Trends in bioconversion of lignocellulose: Biofuels, platform chemicals & biorefinery concept

Microbial 2,3-butanediol production: A state-of-the-art review

The transition from a fossil fuel-based economy to a bio-based economy necessitates the exploitation of synergies, scientific innovations and breakthroughs, and step changes in the infrastructure of chemical industry. Sustainable production of chemicals and biopolymers should be dependent entirely on renewable carbon. White biotechnology could provide the necessary tools for the evolution of microbial bioconversion into a key unit operation in future biorefineries. Waste and by-product streams from existing industrial sectors (e.g., food industry, pulp and paper industry, biodiesel and bioethanol production) could be used as renewable resources for both biorefinery development and production of nutrient-complete fermentation feedstocks. This review focuses on the potential of utilizing waste and by-product streams from current industrial activities for the production of chemicals and biopolymers via microbial bioconversion. The first part of this review presents the current status and prospects on fermentative production of important platform chemicals (i.e., selected C2-C6 metabolic products and single cell oil) and biopolymers (i.e., polyhydroxyalkanoates and bacterial cellulose). In the second part, the qualitative and quantitative characteristics of waste and by-product streams from existing industrial sectors are presented. In the third part, the techno-economic aspects of bioconversion processes are critically reviewed. Four case studies showing the potential of case-specific waste and by-product streams for the production of succinic acid and polyhydroxyalkanoates are presented. It is evident that fermentative production of chemicals and biopolymers via refining of waste and by-product streams is a highly important research area with significant prospects for industrial applications.

Valorization of industrial waste and by-product streams via fermentation for the production of chemicals and biopolymers

Enhanced 2,3-butanediol (BD) production was carried out by Klebsiella pneumoniae SDM. The nutritional requirements for BD production by K. pneumoniae SDM were optimized statistically in shake flask fermentations. Corn steep liquor powder and (NH4)2HPO4 were identified as the most significant factors by the two-level Plackett–Burman design. Steepest ascent experiments were applied to approach the optimal region of the two factors and a central composite design was employed to determine their optimal levels. The optimal medium was used to perform fed-batch fermentations with K. pneumoniae SDM. BD production was then studied in a 5-l bioreactor applying different fed-batch strategies, including pulse fed batch, constant feed rate fed batch, constant residual glucose concentration fed batch, and exponential fed batch. The maximum BD concentration of 150 g/l at 38 h with a diol productivity of 4.21 g/l h was obtained by the constant residual glucose concentration feeding strategy. To the best of our knowledge, these results were new records on BD fermentation.

Enhanced 2,3-butanediol production by Klebsiella pneumoniae SDM

Fermentative production of 2,3-butanediol: A review

Microbial production and downstream processing of 2,3-butanediol

Klebsiella oxytoca fermented 199 g·l−1 high test or invert molasses using batch fermentation with substrate shift to produce 95.2–98.6 g 2,3-butanediol·l−1 and 2,4–4.3 g acetoin·l−1 with a diol yield of 96–100% of the theoretical value and a diol productivity of 1.0–1.1 g·l−1·h−1. Fermentation was performed numerous times with molasses in repeated batch culture with cell recovery. Such repeated batch fermentation, in addition to a high product yield, also showed a very high product concentration. For example, 118 g 2,3-butanediol·l−1 and 2.3 g acetoin·l−1 were produced from 280 g·l−1 of high test molasses. The diol productivity in this fermentation amounted to 2.4 g·l−1·h−1 and can undoubtedly be further increased by increasing the cell concentration. Because the Klebsiella cultures ferment 2,3-butanediol at an extremely high rate once the sugar has been consumed, the culture was inhibited completely by the addition of 15 g ethanol·l−1 and switching off aeration.

The production of 2,3-butanediol by fermentation of high test molasses

In cooperation with the company Copersucar (Brazil), several variants of a fermentation system for the continuous production of butanol and acetone from high-test or invert molasses were developed. These fermentation systems involve a relatively economic batch fermentation requiring little investment, using a continuous culture as the inoculation culture, as well as a modern two-stage continuous culture with cell recycling. For example, 13.3 g·1−1 of solvent (acetone and butanol) are produced with a productivity of 3.3 g·1−1 ·h−1 by two-stage continuous molasses fermentation with cell recycling in the second stage. High-test molasses is converted completely into the products. Butanol and acetone production from molasses is economic in Brazil and the construction of a production plant is planned.

Konrad Schaller

Papers

Microbial production and downstream processing of 2,3-butanediol

The production of 2,3-butanediol by fermentation of high test molasses

Bacterial conversion of molasses to acetone and butanol

Produktion von Aceton und Butanol durch Clostridium acetobutylicum in kontinuierlicher Kultur mit Zellrückführung

Fermentative Verarbeitung von Stärkeabfällen zu Butanol und Aceton