Biotechnological production of xylitol from agroindustrial residues

Batch, fed-batch, and semicontinuous fermentation processes were used for the production of xylitol from sugarcane bagasse hemicellulosic hydrolysate. The best results were achieved by the semicontinuous fermentation process: a xylitol yield of 0.79 g/g with an efficiency of 86% and a volumetric productivity of 0.66 g/L/h.     

Characterisation of dissolving pulp using designed process variables, NIR and NMR spectroscopy, and multivariate data analysis

Two processability variables, filter clogging and alkali resistance, were measured in a series of laboratorycooked viscose pulps. The pulps were also characterised by ¹³CCP/MAS solid state nuclear magnetic resonance (NMR) and near infrared (NIR) spectroscopy. Partial least squares (PLS) regression was used to investigate the information provided by the spectroscopic methods with respect to the processability measurements. The study showed that the alkali resistance, R18, of the pulp and the filter clogging value, Kw, of the laboratoryprepared viscose can be modelled by NIR and multivariate data analysis (MVA). The alkali resistance, R18, of the pulp can also be calculated by NMR and partial least squares (PLS) regression. Analysis of the loading values in the PLS model showed that pulps with high alkali resistance have higher crystallinity than pulps with low alkali resistance. Analysis of variables of the cooking conditions showed that the chemical charge (Na₂O) and pH should be kept low to give high alkali resistance, whereas high Na₂O gives low filter clogging values.     

Remediation of textile effluent using agricultural residues

The sorption of artificial dye effluent made from two different dyes, Solar orange 7 GLL and Solar Jade Green FFB from Clariant, onto three different agricultural residues—barley husk, sugarcane bagasse, and wheat straw—was studied. Twenty percent of 600-μm particle size of these agricultural residues was used as substrates and studied individually. The percentage of dye removal was observed in concentrations of dye varying from 50 to 200 mg/L. The effect of temperature ranging from 25 to 50°C and pH from 6.0 to 12.0 on the dye removal by the substrates was also studied. The effective adsorption of the substrates was calculated.     

Surface characterization of unbleached kraft pulps by means of ESCA

The effect of digestion conditions (amount of effective alkali, digestion time) on the surface compositions of unbleached softwood (Pinus sylvestris) kraft pulp has been investigated by electron spectroscopy for chemical analysis (ESCA). The quantities monitored were the angular dependence of the total O/C ratio, the relative amounts of carbons in different states of oxidation and the adsorption of Al and Ca ions to the carboxyl groups in the surface. Examination of the angular dependence of ESCA intensities shows that the concentration of alkyl carbon is high in a very thin surface layer and that it decreases linearly with decreasing kappa number. The concentration of alkyl carbon is decreased by extraction of the fibres with dichloromethane, but the amount remaining in the surface after extraction still decreases linearly with decreasing kappa number (i.e. it decreases with increasing digestion time). It is suggested that the observed enrichment of alkyl carbon in the outermost surface layers most probably is due to reprecipitation of lignin. In pulp that has not been extracted, there is also strong enrichment of extractives in the surface. This amount increases with increasing effective alkali but is relatively independent of digestion time. ESCA analysis of the Al and Ca bound to the carboxyl groups shows that the amount depends on digestion time; the results are consistent with the notion that the reprecipitated lignin contains carboxyl groups.     

Integrated processes for use of pulps and lignins obtained from sugarcane bagasse and straw

Sugarcane bagasse and straw can be converted into pulps, oils, controlled-release formulations, chelating agents, and composites. This article reviews bagasse and straw conversion efforts in Brazil. Laboratory-scale processes were developed aiming at the integral use of these biomass byproducts. Organosolv pulping and oxidation of lignin are the most promising processes for the rational use of sugarcane residues. Fungal pretreatment and spectroscopic characterization are also discussed.     

