Managing methanogens and homoacetogens to promote reductive dechlorination of trichloroethene with direct delivery of H2 in a membrane biofilm reactor

• Published in: Biotechnology and bioengineering Vol. 109; no. 9; pp. 2200 - 2210
• Main Authors: Ziv-El, Michal, Popat, Sudeep C., Cai, Katherine, Halden, Rolf U., Krajmalnik-Brown, Rosa, Rittmann, Bruce E.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.09.2012; Wiley Subscription Services, Inc
• Subjects: Acetobacterium; Bacteria; Bacteria - metabolism; Bacterial Physiological Phenomena; Biodegradation, Environmental; Biofilms; Bioreactors - microbiology; Bioremediation; Chloroflexi - metabolism; Dehalococcoides; Geobacter; Halogenation; homoacetogenesis; Hydrogen - metabolism; membrane biofilm reactor; methanogenesis; Oxidation-Reduction; Polymerase chain reaction; reductive dechlorination; Scanning electron microscopy; Trichloroethylene - metabolism
• ISSN: 0006-3592; 1097-0290
• DOI: 10.1002/bit.24487

A study with H2‐based membrane biofilm reactors (MBfRs) was undertaken to examine the effectiveness of direct H2 delivery in ex‐situ reductive dechlorination of chlorinated ethenes. Trichloroethene (TCE) could be reductively dechlorinated to ethene with up to 95% efficiency as long as the pH‐increase effects of methanogens and homoacetogens were managed and dechlorinators were selected for during start‐up by creating H2 limitation. Based on quantitative PCR, the dominant bacterial groups in the biofilm at the end of reactor operation were Dehalococcoides, Geobacter, and homoacetogens. Pyrosequencing confirmed the dominance of the dechlorinators and identified Acetobacterium as the key homoacetogen. Homoacetogens outcompeted methanogens for bicarbonate, based on the effluent concentration of acetate, by suppressing methanogens during batch start‐up. This was corroborated by the methanogenesis functional gene mcrA, which was 1–2 orders of magnitude lower than the FTHFS functional gene for homoacetogens. Imaging of the MBfR fibers using scanning electron microscopy showed a distinct Dehalococcoides‐like morphology in the fiber biofilm. These results support that direct addition of H2 can allow for efficient and complete reductive dechlorination, and they shed light into how H2‐fed biofilms, when operated to manage methanogenic and homoacetogenic activity, can be used for ex‐situ bioremediation of chlorinated ethenes. Biotechnol. Bioeng. 2012;109: 2200–2210. © 2012 Wiley Periodicals, Inc. This study sheds light into how H2‐fed biofilms, when operated to manage methanogenic and homoacetogenic activity, can be used for ex‐situ bioremediation of chlorinated ethenes. Successful operation relied on controlling the pH‐increase effects of methanogenesis and homoacetogenesis, and creating a H2 limitation during start‐up to allow dechlorinators to compete against other microorgansims. Methanogens were additionally minimized during continuous flow operation by a limitation in bicarbonate resulting from strong homoacetogenic activity.