Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Lars Rehmann

Abstract

The high cost of substrate and product inhibition in the fermentation broth remains two major problems associated with bio-butanol production. This thesis aims to solve these problems by examining abundant lignocellulosic biomass as potential feedstocks and exploring novel substrates such as carbohydrates derived from microalgae for ABE fermentation. The commonly observed toxic effect after pretreatment of lignocelluslosic biomass was removed by resin adsorption, where the resin could also serve as an in-situ butanol recvoery devices.

Corn cobs (an agricultural waste), switchgrass (an energy crop) and phragmites (an invasive plant in North America) were investigated as substrates for ABE fermentation by Clostridium saccharobutylicum DSM 13864. NaOH pretreatment followed by a washing step was used to reduce the biomass recalcitrance and facilitate the subsequent enzymatic hydrolysis. Total sugar yields for corn cobs, switchgrass and phragmites were 475, 365, and 385 g/kg of raw biomass, respectively. After the subsequent fermentation, an ABE yield of 166, 146, and 150 g/kg raw biomass was obtained.

Although biofuel production from lignocellulosic biomass is considered more sustainable than biofuel from food crops, it still faces many challenges. In order to demonstrate a possible biofuel production strategy using microalgal biomass, lipid extracted microalgae (LEA) was also used as substrates for ABE fermentation. To convert the carbohydrate fraction into solvents (ABE), LEA was either acid hydrolysed into glucose or directly fermented. The highest butanol titers (8.05 g/L) was obtained with the fermentation of acid hydrolysates. However fermenting the hydrolysate required detoxification via a resin, while direct fermentation did not, significantly simplifying the LEA to butanol process.

The resin that was used to detoxify acid hydrolysates of LEA was further investigated for detoxification of lignocellulosic hydrolysates and in-situ butanol recovery. Detoxifcation of acid hydrolyzed phragmites by resin L-493, improved the fermentability signficantly. Resin L-493 was efficient in removing phenolic comopunds present in the phragmites hydrolysates, as well as butanol produced during fermentation.

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