Frequently Asked Questions Regarding Bioaugmentation and KB-1®Q. When should I consider bioaugmentation with KB-1®A. Reasons to consider bioaugmentation include:
Q. Do all chloroethene-contaminated sites need to be bioaugmented with KB-1®A. No. Although the causative microorganism Dehalococcoides is absent from some contaminated sites (i.e., it is not ubiquitous in the environment), it is widely distributed. Dehalococcoides -like species have been detected throughout North America and Europe. At sites where Dehalococcoides is present, addition of an appropriate electron donor alone may successfully stimulate complete reductive dechlorination to ethene in many cases . Q. What percentage of chloroethene contaminated sites need to be bioaugmented with KB-1® ?A. Estimates range from 10% to 50% of chloroethene contaminated sites. Antidotal evidence suggests that there is are geographical or even hydrogeological grouping of sites requiring bioaugmentation. Hydrogeological environments that are fairly permeable have low organic loading, and are more oxidizing are more likely to require bioaugmentation. Whereas, environments exposed to chloroethenes over several decades that have lower permeability, slow moving or stagnant groundwater with higher natural organic content are more likely to possess native Dehalococcoides species. Q. If evidence indicates that Dehalococcoides are present at my site, should I still bioaugment with KB-1®?A. Maybe. It depends on the need to achieve results quickly and the effectiveness of the indigenous Dehalococcoides. A sparse or low population density of indigenous Dehalococcoides may require a long period to grow to a sufficient concentration to efficiently and quickly convert the chloroethenes to ethene . Bioaugmentation can shorten this acclimation period significantly. Another factor to consider is the competency of the indigenous Dehalococcoides species. Research has shown that Dehalococcoides can be divided into subgroups or strains, and not all these strains have the same reductive dechlorination capacity. For example, there are strains of Dehalococcoides that cannot dechlorinate PCE/TCE, but only chlorobenzenes; other strains are inefficient at the VC to ethene dechlorination step (VC tends to accumulate with low ethene production). KB-1® has two strains of Dehalococcoides , including one [Dehalococcoides KB-1/VC (Duhamel et al., 2004)] that is very efficient at dechlorinating VC to ethene, preventing prolonged production or accumulation of VC.. Q. Am I limited in which electron donors I can use with KB-1®?A. No. KB-1® has been demonstrated to work with most commonly used electron donors, including sugars (e.g., glucose, molasses), alcohols (e.g., methanol, ethanol), organic acids (e.g., lactate), vegetable oils (canola), emulsified oils (e.g., EOS™) and slow release compounds e.g. (HRC™). A general rule is any electron donor that when fermented produces hydrogen will support the activity of KB-1®. Q. Is Bioaugmentation with KB-1® expensive?A. No. Contrary to the claims of several electron donor vendors, bioaugmentation is not an expensive option costs are usually significantly less than electron donor costs. Unlike the addition of electron donors, which require repeat or continuous additions we have bioaugmentation is typically a one-time event. Creation of a biological active zone (BAZ) containing KB-1® costs between $1 to $2 per cubic yard for most sites. Q. Can Bioaugmentation Save moneyA. Yes. The introduction of a robust community of dechlorinators reduces wasting electron donors on unwanted microbial processes such as sulfate reduction or methanogenesis. Also, rapid post-bioaugmentation dechlorination rates reduce site remediation time and associated monitoring costs and O&M costs. Q. Does KB-1® migrate in an aquifer?A. Yes. Major et al. (2002) and Cox et al. (2002) have indicated that the Dehalococcoides strains in KB-1® can migrate in aquifers. The rate of migration is relatively slower than groundwater flow velocities. The extent of migration and activity of migrating cells is likely dependent on the distribution of electron donor and chloroethenes. We are conducting additional studies to better understand the factors affecting migration of KB-1®. Q. Are high concentrations of chloroethenes toxic to KB-1®?A. No. KB-1® has been demonstrated to work at very high concentrations of PCE/TCE/cDCE and VC. In fact, KB-1® is being used to enhance the dissolution of PCE and TCE source areas. Q. Are there geochemical conditions that inhibit KB-1® activity?A. Yes. Aerobic conditions are toxic to the Dehalococcoides in KB-1®, however , anaerobic conditions can usually be created in the subsurface by pretreatment with electron donor. High sulfate concentrations (>1000 mg/L) may impact the activity of KB-1® due to competition of sulfate reducing bacteria (SRB) for available electron donor and hydrogen. However, research has shown that bacteria in the KB-1® are able to out-compete SRB when PCE/TCE predominates. Low pH, below 5.2 and above 9.0 has been shown to prevent or inhibit dechlorination, however, pH modification with buffering agents has proven successful in restoring activity. Moderate concentrations of chloroform and 1,1,1-trichloroethane can also inhibit KB-1® activity, these compounds are often reduced by pretreatment with electron donors. Extremely low groundwater temperatures (below 4°C) may also inhibit dechlorination. In most cases, geochemical inhibition issues can be dealt with through informed site management. |
