Recycle of fermentation process water through mitigation of inhibitors in dilute-acid corn stover hydrolysate

Authors: Nichols, Nancy; Mertens, Jeffrey; Dien, Bruce; Hector, Ronald - Ron; Frazer, Sarah

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2019
Publication Date: 11/18/2019
Citation: Nichols, N.N., Mertens, J.A., Dien, B.S., Hector, R.E., Frazer, S.E. 2019. Recycle of fermentation process water through mitigation of inhibitors in dilute-acid corn stover hydrolysate. Bioresource Technology. 9:100349. https://doi.org/10.1016/j.biteb.2019.100349.
DOI: https://doi.org/10.1016/j.biteb.2019.100349

Interpretive Summary: Water consumption is an important consideration for advanced biofuels production. The water footprint of a bioprocessing plant impacts site location, capital costs, and local environmental impact. Present-generation (corn-starch-to-ethanol) facilities directly reuse much of their process water. For next-generation (biomass-to-ethanol) processes, however, the feasibility of recycling process water is unknown. A major obstacle to next-generation bioconversion is the presence of microbial inhibitors. The amount of process water that can be recycled will depend upon the inhibitor load, and re-use of process water will necessitate addressing inhibitors which may be concentrated by water recycle. In this study, a fungus that metabolizes numerous inhibitory chemicals was used to remove inhibitors from biomass sugars, allowing reuse of a portion of the process water and enabling recovery of failed processes. The feasibility of water-reuse, demonstrated in this work, provides a new option to be considered in the design of future biomass refineries.

Technical Abstract: Water consumption is an important consideration for advanced biofuels production, and the need to re-use process water will necessarily include the need to address inhibitors that will be further concentrated by water recycle. During pretreatment of biomass to obtain sugar monomers, organic chemicals are released that are inhibitory to enzymes and microorganisms. Generation of inhibitors necessitates conditioning of biomass hydrolysate and/or development of inhibitor-tolerant biocatalysts to allow fermentation of the sugar monomers. An ascomycete, Coniochaeta ligniaria NRRL 30616, was used to biologically abate inhibitors in dilute-acid pretreated corn stover hydrolysate, allowing reuse of a portion of the liquor in subsequent fermentations. The hydrolysate was successfully reused five times in fermentations using recombinant ethanologenic E. coli, and bioabatement also enabled recovery of failed fermentations. Additionally, bioabatement allowed recycling of the spent liquor for use as process water for pretreatment of corn stover.