Co-metabolic biodegradation of chlorinated ethene in an oxygen- and ethane-based membrane biofilm reactor

Groundwater contamination by chlorinated ethenes is an urgent concern worldwide. One approach for detoxifying chlorinated ethenes is aerobic co-metabilims using ethane (C₂H₆) as the primary substrate. This study evaluated long-term continuous biodegradation of three chlorinated alkenes in a membrane biofilm reactor (MBfR) that delivered C₂H₆ and O₂ via gas-transfer membranes. During 133 days of continuous operation, removals of dichloroethane (DCE), trichloroethene (TCE), and tetrachloroethene (PCE) were as high as 94 % and with effluent concentrations below 5 μM. In situ batch tests showed that the co-metabolic kinetics were faster with more chlorination. C₂H₆-oxidizing Comamonadaceae and "others," such as Methylococcaceae, oxidized C₂H₆ via monooxyenation reactions. The abundant non-ethane monooxygenases, particularly propane monooxygenase, appears to have been responsible for C₂H₆ aerobic metabolism and co-metabolism of chlorinated ethenes. This work proves that the C₂H₆ + O₂ MBfR is a platform for ex-situ bioremediation of chlorinated ethenes, and the generalized action of the monooxygenases may make it applicable for other chlorinated organic contaminants.