Dechlorination of PCE by mixed methanogenic cultures using hollow-fiber membranes

This study investigated the use of hollow-fiber membranes for hydrogen (H ₂) delivery to support the biological reductive dechlorination of tetrachloroethene (PCE). Two experiments were performed in which H ₂ 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 H ₂ (1% H ₂ and 50% H ₂), while negligible dechlorination was observed in control reactors (100% N ₂). The 1%-H ₂-fed reactor outperformed the 50%-H ₂-fed reactor in the first experiment. However, the dechlorinating performance in the two reactors was similar in the second experiment. Despite relatively high H ₂ concentrations (4.6 to 178 μM) that led to H ₂ consumption (and CH ₄ 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 H ₂. Dechlorination was also maintained at aqueous H ₂ 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 H ₂ delivery technology for stimulating the bioremediation of chlorinated ethene-contaminated aquifers.