Lignocellulose dissociation with biological pretreatment towards the biochemical platform: A review

Abstract

Lignocellulose utilization has been gaining great attention worldwide due to its abundance, accessibility, renewability and recyclability. Destruction and dissociation of the cross-linked, hierarchical structure within cellulose hemicellulose and lignin is the key procedure during chemical utilization of lignocellulose. Of the pretreatments, biological treatment, which can effectively target the complex structures, is attractive due to its mild reaction conditions and environmentally friendly characteristics. Herein, we report a comprehensive review of the current biological pretreatments for lignocellulose dissociation and their corresponding degradation mechanisms. Firstly, we analyze the layered, hierarchical structure of cell wall, and the cross-linked network between cellulose, hemicellulose and lignin, then highlight that the cracking of β-aryl ether is considered the key to lignin degradation because of its dominant position. Secondly, we explore the effect of biological pretreatments, such as fungi, bacteria, microbial consortium, and enzymes, on substrate structure and degradation efficiency. Additionally, combining biological pretreatment with other methods (chemical methods and catalytic materials) may reduce the time necessary for the whole process, which also help to strengthen the lignocellulose dissociation efficiency. Thirdly, we summarize the related applications of lignocellulose, such as fuel production, chemicals platform, and bio-pulping, which could effectively alleviate the energy pressure through bioconversion into high value-added products. Based on reviewing of current progress of lignocellulose pretreatment, the challenges and future prospects are emphasized. Genetic engineering and other technologies to modify strains or enzymes for improved biotransformation efficiency will be the focus of future research.

Keywords: Biochemical platform; Biological pretreatment; Cross-linked structure; Lignin barrier; Lignocellulose.

Graphical abstract

Fig. 1

Function of pretreatment [5].

Fig. 2

Schematic diagram of lignocellulose: a) the structure of cell wall; b) three components of lignocellulose [23].

Fig. 3

In situ cleavage routes of β-O-4 aryl ethers initiated [42].

Fig. 4

Model for non-enzymatic deconstruction of lignocellulose cell walls in incipient brown-rot decay. a) Deconstruction of the cell wall structure; b) Chelator-mediated Fenton reaction in wood cell walls; c) Depolymerization of polysaccharide components; d) Deconstruction of the elementary fibril structure [50]. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Proposed degradation pathways of sodium lignin sulfonate by psychrotrophic Arthrobacter sp. C2 [63].

Fig. 6

Expression levels of AA1, AA2, AA3, AA4, and AA6 in different incubation periods (A). Microorganisms from which the AA1 (B), AA2 (C), AA3 (D), AA4 (E), and AA6 (F) come during the peak stage of lignin degradation [67].

Fig. 7

Changes in lignin aromatic and side chain regional components from (A) wheat control and (B) enzyme-treated wheat [77].

Fig. 8

Microstructure of S. obliquus and C. sorokiniana cells, untreated (1) and after thermal hydrolysis (2), ultrasound (3) and enzymatic (4) pre-treatment [83].

Fig. 9

Predicted mechanism/pathways used by B. altitudinis RSP75 for ethanol production [108].

Fig. 10

Surface plots of interaction between (a) temperature and moisture content; (b) temperature and residence time; (c) residence time and moisture content [123].