Toward a sustainable biorefinery using high‐gravity technology

Abstract

The realization of process solutions for a sustainable bioeconomy depends on the effi cient processing of biomass. High-gravity technology is one important alternative to realizing such solutions. The aims of this work were to expand the knowledge-base on lignocellulosic bioconversion processes at high solids content, to advance the current technologies for production of second-generation liquid biofuels, to evaluate the environmental impact of the proposed process by using life cycle assessment (LCA), and to develop and present a technically, economically, and environmentally sound process at high gravity, i.e., a process operating at the highest possible concentrations of raw material. The results and opinions presented here are the result of a Nordic collaborative study within the framework of the HG Biofuels project. Processes with bioethanol or biobutanol as target products were studied using wheat straw and spruce as interesting Nordic raw materials. During the project, the main scientifi c, economic, and technical challenges of such a process were identifi ed. Integrated solutions to these challenges were proposed and tested experimentally, using wheat straw and spruce wood at a dry matter content of 30% (w/w) as model substrates. The LCA performed revealed the environmental impact of each of the process steps, highlighting the importance of the enzyme dose used for the hydrolysis of the plant biomass, as well as the importance of the fermentation yield.

Multi-Step Exploitation of Raw Arundo donax L. for the Selective Synthesis of Second-Generation Sugars by Chemical and Biological Route

“…Lastly, the catalytic runs were carried out employing starting concentrations of substrate up to 17 wt%, a value higher than those reported in the literature, generally under 8 wt% [2,67]. The employment of high starting substrate concentrations is in agreement with the high gravity approach [68], which allows the production of more concentrated hydrolysates. This approach is particularly promising from the industrial perspective, because the higher concentrations of products lead to the increase of productivity and the reduction of capital and operating costs, requiring easier purification steps.…”

“…To improve the sustainability of the process, the high gravity approach was adopted, testing the same experimental conditions (160 • C, 20 min, 0.1-0.3 wt/wt Amberlyst-70/Arundo donax L. weight ratio) at two higher biomass loadings, 9 wt% (runs 4-6, Tables 3 and 4) and 13 wt% (runs 7-9, Tables 3 and 4). It is important to underline that by keeping the Amberlyst-70/Arundo donax L. weight ratio constant and increasing the biomass loading, no significant variations of the biomass solubilisation and the sugars yield occurred, highlighting that these conditions are still favorable to the production of sugars, rather than to that of their degradation products [68]. Regarding the sugar concentrations, working with the Amberlyst-70/Arundo donax L. weight ratio of 0.2 wt/wt, these increased from 9.6 to 27.5 g/L for xylose and from 2.5 to 7.2 g/L for glucose, adopting 5 and 13 wt% biomass loadings, respectively.…”

Insoluble solids at high concentrations repress yeast’s response against stress and increase intracellular ROS levels

“…The experience gained from brewing and starch-based fermentations under high gravity conditions have paved the way for the application of similar strategies during lignocellulose conversion processes. High gravity technologies are necessary to achieve high substrate concentrations, thus allowing high ethanol titers and reducing distillation costs 34 . At high substrate loading yeast cells have to deal with a high IS content during SSF/CBP processes, especially at early stages.…”

A cellulolytic fungal biofilm enhances the consolidated bioconversion of cellulose to short chain fatty acids by the rumen microbiome

“…Within a biorefinery concept, as many biomass components as possible should be valorized in a cost-effective way, targeting a cascade production of different final products. To date, the best-explored and developed biomass biochemical conversion platform is the sugar platform, where the sugars released from the hydrolysis of cellulose and hemicellulose are the intermediates to be fermented to different products (Xiros et al 2016 ). A second platform for biomass exploitation is the syngas platform, in which thermochemical systems convert biomass into syngas (mixture of CO, H 2 , and CO 2 ) as the feedstock to be further converted to the desired products (Munasinghe and Khanal 2010 ).…”