Fermentation is an anaerobic microbial process that breaks down organic material and produces hydrogen, organic acids, and other compounds. In groundwater remediation, these products can support reactions that transform certain contaminants.
How Fermentation Works
During microbial fermentation, microorganisms use organic compounds as food when oxygen and other preferred electron acceptors are limited. Unlike aerobic respiration, fermentation does not require oxygen. The microorganisms partially break down the organic material, producing smaller compounds such as organic acids, alcohols, carbon dioxide, and hydrogen.
The exact products and rates depend on the available food, microbial community, temperature, pH, groundwater chemistry, and competing electron acceptors. Fermentation is therefore not a single reaction with a fixed outcome. It is a group of biological reactions that changes as subsurface conditions change.
Why Fermentation Matters in Bioremediation
Fermentation in bioremediation is important because it can generate the hydrogen used by microorganisms during anaerobic contaminant treatment. In reductive dechlorination, for example, specialized microorganisms use hydrogen as an electron donor while replacing chlorine atoms on chlorinated compounds with hydrogen atoms.
This sequence can transform compounds such as tetrachloroethene (PCE) and trichloroethene (TCE) into less chlorinated daughter products. Complete treatment depends on having the appropriate microorganisms and maintaining suitable groundwater conditions. Fermentation helps create food and hydrogen, but it does not by itself guarantee complete dechlorination.
Electron donor fermentation can also consume competing electron acceptors and help lower oxidation-reduction potential. These changes support the anaerobic conditions needed for reductive processes. However, sulfate reduction and methanogenesis may also consume available hydrogen. Site characterization and monitoring are needed to understand where the injected product is going and how the microbial community is responding.
Selecting and Distributing Electron Donors
Electron donors differ in how quickly they ferment and how long they remain available. Soluble products can provide rapidly available food for microorganisms, while emulsified vegetable oil products are designed for slower, longer-term release. Product selection should reflect the treatment objective, contaminant distribution, soil type, groundwater velocity, injection approach, and expected treatment period.
RNAS products relevant to fermentation include Newman Zone 55, a slow-release emulsified vegetable oil product, and the soluble electron donors Newman Zone QR75 and Newman Zone QR90. The goal is not simply to add more food. The selected electron donor must be distributed through the treatment zone where microorganisms and contaminants can interact.
Poor distribution can leave untreated areas even when sufficient product was injected elsewhere. Excessive demand from naturally occurring electron acceptors may also reduce the amount of hydrogen available for the target process.
Monitoring Fermentation at a Site
Fermentation is usually evaluated indirectly through multiple lines of evidence. Monitoring may include oxidation-reduction potential, dissolved oxygen, pH, organic acids, dissolved gases, electron acceptors, contaminant concentrations, daughter products, and microbial data. No single measurement provides a complete picture.
A declining oxidation-reduction potential and changes in fermentation products may indicate that anaerobic biological activity is developing. Contaminant and daughter-product trends are still needed to determine whether the desired treatment pathway is occurring. pH is especially important because fermentation can produce organic acids, and unfavorable pH can slow microbial activity.
Understanding microbial fermentation helps practitioners connect product selection and distribution with the reactions occurring underground. When site conditions, microorganisms, and electron donor availability are aligned, fermentation can provide the hydrogen and reducing conditions needed to support effective anaerobic bioremediation.
RNAS Technical Insight
Fermentation must be considered together with electron donor distribution, groundwater chemistry, pH, competing electron acceptors, and the microorganisms present. Supplying food alone does not ensure that the desired treatment pathway will occur throughout the treatment zone.
Related RNAS Products
Newman Zone 55
Newman Zone QR75
Newman Zone QR90