, but its success depends on delivering the necessary treatment materials throughout the contaminated area.
Aerobic and Anaerobic Bioremediation
Aerobic bioremediation occurs when oxygen is available and microorganisms use it during contaminant degradation. It is commonly associated with treatment of petroleum hydrocarbons and other compounds that can be degraded under oxygen-rich conditions.
Anaerobic bioremediation occurs under low-oxygen or oxygen-free conditions. Microorganisms use substances other than oxygen during biological reactions. Anaerobic treatment is widely used for chlorinated solvents such as PCE and TCE and may also be used for nitrate, perchlorate, explosives, and selected metals.
In anaerobic systems, an electron donor provides food for microorganisms. As the donor ferments, it produces molecular hydrogen and other compounds that support reductive biological processes. For chlorinated solvents, properly supported microorganisms can remove chlorine atoms through reductive dechlorination and, under suitable conditions, convert PCE and TCE to non-toxic ethene.
Biostimulation and Bioaugmentation
Biostimulation improves the activity of microorganisms already present at a site. This may involve adding an electron donor, oxygen, nutrients, a buffer, or another material needed to establish favorable treatment conditions.
Bioaugmentation adds specialized microorganisms when the organisms required for a treatment pathway are absent or present at concentrations too low for reliable performance. For example, cultures containing Dehalococcoides mccartyi may be used to support complete reductive dechlorination of chlorinated ethenes.
A project may use biostimulation, bioaugmentation, or both. Even when a microbial culture is added, the site must still provide the food, pH, temperature, and geochemical conditions needed for those microorganisms to remain active.
Site Conditions Control Performance
Selecting a biological treatment pathway is only the beginning. Field performance depends on whether treatment materials can reach the contamination and remain available long enough to support the required reactions.
Important site conditions include groundwater velocity, soil permeability, contaminant concentration, pH, temperature, dissolved oxygen, oxidation-reduction potential, competing electron acceptors, and the presence of suitable microorganisms. A product that performs well in coarse sand may not distribute the same way in fine-grained soil. A fast-release electron donor may be appropriate for an immediate demand, while a slow-release donor may be preferred when long-term support is needed.
Poor distribution can leave untreated areas even when the chemistry and microbiology are correct. Injection design, dilution, droplet size, viscosity, retention, and radius of influence can therefore be as important as the product itself.
Contaminants Treated Through Bioremediation
Bioremediation is used to address chlorinated solvents, petroleum hydrocarbons, nitrate, perchlorate, nitrated explosives, and selected metals. The biological mechanism is not the same for every contaminant. Organic contaminants may be degraded, while metals cannot be destroyed and instead may be transformed into a less mobile or less toxic form.
Because treatment mechanisms differ, product selection should be based on the contaminant, the desired biological pathway, and actual site conditions rather than on a single general formula.
RNAS Technical Insight
Successful bioremediation depends on matching the product and delivery method to the site. Microorganisms cannot treat contamination they cannot reach, and they cannot remain active without suitable environmental conditions.
RNAS develops crop-based products for practical field use, including slow- and fast-release electron donors, a high-retention oil, an oxygen scavenger, a colloidal buffer, and bioaugmentation cultures. These products are designed to help establish and maintain the biological conditions required for treatment across a range of soil and groundwater conditions.
Related RNAS Products
- Newman Zone 55 – Slow-release emulsified vegetable oil electron donor.
- Newman Zone HRO – High-retention oil for coarse soils, fractured bedrock, and high groundwater velocity.
- Newman Zone QR75 and Newman Zone QR90 – Fast-release soluble electron donors.
- Newman Zone OS – Oxygen scavenger for establishing reducing conditions.
- Neutral Zone – Colloidal buffer used to help maintain favorable pH.
- SDC-9 – Bioaugmentation culture for chlorinated solvent treatment.