Rice husks

The chemical composition of rice husk ask is similar to that of many common organic fibers and it contains of cellulose 40-50%, lignin 25-30%, ash 15-20% and moisture 8-15%. Typical analyses of rice husk ask is shown in Table 8.2. The content of each of them depends on rice variety, soil chemistry, climatic conditions, and even the geographic localization of the culture. 

The exterior of rice husk ask are composed of dentate rectangular elements, which themselves are composed mostly of silica coated with a thick cuticle and surface hairs. The mid region and inner epidermis contain little silica. Jauberthie et al, confirmed that the presence of amorphous silica is concentrated at the surfaces of the rice husk and not within the husk itself [9]. The properties of rice husk ash and its main composition are presented in Table 8.3. The organic materials consist of cellulose and lignin which turn to CO and CO when rice husk ask burns in air. The ash contains mainly silica (90%), and a small portion of metal oxides ( 5%) and residual carbon obtained from open burning [10]. 

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Oxahc acid manufacture via the oxidation of carbohydrates is stiU actively pursued, especially in China (10—12). In India, processes which produce sihca and oxahc acid have been developed (13,14). The raw materials include agricultural wastes, such as rice husks, nut shell flour, com cobs, baggase, straw, etc. 

Furfural is a natural monomer obtained by the steam acid digestion of corncobs, bagasse, rice husks, oat hulls, or similar materials. It acts as the precursor for the preparation of two important monomers (Scheme 1), adipic acid and hexamethylene diamine, used in the... 

The essential part of the insulation system is the vapour barrier, which must be complete and continuous over the outer (warm) surface. Even materials such as coconut fibre, rice husks, sawdust and wood shavings are successfully used as insulants if the vapour barrier is good. 

Microorganism and cultivation conditions Rhizopus sp. 26R criltivated in 20 g solid substrates composed of wheat bran, rice bran and rice husk (6 12 2) in a plastic bags. Initial pH and moisture content were 5.7 and 58%, respectively. The fungus was incubated at 32°C for 6 days. 

When Rhizopus sp. 26R was cultivated in the solid substrates without addition of rice bran but composed of only wheat bran and rice husk at the ratio of 18 2. The pectinase activity from the culture was approx. 25-35 unit/ml within 2 days and the production remained constant for 4 days (Figure 3). One gram of raw starch from cassava tuber, 1 g of pectin or 0.5 g of yeast extract was added to the solid substrates in order to induce higher activity of the enzsrme. The results showed that either 1 g raw cassava starch or 1 g pectin that was added to the 20 g solid substrates increased the enzyme activity to 1.7 and 2.4 times, respectively (Figure 3). The production of pectinase in soHd substrates with wheat bran and rice husk could be enhanced with the addition of raw cassava starch and pectin. 

Figure 3 Pectinase activity in 20 g of solid substrates composting of wheat bran, rice bran and rice husk (18 0 2) with the addition of 1 g raw starch from cassava tuber, 1 g pectin or 0.5 g yeast extract.

Addition of rice bran to the solid substrates to make the ratio of wheat bran, rice bran and rice husk to 9 9 2 helped increasing the activity of pectinases from Rhizopus sp. 26R as shown in Figure 4. The activity of the enzyme was approx. 4.3 times higher. Moreover, either 1 g of pectin or 0.5 g of yeast extract did not help increasing of the enzyme production. In contrary, the enz5mie activity was decreased 2.6 times to that of the former one. Addition of raw cassava starch to the substrates did no effect to the enzyme production (data not shown). 

Pectinase production in solid substrates of wheat bran, rice bran and rice husk at the different ratios. 

Different ratios of the solid substrates, wheat bran, rice bran and rice husk, were done and the activity of the pectinases was compared in Figure 5. The mixture of wheat bran, rice bran and rice husk in the ratios of 9 9 2 or 6 12 2 appeared to be two of the best composition ratios for growth of the fungus and the pectinase production.The ratio of 6 12 2 was selected for the enzyme production since rice bran was cheaper than wheat bran and locally obtained. 

