Overcoming the recalcitrance (resistance of plant cell walls to deconstruction) of lignocellulosic biomass is a key step in the production of fuels and chemicals. The recalcitrance is due to the highly crystalline structure of cellulose which is embedded in a matrix of polymers-lignin and hemicellulose. The main goal of pretreatment is to overcome this recalcitrance, to separate the cellulose from the matrix polymers, and to make it more accessible for enzymatic hydrolysis. Reports have shown that pretreatment can improve sugar yields to higher than 90% theoretical yield for biomass such as wood, grasses, and corn. This paper reviews different leading pretreatment technologies along with their latest developments and highlights their advantages and disadvantages with respect to subsequent hydrolysis and fermentation. The effects of different technologies on the components of biomass (cellulose, hemicellulose, and lignin) are also reviewed with a focus on how the treatment greatly enhances enzymatic cellulose digestibility.

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Chemical and physicochemical pretreatment of lignocellulosic biomass: a review.

Trametes hirsuta and a purified laccase from this organism were able to degrade triarylmethane, indigoid, azo, and anthraquinonic dyes. Initial decolorization velocities depended on the substituents on the phenolic rings of the dyes. Immobilization of the T. hirsuta laccase on alumina enhanced the thermal stabilities of the enzyme and its tolerance against some enzyme inhibitors, such as halides, copper chelators, and dyeing additives. The laccase lost 50% of its activity at 50 mM NaCl while the 50% inhibitory concentration (IC(50)) of the immobilized enzyme was 85 mM. Treatment of dyes with the immobilized laccase reduced their toxicities (based on the oxygen consumption rate of Pseudomonas putida) by up to 80% (anthraquinonic dyes). Textile effluents decolorized with T. hirsuta or the laccase were used for dyeing. Metabolites and/or enzyme protein strongly interacted with the dyeing process indicated by lower staining levels (K/S) values than obtained with a blank using water. However, when the effluents were decolorized with immobilized laccase, they could be used for dyeing and acceptable color differences (DeltaE*) below 1.1 were measured for most dyes.

https://repositorium.sdum.uminho.pt/bitstream/1822/2402/1/28.pdf

Decolorization and detoxification of textile dyes with a laccase from Trametes hirsuta.

Lignocellulose pretreatment severity – relating pH to biomatrix opening

Insight into progress in pre-treatment of lignocellulosic biomass

To improve world energy security, lignocellulosic substrates are being used to generate inexpensive renewable biofuel. Pretreatment of these biomasses is pre-requisite to obtain fermentable sugar for production of ethanol. Crystallinity, degree of polymerization, particle size, and accessible surface area of biomass often limits decrystallization of cellulose and depolymerization of hemicellulose during pretreatment. Various pretreatment technologies employed to diverse biomasses, their mechanism of action, feasibility and practicability for production of bioethanol and other bio-based products has been compared in this article. Intelligent combinatorial pretreatment approaches such as microwave-acidalkali, ultrasound-surfactant, supercritical carbon dioxide and hot water-acid have been applied to increase sugar yield from a wide variety of feedstocks such as sugarcane bagasse, sugarcane top, corn stover, and switchgrass. Biological pretreatment using white, brown and soft rot fungi are attractive in terms of being cost effective, low energy requiring, and eco-friendly. Emphasis to optimize integrated biorefining processes, delineate pretreatment chemistries and their impact on cellulosic biomass to obtain greater yield of fuels and co-products are the highlights of this article. V C 2015 American Institute of Chemical Engineers Environ Prog, 00: 000–000, 2015

Recent advances in pretreatment technologies for efficient hydrolysis of lignocellulosic biomass

Wheat straw (Triticum aestivum) and beech (Fagus sylvatica), were used to evaluate the effects of two pre-treatment processes (alkaline wet oxidation and enzyme treatment with laccase) on lignocellulosic materials for applications in particleboards and fiberboards. Wheat straw and beech fibers reacted differently in the two processes. The chemical composition changed little following enzyme treatment. After alkaline wet oxidation, fibers enriched in cellulose were obtained. With both materials, almost all hemicellulose (80%) together with a large portion of the lignin were solubilised by alkaline wet oxidation, but essentially all cellulose remained in the solid fraction. Following enzyme treatment most material remained as a solid. For wheat straw, reaction with acetic anhydride indicated that both treatments resulted in more hydroxyl groups being accessible for reaction. The enzyme treatment gave a more reactive surface than alkaline wet oxidation for wheat straw, whereas the opposite was obser...

S. Mallon

Papers

Comparison of the chemical properties of wheat straw and beech fibers following alkaline wet oxidation and laccase treatments