Hydrogen gas (H2) is an attractive fuel carrier
due
to its high specific enthalpy; moreover, it is a clean source of energy
because in the combustion reaction with oxygen (O2) it
produces water as the only byproduct. The microbial electrolysis cell
(MEC) is a promising technology for producing H2 from simple
or complex organics present in wastewater and solid wastes. Methanogens
and non-archaeal methane (CH4)-producing microorganisms
(NAMPMs) often grow in the MECs and lead to rapid conversion of produced
H2 to CH4. Moreover, non-archaeal methane production
(NAMP) catalyzed by nitrogenase of photosynthetic bacteria was always
overlooked. Thus, suppression of CH4 production is required
to enhance H2 yield and production rate. This review comprehensively
addresses the principles and current state-of-the-art technologies
for suppressing methanogenesis and NAMP in MECs. Noteworthy, specific
strategies aimed at the inhibition of methanogenic enzymes and nitrogenase
could be a more direct approach than physical and chemical strategies
for repressing the growth of methanogenic archaea. In-depth studies
on the multiomics of CH4 metabolism can possibly provide
insights into sustainable and efficient approaches for suppressing
metabolic pathways of methanogenesis and NAMP. The main objective
of this review is to highlight key concepts, directions, and challenges
related to boosting H2 generation by suppressing CH4 production in MECs. Finally, perspectives are briefly outlined
to guide and advance the future direction of MECs for production of
high-purity H2 based on genetic and metabolic engineering
and on the interspecific interactions.
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