Process development for platform chemical production from agricultural and forestry residues
Doktorsavhandling, 2021

As part of a bio-based economy, biorefineries are envisaged to sustainably produce platform chemicals via biochemical conversion of agricultural and forestry residues. However, supply risks, the recalcitrance of lignocellulosic biomass, and inhibitor formation during pre­treatment impair the economic feasibility of such biorefineries. In this thesis, process design and assessment were developed with the aim of addressing these hurdles and improving the cost-effectiveness of lignocellulose-derived platform chemicals.

To expand the feedstock base and reduce operational costs, logging residues served as underutilised and inexpensive raw material. The major impediment in converting logging residues was their high recalcitrance and low cellulose content, which resulted in low attainable ethanol titres during simultaneous saccharification and co-fermentation (SSCF). Pretreatment optimisation reduced inhibitor formation and recalcitrance, and led to enzymatic hydrolysis yields at par with those obtained for stem wood, despite the less favourable chemical composition. Upgrading logging residues with carbohydrate-rich oat hulls increased ethanol titres to >50 g/L using batch SSCF at 20% WIS loadings, demonstrating the potential to further decrease downstream processing costs.

To alleviate the toxicity of inhibitors generated during pretreatment, preadaptation was applied to Saccharomyces cerevisiae. Exposure to the inhibitors in the pretreated liquid fraction improved ethanol production during subsequent fermentation. Transferring the concept of preadaptation to lactic acid production by Bacillus coagulans cut the process times by half and more than doubled the average specific lactic acid productivity, showcasing how preadaptation could decrease operational costs.

To assess the performance and robustness of process designs against process input variations, a multi-scale variability analysis framework was developed. The framework included models for bioprocess, flowsheet, techno-economic, and life cycle assessment. In a case study, multi-feed processes, in which solids and cells are fed to the process using model-based predictions, were more robust against variable cellulolytic activities than batch SSCFs in a wheat straw-based ethanol biorefinery. The developed framework can be used to identify robust biorefinery process designs, which simultaneously meet technological, economic, and environmental goals.

multi-scale variability analysis

logging residues


lactic acid





platform chemicals

multi-feed SSCF

mixed feedstocks

Opponent: Prof. Krist V. Gernaey, Process and Systems Engineering Center (PROSYS), Department of Chemical and Biochemical Engineering, Technical University of Denmark, Denmark


David Nickel

Chalmers, Biologi och bioteknik, Industriell bioteknik

Nickel, D. B., Nielsen, F., Franzén, C. J. Response surface modelling identifies dilute acid-catalysed steam pretreatment conditions with high sugar yields and minimal inhibitor formation for spruce logging residues

Nickel, D. B., Nielsen, F., Franzén, C. J. Upgrading low-value logging residues with oat hulls in integrated ethanol production: Effects on the design of batch and model-based multi-feed SSCFs

Platform chemical production is a major driver for the consumption of fossil resources. Biorefineries are envisaged to sustainably produce these bulk intermediates from agricultural and forestry to meet climate objectives and transition towards a bio-based society. In biorefineries, sugars stored in lignocellulosic biomass are released and converted by microorganisms into desired products. However, the economic feasibility of these biorefineries suffers from supply risks, a high resistance of biomass against its conversion into sugars, and the formation of inhibitors to microbial product formation during biomass processing.

In my thesis I address these challenges by developing process designs and assessments to improve the performance of lignocellulose-based ethanol and lactic acid production. Logging residues, a low-cost, underutilised biomass, were used to increase the supply potential and reduce process costs. Drawbacks caused by the low compositional quality of logging residues were alleviated by optimising the pretreatment, which prepares the biomass for enzymatic sugar release, and by upgrading the low sugar content of the logging residues with sugar-rich oat hulls. The upgrading strategy increased ethanol concentrations to >50 g/L, which reduces product separation and purification costs. Preadaptation, in which cells are cultured in diluted inhibitors during growth, was used to increase inhibitor tolerance of Bacillus coagulans. Applied to lactic acid production from wheat straw by Bacillus coagulans, preadaptation significantly shortened process times and increased volumetric productivities, and, thus, improved fermentation performance and process economics. To consistently evaluate process designs from technical, economic, and environmental perspectives while taking process input variations into account, in a collaborative effort we developed the so-called multi-scale variability analysis framework. The framework can predict the effects of such variations at multiple dimensions and help stakeholders to choose more robust process designs.

The results of my research contribute to advance towards cost-competitiveness with fossil fuel-based platform chemicals.

Bioetanol från gran och havreskal via processen "High Gravity Multifeed"-samtidig försockring och jäsning

Energimyndigheten (2015-007008), 2016-01-01 -- 2019-12-31.


Hållbar utveckling



Industriell bioteknik

Förnyelsebar bioenergi

Kemiska processer





Livsvetenskaper och teknik (2010-2018)



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4891





Opponent: Prof. Krist V. Gernaey, Process and Systems Engineering Center (PROSYS), Department of Chemical and Biochemical Engineering, Technical University of Denmark, Denmark

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