Maximizing long-term biohydrogen production with Clostridium thermocellum in high solids lignocellulosic biomass fermentations

Biological hydrogen production from lignocellulosic biomass sustainably
couples organic waste reduction with renewable energy generation.
Efficient conversion is challenged by the structural complexity of
lignocellulose and resulting recalcitrance to enzymatic degradation.
Clostridium thermocellum natively breaks down biomass with some of the
most effective hemi-/cellulases systems (i.e., cellulosomes) and generates
hydrogen in anaerobic cultivation, creating a compelling platform for
lignocellulosic biohydrogen production. Achieving commercially viable
production rates requires balancing high biomass loading and throughput
against uniform mixing conditions required for enzyme dispersion, pH and
temperature control, and efficient hydrogen and metabolite removal in
continuous operation. To address these barriers to process
intensification, we implemented novel reactor and process designs for
high-solids lignocellulosic biomass fermentations using the C.
thermocellum KJC19-9 strain, genetically engineered for co-utilization of
cellulose and hemicellulose sugars (i.e., xylose). Via computational fluid
dynamics (CFD) modeling and experimental validation, we achieved a
>50% improvement in biohydrogen production with an improved
anchor-type impeller morphology, coupled to a threefold reduction in
agitation rate. To further reduce rheological constraints and accumulation
of toxic metabolites, we then transitioned the process to sequencing
fed-batch operation. The resulting process generated 24.87 L H2/L from 480
g/L of deacetylated and mechanically refined (DMR)-pretreated corn stover
biomass over 16 days while converting >95% of influent cellulose
and hemicellulose, setting a new performance benchmark for continuous
production of biohydrogen from lignocellulose.