https://faculty.washington.edu/renatab/courses/PSE490/downloads/pretreatment.pdf

Features of promising technologies for pretreatment of lignocellulosic biomass.

Lignocelluloses are often a major or sometimes the sole components of different waste streams from various industries, forestry, agriculture and municipalities. Hydrolysis of these materials is the first step for either digestion to biogas (methane) or fermentation to ethanol. However, enzymatic hydrolysis of lignocelluloses with no pretreatment is usually not so effective because of high stability of the materials to enzymatic or bacterial attacks. The present work is dedicated to reviewing the methods that have been studied for pretreatment of lignocellulosic wastes for conversion to ethanol or biogas. Effective parameters in pretreatment of lignocelluloses, such as crystallinity, accessible surface area, and protection by lignin and hemicellulose are described first. Then, several pretreatment methods are discussed and their effects on improvement in ethanol and/or biogas production are described. They include milling, irradiation, microwave, steam explosion, ammonia fiber explosion (AFEX), supercritical CO2 and its explosion, alkaline hydrolysis, liquid hot-water pretreatment, organosolv processes, wet oxidation, ozonolysis, dilute- and concentrated-acid hydrolyses, and biological pretreatments.

/pdf/pretreatment-of-lignocellulosic-wastes-to-improve-ethanol-zbwx58h962.pdf

Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: a review.

Trends in biotechnological production of fuel ethanol from different feedstocks.

http://www.loewenlabs.com/peter/wp-content/themes/atahualpa/Manuscripts/BA_29_675.pdf

Biomass pretreatment: fundamentals toward application

https://www.cell.com/trends/biotechnology/pdf/S0167-7799(06)00254-X.pdf

Bio-ethanol--the fuel of tomorrow from the residues of today.

Whole treechips obtained from softwood forest thinnings were pretreated via single-and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity tomaximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.

Two-stage dilute-acid pretreatment of softwoods.

Typical pretreatment requires high-energy (steam and electricity) and corrosion-resistant, high-pressure reactors. A review of the literature suggests that fungal pretreatment could potentially lower the severity requirements of acid, temperature and time. These reductions in severity are also expected to result in less biomass degradation and consequently lower inhibitor concentrations compared to conventional thermochemical pretreatment. Furthermore, potential advantages of fungal pretreatment of agricultural residues, such as corn stover, are suggested by its effectiveness in improving the cellulose digestibility of many types of forage fiber and agricultural wastes. Our preliminary tests show a three- to five-fold improvement in enzymatic cellulose digestibility of corn stover after pretreatment with Cyathus stercoreus; and a ten- to 100-fold reduction in shear force needed to obtain the same shear rate of 3.2 to 7 rev/s, respectively, after pretreatment with Phanerochaete chrysosporium.

Microbial pretreatment of biomass: potential for reducing severity of thermochemical biomass pretreatment.

Microbial Pretreatment of Biomass

Selective thinning of forests in the western United States will generate a large, sustainable quantity of softwood residues that can be an attractive feedstock for fuel ethanol production. The major species available from thinning of forests in northern California and the eastern Rocky Mountains include white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii), and Ponderosa pine (Pinus ponderosa). Douglas fir chips were soaked in 0.4% sulfuric acid solution, then pretreated with steam at 200 – 230°C for 1 – 5 min. After pretreatment, 90 – 95% of the hemicellulose and as much as 20% of the cellulose was solubilized in water, and 90% of the remaining cellulose can be hydrolyzed to glucose by cellulase enzyme. The prehydrolysates, at as high as 10% total solid concentration, can be readily fermented by the unadapted yeastSaccharomyces cerevisiae D5A.

Dilute acid pretreatment of softwoods

a) acid-soaking, draining and dewatering a lignocllulosic biomass; b) first-stage hydrolysis at a temperature of from 130°C to 220°C and flashing hydrolysate in two consecutive tanks; c) recovering soluable sugars by a counter-current extractor; d) second-stage acid and metal salt impregnation and dewatering of washed-first stage solids; e) second-stage hydrolysis at a temperature from 190°C to 240°C and flashing hydrolysate in two consecutive tanks; f) first-stage fermentation of extract promoting yeasts growth; g) fermentation of second-stage hydrolysate and recovering the alcohol

Fred A. Keller

Papers

Two-stage dilute-acid pretreatment of softwoods.

Microbial pretreatment of biomass: potential for reducing severity of thermochemical biomass pretreatment.

Microbial Pretreatment of Biomass

Dilute acid pretreatment of softwoods

Ethanol production with dilute acid hydrolysis using partially dried lignocellulosics