Figure 5 Pectinase activity in solid substrates of wheat bran, rice bran and rice husk at different ratios of substrates. Initial moisture content 66 % Incubation temperature 32°C Initial pH 5.7...

Figure 6,7 and 8 showed the results of the pectinase activity when produced in the solid substrates containing wheat bran, rice bran and rice husk in the ratio of 6 12 2. The highest activity obtained when the strain was grown on the solid substrates with 58 % initial moisture content, pH adjusted to 5.7 and incubation temperature was at 32°C. Under these conditions, the highest activity of the enzyme that could be obtained from Rhizopus sp. 26R was ca. 700 units of enzyme activity per gram of solid substrates. 

The production of the pectinases in the sohd substrates composed of wheat bran, rice bran and rice husk (6 12 2) was considerably very low. The spore inoculum of Rhizopus sp. 26R was prepared on raw cassava starch agar which the cost estimation was US 1.0 per 1 litre. Wheat bran, rice bran and rice husk were approx. US 64 per 50 kg. The total cost of the production of pectinases from Rhizopus sp. 26R in the sohd substrates, when considered only on the substrates was estimated to be only US 178 - 180 for 10 million units of crude pectinase. 

The enzyme production in the solid substrates composed of wheat bran and rice husk (18 2) could be increased by the addition of either 1 g raw cassava starch or 1 g pectin to a 20 g substrates. The enzyme activity increased approx. 1.7 and 2.4 times, respectively. 

Addition of rice bran to the mixture of wheat bran and rice husk was the best substrates for the fungal pectinase production. The solid substrates that composed of wheat bran, rice bran and rice husk at the ratio of 6 12 2 was selected to be the best since rice bran are easily found in South-east Asian countries. Addition of either raw cassava starch or pectin as inducer is not needed. On the otherhand, pectin even inhibited the activity of the enzyme as well as that reported by Elegado and Fujio (6). 

Bansal, V., Ahmad, A., Sastry, M. (2006) Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica. Journal of the American Chemical Society, 128, 14059-14066. 

Chen, G. Fang, M. Luo, Z. Li, X. Shi, Z. Cen, K. Ni, M. Preto, I., Experimental research on rice husk combustion in CFB boiler and the design of a 35 t/h rice husk-fired CFB Boiler. 14th International Conference on Fluidized Bed Combustion, ASME, Vancouver, 1997. 

Prasad, T., S.P. Arora, and R.C. Chopra. 1982. Selenium toxicity as induced by feeding rice husk to buffalo calves a clinical case report. Indian Vet. Jour. 59 235-237. 

Mills that process rice may also generate process heat, that can be used for direct heating, steam generation, mechanical power or electrical power. For every five tons of rice milled, one ton of husks with an energy content equivalent to one ton of wood is left as residue. A rice mill in Louisiana has satisfied all its power needs since 1984 from an on-site rice-husk power plant. The plant sells surplus energy to the local utility. 

Poplar (hardwood) Pine (softwood) Corn stover Rice husk Cotton seed hulls... 

Commercial gasifiers are available in a range of sizes and types, and run on a variety of fuels, including wood, charcoal, coconut shells and rice husks. Power output is determined by the economic supply of biomass, which is limited to 80 MW in most regions. The producer gas is affected by various gasification processes from various biomass feedstocks. Table 6.7 shows composition of gaseous products from various biomass fuels by different gasification methods. 

This compound is one of the more important furan derivatives, and is commercially available from pentosans (polysaccharides) which are present in rice husks, oats and corn residues (furfur is the Latin name for bran ). When treated with sulfuric acid, pentosans decompose into pentoses, which then undergo dehydration to the aldehyde (Scheme 6.31). 

The momilactones are a group of growth inhibitors which have been isolated from rice husks. X-Ray analysis of momilactone C (56) and of annonalide (57) (from Annona coriaceaf established the unusual 9-/3H stereochemistry. Annonalide has been converted into momilactone B (58). Momilactone A has the... 

Iron (III) hydroxide waste Especially for heavy metals removal from wastewater, iron (III) hydroxide waste and waste slurry from the fertilizer industry, xanthate, rice husk, carbon, and coconut shell have been studied and can be considered as alternatives. 

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