Dechlorination of PCE by Mixed Methanogenic Cultures Using Hollow-Fiber Membranes

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The study investigated the use of hollow-fiber membranes for hydrogen (H2) delivery to support the biological reductive dechlorination of tetrachloroethene (PCE) Two experiments were performed in which H2 was supplied through membranes placed in stirred batch reactors containing a mixed methanogenic/dechlorinating culture and PCE (≤10 µM. Reductive dechlorination of PCE to cis-dichloroethene was sustained in the reactors receiving H2 (1% H2 and 50% H2), while negligible dechlorination was observed in control reactors (100% N2). The 1%-H2-fed reactor outperformed the 50%-H2-fed reactor in the first experiment. However, the dechlorinating performance in the two reactors was similar in the second experiment. Despite relatively high H2 concentrations (4.6 to 178 µM) that led to H2 consumption (and CH4 production) by methanogens, dechlorination was effectively maintained for the duration of the experiments (35 to 62 days). The results of this study are significant in that dechlorination was sustained in a minimal medium by membrane-delivered H2. Dechlorination was also maintained at aqueous H2 concentrations that exceeded the thermodynamic thresholds for not only dechlorination (<0.1 to 2 nM, but also methanogenesis (∼10 nM) and homoacetogenesis (94 to 400 nM. The results of these experiments suggest that membranes are a promising H2 delivery technology for stimulating the bioremediation of chlorinated ethene-contaminated aquifers.