Towards industrial application of fungal pretreatment in 2G biorefinery: scale-up of solid-state fermentation of wheat straw

Miguel Álvarez Pallín,Sandra González-Rodríguez,Gemma Eibes,María López-Abelairas,María Teresa Moreira,Juan M Lema,Thelmo A Lú-Chau

doi:10.1007/s13399-022-02319-1

Miguel Álvarez Pallín, Sandra González-Rodríguez + Show 5 more

Open Access

https://doi.org/10.1007/s13399-022-02319-1

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Abstract

Fungal pretreatment of lignocellulosic biomass for bioethanol production is an environmental-friendly alternative to steam explosion. However, this biological pretreatment has been tested on a small scale, where most of the typical problems of solid-state fermentations (SSF), such as limited aeration or temperature control, are not observed. The main objective of this study was to assess the feasibility of the fungal pretreatment of lignocellulosic biomass (wheat straw) at a demonstration scale using the white-rot fungus Irpex lacteus to improve straw digestibility. Different configurations were evaluated for the design of a 22 L SSF reactor, but a versatile vertical design that can operate as a packed-bed and as a tray reactor was selected. The wheat straw digestibility obtained in the SSF bioreactor after 21 days of pretreatment (60.6%) was similar to that achieved on a small scale (57.9%). In addition, the most common online monitoring variables (temperature and CO2 production) correlate with the fungal action on wheat straw. As well as the weight loss, obtaining comparable results at flask and reactor scale (30 and 34.5%, respectively).Graphical abstract

Highlights

The energy sector is heavily dependent on non-renewable fossil fuels, which has led to energy instability and environmental problems associated with greenhouse gas emissions
In the selection of the solid-state fermentations (SSF) bioreactor design, a rotating drum bioreactor (RDB) or any other design with agitation was ruled out because we have previously observed that I. lacteus tends to agglomerate into wheat straw during fungal colonisation, so periodic agitation of the solid matrix content in the SSF would be unfeasible
An increase in sugars was observed at the end of the experiment, especially total reducing sugars. These results demonstrate the ability of I. lacteus to degrade wheat straw polysaccharides under the specified conditions, especially in the absence of initial reducing sugars to incorporate into its metabolism

Summary

Introduction

The energy sector is heavily dependent on non-renewable fossil fuels, which has led to energy instability and environmental problems associated with greenhouse gas emissions. In order to tackle climate change, the EU has a target to reduce CO2 emissions by at least 40% by 2030 [1]. In line with this target, the search for more environmental-friendly renewable energy sources has gained particular prominence in recent years, with the aim of securing the supply of more efficient and less costly energy sources. Bioethanol is mainly produced in first-generation (1G) biorefineries through the fermentation of sugars obtained from grains or crops. This bioethanol production system has the disadvantage of competition with food crops [2]. The transformation of these renewable resources requires a conditioning or pretreatment step because this type of feedstock has a complex lignocellulosic structure, which requires the subsequent hydrolysis of cellulose and hemicellulose [4]

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