US EPA

1510714 

Journal Article 

High rate, high-yield production of methanol by ammonia oxidizing bacteria 

Taher, E; Chandran, K 

In Press 

1 

Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 

English 

23473425 

10.1021/es3042912 

The overall goal of this study was to develop an appropriate biological process for achieving autotrophic conversion of methane (CH4) to methanol (CH3OH). In this study, we employed ammonia oxidizing bacteria (AOB) to selectively and partially oxidize CH4 to CH3OH. In fed-batch reactors using mixed nitrifying enrichment cultures from a continuous bioreactor, up to 59.89 ± 1.12 mg COD/L of CH3OH was produced within an incubation time of 7 h, which is approximately ten times the yield obtained previously using pure cultures of Nitrosomonas europaea. The maximum specific rate of CH4 to CH3OH conversion obtained during this study was 0.82 mg CH3OH COD/mg AOB biomass COD-d, which is 1.5 times the highest value reported with pure cultures. Notwithstanding these positive results, CH4 oxidation to CH3OH by AOB was inhibited by NH3 (the primary substrate for the oxidative enzyme, ammonia monooxygenase, AMO) as well as the product, CH3OH, itself. Further, oxidation of CH4 to CH3OH by AOB was also limited by reducing equivalents supply, which could be overcome by externally supplying hydroxylamine (NH2OH) as an electron donor. Therefore, a potential optimum design for promoting CH4 to CH3OH oxidation by AOB could involve supplying NH3 (needed to maintain AMO activity) uncoupled from the supply of NH2OH and CH4. Partial oxidation of CH4 containing gases to CH3OH by AOB represents an attractive platform for the conversion of a gaseous mixture to an aqueous compound, which could be used as a commodity chemical. Alternately, the nitrate and CH3 OH thus produced could be channeled to a downstream anoxic zone in a biological nitrogen removal process to effect nitrate reduction to N2, using an internally produced organic electron donor.