Enzymatic approaches in paper industry for pulp refining and biofilm control

Enzymatic pretreatment for cellulose nanofiber production: Understanding morphological changes and predicting reducing sugar concentration

Enzymatic pretreatment plays a crucial role in producing cellulose nanofibers (CNFs) before fibrillation. While previous studies have explored how treatment severity affects CNF characteristics, there remains a lack of suitable parameters to monitor real-time enzymatic processes and fully comprehend the link between enzymatic action, fibrillation, and CNF properties. This study focuses on evaluating the impact of enzyme charge (using a monocomponent endoglucanase) and treatment time on cellulose fiber morphology and reducing sugar generation. For the first time, a random forest (RF) model is developed to predict reducing sugar concentration based on easily measurable process conditions (e.g., stirrer power consumption) and fiber/suspension characteristics like fines content and apparent viscosity. Polarized light optical microscopy was found to be a suitable technique to evaluate the morphological changes that fibers experience during enzymatic pretreatment. The research also revealed that endoglucanases initially induce surface fibrillation, releasing fine fibers into the suspension, followed by fiber swelling and shortening. Furthermore, the effect of enzymatic pretreatment on resulting CNF characteristics was studied at two fibrillation intensities, indicating that a high enzyme charge and short treatment times (e.g., 90 min) are sufficient to produce CNFs with a nanofibrillation yield of 19-23 % and a cationic demand ranging from 220 to 275 μeq/g. This work introduces a well-modeled enzymatic pretreatment process, unlocking its potential and reducing uncertainties for future upscaling endeavors.

Eco-friendly Bleaching of Agrowaste Wheat Straw Using Crude Alkalo-Thermotolerant Cellulase-Free Xylano-Pectinolytic Enzymes

The aim of this study was to evaluate the potential of xylanase-pectinase enzymes in bleaching of wheat straw pulp, just to cut down the toxic wastes, in order to manage the environmental pollution. The appropriate parameters of bleaching were evaluated, and best conditions were xylanase and pectinase dose of 5.0 and 1.66 IU/g of pulp, respectively, along with material to liquid ratio of 1:7.5 (g/ml), temperature 55 °C, treatment time 3 h, Tween-80 1%, and pH 8.5. The release of reducing sugar and other non-cellulosic impurities, phenolic-hydrophobic-lignin was maximum at best bleaching conditions. Prebleaching of wheat straw pulp using these enzymes showed 14.75% decline in kappa number. Enzymatic bleaching plus 100% chemical bleaching also led to 27.90% reduction in yellowness. Using this methodology, the consumption of active chlorine was reduced up to 25%, along with an increase in burst index (7.98%), tear index (3.42%), breaking length (5.30%), viscosity (11.22%), gurley porosity (12.50%), and double-fold number (23.08%), which exhibits a remarkable enhancement in all the properties of pulp treated with enzymes. Microscopic images also confirm the effectiveness of enzymatic treatment in bleaching of wheat straw pulp. BOD and COD values of effluent also decreased by 20.74 and 17.87%, respectively. This research focussing on producing better grade paper using an eco-friendly approach would certainly benefit the paper and pulp industry. This is the first report, depicting bleaching capability of xylanase-pectinase enzymes for soda-anthraquinone pulp of wheat straw.

Slime control in paper mill using biological agents as biocides

The environmental conditions of paper mills are suitable for the growth of slime-forming microorganisms due to the supply of nutrients, favorable temperature, and moisture. The slime formation causes the spoilage of raw materials & additives, breaks in the paper during papermaking, loss of production, reduces the hygienic quality of the end products, produces off-spec and rejected products, creates microbiological corrosion, and produces harmful gases. The main microorganisms are Bacteria (mainly Bacillus spp., Achromobacter spp., Enterobacter spp., Pseudomonas spp., Clostridium, etc.), Fungi (Aspergillus, Penicillium, Saccharomyces, etc.), and Algae. Besides the use of conventional toxic chemical biocides or slimicides, slime formation can also be controlled in an eco-friendly way using enzymes, bacteriophages, biodispersants, and biocontrol agents alone or along with biocides to remove the slime. Enzymes have shown their effectiveness over conventional chemicals due to nontoxic and biodegradable nature to provide clean and sustainable technology. Globally enzymes are being used at some of the paper mills and many enzymatic products are presently being prepared and under the trail at laboratory scale. The specificity of enzymes to degrade a specific substrate is the main drawback of controlling the mixed population of microorganisms present in slime. The enzyme has the potential to provide the chemical biocide-free solution as a useful alternative in the future with the development of new technologies. Microorganisms control in the paper mill may appear as a costly offer but the cost of uncontrolled microbial growth can be much higher leading to slime production and large economic drain.

