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Bioremediation of Chlorinated Solvents Using Alternate Electron Acceptors
Published in John E. Matthews, Handbook of Bioremediation, 2017
Several studies provide evidence for anaerobic transformation of chlorinated solvents by pure cultures of bacteria (Table 8.2). The bacteria involved ranged from strict anaerobic microorganisms, such as methanogens, sulfate-reducers, and Clostridia to facultative anaerobes such as Escherichia coli or Pseudomonas putida. Reductive dechlorination was the predominant reaction pathway. Consequently, the chlorinated solvent biotransformation studies with environmental samples (mixed microbial cultures) and pure bacterial cultures indicate that a broad variety of bacteria possess the enzymatic capability to reductively dechlorinate the compounds. An electron donor, such as low molecular weight organic compounds (lactate, acetate, methanol, glucose, etc.) or H2, must be available to provide reducing equivalents for reductive dechlorination. Toluene was recently found to be a suitable electron donor for the reductive dechlorination of PCE to DCE in anaerobic aquifer microcosms (Sewell and Gibson, 1991).
Anaerobic Bioreactors For The Treatment of Chlorinated Hydrocarbons
Published in Devarajan Thangadurai, Jeyabalan Sangeetha, Industrial Biotechnology, 2017
Ricardo Alfán-Guzmán, Matthew Lee, Michael Manefield
In the anaerobic mode of degradation the organochlorine serves as electron acceptor instead of O2. Reductive dechlorination generally involves the sequential replacement of a chlorine atom on a chlorinated hydrocarbon with a hydrogen atom (Figure 14.3) and has been observed to occur both directly and cometabolically. In direct dechlorination, the mediating bacteria use the chlorinated hydrocarbons as an electron acceptor in energy-producing redox reactions. Cometabolic mechanisms occur under iron reducing, sulfate reducing or methanogenic environments when bacteria incidentally dechlorinate organochlorines in the process of using another electron acceptor to generate energy. Dehalofermantation is another well-known mechanism. During this process, bacteria use chlorinated compounds as sole carbon and energy sources in the absence of an exogenous electron acceptor (US-EPA, 2000; Smidt and de Vos, 2004; Reineke et al., 2011; Lee et al., 2012).
Remedial Actions
Published in Benjamin Alter, Environmental Consulting Fundamentals, 2019
The most common negatively charged ion dealt with by ISCR is chlorine, a halogen. Removal of chlorine from the molecular structure of a contaminant is a process known as reductive dechlorination. It transforms common, toxic chlorinated solvents such as PCE and TCE, into harmless compounds, such as ethene, as shown in Figure 9.8. In essence, the dechlorination process reverses the method in which the PCE was manufactured, which was by adding chlorine atoms to ethene, a two-carbon alkene structure. Reversing the process requires substitution of a chlorine atom with a hydrogen atom, thus converting the PCE into TCE. This process is repeated until all four chlorine atoms have been removed from the molecular structure.
Promoted reductive removal of chlorinated organic pollutants co-occurring with facilitated methanogenesis in anaerobic environment: A systematic review and meta-analysis
Published in Critical Reviews in Environmental Science and Technology, 2022
Jie Cheng, Jing Yuan, Shuyao Li, Xueling Yang, Zhijiang Lu, Jianming Xu, Yan He
Numerous previous studies have explored the removal of chlorinated organic pollutants (COPs) from different perspectives, e.g., dichloromethane (DCM) dissipation in aerosol (Jia et al., 2017), trichlorophenol (TCP) reduction under weak electrical stimulation (Lin et al., 2019), carbon tetrachloride (CT) elimination in anaerobic fixed film bioreactor (Lorah et al., 2015), hexachlorobenzene (HCB) biodegradation with the addition of sludge (Vandermeeren et al., 2014). Particularly, the way for environmental removal of COPs through anaerobic reductive dechlorination has been received increased attention during recent decades because of the highly-effective, eco-friendly and cost-competitive advantages (Xue et al., 2017). Microbial-mediated reductive dechlorination was essentially a step-by-step redox reaction where chlorine detached from carbon via the breakdown of covalent bond, accompanied with the electron accepting driven by electron flow from hydrogen, reducing minerals and carbon substrates (Bosso & Cristinzio, 2014). A body of studies have proved the reductive removal of COPs was accompanied with the anaerobic reduction processes of many elements like N, Fe, S (Smidt & De Vos, 2004; Xu et al., 2015). Fe(III) reduction was found coupling with COP reduction (Xu et al., 2014). The preference of these two processes was suggested closely related to Fe(III) speciation and concentrations of all substrates and products (Wang et al., 2020). For example, Fe(III) reduction enhanced dichlorodiphenyltrichloroethane (DDT) degradation (Chen et al., 2013) or helped dechlorination of trichloroethylene (TCE) to ethane (Wei & Finneran, 2011), while the supplement of Fe(III) significantly inhibited dechlorination rate of PCB (Xu et al., 2018). SO42− reduction also showed complicated interaction with COP reductive removal (Zhang et al., 2017). A certain Fe/S mole ratio led a positive effect to accelerate PCP dechlorination (Xue et al., 2017). The application of urea increased soil NH4+-N contents, which severed as electron donors, and subsequently accelerated HCB reductive dechlorination (Liu et al., 2010b). With the moderate but not overload nitrate supplement, NO3− reduction could shift more available electrons to dechlorination also regulate the growth of core microbial groups to facilitate PCP anaerobic removal (Cheng et al., 2019).