Biomedical Engineering Reference
In-Depth Information
CHAPTER 7
BIOAUGMENTATION FOR AEROBIC DEGRADATION
OF CIS -1,2-DICHLOROETHENE
Laura K. Jennings, 1 Cloelle G.S. Giddings, 1 James M. Gossett 1 and Jim C. Spain 2
1 Cornell University, Ithaca, NY 14853; 2 Georgia Institute of Technology, Atlanta, GA 30332
7.1 INTRODUCTION
Incomplete reductive dechlorination of perchloroethene (PCE) or trichloroethene (TCE) in the
subsurface often results in the accumulation of the suspected carcinogen, cis -1,2-dichloroethene
( cis -DCE) and the known carcinogen, vinyl chloride (VC) (Adamson et al., 2003 ; Ellis et al.,
2000 ; Hendrickson et al., 2002 ; Singh et al., 2004 ). Persistence of VC and cis -DCE due to
incomplete reductive dechlorination can be attributed to the absence of bacteria capable of
complete reductive dechlorination or to environmental conditions that are not conducive
to reductive dechlorination. Whereas bacteria that can partially dechlorinate PCE or TCE to
cis -DCE [e.g., Dehalobacter restrictus (Holliger et al., 1998 ) and Dehalospirillum multivorans
(Scholz-Muramatsu et al., 1995 )] are common, only Dehalococcoides spp. completely dechlori-
nate PCE to ethene (Maym ยด -Gatell et al., 1997 ; Seshadri et al., 2005 ). Bioaugmentation with
Dehalococcoides spp. has been shown to stimulate reductive dechlorination in the laboratory
(Schaefer et al., 2009 ; Sleep et al., 2006 ) and at the field scale (Ellis et al., 2000 ; Hood et al., 2008 ;
Lendvay et al., 2003 ; Major et al., 2002 ).
Insufficient electron donor or the presence of oxygen can inhibit reductive dehalogenation
even when appropriate bacteria are present. VC and cis -DCE that accumulate from incomplete
reductive dechlorination can migrate downgradient into aerobic zones. Under these circum-
stances, it may be more effective to oxidize the compound aerobically, rather than try to create
subsurface conditions suitable for reductive dechlorination. Another possibility is to create or
enlarge an aerobic zone downgradient, to facilitate aerobic oxidation. Organisms that oxidize
VC appear to be widespread, and as a result VC often degrades quickly under aerobic
conditions (Coleman et al., 2002b ).
In contrast, reports of bacteria able to degrade cis -DCE aerobically are very rare. Several
organisms can catalyze the cometabolic oxidation of cis -DCE (Hopkins and McCarty, 1995 ;
Semprini, 1995 ; Semprini et al., 1990 ). They transform the chlorinated solvent, but do not obtain
any energy or growth from the process. Consequently, the addition of a growth substrate such
as methane, phenol, propane or toluene is required for transformation (Hopkins and McCarty,
1995 ; Bradley and Chapelle, 2000 ). Bioaugmentation to stimulate cometabolic oxidation is
limited by the requirement for cosubstrate, which can cause competitive inhibition since both
the contaminant and the primary substrate are often transformed by the same enzyme. Other
problems with cometabolism include excessive growth, resulting from the high dose of primary
substrate, leading to clogging of injection wells and aquifer, as well as oxygen demands that are
difficult to satisfy (McCarty et al., 1998 ). Furthermore, the production of reactive intermediates
during the cometabolic oxidation of chlorinated solvents can damage enzymes and cells,
causing loss of degradation activity and cell viability (Alvarez-Cohen and Speitel, 2001 ).
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