- Chlorinated aliphatic hydrocarbons (CAHs) like trichloroethene (TCE) were mostly used to replace drying cleaning fluids which contained hydrocarbons like benzene, and were highly flammable. Through improper disposal, storage, and spills, TCE and its downstream products, like cis-dichloroethene (cDCE) and vinyl chloride (VC), leached into groundwater and threaten human and environmental health. An anaerobic organo-halide respiring bacterium, Dehalocccoides mccartyi, can be used to completely dehalogenate TCE to ethene, a non-toxic end-product. Dehalocccoides mccartyi uses CAHs as electron acceptors and hydrogen as the electron donor.
Dehalocccoides mccartyi is a strict anaerobe. Because of this, field tests with anaerobic bacteria must include technologies to protect cultures from oxygen exposure during injection into contaminated wells. Currently, nitrogen blankets are used to protect cultures, but these technologies can be expensive. These challenges could be addressed through anaerobic encapsulation, the process of entrapping cells in a gel matrix to act as a physical barrier between bacteria and the surrounding environment. In addition, encapsulation is an inexpensive technology.
The objective of this study was to determine the methodology for anaerobically encapsulating a culture highly enriched with Dehalococcoides mccartyi in sodium alginate gel matrix, compare suspended cell performance with encapsulated cell performance, and determine the effects of oxygen on encapsulated cells. These objectives were achieved by creating an anaerobic 4% wt sodium alginate gel bead solution and combining it with the culture in an anaerobic glove box resulting in a 2% wt sodium alginate – culture solution. Beads were formed by extrusion through a 23G needle into a 0.25% calcium chloride solution. Encapsulated Dehalococcoides mccartyi produced TCE dehalogenation rates comparable to suspended culture. However, gel beads deteriorated after two weeks. In addition, rates of TCE dehalogenation decreased after exposure to 0.97% oxygen in the headspace.
- Key Words: Bioremediation, Chlorinated Solvents, Encapsulation, Anaerobic, Dehalococcoides