Effect of using a nitrogen atmosphere on enzyme hydrolysis at high corn stover loadings in an agitated reactor

Authors: DOS SANTOS, ANOTONIO CARLOS - Purdue University; XIMENES, EDWARDO - Purdue University; THOMPSON, DAVID - Idaho National Laboratory; RAY, ALLISON - Idaho National Laboratory; SZETO, RYAN - Purdue University; ERK, KENDRA - Purdue University; Dien, Bruce; LADISCH, MICHAEL - Purdue University

Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2020
Publication Date: 8/3/2020
Citation: Dos Santos, A.C.F., Ximenes, E., Thompson, D.N., Ray, A.E., Szeto, R., Erk, K., Dien, B.S., Ladisch, M.R. 2020. Effect of using a nitrogen atmosphere on enzyme hydrolysis at high corn stover loadings in an agitated reactor. Biotechnology Progress. 36(6). Article e3059. https://doi.org/10.1002/btpr.3059.
DOI: https://doi.org/10.1002/btpr.3059

Interpretive Summary: Bioproducts and biofuels add hundreds of billions of dollars each year to the domestic economy. It is largely based on the use of row crops such as small grains and fiber plants. The breath of the bioeconomy could be expanded multiple fold if agricultural residues, primarily corn stover, was also used as a feedstock; corn stover is all of the above ground plant residue left in the field after harvest of the corn kernels. The major obstacle to realizing this dream is economics; converting corn stover to useful sugars is too expensive and enzymes used within the process are a major expense. This article describes new techniques for reducing the amount of enzyme needed for processing corn stover while simultaneously increasing the sugar yield. In one case, it is as simple as flushing a reaction tank with nitrogen. This information can be used to directly benefit companies now working on converting plant wastes to sugars for subsequent conversion to chemicals and biofuels.

Technical Abstract: Solids loadings of 200 g/L of lignocellulose are necessary to achieve minimum ethanol titers of 5% while resulting in smaller reactor volumes. However, increasing the concentration of pretreated solids also decreases the extent of enzyme catalyzed cellulose hydrolysis even though the enzyme to cellulose ratio is constant. We confirm that agitation with marine impellers under nitrogen atmosphere minimizes this effect over the range of 100 of 200 g/L. An agitated slurry of 200 g / L corn stover, pretreated at liquid hot water conditions and hydrolyzed with 3.6 mg enzyme per g biomass solids in citrate buffer (pH 5.0) for 72 hours under nitrogen blanket yields 55% glucose compared to 45% in air with agitation and 34 % without agitation. Mixing promotes biomass / enzyme contact and disperses localized buildup of inhibitors, while nitrogen displaces dissolved oxygen and restricts contact of air with enzyme, so it is not deactivated by oxygen.