Combined Biological and Chemical/Physicochemical Pretreatment Methods of Lignocellulosic Biomass for Bioethanol and Biomethane Energy Production—A Review

Abstract

Lignocellulosic biomass is a low-cost and environmentally-friendly resource that can be used to produce biofuels such as bioethanol and biogas, which are the leading candidates for the partial substitution of fossil fuels. However, the main challenge of using lignocellulosic materials for biofuel production is the low accessibility to cellulose for hydrolysis of enzymes and microorganisms, which can be overcome by pretreatment. Biological and chemical pretreatments have their own disadvantages, which could be reduced by combining the two methods. In this article, we review biological–chemical combined pretreatment strategies for biogas and bioethanol production. The synergy of fungal/enzyme–NaOH pretreatment is the only biological–chemical combination studied for biogas production and has proven to be effective. The use of enzyme, which is relatively expensive, has the advantage of hydrolysis efficiency compared to fungi. Nonetheless, there is vast scope for research and development of other chemical–biological combinations for biogas production. With respect to ethanol production, fungal–organosolv combination is widely studied and can achieve a maximum of 82% theoretical yield. Order of pretreatment is also important, as fungi may reduce the accessibility of cellulose made available by prior chemical strategies and suppress lignin degradation. The biofuel yield of similarly pretreated biomass can vary depending on the downstream process. Therefore, new strategies, such as bioaugmentation and genetically engineered strains, could help to further intensify biofuel yields.

Hydrothermal Treatment of Biomass Feedstocks for Sustainable Production of Chemicals, Fuels, and Materials: Progress and Perspectives

“…In SHF, hydrolysis of lignocellulosic biomass is separated from ethanol fermentation . In SSCF, multiple microorganisms are sequentially applied in different fermentation periods to improve the utilization of sugars . Direct microbial conversion (DMC) is also used for ethanol production in which single- or cocultures of fermentative agents are used for cellulase production, biomass hydrolysis, and ethanol fermentation in a single reactor, thus decreasing the overall capital investment needed .…”

“…611 Direct microbial conversion (DMC) is also used for ethanol production in which single-or cocultures of fermentative agents are used for cellulase production, biomass hydrolysis, and ethanol fermentation in a single reactor, thus decreasing the overall capital investment needed. 611 Other types of fermentation processes including dark fermentation (conversion of organic substrates to biohydrogen) and photo fermentation (a natural process for conversion of sunlight into fermentation products through a metabolic pathway of ethanol synthesis) are potentially integrated with hydrothermal treatment for biomass conversion. 606 Fermentation of ethanol can be performed in different reactor systems such as batch, repeated batch, fed-batch, or continuous mode.…”

Overview of Numerical Simulation of Solid-State Anaerobic Digestion Considering Hydrodynamic Behaviors, Phenomena of Transfer, Biochemical Kinetics and Statistical Approaches

“…This low presence can be explained by the lack of in-depth knowledge of the processes and the complex industrial control, as mentioned above. The scientific barriers of the sector are based on various technical aspects [3,4,8,13,14]:…”

Engineered yeasts and lignocellulosic biomaterials: shaping a new dimension for biorefinery and global bioeconomy

“…In each case, sugars are converted into chemical intermediates, such as alcohols. In comparison, the intermediates of the biochemical method are less expensive than those of the thermochemical method [ 130 ], which makes biochemical conversion more appealing. The biomass components (cellulose and hemicellulose) are first broken down into component sugars by cellulolytic enzymes which are further fermented to bioethanol by a series of biochemical processes [ 58 ].…”

“…The best that has been reported is the combination of various biological – chemical/physicochemical pre-treatment strategies. Meenakshisundaram et al [ 130 ] gave a full compilation of the importance of this combined treatments as shown in Table 4 .…”