Removal of hard COD from acidic eucalyptus kraft pulp bleach plant effluent streams using oxidoreductases

The bleach plant of a pulp and paper (P&P) mill presents a major source of wastewater containing toxic organic matter characterized as chemical oxygen demand (COD). Due to their high oxidizing power, oxidoreductases hold promise to be a key solution for the removal of dissolved organic material. Here, four oxidoreductases from different enzyme families were selected to treat bleach plant effluents. Haloperoxidase treatment of the final effluent resulted in the highest levels of decolorization (71%) and reduction of aromatic compounds (36%). Using single compound analysis, 27 low molecular weight compounds were found to be persistent throughout the wastewater treatment process and, therefore, classified as hard COD. The tested enzymes efficiently removed several of the identified COD compounds. Hence, this study suggests that the application of oxidoreductases will serve as an environmental-friendly solution for reducing waste from P&P production.

Purification and characterization of two thermostable xylanases from a halotolerant Bacillus sp. Asc6BA isolated from Salar de Ascotán, Atacama Desert

Two extracellular xylanases, denominated X2 and X3, were purified and characterized from the halotolerant bacterium Bacillus sp. Asc6BA isolated from "Salar de Ascotán" in the Atacama Desert. Xylanases were purified by anion exchange, cation exchange and size exclusion liquid chromatography. Xylanase X2 and X3 were purified ~ 690-fold and ~ 629-fold, respectively, compared to the concentrated extracellular fraction with a final specific activity of 169 and 154 u mg^-1, respectively. Optimal conditions of pH and temperature of xylanolytic activity were 6.0 and 60 °C for X2 and 7.0 and 60 °C for X3. Half-life of X2 xylanase was 30 min at 50 °C, while X3 xylanase was remarkably more thermostable, retaining more than 70% of its activity after 32 h of incubation at 50 °C. X2 exhibited K_m, V_max and k_cat values of 7.17 mg mL^-1, 1.28 mM min^-1 mg^-1 and 425.33 s^-1, respectively. X3 exhibited K_m, V_max and k_cat values of 6.00 mg mL^-1, 19.25 mM min^-1 mg^-1 and 82,515 s^-1, respectively. In addition to their thermal stabilities, these enzymes were shown to be resistant to freeze-drying. These stability properties, in addition to the ability of these enzymes to be active in a wide range of temperatures and pHs, make these xylanases good candidates for industrial applications.

Enzyme-assisted pulp refining: an energy saving approach

Energy conservation has become an essential step in pulp and paper industry due to diminishing fossil reserves and high cost of energy. Refining is a mechanical treatment of pulp that modifies the structure of the fibres in order to achieve desired paper-making properties. However, it consumes considerable amount of energy. The electrical power consumption has a direct impact on paper manufacturing cost. Therefore, there is a requirement to minimize the energy cost. Enzyme-assisted refining is the environment friendly option that reduces the energy consumption for papermaking. Enzyme-assisted refining is defined as mechanical refining after pretreatment of pulp with enzymes such as cellulases and hemicellulases. It not only reduces the energy consumption but also improves the quality of finished paper. Enzymes improve the beatability of pulp at same refining degree (°SR) and desired paper properties can be achieved at decreased refining time. The selection of suitable enzyme, optimization of enzyme dose and appropriate reaction time are the key factors for energy reduction and pulp quality improvement during enzyme-assisted refining.

Effects of enzymes on the refining of different pulps

Comparative studies of the effects of two commercial enzyme formulations on fiber refining were conducted. Extensive basic characterisation of the enzymes involved, assessment of their hydrolytic activities on different model substrates as well as on different pulps (softwood sulfate, softwood sulfite, hardwood sulfate) were evaluated. Both enzyme formulations showed endoglucanase as well as some xylanase and β-glucosidase activity. In addition, Enzyme A reached a CMC end viscosity of 19.5 mPa compared to 11.1 mPa for Enzyme B. Reducing sugar release almost doubled from 695 μmol mL^-1 for hardwood sulfate pulp to 1300 μmol mL^-1 for softwood sulfite pulp with Enzyme B under the same conditions. Enzyme A increased the degree of refining even under non-ideal conditions from 23 °SR to up to 50 °SR. Further characterization of hand sheets, made from enzyme pre-treated and refined cellulose fibers with Enzyme A and B, showed that Enzyme A had the best effects leading to hand sheets with increased tensile strength and low air permeability. In summary, the increase in the degree of refining seen for Enzyme A correlated to higher xylanase and β-glucosidase activity and lower endoglucanase activity.

