Fermentations lignocellulose

Kiely et al. operated microbial fuel cells for more than a year with individual endproducts of lignocellulose fermentation (acetic add, formic add, lactic acid, succinic acid, or ethanol) to investigate the long-term cathode performance and bacterial commimities. Cathode performance degraded over time, as shown by an increase in power of up to 26% when the cathode biofihn was removed, and 118% using new cathodes [58]. For submerged air cathodes in two-chamber... 

Second-generation biofuel technologies make use of a much wider range of biomass feedstock (e.g., forest residues, biomass waste, wood, woodchips, grasses and short rotation crops, etc.) for the production of ethanol biofuels based on the fermentation of lignocellulosic material, while other routes include thermo-chemical processes such as biomass gasification followed by a transformation from gas to liquid (e.g., synthesis) to obtain synthetic fuels similar to diesel. The conversion processes for these routes have been available for decades, but none of them have yet reached a high scale commercial level. 

Various processes have been developed for hydrolyzing lignocellulose to its major constituents, i.e., to sugars and (partly) depolymerized lignin. The lignin is usually precipitated from the aqueous solution and either used as chemical feedstock or burned as process fuel. The aqueous sugar solution is then applied for fermentation to ethanol after neutralization and purification. 

Various solvents are being investigated to dissolve lignocellulosic materials. Some approaches focus on the selective depolymerization and extraction of lignin and hemicellulose as pre-treatment to produce clean cellulose fibers for subsequent fermentation or for pulping. Other approaches attempt to dissolve the whole lignocellulose with or without depolymerization. The liquefaction processes that are carried out at high temperature (>300 °C), and produce a complex oil mixture, are discussed above with the pyrolysis processes. 

Detailed discussion of the classical wood pulping processes - e.g., the Sulfite and Kraft processes - is available in the literature [14]. Pre-treatments that aim to facilitate the fermentation of lignocellulosic materials are also discussed elsewhere [49, 62-64]. 

We can illustrate fermentation processes using the process developed by Iogen to convert lignocellulosic materials such as wheat straw into ethanol (Fig. 2.10) [66]. The straw is chopped and milled prior to a steam-explosion pre-treatment to... 

Conversion of lignocellulose into transportation fuels via pyrolysis and subsequent oil upgrading [72], via gasification and subsequent Fischer-Tropsch or methanol synthesis [3], via hydrolysis and subsequent fermentation to ethanol or subsequent conversion into ethyl levulinate [45, 46, 73]. 

Lignocellulose biomass is a mixture of phenolic lignin and carbohydrates -cellulose and hemi-cellulose. It grows abundantly on earth and is largely available as agricultural and forestry residues. Lignocellulose can be converted via four major routes pyrolysis, gasification, hydrolysis and fermentation. 

Further research is also needed in this area. Particularly, (a) to create a new generation of cheap enzymes for hydrolysis of cellulose and lignocellulose to fermentable sugars (able to complete the biomass hydrolysis during fermentation) (b) to develop improved biocatalysts that allow us to simplify the process and reduce energy input and (c) to improve separation and recovery. 

It may be estimated that ethanol yields from lignocellulosics will range between 0.12 and 0.32 L kg-1 undried feedstock, depending upon the efficiency of five-carbon sugar conversion [26]. Other types of fermentation, including bacterial fermentation under aerobic and anaerobic conditions, can produce various other products from the sugar stream, including lactic acid. 

Biocatalytic conversion of lignocellulose into bioethanol, which requires upgrading of existing processes of fermenting sugars by using enzymatic-enhanced pretreatment of (hemi)cellulose. New, improved biocatalysts are needed for this route. 

A literature survey indicated that very little work has been done to produce an optimal cellulase system as described above. Here, we used solid-state fermentation (SSF) to achieve this objective. SSF processes, such as the "koji" process, have been used extensively for amylase production on wheat bran in Japan its application was extended to cellulase production on wheat bran and Ugnocellulosic materials by Toyama (13), Since then, wheat bran has become an important substrate for producing various products by SSF (14-20), In this study, we tested various lignocellulosic substrates for the production of cellulase and )3-glucosidase from T, reesei QMY-1 by SSF. 

Pretreatment of Substrate. Several different lignocelluloses were pretreated with NaOH. This pretreatment partially solubilizes the hemicelluloses and lignin and swells the cellulose so that the organism can utilize it for its growth and for production of a cellulase system in SSF. The treated lignocelluloses were not washed. The NaOH treatment is done with a minimum amount of water so that, after the addition of nutrient solution and inoculum, the moisture content is less than 80% wt/wt and there is no free water in the medium. More water was added to make suspensions of different lignocellulosic substrates of the desired concentration (1% or 5%) for liquid-state (submerged) fermentation (LSF). 

Recent studies have proven ethanol to be an ideal liquid fuel for transportation and renewable lignocellulosic biomass to be an attractive feedstock for ethanol fuel production by fermentation (1,2). The major fermentable sugars from hydrolysis of lignocellulosic biomass, such as rice and wheat straw, sugarcane bagasse, corn stover, corn fiber, softwood, hardwood, and grasses, are D-glucose and D-xylose except that softwood... 

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