1 research outputs found
High-Rate, High-Yield Production of Methanol by Ammonia-Oxidizing Bacteria
The
overall goal of this study was to develop an appropriate biological
process for achieving autotrophic conversion of methane (CH<sub>4</sub>) to methanol (CH<sub>3</sub>OH). In this study, we employed ammonia-oxidizing
bacteria (AOB) to selectively and partially oxidize CH<sub>4</sub> to CH<sub>3</sub>OH. In fed-batch reactors using mixed nitrifying
enrichment cultures from a continuous bioreactor, up to 59.89 ±
1.12 mg COD/L of CH<sub>3</sub>OH was produced within an incubation
time of 7 h, which is approximately ten times the yield obtained previously
using pure cultures of <i>Nitrosomonas europaea</i>. The
maximum specific rate of CH<sub>4</sub> to CH<sub>3</sub>OH conversion
obtained during this study was 0.82 mg CH<sub>3</sub>OH COD/mg AOB
biomass COD-d, which is 1.5 times the highest value reported with
pure cultures. Notwithstanding these positive results, CH<sub>4</sub> oxidation to CH<sub>3</sub>OH by AOB was inhibited by NH<sub>3</sub> (the primary substrate for the oxidative enzyme, ammonia monooxygenase,
AMO) as well as the product, CH<sub>3</sub>OH, itself. Further, oxidation
of CH<sub>4</sub> to CH<sub>3</sub>OH by AOB was also limited by reducing
equivalents supply, which could be overcome by externally supplying
hydroxylamine (NH<sub>2</sub>OH) as an electron donor. Therefore,
a potential optimum design for promoting CH<sub>4</sub> to CH<sub>3</sub>OH oxidation by AOB could involve supplying NH<sub>3</sub> (needed to maintain AMO activity) uncoupled from the supply of NH<sub>2</sub>OH and CH<sub>4</sub>. Partial oxidation of CH<sub>4</sub>-containing gases to CH<sub>3</sub>OH by AOB represents an attractive
platform for the conversion of a <i>gaseous</i> mixture
to an <i>aqueous</i> compound, which could be used as a
commodity chemical. Alternately, the nitrate and CH<sub>3</sub> OH
thus produced could be channeled to a downstream anoxic zone in a
biological nitrogen removal process to effect nitrate reduction to
N<sub>2</sub>, using an <i>internally</i> produced organic
electron donor