Low pH Inhibition of Reductive Dechlorination - Revision history

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← Older revision		Revision as of 02:00, 28 April 2022
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−	'''~~CONTRIBUTOR~~(S):''' [[Dr. Robert Borden, P.E.]]	+	'''Contributor(s):''' [[Dr. Robert Borden, P.E.]]

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 [[wikipedia: Halorespiration | Organohalide-respiring bacteria]] are generally sensitive to pH.  Reductive dechlorination of [[Chlorinated Solvents | tetrachloroethene (PCE)]] to [[Chlorinated Solvents | trichloroethene (TCE)]] and then to [[Chlorinated Solvents | cis-1,2-dichloroethene(cDCE)]] can occur at a pH as low as 5.5.  However, rates of cDCE reduction to [[Chlorinated Solvents | vinyl chloride (VC)]] and then to ethene are reduced below a pH of 6.0.  For efficient dechlorination to non-toxic end products, aquifer pH should be maintained above 6.0 during [[Bioremediation - Anaerobic | enhanced reductive dechlorination (ERD)]].
 <div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 '''Related Article(s):'''
 *[[Bioremediation - Anaerobic| In Situ Anaerobic Bioremediation]]
 *[[pH Buffering in Aquifers]]

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 *[[Bioremediation - Anaerobic| In Situ Anaerobic Bioremediation]]
 *[[Biodegradation - Reductive Processes]]
 *[[Design Tool - Base Addition for ERD]]
 *[[Chlorinated Solvents]]

@@ Line 7: / Line 7: @@
 *[[Bioremediation - Anaerobic| In Situ Anaerobic Bioremediation]]
 *[[Biodegradation - Reductive Processes]]
-*[[Design Tool for Estimating Base Required during ERD]]
+*[[Design Tool - Base Addition for ERD]]
 *[[pH Buffering in Aquifers]]
 *[[Chlorinated Solvents]]

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 [[File:Borden1w2 Figure1.png|right|thumbnail| 550 px|Figure 1.  Relative Dechlorination Rates (R<sub>pH</sub> /R<sub>max</sub>) versus pH for Consortia SL2-PCEa, SL2-PCEb, AQ-1, and PM (adapted from Lacroix et al. 2014)<ref name= "Lacroix2014"/>. ]]
 ==Low pH Tolerant Enrichments==
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 Acids are produced during ERD that can cause pH to decline, inhibiting further dechlorination.  Reduction of PCE to TCE to cDCE can occur at pH down to 5.5 or possibly lower.  However, rates of cDCE reduction to VC to ethene are reduced below a pH of 6.0.  For efficient dechlorination to non-toxic end products, the aquifer pH should be maintained above 6.0 during ERD.
-<BR clear="left">
 ==References==
 <references />

@@ Line 67: / Line 67: @@
 where R<sub>max</sub>  is the maximum dechlorination rate at the optimal pH (pH<sub>opt</sub>), and n and σ are empirical fitting parameters (Table 2).  Graphs of relative dechlorination rates (R<sub>pH</sub> / R<sub>max</sub>) are shown in Figure 1.  Dechlorination of PCE to cDCE can continue at pH below 5.5. However, dechlorination of cDCE to VC and VC to ethene is severely inhibited below a pH of 5.5.
-[[File:Borden1w2 Table 2.PNG|left| thumbnail|600 px| (from Lacroix et al. 2014)<ref name= "Lacroix2014"/>]]
+[[File:Borden1w2 Table 2.PNG|left| thumbnail|550 px| (from Lacroix et al. 2014)<ref name= "Lacroix2014"/>]]
-[[File:Borden1w2 Figure1.png|left|thumbnail| 600 px|Figure 1.  Relative Dechlorination Rates (R<sub>pH</sub> /R<sub>max</sub>) versus pH for Consortia SL2-PCEa, SL2-PCEb, AQ-1, and PM (adapted from Lacroix et al. 2014)<ref name= "Lacroix2014"/>. ]]
+[[File:Borden1w2 Figure1.png|right|thumbnail| 550 px|Figure 1.  Relative Dechlorination Rates (R<sub>pH</sub> /R<sub>max</sub>) versus pH for Consortia SL2-PCEa, SL2-PCEb, AQ-1, and PM (adapted from Lacroix et al. 2014)<ref name= "Lacroix2014"/>. ]]
 ==Low pH Tolerant Enrichments==

