In Situ Bioremediation

Bioremediation—using microbes to degrade contaminants in situ—has been widely applied for petroleum hydrocarbons (gasoline and diesel). In some cases biostimulation is used, where indigenous hydrocarbon-utilizing microbes are supplied with nutrients to stimulate growth and degradation. In the last decade, significant advances have been made in our understanding of microbial transformations of a wide variety of contaminants under different redox conditions present in the subsurface. One of the most exciting new technologies is the discovery of novel bacteria that carry out the reductive dechlorination of chlorinated solvents to nonchlorinated end products. These strictly anaerobic bacteria are highly effective, but are not present at all sites, and therefore bioaugmentation—the addition of exogenous microbial culture to a site—has become an accepted technology for chlorinated solvents, in particular for perchloroethene (dry cleaning solvent) and trichloroethene (primary industrial degreaser) (Major et al, 2002, Hood et al, 2008).

How Reductive Dechlorination Occurs – Credit: Marie Manchester, BioZone (Prof Edwards)

Edwards and partner Geosyntec Consultants developed the first commercial chlorinated ethene bioaugmentation culture, KB-1, that has been deployed at over 200 sites in North America and Europe since 2002. KB-1 is produced in Guelph, Ontario by SiREM labs (www.siremlabs.com). KB-1 was approved for use in Canada through the New Substances Notification Regulations (2008) and deployed now at several sites in Canada. The key microbe in culture KB-1, Dehalococcoides, completely dechlorinates chloroethenes to environmentally benign ethene (Duhamel et al 2004). Other novel microbes, both aerobes and anaerobes, have also been discovered in the last decade that metabolize compounds once thought to be recalcitrant, including other halogenated compounds such as chloroform ( Grostern et al, 2010) and some of the hydrocarbons found in coal tar (Davidova et al., 2007; Andreoni and Gianfreda, 2007). These microbes are nature’s recyclers, and it is incumbent on us to take advantage of such potentially low cost transformation reactions. There is also need for a better knowledge of the enzymes responsible for biotransformation reactions to fundamentally understand the kinetics and limitations of the reactions. The figure below shows the role of Dehalococcoides, Geobacter, methanogens, and acetogens in KB-1 culture during TCE degradation.

Pathways KB-1 takes to biodegrade TCE – Credit: Laura Hug, PhD – BioZone (Prof Edwards)

In particular in the context of this proposal, we intend to determine optimum strategies for combined remedies, where one remedy might improve bioavailability or biodegradability. For example, thermal technologies are known to produce intermediates that may be more biodegradable than the parent compounds (Friij et al, 2007), and NZVI treatment produces hydrogen that can serve as a substrate to dechlorinating bacteria (Xiu et al, 2010).

For more about biodegradation and how to harness contaminant biodegraders, visit Prof Edwards website.

How does it work?