Бурение грунтовых зондов, установка энергетических колодцев

Cellulases are enzymes produced mainly by bacteria, fungi and protozoans. Efficient and economical production of cellulases is a very important aspect as the cost of the cellulase enzymes is a sig­nificant component in the final cellulosic ethanol production cost in this route. A list of microorganisms producing cellulases are shown in Table 6.1. The most frequently reported source of cellulases is the fungus Trichoderma reesei, probably the most studied cellulo­lytic microorganism. Among the various microorganisms capable of synthesizing cellulase enzymes, T. reesei produces an extracellu­lar, stable, and efficient cellulase enzyme system [17]. However, the

low-glucosidase activity of the enzyme system from T. reesei leads to incomplete hydrolysis of cellobiose in the reaction mixture, and as a result inhibition of the enzymes. The most common method for the production of cellulases is submerged fermentation technol­ogy (SmF), which involves growing the microorganisms in a sub­merged culture.

Another alternative approach for the cellulase production is the solid state fermentation (SSF), where a solid substance is used for supporting the growth of cellulolytic microorganisms. Until recently the substrate used by many researchers for the cellulases production was pure forms of cellulose. However there are a num­ber of recent attempts to utilize raw biomass forms and agricul­tural wastes as supports for the growth of fungi and bacteria that can produce cellulases. This includes: production of cellulases from Aspergillus niger NS-2 in solid-state fermentation on agri­cultural and kitchen waste residues [39]; utilization of eggshell waste in cellulase production by Neurospora crassa under wheat bran-based solid-state fermentation [40]; use of Jatropha curcas seed cake as substrate for production of xylanase and cellulase by Aspergillus niger FGSCA733 in solid-state fermentation [41]; okara for production of cellobiase-rich cellulases preparation by a selected Bacillus subtilis Pa5 [42]; palm fruit bunch fiber [43] as a support for the production of cellulase enzymes during the solid — state fermentation.

The most desired qualities of cellulases that used in the lignocel — lulosic biomass saccharification step in the ethanol production are highly specific activity, high rate of turnover with native cellulose/ biomass as substrate, thermostability, decreased susceptibility to enzyme inhibition by cellobiose and glucose, selective adsorption on cellulose, synergism among the different enzymes and ability to withstand shear forces [44]. There are attempts to achieve these characteristics through gene engineering approaches, over expres­sion techniques and developing optimal enzyme cocktails and conditions for hydrolysis. Lignocellulosic biomass saccharification efficiency of a multienzyme complex depends both on properties of individual enzymes and their ratio in the multienzyme cocktail [45]. The ideal cellulase complex must be highly active on the selected biomass feedstock with minimum pretreatment, able to completely hydrolyze the biomass, operate well at mildly acidic pH, withstand process stress, and most importantly, be cost effective.

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