478

31 Critical Issues That Can Underpin the Drive for Sustainable Anaerobic Biorefinery

Physical

Mechanical comminution:

Pyrolysis:

Liquid hot water:

Ammonia fiber explosion:

Oxidative delignification

Alkali treatment:

Biological consortium:

Enzyme treatment:

Organosolv process:

Acid treatment:

Carbon dioxide explosion:

Steam explosion (i.e. auto-hydrolysis):

High-energy radiation:

Glycerol:

Microwave:

Wet oxidation:

+ Increase specific surface area

+ Reduce degree of polymerization

+ Reduce cellulose crystallinity

– Energy-intensive

+ Partial depolymerization of lignin

+ Hydrolysis of hemicelluloses

+ Reduce cellulose crystallinity

– Energy-intensive

– Slow and costly process

+ Sample and high downsteam enzymatic

efficiency

+ Limited use of chemicals

– Energy-intensive

+ High solids capacity

+ No generation of toxins

– High equipment costs

+ High reaction rates

+ Significantly improved hydrolysis

– Formation degradation products

– Disposal of neuralization salts is required

+ Selective method

+ Effective for high-lignin wastes

– High chemical costs

+ Significantly reduces phenoloc compounds

+ No generation of toxins

+ No generation of hydrolysis inhibitors

– Long processing time

– High enzyme costs

+ High conversion of organic polymers

– Inhibition hydrolysis

– High process costs

+ Improved gas quality and yield

– Low energy efficiency

– No emission free process

+ Low costs

+ Minimized degradation products due

to low temperatures

– High amount solubiliaed products

– Energy-intensive

+ High selectivity for reaction with lignin

– High process costs

Hydrogen peroxide, ozonolysis, sulfer trioxide

i.e. Phanerochaete chrysosporium, Ceriporiala cerata,

endoglucanase, Trichoderma reesel

+ Effective lignin removal

+ No residues

+ Utilize low temperature and pressure

– Increased lignin content

– Conversion alkali into irrecoverable salts

+ Significantly increased hydrolysis

+ Elimination hazardous chemicals

– Sugar consumption

+ Effective delignification

+ High cellulose conversion

– Many uncertainties

+ Effective disruption lignocellulose

architecture

+ Energy efficient

+ High process speed

– Negative effects gasification of substrate

Physicochemical

Chemical

Biological

Others

Figure 31.5

Pros and cons of lignocellulosic waste pretreatment methods.. Source: Zhang

et al. [19]; Calabro et al. [20]; Chaturvedi and Verma [21]; Hou et al. [22]; Lemões et al. [23];

Rosero-Henao et al. [24].

The efficacy of each pretreatment technique is considerably dependent on

biomass composition and properties such as cellulose crystallinity, lignin fraction

and structure, acetylation degree of hemicelluloses. A cost-effective pretreatment

for lignocellulosic biomass must meet the following requirements: (i) enhance

the ability to produce sugars, (ii) avoid the loss of cellulose and hemicelluloses,

and (iii) minimize the production of inhibitors. However, an optimal pretreatment