Does Acid Addition Improve Liquid Hot Water Pretreatment of Lignocellulosic Biomass towards Biohydrogen and Biogas Production?

Georgia Antonopoulou,George Dimitrellos,Gerasimos Lyberatos

doi:10.3390/su12218935

Abstract

The effect of liquid hot water (LHW) pretreatment with or without acid addition (A-LHW) on the production of hydrogen—through dark fermentation (DF)—and methane—through anaerobic digestion (AD)—using three different lignocellulosic biomass types (sunflower straw (SS), grass lawn (GL), and poplar sawdust (PS)) was investigated. Both pretreatment methods led to hemicellulose degradation, but A-LHW resulted in the release of more potential inhibitors (furans and acids) than the LHW pretreatment. Biological hydrogen production (BHP) of the cellulose-rich solid fractions obtained after LHW and A-LHW pretreatment was enhanced compared to the untreated substrates. Due to the release of inhibitory compounds, LHW pretreatment led to higher biochemical methane potential (BMP) than A-LHW pretreatment when both separated fractions (liquid and solid) obtained after pretreatments were used for AD. The recovered energy in the form of methane with LHW pretreatment was 8.4, 12.5, and 7.5 MJ/kg total solids (TS) for SS, GL, and PS, respectively.

Highlights

Much research effort has been conducted for the transition from a fossil-fuel-based economy to a bio-economy, in which renewable resources of biological origin are used to sustainably produce food, energy, and new materials
A-liquid hot water (LHW) was more severe for all substrates compared to the LHW pretreatment
acid LHW (A-LHW) pretreatment resulted in lower solid material recovery and higher reduction of the hemicellulose fraction due to solubilization (75.6 ± 2.6% and 40.5% for sunflower straw (SS), 68.0 ± 1.8% and 27.0% for grass lawn (GL), and 80.3 ± 2.3% and 29.8% for poplar sawdust (PS)) compared to the respective values for LHW pretreatment (81.6 ± 2.2% and 31.8% for SS, 74.1 ± 1.7% and 8.4% for GL, and 88.5 ± 2.2% and 21.8%, for PS)

Summary

Introduction

Much research effort has been conducted for the transition from a fossil-fuel-based economy to a bio-economy, in which renewable resources of biological origin are used to sustainably produce food, energy, and new materials. Lignocellulosic biomass is considered among the most promising sources for the production of alternatives to petroleum-based fuels—the biofuels, which address the aforementioned challenges for a sustainable bio-economy model [2]. Very low hydrogen yields have been reported for raw, untreated lignocellulosic substrates [2]. This is mainly due to the complex structure of the biomass, which limits the accessibility of microorganisms or enzymes, reducing its biodegradability and resulting in lower methane/hydrogen yields compared to the theoretical ones [3,9]. In order to reduce the structural and compositional barriers, an appropriate pretreatment method should be applied, leading to improved biofuel yields [9]

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Conclusion