Accelerated cellulosic ethanol production using continuous cascade fermentation and engineered thermophilic bacteria

Project Summary - Enchi SBIR Application to the USDA October 2022Title: Accelerated cellulosic ethanol production using continuous cascade fermentation andengineered thermophilic bacteria.Project Directors: Christopher D. Herring (PD) Lee R. Lynd (Co-PD).Enchi Corp. aims to develop consolidated bioprocessing (CBP) for conversion of cellulosicbiomass into fuels and chemicals at low cost and without added enzymes or thermochemicalpretreatment. This SBIR project targets the application of CBP with the shortest path tocommercial deployment in the US: conversion of corn stover to ethanol co-located at an operatingcorn ethanol plant.The overall objective of Phase I is to provide proof-of-concept for continuouscascade fermentation as a means to achieve a > 2-fold reduction in reaction time to achieve highconversion - directly impacting the cost of fermenters the largest contributor to capital costs.Technical analysis presented herein shows that: 1) Cascade continuous processing offers several- fold shorter CBP reaction times compared to batch or single-stage continuous processing - abenefit specific to CBP and not applicable to processes with added cellulase; 2) A singlecontinuous bioreactor brought to steady-state and subsequently operated in batch mode by turningoff the feed exhibits the same qualitative behavior and similar quantitative behavior as cascadecontinuous fermentation and is thus a valid and practical system for demonstrating the merits ofcontinuous cascade processing. Using economic models developed in consultation with POET weproject robust investment returns at a production capacity and cost an order of magnitude smallerthan the demonstration cellulosic ethanol plants built over the last decade.The proposed workplan involves determining the maximum solids loading at which fractionalcarbohydrate solubilization is undiminshed in continuous culture obtaining solubilization vs. timecurves for the above-described operating strategy comparison to fermentations performed in batchmode and technoeconomic analysis.Realization of Phase I objectives will validate cascade continuous fermentation as a means tosubstantially accelerate conversion of corn stover via CBP resulting in lower capital costs andhigher investment returns. Improved technology for low-cost conversion of corn stover to ethanolwould lead to increased revenue and job creation for both corn farmers and fuel producers andwould represent an important step toward realizing the long-anticipated vision of expanded use ofcellulosic feedstocks in the bioeconomy and in rural America.