Abstract
Methane is a greenhouse gas and significantly contributes to global warming. Methane biofiltration with immobilized methane-oxidizing bacteria (MOB) is an efficient and eco-friendly approach for methane elimination. To achieve high methane elimination capacity (EC), it is necessary to use an exceptional support material to immobilize MOB. The MOB consortium was inoculated in biofilters to continuusly eliminate 1% (v/v) of methane. Results showed that the immobilized MOB cells outperformed than the suspended MOB cells. The biofilter packed with fly ash ceramsite (FAC) held the highest average methane EC of 4.628 g h–1 m–3, which was 33.4% higher than that of the biofilter with the suspended MOB cells. The qPCR revealed that FAC surface presented the highest pmoA gene abundance, which inferred that FAC surface immobilized the most MOB biomass. The XPS and contact angle measurement indicated that the desirable surface elemental composition and stronger surface hydrophilicity of FAC might favor MOB immobilization and accordingly improve methane elimination.
Highlights
Methane is the second-largest greenhouse gas, which has approximately a 25 times global warming potential than that of carbon dioxide for a 100-year horizon (Veillette et al, 2012; Limbri et al, 2013)
The results demonstrated that MFAC was the most effective methane eliminator, and followed by MCC, MAC, and MC
The metal hydroxides might be formed on ceramsite surface instead of metal oxides, and the covalent bonds could be formed between bacterial cells and metal hydroxides, which might facilitate the bacterial adhesion and immobilization (Cohen, 2000)
Summary
Methane is the second-largest greenhouse gas, which has approximately a 25 times global warming potential than that of carbon dioxide for a 100-year horizon (Veillette et al, 2012; Limbri et al, 2013). Methane is emitted from natural and anthropocentric processes, including wetlands, oceans, forests, paddy fields, manure management, livestock, landfills, coal mines, and biogas upgrading process (Conrad, 2009). 55% of anthropogenic methane emissions hold methane concentrations lower than 3% (v/v), and the emitted lean methane is difficult to be treated by the thermal oxidation process (Melse and Van der Werf, 2005; Ramirez et al, 2012a). Methane could be naturally oxidized by methane-oxidizing bacteria (MOB). MOB are widely distributed aerobic microorganisms, which use methane as carbon and energy sources (Im et al, 2011; Ramirez et al, 2012b). MOB initially oxidize methane into methanol by methane monooxygenase (MMO), and methanol is converted into formaldehyde by methanol dehydrogenase (MDH). A part of formaldehyde is oxidized into formate by formaldehyde dehydrogenase (FADH) and subsequently converted into CO2 by formate dehydrogenase (FDH)
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