(106f) Fermentation Design and Gas Transfer Considerations for Biochemical Methane Conversion

Authors: 
Stone, K., Auburn University
Hilliard, M., Auburn University
He, Q. P., Auburn University
Wang, J., Auburn University

Fermentation Design and Gas Transfer Considerations
for Biochemical Methane Conversion

Kyle
Stone, Matthew Hilliard, Q. Peter He, and Jin Wang

Department
of Chemical Engineering, Auburn University, Auburn, AL, 36849, USA

Methane
is an essential component of the global carbon cycle and one of the most powerful
greenhouse gases (GHGs) with a global warming potential over 20 times that of
CO2. Yet, methane is a rich source of carbon and energy that is
utilized for heat, fuel synthesis, and valued chemical production. In addition,
there is a rapid expansion of global methane supply predominantly because of
increased production of natural gas [1] and biogas [2].
Due to concerns about climate change, abundance of supply, and favorable
economic conditions, there has been growing interest in biological processes as
a sustainable and efficient way of converting methane to valuable products
while reducing GHG emissions.

These biological
processes utilize the largely aerobic bacteria called methanotrophs that
consume methane as their sole source for carbon and energy. Due to their unique
metabolism, methanotrophs can convert methane at ambient temperatures and
pressures to many different products. Specifically, methanotrophs have the
natural ability to produce methanol, valued proteins, biopolymers, lipids (for
biodiesel), organic acids, sucrose, and ectoine [3,4].
With genetic modification, methanotrophs can also produce non-native products
such as carotenoids, isoprene, 1,4 butanediol, and farnesene [3,4].
Several of these products can potentially be simultaneously generated with
specifically designed processes [4].

However, all processes
with methanotrophs face several challenges, such as clean sources of methane,
biocatalyst modification, and process design. For process design, the most influential
factor is efficient gas-liquid transfer (i.e., methane and/or oxygen gas
transfer to the liquid medium where cells reside). The gas-liquid transfer of
the poorly soluble methane and oxygen can be strongly affected by reactor
design and mass transfer enhancing agents in the liquid medium.

In this work we review
recent progress about effective gas transfer for bioprocesses with
methanotrophs. One focus will be on the
quantification of methane transfer rate and cellular uptake rate. We
will also provide a detailed review and discussion of the bioreactor configurations
and the influence of these systems on gas-liquid transfer. Finally, we will
discuss gas-liquid transfer enhancement with promoting agents. Recommendations will
be provided and potential research areas for methane conversion through
methanotrophs will be discussed.

[1]
International Energy Statistics: Natural gas proved reserves, (2015).
http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=3&pid=3&aid=6.

[2]
Biogas Opportunities Roadmap, U.S. Department of Agriculture, U.S.
Environmental Protection Agency, U.S. Department of Energy, 2014.

[3]
P.J. Strong, S. Xie, W.P. Clarke, Methane as a resource: can the methanotrophs
add value?, Environ. Sci. & Technol. (2015).

[4]
P.J. Strong, M. Kalyuzhnaya, J. Silverman, W.P. Clarke, A methanotroph-based
biorefinery: potential scenarios for generating multiple products from a single
fermentation, Bioresour. Technol. (2016).