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- Nilvebrant, NO, et al.
(författare)
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Enzymatic degradation of oxalic acid for prevention of scaling
- 2002
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Ingår i: Progress in Biotechnology (Biotechnology in the Pulp and Paper Industry - 8th ICBPPI ). - 0921-0423. ; 21, s. 231-238
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Konferensbidrag (refereegranskat)abstract
- Formation of calcium oxalate incrusts, scaling, may cause severe problems in the pulp and paper industry. Enzymatic degradation of oxalic acid provides a novel approach to eliminate the problems with calcium oxalate precipitation. The performance of two oxalate-degrading enzymes, oxalate oxidase from barley and oxalate decarboxylase from Aspergillus, was tested in model experiments with respect to catalytic efficiency under different conditions, including pH, temperature and enzyme concentration. Oxalate decarboxylase was found to be more sensitive to temperature variations than oxalate oxidase, which was selected for further experiments. Authentic samples from pulp bleach plants were used to test the performance of oxalate oxidase. The results showed that oxalic acid could be degraded enzymatically also in the industrial bleaching filtrates, which were obtained from D-, E-, O-, OP-, PO-, Q-, QP-, and Z-stages. The bleaching filtrates contained compounds that inhibited the action of oxalate oxidase. The degree of inhibition was strongly dependent on the filtrate and could be alleviated by dilution.
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- Nilvebrant, N.-O., et al.
(författare)
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Limits for alkaline detoxification of dilute-acid lignocellulose hydrolysates
- 2003
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 107:1-3, s. 615-628
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Tidskriftsartikel (refereegranskat)abstract
- In addition to fermentable sugars, dilute-acid hydrolysates of lignocellulose contain compounds that inhibit fermenting microorganisms, such as Saccharomyces cerevisiae. Previous results show that phenolic compounds and furan aldehydes, and to some extent aliphatic acids, act as inhibitors during fermentation of dilute-acid hydrolysates of spruce. Treatment of lignocellulose hydrolysates with alkali, usually in the form of overliming to pH 10.0, has been frequently employed as a detoxification method to improve fermentability. A spruce dilute-acid hydrolysate was treated with NaOH in a factorial design experiment, in which the pH was varied between 9.0 and 12.0, the temperature between 5 and 80°C, and the time between 1 and 7 h. Already at pH 9.0, >25% of the glucose was lost when the hydrolysate was treated at 80°C for 1 h. Among the monosaccharides, xylose was degraded faster under alkaline conditions than the hexoses (glucose, mannose, and galactose), which, in turn, were degraded faster than arabinose. The results suggest that alkali treatment of hydrolysates can be performed at temperatures below 30°C at any pH between 9.0 and 12.0 without problems with sugar degradation or formation of inhibiting aliphatic acids. Treatment with Ca(OH)2 instead of NaOH resulted in more substantial degradation of sugars. Under the harsher conditions of the factorial design experiment, the concentrations of furfural and 5-hydroxymethylfurfural decreased while the total phenolic content increased. The latter phenomenon was tentatively attributed to fragmentation of soluble aromatic oligomers in the hydrolysate. Separate phenolic compounds were affected in different ways by the alkaline conditions with some compounds showing an increase in concentration while others decreased. In conclusion, the conditions used for detoxification with alkali should be carefully controlled to optimize the positive effects and minimize the degradation of fermentable sugars.
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