Volume 6 Issue 4

Lignocellulosic carbohydrates, i.e. cellulose and hemicellulose, have abundant potential as feedstock for production of biofuels and chemicals. However, these carbohydrates are generally infiltrated by lignin. Breakdown of the lignin barrier will alter lignocelluloses structures and make the carbohydrates accessible for more efficient bioconversion. White-rot fungi produce ligninolytic enzymes (lignin peroxidase, manganese peroxidase, and laccase) and efficiently mineralise lignin into CO2 and H2O. Biological pretreatment of lignocelluloses using white-rot fungi has been used for decades for ruminant feed, enzymatic hydrolysis, and biopulping. Application of white-rot fungi capabilities can offer environmentally friendly processes for utilising lignocelluloses over physical or chemical pretreatment. This paper reviews white-rot fungi, ligninolytic enzymes, the effect of biological pretreatment on biomass characteristics, and factors affecting biological pretreatment. Application of biological pretreatment for enzymatic hydrolysis, biofuels (bioethanol, biogas and pyrolysis), biopulping, biobleaching, animal feed, and enzymes production are also discussed.

Retting is the main challenge faced during the processing of bast plants for the production of long fibre. The traditional methods for separating the long bast fibres are by dew and water retting. Both methods require 14 to 28 days to degrade the pectic materials, hemicellulose, and lignin. Even though the fibres produced from water retting can be of high quality, the long duration and polluted water have made this method less attractive. A number of other alternative methods such as mechanical decortication, chemical, heat, and enzymatic treatments have been reported for this purpose with mixed findings. This paper reviews different types of retting processes used for bast plants such as hemp, jute, flax, and kenaf, with an emphasis on kenaf. Amongst the bast fibre crops, kenaf apparently has some advantages such as lower cost of production, higher fibre yields, and greater flexibility as an agricultural resource, over the other bast fibres. The fibres produced from kenaf using chemical retting processes are much cleaner but low in tensile strength. Enzymatic retting has apparent advantages over other retting processes by having significantly shorter retting time and acceptable quality fibres, but it is quite expensive.

Paper aging and conservation are matters of concern to those responsible for archives and library collections. Wood-derived fibers are mainly composed of cellulose, hemicelluloses, and lignin, but paper composition can also include additives, such as starch, minerals, and synthetic polymers. Therefore, paper is a multi-component material, and because of its complex and varied nature, research findings in paper chemistry can be difficult to interpret. Deterioration of paper is caused by many factors such as acid hydrolysis, oxidative agents, light, air pollution, or the presence of microorganisms. The origin of the cellulosic material, as well as pulping and papermaking procedures, additives, and storage conditions play a crucial role. The chemical changes occurring within paper thus involve multi-parameter processes. The purpose of this review, which mainly focuses on the most recent decade, is to provide a description of the more important changes produced by aging and an update of the new tools available for the study of paper deterioration and its conservation.

To deeply understand the factors that affect the conversion of lignocellulosic biomass to fermentable sugars, experimental results should be bridged with process simulations. The objective of this paper is to review published research on modeling of the pretreatment process using leading technologies such as dilute acid, alkaline, and steam explosion pretreatment, as well as the enzymatic hydrolysis process for converting lignocellulose to sugars. The most commonly developed models for the pretreatment are kinetic models with assumptions of a first-order dependence of reaction rate on biomass components and an Arrhenius-type correlation between rate constant and temperature. In view of the heterogeneous nature of the reactions involved in the pretreatment, the uses of severity factor, artificial neural network, and fuzzy inference systems present alternative approaches for predicting the behavior of the systems. Kinetics of the enzymatic hydrolysis of cellulosic biomass has been simulated using various modeling approaches, among which the models developed based on Langmuir-type adsorption mechanism and the modified Michaelis-Menten models that incorporate appropriate rate-limiting factors have the most potential. Factors including substrate reactivity, enzyme activity and accessibility, irreversible binding of enzymes to lignin, and enzyme deactivation at high conversion levels, need to be considered in modeling the hydrolysis process. Future prospects for research should focus on thorough understanding of the interactions between biomass reactants and chemicals/enzymes — the key to developing sophisticated models for the entire conversion process.