Integrative isotopic and molecular approach for the diagnosis and implementation of an efficient in-situ enhanced biological reductive dechlorination of chlorinated ethenes

Abstract

Based on the previously observed intrinsic bioremediation potential of a site originally contaminated with perchloroethene (PCE), field-derived lactate-amended microcosms were performed to test different lactate isomers and concentrations, and find clearer isotopic and molecular parameters proving the feasibility of an in-situ enhanced reductive dechlorination (ERD) from PCE-to-ethene (ETH). According to these laboratory results, which confirmed the presence of Dehalococcoides sp. and the vcrA gene, an in-situ ERD pilot test consisting of a single injection of lactate in a monitoring well was performed and monitored for 190 days. The parameters used to follow the performance of the ERD comprised the analysis of i) hydrochemistry, including redox potential (Eh), and the concentrations of redox sensitive species, chlorinated ethenes (CEs), lactate, and acetate; ii) stable isotope composition of carbon of CEs, and sulphur and oxygen of sulphate; and iii) 16S rRNA gene sequencing from groundwater samples. Thus, it was proved that the injection of lactate promoted sulphate-reducing conditions, with the subsequent decrease in Eh, which allowed for the full reductive dechlorination of PCE to ETH in the injection well. The biodegradation of CEs was also confirmed by the enrichment in 13 C and carbon isotopic mass balances. The metagenomic results evidenced the shift in the composition of the microbial population towards the predominance of fermentative bacteria. Given the success of the in-situ pilot test, a full-scale ERD with lactate was then implemented at the site. After one year of treatment, PCE and trichloroethene were mostly depleted, whereas vinyl chloride (VC) and ETH were the predominant metabolites. Most importantly, the shift of the carbon isotopic mass balances towards more positive values confirmed the complete reductive dechlorination, including the VC-to-ETH reaction step. The combination of techniques used here provides complementary lines of evidence for the diagnosis of the intrinsic biodegradation potential of a polluted site, but also to monitor 3 the progress, identify potential difficulties, and evaluate the success of ERD at the field scale.

Bioremediation of contaminated soil and groundwater by in situ biostimulation

“…In addition to acting as an electron donors, added carbon sources can generally promote microbial growth, oxygen consumption, and creation of anoxic conditions required for reductive dechlorination. Lactate, one of the most commonly used substrates, and ethanol both results in the fermentation of acetate (Hood et al, 2008;Blázquez-Pallí et al, 2019). As the remediation of chlorinated hydrocarbons is often a long-duration process, slowly releasing carbon and electron sources can also be used, such as whey, fatty acid mixtures, vegetable oil, carboxymethylcellulose, polylactic acid, polyhydroxyalkanoates, etc.…”

Respiratory protein interactions in Dehalobacter sp. strain 8M revealed through genomic and native proteomic analyses

“…Bioremediation using organohalide-respiring bacteria (OHRB) is a feasible and low-cost strategy to treat contaminated groundwater (Bl azquez-Pallí et al, 2019;Jugder et al, 2016). OHRB are anaerobic microorganisms characterized by their ability to gain energy for growth by using halogenated compounds as terminal electron acceptors, yielding less-halogenated compounds as products (Wang et al, 2018).…”

Combining nanoscale zero-valent iron and anaerobic dechlorinating bacteria to degrade chlorinated methanes and 1,2-dichloroethane

“…At the heart of this process are membrane-bound reductive dehalogenases, which use chlorinated compounds as electron acceptors to generate cellular energy while using H 2 as electron donor (Koenig et al 2015 ; Richardson 2013 ; Wang et al 2016 ). As for nZVI, enhanced biological reductive dechlorination has been proven to be an effective in situ treatment to remove chlorinated compounds in anoxic groundwaters with a relatively low cost compared to other physicochemical techniques (Chen et al 2015 ; Blázquez-Pallí et al 2019 ). To date, dichloroelimination of 1,2-DCA to ethene under anaerobic conditions has been demonstrated for several ORB, including Dehalococcoides mccartyi , Dehalogenimonas , Desulfitobacterium , Sulfurospirillum , and Dehalobacter (De Wildeman et al 2003 ; Maymó-Gatell et al 1999 ; Moe et al 2009 ; Grostern and Edwards 2006 ; van der Zaan et al 2009 ).…”