Cellulosic materials fermentation

Processes have been developed in North America to pilot scale growing the bacterium Cellulomonas or the fungus Trichoderma on pre-treated milled cellulosic material in conventional fermentors, ie in a liquid medium. However, preparation costs are considerably higher than with solid-substrate fermentations. 

Cellulosic hollow fibers, 16 18-20 Cellulosic materials, in ethanol fermentation, 10 535—536 Cellulosic membranes, in hemodialysis,... 

Two broad areas of application for xylanolytic enzymes have been identified (1). The first involves the use of xylanases with other hydrolytic enzymes in the bioconversion of wastes such as those from the forest and agricultural industries, and in the clarification and liquification of juices, vegetables and fruits. For these purposes, the enzyme preparations need only to be filtered and concentrated as essentially no further purification is required. Several specific examples of applications involving crude xylanase preparations include bioconversion of cellulosic materials for subsequent fermentation (2) hydrolysis of pulp waste liquors and wood extractives to monomeric sugars for subsequent production of single cell protein (3-5). Xylose produced by the action of xylanases can be used for subsequent production of higher value compounds such as ethanol (6), xylulose (7) and xyIonic acid (8-9). 

While this reaction is substantially exothermic (6), it provides an intriguing approach to the production of fuels from renewable resources, as the required acids (including acetic acid, butyric acid, and a variety of other simple aliphatic carboxylic acids) can be produced in abundant yields by the enzymatic fermentation of simple sugars which are, in turn, available from the microbiological hydrolysis of cellulosic biomass materials ( ] ) These considerations have led us to suggest the concept of a "tandem" photoelectrolysis system, in which a solar photoelectrolysis device for the production of fuels via the photo-Kolbe reaction might derive its acid-rich aqueous feedstock from a biomass conversion plant for the hydrolysis and fermentation of crop wastes or other cellulosic materials (4). 

Cellulosic Materials. Over 900 x 106 metric tons of carbohydrate-containing cellulosic wastes are generated annually. The technology for converting this material into ethanol is available, but the stoichiometry of the process is disadvantageous. Even if each step in the process of the conversion of cellulose to ethanol proceeded with 100% yields, almost two-thirds of the mass would disappear during the sequence, most of it as carbon dioxide in the fermentation of glucose to ethanol. This amount of carbon dioxide leads to a disposal problem rather than to a raw material credit (209). 

Ravinder, T., Ramesh, B., Seenayya, G. and Reddy, G. 2000. Fermentative Production of Acetic Acid from Various Pure and Natural Cellulosic Materials by Clostridium Lentocellum SG6. W. J. Microbiol. Biotechnol., 16, 507-512. 

In solid-state fermentation, the productivity per unit reactor volume is high and the solid cellulase koji can be directly applied to hydrolyze cellulosic materials. 

The most attractive features of solid-state fermentation include low capital investment and low operational costs. These features are favorable in the hydrolysis of cellulosic materials because the cost of cellulase is a key factor for commercial production. Currently, cellulase production by submerged culture has made great progress and been commercialized, while solid-state fermentation is only operated on a small scale in a few countries, such as China, and further efforts in research and development are still needed in order to improve the process and the equipment. 

It is a commonly held view that cellulase is an inducible enzyme, and that cellulose is the best inducer. In solid-state fermentation for cellulase production, cellulosic materials act as either the carbon source or the inducer. Some of the raw materials for solid-state fermentation and their composition are listed in Table 1. From Table 1 it is very clear that the raw materials for cellulase production using solid-state fermentation are abundant and cheap. Proper pretreatment of raw materials is generally required. The nitrogen source for solid-state fermentation includes inorganic compounds, such as urea and (NH4)2SO4, or natural products, such as bran. 

Pulverization can reduce the size as well as the crystallinity of cellulosic materials and increase the surface area and bulk density. It is also possible to separate part of the hgnin from carbohydrates which makes it easier for microorganisms to digest cellulose. Various equipment, such as a compression mill, a bead mill, an extruder, a roll mill and disc refiners, etc., can be used for pulverization. Unfortunately these methods tend to be very expensive and too energy intensive. For sohd-state fermentation, if the particles are too fine, the oxygen mass transfer will become a big problem therefore, hghtly crushed or just ground raw material will suffice. 

Alkali treatment of cellulosic materials can remove hgnin as well as part of the hemicellulose and expose cellulose for fungi to digest. In addition, the alkah treatment method can swell and disrupt the structure of cellulose. Commonly used alkalis includes NaOH, Ca(OH)2 or CaO and aqueous as well as gaseous NH3. For solid-state fermentation, after alkah treatment, the cellulosic materials do not need to be washed, because all the solubilized hgnin and hemicellulose can be retained in the raw material [15]. After the addition of other nutrients, the pH has to be adjusted to a value of approx. 6.5 with H2SO4. 

In the submerged fermentation process for cellulase production, crystal cellulose and paper pulp are commonly used substrates which are expensive. The solid-state fermentation for cellulase production should use a cheap medium. Because cellulase is an inducible enzyme, the inducer must be included in the medium. Cellulose is the best inducer [45,46] and its hydrolysate (glucose) is the carbon source for microbes to grow therefore, cellulosic material is the basic component in the medium. Complex nitrogen sources are used to supply nitrogen and to regulate the pH value. Other nutrient salts, such as Mn + and Zn etc., should also be involved in the medium. 

Pretreatment technology for cellulosic materials for commercial production of cellulase by solid-state fermentation for various raw materials with low cost ... 

Processes for the bioproduction of ethanol from cellulosic materials have been studied extensively. Some of the process steps are specialized and beyond the scope of this chapter. However, there are many recent review articles dealing with some specific subjects. Basically, the processes consist of a number of steps. They are availability and collection of raw feedstock [20], size reduction, pretreatment, fractionation of biomass components, enzyme production [21, 22], saccharification, enzyme recycle [23, 24], pentose fermentation, improvement of pentose-fermenting biocatalyst, overcoming of product inhibition, overcoming inhibition by substrate-derived inhibitors, ethanol recovery [25], steam generation and recycling [26], waste treatment, and by-product utilization. 

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