Effects of bioaugmentation on enhanced reductive dechlorination of 1,1,1-trichloroethane in groundwater: a comparison of three sites

Abstract

Microcosm studies investigated the effects of bioaugmentation with a mixed Dehalococcoides (Dhc)/Dehalobacter (Dhb) culture on biological enhanced reductive dechlorination for treatment of 1,1,1-trichloroethane (TCA) and chloroethenes in groundwater at three Danish sites. Microcosms were amended with lactate as electron donor and monitored over 600 days. Experimental variables included bioaugmentation, TCA concentration, and presence/absence of chloroethenes. Bioaugmented microcosms received a mixture of the Dhc culture KB-1 and Dhb culture ACT-3. To investigate effects of substrate concentration, microcosms were amended with various concentrations of chloroethanes (TCA or monochloroethane [CA]) and/or chloroethenes (tetrachloroethene [PCE], trichloroethene [TCE], or 1,1-dichloroethene [1,1-DCE]). Results showed that combined electron donor addition and bioaugmentation stimulated dechlorination of TCA and 1,1-dichloroethane (1,1-DCA) to CA, and dechlorination of PCE, TCE, 1,1-DCE and cDCE to ethane. Dechlorination of CA was not observed. Bioaugmentation improved the rate and extent of TCA and 1,1-DCA dechlorination at two sites, but did not accelerate dechlorination at a third site where geochemical conditions were reducing and Dhc and Dhb were indigenous. TCA at initial concentrations of 5 mg/L inhibited (i.e., slowed the rate of) TCA dechlorination, TCE dechlorination, donor fermentation, and methanogenesis. 1 mg/L TCA did not inhibit dechlorination of TCA, TCE or cDCE. Moreover, complete dechlorination of PCE to ethene was observed in the presence of 3.2 mg/L TCA. In contrast to some prior reports, these studies indicate that low part-per million levels of TCA (< 3 mg/L) in aquifer systems do not inhibit dechlorination of PCE or TCE to ethene. In addition, the results show that co-bioaugmentation with Dhc and Dhb cultures can be an effective strategy for accelerating treatment of chloroethane/chloroethene mixtures in groundwater, with the exception that all currently known Dhc and Dhb cultures cannot treat CA.

A study of chlorinated solvent contamination of the aquifers of an industrial area in central Italy: a possibility of bioremediation

“…Lactate-amended microcosms showed the shortest lag-phase (i.e., time prior to the onset of dechlorination) and the highest initial dechlorination rate; similar results were obtained by Aulenta et al (2005b) . As in other studies, highly chlorinated parent compounds are dechlorinated more quickly than their lesser chlorinated daughter products ( Scheutz et al, 2014 ; Miura et al, 2015 ) The microcosms amended with lactate and butyrate showed a complete dechlorination, but the lactate seems to be the best electron donor. The adding of digester sludge, with a strictly anaerobic microbial community, led to a quicker dechlorinating activity compared to the amended treatments.…”

Stable carbon isotope analysis to distinguish biotic and abiotic degradation of 1,1,1-trichloroethane in groundwater sediments

“…Degradation of 1,1,1-TCA in all biotic microcosms including the biotic control has been documented by the isotope data, and mass and isotope balance have confirmed that 1,1-DCA is not a The degradation rates for 1,1,1-TCA in biotic control and stimulated microcosms and initially in bioaugmented microcosms (0.0023-0.0056 d À1 ) are relatively low compared to biodegradation rates (Scheutz et al, 2013). However, significant carbon isotope enrichment factors (À10‰ to À14‰) are observed.…”

“…Elsner and Hofstetter (2011) proposed an abiotic pathway for 1,1,1-TCA (via organochloride radical and/or carbanion) with primarily non-chlorinated degradation products (including acetaldehyde and ethane) analogue to the abiotic pathway for carbon tetrachloride (CTET) degradation (to carbon monoxide and formate or carbon disulfide) by pyrite and FeS observed by Kriegman-King and Reinhard (1994) and Devlin and Müller (1999), respectively, and reviewed by Elsner and Hofstetter (2011). In a treatability study for 1,1,1-TCA bioremediation for 3 clay till sites in Denmark by Scheutz et al (2013) it was inferred from degradation results and mass balance determinations that an alternate biologically mediated 1,1,1-TCA degradation pathway (without accumulation of 1,1-DCA and CA) contributed to 1,1,1-TCA loss in intrinsic controls.…”

Efficacy of forming biofilms by Pseudomonas migulae AN-1 toward in situ bioremediation of aniline-contaminated aquifer by groundwater circulation wells

“…Our data demonstrate that biofilms formed by AN-1 added in GCWs greatly improved remediation of aniline. It as a case study shows the advantage of such an in situ remediation strategy: (a) Biofilms in GCWs can biodegrade the remaining low-volatile contaminants which cannot be removed by aeration; (b) Biodegradation mainly occurs in the well and it is easy to be monitored and controlled; (c) The carriers with biofilms can be replaced conveniently to maintain efficiency; (d) This system can disperse planktonic degrading bacteria among the area of circle radius by hydraulic actions, which is similar to bioaugmentation, contributing to enhance the remediation efficiency (Lyon and Vogel 2013;Scheutz et al 2014). However, due to the complexity of contaminated sites, GCWs should be widely focused on and further investigated.…”