Enrichment of methanotrophic consortium and its aerobic cometabolism of mixed vinyl chloride pollutants using methane gas and micro- and nano-bubbles

Abstract

Chlorinated ethylenes (CEs) are widely used in various industries, making them common groundwater pollutants. The reductive dechlorination applied to deal with CEs has the drawback of lower-chlorinated CEs accumulation. Aerobic co-metabolism relying on methanotrophs is an attractive strategy to deal with CEs because of its fast CE degrading rate and no lower-chlorinated CEs accumulation. In this study, one methanotrophic consortium was acclimated with methane and TCE concentrations for five phases. The bacterial community and methane monooxygenase (MMO) functional genes were analyzed during enrichment. The methane gas and micro-nano bubbles (MNBs) were applied to perform batch experiments using the acclimated methanotrophic consortium as the inoculum. The results indicated that a methanotrophic consortium M-5%-0.2 was successfully acclimated. Genus Methylocystis was dominant in the acclimated consortium M-5%-0.2, and the particulate methane monooxygenase gene (pmoA) could be detected. With different CEs combinations and 5% methane gas, 0.2 and 0.3 mg/L cis-1,2-DCE and VC could be entirely removed. TCE removal efficiencies were 38.8% and 40.2%, as the TCE concentrations were 0.2 and 0.3 mg/L, respectively. CEs removal pattern was similar in the presence of various methane MNBs ratios. The priority order of CEs removal was VC > cis-1,2-DCE > TCE. The degradation efficiencies of 0.2 mg/L TCE, cis-1,2-DCE, and VC were 17.4%, 78.4%, and 100% when adding 24% methane MNBs water as the carbon source. The methanotrophic consortium M-5%-0.2 could utilize the methane MNBs having a diameter larger than 235 nm. In conclusion, the aerobic co-metabolism strategy using methane MNBs has the potential to be applied for CEs bioremediation.