Analysis of spatio-temporal fungal growth dynamics under different environmental conditions

Traditionally, fungal growth dynamics were assessed manually, limiting the research to a few environmental conditions and/or fungal species. Fortunately, more automated ways of measurement are gaining momentum due to the availability of cheap imaging and processing equipment and the development of dedicated image analysis algorithms. In this paper, we use image analysis to assess the impact of environmental conditions on the growth dynamics of two economically important fungal species, Coniophora puteana and Rhizoctonia solani. Sixteen environmental conditions combining four temperatures (15, 20, 25 and 30 °C) and four relative humidity (RH) conditions (65, 70, 75 and 80% RH) were tested. Fungal growth characteristics were extracted from images of the growing fungi, taken at regular points in time. Advanced time series analysis was applied to quantitatively compare the effect of the environmental conditions on these growth characteristics. The evolution of the mycelial area and the number of tips over time resulted in typical sigmoidal growth curves. Other growth characteristics such as the mean hyphal segment length did not vary significantly over time. Temperature and RH usually had a combined effect on the growth dynamics of the mycelial area and the number of tips. When defining optimal growth conditions for a fungus, it is therefore of primordial importance that the effect of temperature and RH is assessed simultaneously. At the most extreme conditions we tested, the mycelium most probably experienced water stress when developing over the inert Petri dish surface. An RH of 65% (independent of temperature) for C. puteana and a temperature of 30 °C (independent of RH) for both C. puteana and R. solani therefore always resulted in limited fungal growth, while the optimal growing conditions were at 20 °C and 75% RH and at 25 °C and 80% RH for R. solani and at 20 °C and 75% RH for C. puteana. The method applied in this study offers an updated and broader alternative to classical and narrowly focused studies on fungal growth dynamics, and is well suited to efficiently assess the effect of environmental conditions on fungal growth.

Cellulose Biomaterials for Tissue Engineering

In this review, we highlight the importance of nanostructure of cellulose-based biomaterials to allow cellular adhesion, the contribution of nanostructure to macroscale mechanical properties, and several key applications of these materials for fundamental scientific research and biomedical engineering. Different features on the nanoscale can have macroscale impacts on tissue function. Cellulose is a diverse material with tunable properties and is a promising platform for biomaterial development and tissue engineering. Cellulose-based biomaterials offer some important advantages over conventional synthetic materials. Here we provide an up-to-date summary of the status of the field of cellulose-based biomaterials in the context of bottom-up approaches for tissue engineering. We anticipate that cellulose-based material research will continue to expand because of the diversity and versatility of biochemical and biophysical characteristics highlighted in this review.

Predicting the most appropriate wood biomass for selected industrial applications: comparison of wood, pulping, and enzymatic treatments using fluorescent-tagged carbohydrate-binding modules

BACKGROUND

Lignocellulosic biomass will progressively become the main source of carbon for a number of products as the Earth's oil reservoirs disappear. Technology for conversion of wood fiber into bioproducts (wood biorefining) continues to flourish, and access to reliable methods for monitoring modification of such fibers is becoming an important issue. Recently, we developed a simple, rapid approach for detecting four different types of polymer on the surface of wood fibers. Named fluorescent-tagged carbohydrate-binding module (FTCM), this method is based on the fluorescence signal from carbohydrate-binding modules-based probes designed to recognize specific polymers such as crystalline cellulose, amorphous cellulose, xylan, and mannan.

RESULTS

Here we used FTCM to characterize pulps made from softwood and hardwood that were prepared using Kraft or chemical-thermo-mechanical pulping. Comparison of chemical analysis (NREL protocol) and FTCM revealed that FTCM results were consistent with chemical analysis of the hemicellulose composition of both hardwood and softwood samples. Kraft pulping increased the difference between softwood and hardwood surface mannans, and increased xylan exposure. This suggests that Kraft pulping leads to exposure of xylan after removal of both lignin and mannan. Impact of enzyme cocktails from Trichoderma reesei (Celluclast 1.5L) and from Aspergillus sp. (Carezyme 1000L) was investigated by analysis of hydrolyzed sugars and by FTCM. Both enzymes preparations released cellobiose and glucose from pulps, with the cocktail from Trichoderma being the most efficient. Enzymatic treatments were not as effective at converting chemical-thermomechanical pulps to simple sugars, regardless of wood type. FTCM revealed that amorphous cellulose was the primary target of either enzyme preparation, which resulted in a higher proportion of crystalline cellulose on the surface after enzymatic treatment. FTCM confirmed that enzymes from Aspergillus had little impact on exposed hemicelluloses, but that enzymes from the more aggressive Trichoderma cocktail reduced hemicelluloses at the surface.

