Bioremediation

The Basics

As people eat food and breathe air to derive energy for growth, microbes, which are often referred to as bugs, also eat and respire to derive energy for growth. Fundamentally, bioremediation involves creating geochemical conditions conducive to microbial growth. Thus, the resource that is responsible for the remediation, that is, the bugs, is a growing resource. As long as we can keep the bugs happy by providing them with something to eat and breathe, they will continue to degrade the contaminants.

The challenge, of course, is keeping the bugs in the correct geochemical conditions over an extended time period.

It is important to note that bioremediation only occurs in the aqueous phase. The bugs cannot degrade non-aqueous phase liquids directly. That said, some bugs can thrive in high aqueous phase concentrations of contaminants. Because there is an equilibrium constant between the NAPL and aqueous phases, as the bugs lower the aqueous phase concentrations, the NAPL will dissolve more quickly. Thus, bioremediation can work at sites where NAPL is present. Of course, we are now dealing with a dissolution limited system, which will take time to remediate. That is OK, as the bugs can continue to thrive.

Furthermore, the bugs need to be able to get to the contaminant. If, for example, the contaminant is in a tight unit, such as clay, contact may not be possible. This, too, might be acceptable, as the contaminant flux to a receptor is likely to be insignificant from a low permeability stratum. Due to concentration gradients, the contaminant will diffuse out of the clay into the clean higher permeability units. This is sometimes called back diffusion. As long as we maintain the proper geochemistry, the bugs will be able to degrade the contaminant. Thus, you can think of bioremediation as a containment technology.

Typical geochemical parameters that are important include pH, oxidation-reduction potential, temperature and the presence of inhibitory compounds or elements, such as chloroform or heavy metals.

Generally, we use aerobic organisms, that is, bugs that respire oxygen, to degrade petroleum hydrocarbons, and anaerobic organisms to degrade chlorinated solvents. The aerobic organisms tend to be ubiquitous, while the anaerobic ones may be found less frequently; however, we can usually add the bugs that we need. The aerobic bugs eat the contaminants, while the anaerobic ones respire the contaminants. We call these special anaerobic bugs halorespiring organisms.

Perhaps the most critical issue regarding the successful implementation of a biologically based remedy is the delivery of the remedial amendments to maintain the proper geochemical conditions over a prolonged time period.

Definitions

Biostimulation – Promoting indigenous bug growth by providing substrates, sometimes called food or electron donors, to help the microbes grow. For chlorinated solvents, the substrates ferment and yield hydrogen. The bugs eat the hydrogen and respire the solvent, which, in this case, is the electron acceptor.

Bioaugmentation – Adding the right bugs, which is especially important for the reductive dechlorination of chlorinated ethenes, such as PCE and TCE. Dehalococcoides is the only known organism that has been shown to degrade PCE and TCE down to non-toxic ethene. Although it is a naturally occurring microbe, it may not be at your site in sufficient quantities to adequately reduce the concentrations of the solvents. Also, not all variants of Dhc are able to degrade vinyl chloride efficiently.

The Companies Dajak Represents

Bioremediation of chlorinated solvents requires an electron donor (food source) and suitable bacteria. EOS Remediation and SiREM provide products and services related to enhancing the bioremediation of chlorinated solvents.

EOS Remediation

Long-lasting, time released substrate – EOS® continues to ferment for three to five years
Ideal for source zone remediation and permeable reactive barriers – the emulsion droplets stick to the matrix
EOS comes ready to use and inject – other products require on-site emulsification
Uniform droplet size allowing for the ready transport into the aquifer
Quite inexpensive compared to other electron donors
Safe – EOS is a food grade substrate
Outstanding customer support

SiREM