Abstract

With regard to social and environmental sustainability, second-generation biofuel and biogas production from lignocellulosic material provides considerable potential, since lignocellulose represents an inexhaustible, ubiquitous natural resource, and is therefore one important step towards independence from fossil fuel combustion. However, the highly heterogeneous structure and recalcitrant nature of lignocellulose restricts its commercial utilization in biogas plants. Improvements therefore rely on effective pretreatment methods to overcome structural impediments, thus facilitating the accessibility and digestibility of (ligno)cellulosic substrates during anaerobic digestion. While chemical and physical pretreatment strategies exhibit inherent drawbacks including the formation of inhibitory products, biological pretreatment is increasingly being advocated as an environmentally friendly process with low energy input, low disposal costs, and milder operating conditions. Nevertheless, the promising potential of biological pretreatment techniques is not yet fully exploited. Hence, we intended to provide a detailed insight into currently applied pretreatment techniques, with a special focus on biological ones for downstream processing of lignocellulosic biomass in anaerobic digestion.

Highlights

  • It is known that CO2 production from fossil fuel combustion is a major contributor to global warming, these energy carriers are still the most important resources for global energy generation [1]

  • Biogas production from anaerobic digestion (AD) processes is considered as an attractive source for green energy [3,4] and, endeavors have been made to increase the share of biogas in global energy production

  • The main objectives of this work are, (i) to present a short update on the currently available pretreatment strategies for enhanced disintegration of lignocellulosic resources and their application, and (ii) to review biological pretreatments currently applied for enhanced biogas production

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Summary

Introduction

It is known that CO2 production from fossil fuel combustion is a major contributor to global warming, these energy carriers are still the most important resources for global energy generation [1]. Biogas production from anaerobic digestion (AD) processes is considered as an attractive source for green energy [3,4] and, endeavors have been made to increase the share of biogas in global energy production. Energies 2018, 11, 1797 of lignocellulosic materials (second-generation biofuels) for bio-methane production was substantially accelerated during the past years, offering ecological as well as economic advantages [6]. Lignin resists (complete) degradation under anaerobic conditions, posing a challenge regarding the overall degradability of lignocellulose in AD. In this context, enhancing the substrate conversion to overcome the degradation resistance of lignocellulosic resources is of utmost importance to achieving environmentally friendly and economically feasible processes [7,8]. The main objectives of this work are, (i) to present a short update on the currently available pretreatment strategies for enhanced disintegration of lignocellulosic resources and their application, and (ii) to review biological pretreatments currently applied for enhanced biogas production

Lignocelluloses
Cellulose
Hemicellulose
Lignin
Biodegradation of Lignocellulose
Concepts of Pretreatment
Physical and Chemical Pretreatment
Biological Pretreatment
Micro-Aerobic Pretreatment
Physical Separation of Digestion Phases or Microbial Consortia
Aerobic Pretreatment with Defined Fungal Cultures
By-Product Formation
Findings
Closing Remarks—Conclusions
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