CONCLUSIONS

Overall, this study indicates that treatment with enzymes from Trichoderma is appropriate for generating crystalline cellulose at fiber surface. Applications such as nanocellulose or composites requiring chemical resistance would benefit from this enzymatic treatment. The milder enzyme mixture from Aspergillus allowed for removal of amorphous cellulose while preserving hemicelluloses at fiber surface, which makes this treatment appropriate for new paper products where surface chemical responsiveness is required.

Increasing efficiency of enzymatic hemicellulose removal from bamboo for production of high-grade dissolving pulp

To improve the efficiency of enzymatic hemicellulose removal from bamboo pre-hydrolysis kraft pulp, mechanical refining was conducted prior to enzyme treatment. Refining significantly improved the subsequent hemicellulose removal efficiency by xylanase treatment. Results showed that when PFI refining was followed by 3h xylanase treatment, the xylan content of the bamboo pre-hydrolysis kraft pulp (after first stage oxygen delignification) could be decreased to 2.72% (w/w). After bleaching of enzyme treated pulp, the alpha-cellulose content was 93.4% (w/w) while the xylan content was only 2.38%. The effect of refining on fibre properties was investigated in terms of freeness, water retention value, fibre length and fibrillation characteristics. The brightness, reactivity and viscosity were also determined to characterize the quality of final pulp. Results demonstrated the feasibility of combining refining and xylanase treatment to produce high quality bamboo dissolving pulp.

Effect of Cellulases and Xylanases on Refining Process and Kraft Pulp Properties

Samples of bleached kraft pine cellulosic pulp, either treated with an enzyme preparation (a Thermomyces lanuginosus xylanase, an Aspergillus sp. cellulase, and a multienzyme preparation NS-22086 containing both these activities) or untreated, were refined in a laboratory PFI mill. The treatment with cellulases contained in the last two preparations significantly improved the pulp’s susceptibility to refining (the target freeness value of 30°SR was achieved in a significantly shorter time), increased water retention value (WRV) and fines contents while the weighted average fiber length was significantly reduced. These changes of pulp parameters caused deterioration of paper strength properties. The treatment with the xylanase, which partially hydrolyzed xylan, small amounts of which are associated with cellulose fibers, only slightly loosened the structure of fibers. These subtle changes positively affected the susceptibility of the pulp to refining (refining energy was significantly reduced) and improved the static strength properties of paper. Thus, the treatment of kraft pulps with xylanases may lead to substantial savings of refining energy without negative effects on paper characteristics.

Concomitant production of xylanases and cellulases from Trichoderma longibrachiatum MDU-6 selected for the deinking of paper waste

Sixty fungal cultures were isolated from agricultural soil, industrial soil, forest canopy soil having decomposed leaf litter and compost samples collected from different regions of India. Fifteen fungal cultures were selected qualitatively for the production of xylanase and cellulases and were identified employing ITS, NS and MNS primers. The enzyme cocktail consisting of 3811 IU g(-1) of xylanase and 9.9 IU g(-1) of cellulase from Trichoderma longibrachiatum MDU-6 was selected quantitatively for the deinking of diverse paper wastes. The enzyme production increased two fold when produced at tray level in comparison with flasks. The enzyme cocktail was effective in the deinking of old newspaper samples with significant removal of chromophores, phenolics and hydrophobic compounds and less sugar loss. While in case of examination papers and laser printed papers, ink removal was not very significant. Moreover, the sugar loss was significantly high in case of examination papers. The deinking results were further confirmed with FTIR analysis. Deinked newspaper pulp sample shows brightness of 52%, which was 9.6% high than its control sample. The ERIC value for deinked newspaper pulp was found to be 655.9 ppm. Thereafter, the deinked newspaper pulp was examined under light microscope after differential staining with safranin and malachite green and also examined under scanning and transmission electron microscope, which revealed fibrillation and perforation.