@@ Line 22: / Line 22: @@
 ==Introduction==
-[[Bioremediation - Anaerobic | Enhanced reductive dechlorination (ERD)]] is commonly used to treat chlorinated solvents and related contaminants in groundwater by providing a fermentable organic substrate to serve as both an electron donor and a carbon source to stimulate microbially mediated [[Biodegradation - Reductive Processes| reductive dechlorination]]<ref>AFCEE, NFESC, ESTCP, 2004. Principles and Practices of Enhanced Anaerobic Bioremediation of Chlorinated Solvents. Parsons Corporation. Air Force Center for Environmental Excellence, Naval Facilities Engineering Service Center, and Environmental Security Technology Certification Program. [[media:AFCEE_Principles_and_Practices.pdf| Report PDF]]</ref><ref>ITRC, 2008. Enhanced attenuation of chlorinated organics (EACO-1): A decision framework for site transition. Washington, D.C.: Interstate Technology & Regulatory Council, Enhanced Attenuation: Chlorinated Organics Team[[media:2008-ITRC-EACO_1.pdf| Report pdf]]</ref><ref>Stroo, H.F., West, M.R., Kueper, B.H., Borden, R.C., Major, D.W. and Ward, C.H., 2014. In Situ Bioremediation Of Chlorinated Ethene Source Zones. In Chlorinated Solvent Source Zone Remediation (pp. 395-457). Springer New York. [http://dx.doi.org/10.1007/978-1-4614-6922-3_12 doi:10.1007/978-1-4614-6922-3_12]</ref>.  During ERD, the pH may decline as [[wikipedia:Hydrochloric acid | hydrochloric acid (HCl)]] is produced during reductive dechlorination<ref>Vogel, T.M. and McCarty, P.L., 1985. Biotransformation of tetrachloroethylene to trichloroethylene, dichloroethylene, vinyl chloride, and carbon dioxide under methanogenic conditions. Applied and Environmental Microbiology, 49(5), pp.1080-1083.[[Media:1985-Vogel-Biotransformation_of_PCE_to_TCE,_DCE,_VC.pdf | Report.pdf]]</ref> <ref>Mohn, W.W. and Tiedje, J.M., 1992. Microbial reductive dehalogenation. Microbiological reviews, 56(3), pp.482-507.[[Media:1992-Mohn-Microbial_Reductive_Dehalogenation.pdf | Report.pdf]]</ref> and carbonic acid and organic acids are produced by substrate fermentation.  However, dechlorinating bacteria appear to be particularly sensitive to pH changes with dechlorination of cDCE and VC to ethene completely inhibited at a pH of 5.5<ref name= "Rowlands2004">Rowlands, D., 2004.  Development of optimal pH for degradation of chlorinated solvents by the KB-1TM anaerobic bacterial culture.  M.S. Thesis, University of Guelph, Guelph, ON, Canada</ref><ref name= "Vainberg2006">Vainberg, S., Steffan, R.J., Rogers, R., Ladaa, T., Pohlmann, D. and Leigh, D., 2006.  Production and application of large-scale cultures for bioaugmentation. Proc 5th Internat Conf Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, USA.  May 22-25.  Paper No. A-50.</ref><ref name= "Eaddy2008">Eaddy, A., 2008. Scale-up and characterization of an enrichment culture for bioaugmentation of the P-area chlorinated ethene plume at the Savannah River site. M.S. Thesis, Clemson University, Clemson, SC, USA. [[media:2008-Eaddy-Scale_Up_and_Characterization_Thesis_Final_pdf.pdf| Report.pdf]]</ref><ref name= "Yang2017a"/>, resulting in a significant decline in degradation rates<ref>Duhamel, M., Wehr, S.D., Yu, L., Rizvi, H., Seepersad, D., Dworatzek, S., Cox, E.E. and Edwards, E.A., 2002. Comparison of anaerobic dechlorinating enrichment cultures maintained on tetrachloroethene, trichloroethene, cis-dichloroethene and vinyl chloride. Water Research, 36(17), pp.4193-4202. [https://doi.org/10.1016/s0043-1354(02)00151-3 doi: 10.1016/S0043-1354(02)00151-3]</ref><ref>McCarty, P.L., Chu, M.Y. and Kitanidis, P.K., 2007. Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater. European Journal of Soil Biology, 43(5-6), pp.276-282. doi: 10.1016/j.ejsobi.2007.03.004. [[media: 2007-McCarty-Electron_donor_and_pH_relationships....pdf| Report.pdf]]</ref>.
+[[Bioremediation - Anaerobic | Enhanced reductive dechlorination (ERD)]] is commonly used to treat chlorinated solvents and related contaminants in groundwater by providing a fermentable organic substrate to serve as both an electron donor and a carbon source to stimulate microbially mediated [[Biodegradation - Reductive Processes| reductive dechlorination]]<ref>AFCEE, NFESC, ESTCP, 2004. Principles and Practices of Enhanced Anaerobic Bioremediation of Chlorinated Solvents. Parsons Corporation. Air Force Center for Environmental Excellence, Naval Facilities Engineering Service Center, and Environmental Security Technology Certification Program. [[media:AFCEE_Principles_and_Practices.pdf| Report.pdf]]</ref><ref>ITRC, 2008. Enhanced attenuation of chlorinated organics (EACO-1): A decision framework for site transition. Washington, D.C.: Interstate Technology & Regulatory Council, Enhanced Attenuation: Chlorinated Organics Team[[media:2008-ITRC-EACO_1.pdf| Report.pdf]]</ref><ref>Stroo, H.F., West, M.R., Kueper, B.H., Borden, R.C., Major, D.W. and Ward, C.H., 2014. In Situ Bioremediation Of Chlorinated Ethene Source Zones. In Chlorinated Solvent Source Zone Remediation (pp. 395-457). Springer New York. [http://dx.doi.org/10.1007/978-1-4614-6922-3_12 doi:10.1007/978-1-4614-6922-3_12]</ref>.  During ERD, the pH may decline as [[wikipedia:Hydrochloric acid | hydrochloric acid (HCl)]] is produced during reductive dechlorination<ref>Vogel, T.M. and McCarty, P.L., 1985. Biotransformation of tetrachloroethylene to trichloroethylene, dichloroethylene, vinyl chloride, and carbon dioxide under methanogenic conditions. Applied and Environmental Microbiology, 49(5), pp.1080-1083.[[Media:1985-Vogel-Biotransformation_of_PCE_to_TCE,_DCE,_VC.pdf | Report.pdf]]</ref> <ref>Mohn, W.W. and Tiedje, J.M., 1992. Microbial reductive dehalogenation. Microbiological reviews, 56(3), pp.482-507.[[Media:1992-Mohn-Microbial_Reductive_Dehalogenation.pdf | Report.pdf]]</ref> and carbonic acid and organic acids are produced by substrate fermentation.  However, dechlorinating bacteria appear to be particularly sensitive to pH changes with dechlorination of cDCE and VC to ethene completely inhibited at a pH of 5.5<ref name= "Rowlands2004">Rowlands, D., 2004.  Development of optimal pH for degradation of chlorinated solvents by the KB-1TM anaerobic bacterial culture.  M.S. Thesis, University of Guelph, Guelph, ON, Canada</ref><ref name= "Vainberg2006">Vainberg, S., Steffan, R.J., Rogers, R., Ladaa, T., Pohlmann, D. and Leigh, D., 2006.  Production and application of large-scale cultures for bioaugmentation. Proc 5th Internat Conf Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, USA.  May 22-25.  Paper No. A-50.</ref><ref name= "Eaddy2008">Eaddy, A., 2008. Scale-up and characterization of an enrichment culture for bioaugmentation of the P-area chlorinated ethene plume at the Savannah River site. M.S. Thesis, Clemson University, Clemson, SC, USA. [[media:2008-Eaddy-Scale_Up_and_Characterization_Thesis_Final_pdf.pdf| Report.pdf]]</ref><ref name= "Yang2017a"/>, resulting in a significant decline in degradation rates<ref>Duhamel, M., Wehr, S.D., Yu, L., Rizvi, H., Seepersad, D., Dworatzek, S., Cox, E.E. and Edwards, E.A., 2002. Comparison of anaerobic dechlorinating enrichment cultures maintained on tetrachloroethene, trichloroethene, cis-dichloroethene and vinyl chloride. Water Research, 36(17), pp.4193-4202. [https://doi.org/10.1016/s0043-1354(02)00151-3 doi: 10.1016/S0043-1354(02)00151-3]</ref><ref>McCarty, P.L., Chu, M.Y. and Kitanidis, P.K., 2007. Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater. European Journal of Soil Biology, 43(5-6), pp.276-282. doi: 10.1016/j.ejsobi.2007.03.004. [[media: 2007-McCarty-Electron_donor_and_pH_relationships....pdf| Report.pdf]]</ref>.
 ==Effect of pH on Bioremediation Processes==

