Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 2, Pages: 925-935  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal weblink:  
A Critical Review on the Various Pretreatment  
Technologies of Lignocellulosic Materials  
Amirreza Talaiekhozani , Shahabaldin Rezania  
Department of Civil Engineering, Jami Institute of Technology, Isfahan, Iran  
Department of Environment and Energy, Sejong University, Seoul 05006, South Korea  
Received: 12/01/2020  
Accepted: 11/06/2020  
Published: 20/09/2020  
Nowadays, finding new sources of renewable energy is an absolutely essential need for human. Production of biofuel is a  
suitable way to find such a renewable energy source. Pretreatment is considered as an important step for biofuel production.  
The aim of this study was to collect recent achievements in pretreatment techniques to have a comprehensive and precious  
source about this topic. In this study many pretreatment techniques: microwaves, biological, alkaline, ionic liquid, organic  
solvent, acidic, mechanical, pyrolysis, steam, wet oxidation, ammonia fiber explosion and liquid hot techniques have been  
introduced. Although several new techniques have been developed to pretreatment of lignocellulosic biomasses, many  
obstacles are still needed to be overcome to use these techniques for industrial application.  
Keywords: Lignocellulosic biomass, Pretreatment, Biofuel production, Energy production  
Energy demand is increased every day by developing  
biofuels production such as biohydrogen, biogas, and  
bioalcohols is necessary. Lignocellulosic biomasses are  
inexpensive and abundance; therefore, these types of  
biomasses are attractive to be used as row materials for  
biofuel production (6). Raw lignocellulosic biomass  
cannot easily used for biofuel production due to  
existence of some recalcitrant compounds and very  
complex structure (7). Consequently, pretreatment is so  
important to have a fast and efficient conversion of  
lignocellulosic biomasses to final products. Several  
futures have been introduced for an ideal pretreatment  
technique such as feasible and effective with high solids  
loadings, lower energy demand and moderate cost,  
preserving solubilized carbohydrates, avoiding formation  
of inhibitors to the subsequent fermentation step,  
industries (1). Nowadays, fossil fuels are considered as  
main source of energy worldwide (2). Since fossil fuels  
are not renewable, many studies have been carried out to  
find alternative energy sources (3). Therefore,  
lignocellulosic biomass conversion to biological fuels  
has attracted a huge amount of scientist’s attention (4).  
Pretreatment process is the first stage for biomass  
conversion to biofuel. Many studies reported the  
importance of pretreatment step on biofuel production  
processes (5). The well-known technique for biomass  
pretreatment is thermochemical technique. This  
techniques is faced whit several economic,  
environmental, and technical difficulties. That is why  
finding more appropriate pretreatment techniques for  
Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 2, Pages: 925-935  
producing highly digestible feedstock, and little or no  
biomass size reduction (8). Although many pretreatment  
techniques have been developed by scientists, there is no  
technique that to have all the above mentioned futures.  
Various developed techniques for pretreatment of  
lignocellulosic biomass have been categorized in Figure  
cultivation of this plant is faced with several difficulties  
(24). Based on the above mentioned explanations, it is  
necessary to find an alternative way to produce biofuels.  
Lignocellulosic biomasses including cereal straws which  
are widely cultivated worldwide may consider as a  
suitable feedstock for biofuel production. Cereal straws  
are usually burned by farmers which produces a large  
amount of air pollutants (25). Several inexpensive  
lignocellulosics agricultural waste are accessible such as  
wheat straw, rice straw, softwood, switch grass, salix,  
willow, timber species, rice hull, and sugarcane baggase  
as a feedstock for biofuel production. In some countries  
that have a wide agricultural activities the agricultural  
wastes have a good potential to produce biofuels.  
Different biofuel production yields can be obtained using  
various crops. The cost of biofuel production depends on  
the cost of agricultural wastes, transportation method of  
agricultural wastes from farms to factories, and  
processing technology. Also, government policies about  
biofuel production can be considered as an influential  
factor on biofuel cost. The cost of biofuel production and  
market price are other factors which are effective on final  
biofuel cost. Seasonal availability of agricultural wastes  
depend on the type of it; for example cotton stalk is  
available between January and March whereas maize  
stalk is available from August and December.  
Information about seasonal availability of agricultural  
wastes is very important to guarantee the feedstock  
availability all over the year for the biofuel factory. The  
most important part of plant cell wall is composed of  
lignocellulos. Lignocellulos is a natural and complex  
composite including lignin, hemicellulose, and  
biopolymers— cellulose (26, 27). Some other materials  
such as ash can be found herewith lignocellulosic  
biomass. Lignocellulosic biomass is a heterogeneous  
composite of lignin and carbohydrate polymers which  
contains up to 75% of carbohydrates (based on dry  
weight) (24). Lignocellulosic biomass contains complex  
sugars; therefore, it is not readily converted to biofuel.  
Also, it is contains several polysaccharides including  
hemi-cellulose and cellulose which require to be  
converted to the monosaccharide. Lignin, hemicellulose,  
and Cellulose are strictly associated with each other so  
this association can almost stop the access to the  
hydrolytic agents. The lignin should be eliminated or  
modified to access the hydrolytic agents using different  
chemical or biological techniques (28). Cellulose