The Control of Microbiological Problems∗∗Some excerpts taken from Bajpai P (2012). Biotechnology for Pulp and Paper Processing with kind permission from Springer Science1Business Media

Methods used to control microbiological problems are discussed. Good housekeeping and regular inspection of all areas, effective boilouts, and regularly scheduled washups reduce slime development. Conventional slime control methods generally employ combinations of biocides. Alternative control measures use enzymes, biodispersants, bacteriophages, competing organisms, and biological complex formers. Using enzymes for slime control is expected to bring important benefits to the pulp and paper industry. Enzymes represent a clean and sustainable technology: they are nontoxic, readily biodegradable, and are produced using renewable raw materials. Use of enzymes in combination with biodispersants appears to be a promising method for slime control.

Effect of commercial cellulases and refining on kraft pulp properties: correlations between treatment impacts and enzymatic activity components

The importance of enzymes as biotechnological catalysts for paper industry is now recognized. In this study, five cellulase formulations were used for fibre modification. The number of PFI revolutions decreased by about 50% while achieving the same freeness value (decrease in CSF by 200 mL) with the enzymatic pretreatment. The physical properties of handsheets were modified after enzymatic pretreatment followed by PFI refining. A slight decrease in tear strength was observed with enzymes C1 and C4 at pH 7 while the most decrease in tear was observed after C2, C3, C5 treatments. C1 and C4 which had xylanase activity improved paper properties, while other enzymes had a negative impact. Therefore, the intricate balance between cellulolytic and hemicellulolytic activity is the key to optimizing biorefining and paper properties. It was also observed that C1 impact was pH dependent, which supports the importance of pH in developing an enzymatic strategy for refining energy reduction.

Aging biofilm from a full-scale moving bed biofilm reactor: characterization and enzymatic treatment study

Effective removal of aging biofilm deserves to receive more attention. This study aimed to characterized aging biofilm from a full-scale moving bed biofilm reactor treating pharmaceutical wastewater and evaluate the hydrolysis effects of biofilm by different enzymatic treatments. Results from FTIR and biochemical composition analyses showed that it was a predominately organic-based biofilm with the ratio of total protein (PN) to polysaccharide (PS) of 20.17. A reticular structure of extracellular polymeric matrix (EPM) with filamentous bacteria as the skeleton was observed on the basal layer through SEM-EDS test. Among the four commercial proteases and amylases from Genencor®, proteases were shown to have better performances than amylases either on the removal of MLSS and PN/MLSS or on DOC (i.e., dissolved organic carbon)/MLSS raising of biofilm pellets. Difference of dynamic fluorescence characteristics of dissolved organic matters after treated by the two proteases indicated distinguishing mechanisms of the treating process.

Microbial degradation characteristics and kinetics of novel pyrimidynyloxybenzoic herbicide ZJ0273 by a newly isolated Bacillus sp. CY

ZJ0273 (propyl 4-(2-(4,6-demethoxy pyrimidin-2-yloxy)benzylamino)benzoate) is a novel herbicide developed in China for oilseed crop. Sixteen bacteria capable of utilizing ZJ0273 as the sole carbon source were isolated from soils. One of the isolates was designated as Bacillus sp. CY based on its physiological and biochemical characteristics and phylogenetic analysis of 16S rDNA sequences. The present study aimed to investigate the ZJ0273 degradation characteristics and kinetics by Bacillus sp. CY which has the ability to utilize ZJ0273 as the sole source of carbon and energy under aerobic conditions. The optimum biodegradation temperature, pH, and ZJ0273 initial concentration were 20-40 °C, 5.0-9.0, and 50-400 mg/l, respectively. Strain CY degraded 65 % of ZJ0273 (initial concentration of 50 mg/l) during 30 days of incubation in basal mineral medium at pH 8.0 and 35 °C. DT50 (half-life value), k (degradation rate constant of ZJ0273), and R (2) are 19.20 days, 0.0361 day(-1), and 0.9464, respectively.

Analysis of monosaccharides and oligosaccharides in the pulp and paper industry by use of capillary zone electrophoresis: a review

Carbohydrate analysis is an important source of the information required for understanding and control of pulp and paper processes. The behavior of cellulose and hemicelluloses in the process, carbohydrate-lignin interactions, and the enzymatic treatment of fibers are examples of situations for which reliable, fast, qualitative, and quantitative methods are required. New uses of lignocellulosic material have further increased the need for carbohydrate analysis. This review collates and summarizes the most important findings and approaches in the analysis of wood-based carbohydrates by use of capillary zone electrophoresis and provides an analysis of the effect of different conditions on the separation, showing the advantages and limitations of the methods used. It provides guidelines for achieving higher quality and improved separation efficiency in carbohydrate analysis.