@@ Line 32: / Line 32: @@
 Table 1 shows the range and optimum pH for growth of bacteria that reduce PCE to TCE and cDCE.  Zhuang and Pavlostathis (1995)<ref>Zhuang, P. and Pavlostathis, S.G., 1995. Effect of temperature, pH and electron donor on the microbial reductive dechlorination of chloroalkenes. Chemosphere, 31(6), pp.3537-3548. [https://doi.org/10.1016/0045-6535(95)00204-L doi:10.1016/0045-6535(95)00204-L]</ref> found that neutral pH was optimum for reductive dechlorination by a methanogenic mixed culture capable of dechlorinating PCE to VC.  Vainberg et al. (2006)<ref name= "Vainberg2006"/> reported an optimum pH of 6.0-6.8 for dechlorination of PCE by the SDC-9<sup>™</sup> bioaugmentation culture.  Dechlorination of PCE and TCE to cDCE can occur at pH down to 5.5<ref>Vainberg, S., Condee, C.W. and Steffan, R.J., 2009. Large-scale production of bacterial consortia for remediation of chlorinated solvent-contaminated groundwater. Journal of Industrial Microbiology & Biotechnology, 36(9), pp.1189-1197. [https://doi.org/10.1007/s10295-009-0600-5 doi: 10.1007/s10295-009-0600-5]</ref>.
-{|- class="wikitable" style="width: 60%; margin: auto;"
 |+<div align="left">Table 1. Range and optimum pH for growth of pure cultures reducing PCE <span style="font-weight:normal;">(adapted from Damborský, 1999<ref>Damborský, J., 1999. Tetrachloroethene-dehalogenating bacteria. Folia microbiologica, 44(3), pp.247-262. [https://doi.org/10.1007/bf02818543 doi: 10.1007/BF02818543][[Media:1999-Damborsky-Tetrachloroethene-Dehalogenating_Bacteria.pdf | Report.pdf]]</ref>; Yang et al. 2017a<ref name= "Yang2017a"/>)</span></div>
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