Feasibility of methane bioconversion to methanol by acid-tolerant ammonia-oxidizing bacteria. (1st June 2021)

• Record Type: Journal Article
• Authors: Zhang, Junji; Hu, Zhetai; Liu, Tao; Wang, Zhiyao; Guo, Jianhua; Yuan, Zhiguo; Zheng, Min
• Is Part Of: Water research. Volume 197(2021)
• Publication Date: 2021-06-01
• Subjects: Methane bioconversion to methanol -- Ammonia-oxidizing bacteria (AOB) -- Low pH -- Biogas utilization -- Candidatus 'Nitrosoglobus'; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.117077
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: An acid-tolerant AOB culture enables conversion of methane to methanol at pH 5. Methane oxidation under acidic condition is robust against CO2 and H2 S in biogas. Methanol yield under acidic condition is about 30–40%. The addition of ammonium can significantly increase methanol production rate. Abstract: Bioconversion of biogas to value-added liquids has received increasing attention over the years. However, many biological processes are restricted under acidic conditions owing to the excessive carbon dioxide (CO2, 30–40% v / v ) in biogas. Here, using an enriched culture dominated by acid-tolerant ammonia-oxidizing bacteria (AOB) ' Candidatus Nitrosoglobus', this study examined the feasibility of producing methanol from methane in the CO2 -acidified environment (i.e. pH of 5.0). Within the tested dissolved methane range (0.1–0.9 mM), methane oxidation by the acid-tolerant AOB culture followed first-order kinetics, with the same rate constant (i.e. 0.43 (L/(g VSS‧h)) between pH 7.0 and 5.0. The acidic methane oxidation showed robustness against high dissolved concentrations of CO2 (up to 4.06 mM) and hydrogen sulfide (H2 S up to 0.11 mM), which led to a high methanol yield of about 30–40%. As such, the raw biogas containing toxic CO2 and H2 S can directly serve for methanol production by this acid-tolerant AOB culture, economizing a conventionally costly biogas upgradation process. Afterwards, two batch reactors fed with methane and oxygen intermittently both obtained a final concentration of 1.5 mM CH3 OH (equal to 72 mg chemical oxygen demand/L) in the liquid, suggesting it is a useful carbon source to enhance denitrification in wastewater treatment systems. In addition, ammonia availability was identified to be critical for a higher rate of this AOB-mediated methanol production. Overall, our results for the first time demonstrated the capability of a novel acid-tolerant AOB culture to oxidize methane, and also illustrated the technical feasibility to utilize raw biogas for methanol production at acidic conditions. Graphical abstract: Image, graphical abstract