Dichloromethane utilization in a packed-bed reactor in the presence of various electron acceptors

Dichloromethane, added as sole source of carbon and energy, was utilized by microorganisms in a packed-bed reactor under carbon dioxide-, sulfate-, nitrate- and nitrite-reducing conditions. Only in the presence of nitrite (4 mM) was the transformation of dichloromethane partly inhibited. The maximum transformation rate for dichloromethane under carbon dioxide reducing conditions was 1.25 kg m−3 d−1. Carbon dioxide, acetate and formate were detected as (intermediate) products of dichloromethane transformation in the reactor, indicating that it was a fermentative process. Both acetate and formate, when formed, were further utilized. The type of microorganisms that utilized formate and acetate depended on the electron acceptor present in the reactor. When carbon dioxide was the only electron acceptor available, acetate and formate were utilized by methanogens as indicated by methane production. When sulfate, nitrate or nitrite were present in the reactor, acetate and formate were utilized by sulfate-, nitrate- or nitrite-reducing microorganisms, respectively. Inhibition of methanogens with 2-bromoethane sulfonic acid or of sulfate reduction with molybdate had no effect on the utilization of dichloromethane in enrichment cultures from the reactor. Also the presence of nitrate or nitrite was not necessary for the transformation of dichloromethane. These results suggested that neither methanogens nor sulfate-, nitrate- and nitrite-reducers were involved in the transformation of dichloromethane but that these organisms only utilized acetate and formate, the products of dichloromethane fermentation in the reactor.