Alternatives for the reduction of Cu(II) ion levels in hemodialysis membranes produced from sugar-cane bagasse

The objective of the present study was to seek alternatives for the reduction of Cu(II) ion levels in hemodialysis membranes produced by the cuprammonium process. The alternatives used were: (a) replacement of the solvent Cu(NH₃)₄(OH)₂, used in the original process, with Cu(EDA)₂(OH)₂, and (b) increasing the reflux time of the bagasse purification process from 1.5 to 3.0 h. The experimental results were obtained by analysis of Cu(II) content in the membranes by atomic absorption, by complexometry via UV/Vis spectroscopy of the solutions of filter paper, bagasse and lignin, and by monitoring the various stages of the purification process (by FTIR and by loss of mass), i.e. pretreatment with 0.25 M NaOH followed by treatment with 4.2 M EDA and reflux with EtOH/HNO₃ (20%, v/v). The results showed that the Cu(II) content in the membranes decreased with the use of the Cu(EDA)₂(OH)₂ solvent, that the purification process could not be improved further since cellulose degradation was observed, and that the Cu(II) content in the membranes produced was still to high for their use for hemodialysis treatment.     

Production and characterization ofPhanerochaete chrysosporium lignin peroxidases for pulp bleaching

The production of lignin peroxidase fromPhanerochaete chrysosporium was studied using immobilized mycelia in nylon-web cubes in semicontinuous fermentation using glucose pulses or ammonium tartrate pulses. Consistent enzyme production was achieved when glucose pulses were used, leading to an average activity of 253 U/L. The crude enzyme was added to eucalyptus kraft pulp before conventional and ECF bleaching sequences. Optimization of the enzymatic pretreatment led to the following operational conditions: enzyme load of 2 U/g of pulp, hydrogen peroxide addition rate of 10 ppm/h, and reaction time of 60 min. Pulp final characteristics were dependent on the chemical treatment sequence that followed enzymatic pretreatment. The chief advantage of enzymatic pretreatment was pulp viscosity preservation, which was observed in most of the experiments carried out with seven different chemical treatment sequences     

Surface properties of CTMP fibers modified with xylans

This study investigated the effect of modification with xylan on the surface properties of chemithermomechanical pulp (CTMP) from spruce. The surface modifications were carried out by controlled sorption of birch xylan from solution at high temperature and high pH. Several different analysis techniques were used to study the effects on fiber surface composition and morphology. The ESCA technique showed a reduction in the amount of carbons not bound to oxygen in the C(1s) resolved peak after treatment. Variations in surface topography between untreated samples and samples with xylan were studied with SEM and AFM in the tapping mode. Scanning electron micrographs show micrometersized xylan particle structures spread over the fiber surfaces. AFM images reveal differences in the fine structure of fibers. The modified fibers exhibit a nanometersized, bumplike morphology not seen on the untreated fibers. The wetting properties of single fibers were determined with the Wilhelmy plate technique and the water sorption of CTMP paper sheets was studied using a dynamic contactangle tester. The surface modification of CTMP with xylan significantly decreased the advancing contact angle of single fibers and also improved the water sorption of sheets.     

Evaluation of inoculum of Candida guilliermondii grown in presence of glucose on xylose reductase and xylitol dehydrogenase activities and xylitol production during batch fermentation of sugarcane bagasse hydrolysate

The effect of glucose on xylose-xylitol metabolism in fermentation medium consisting of sugarcane bagasse hydrolysate was evaluated by employing an inoculum of Candida guilliermondii grown in synthetic media containing, as carbon sources, glucose (30 g/L), xylose (30 g/L), or a mixture of glucose (2 g/L) and xylose (30 g/L). The inoculum medium containing glucose promoted a 2.5-fold increase in xylose reductase activity (0.582 IU/mg_prot) and a 2-fold increase in xylitol dehydrogenase activity (0.203 IU/mg_prot) when compared with an inoculum-grown medium containing only xylose. The improvement in enzyme activities resulted in higher values of xylitol yield (0.56 g/g) and productivity (0.46 g/[L·h]) after 48 h of fermentation.     

Grafting of acrylamide onto cellulosic fibers via dielectric-barrier discharge

Fully bleached kraft pulp (BKP) and thermomechanical pulp (TMP) fibers were grafted with acrylamide via dielectric-barrier discharge treatment at various treatment dosages. The results indicate that increased dielectric-barrier discharge treatment leads to the increased polymerization and incorporation of acrylamide onto fiber surfaces. Greater incorporation of poly(acrylamide) occurs on the BKP fibers than the TMP at the same treatment conditions. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) indicate that dielectric-barrier discharge initiated modifications to fiber surface topo-chemistry occur across the fiber such that the sheet is randomly peppered with modified areas; however, it occurs in patches on individual fibers as opposed to occurring as an evenly distributed thin film. SEM and elemental analysis also showed that the incorporation of acrylamide onto the fiber surface increases with increased treatment dosages.