David Ibarra

Lignin-Derived Compounds as Efficient Laccase Mediators for Decolorization of Different Types of Recalcitrant Dyes

ABSTRACT Ten phenols were selected as natural laccase mediators after screening 44 different compounds with a recalcitrant dye (Reactive Black 5) as a substrate. Their performances were evaluated at different mediator/dye ratios and incubation times (up to 6 h) by the use of Pycnoporus cinnabarinus and Trametes villosa laccases and were compared with those of eight known synthetic mediators (including -NOH- compounds). Among the six types of dyes assayed, only Reactive Blue 38 (phthalocyanine) was resistant to laccase-mediator treatment under the conditions used. Acid Blue 74 (indigoid dye), Reactive Blue 19 (anthraquinoid dye), and Aniline Blue (triarylmethane-type dye) were partially decolorized by the laccases alone, although decolorization was much more efficient and rapid with mediators, whereas Reactive Black 5 (diazo dye) and Azure B (heterocyclic dye) could be decolorized only in the presence of mediators. The efficiency of each natural mediator depended on the type of dye to be treated but, with the only exception being Azure B (<50% decolorization), nearly complete decolorization (80 to 100%) was attained in all cases. Similar rates were attained with the best synthetic mediators, but the reactions were significantly slower. Phenolic aldehydes, ketones, acids, and esters related to the three lignin units were among the best mediators, including p-coumaric acid, vanillin, acetovanillone, methyl vanillate, and above all, syringaldehyde and acetosyringone. The last two compounds are especially promising as ecofriendly (and potentially cheap) mediators for industrial applications since they provided the highest decolorization rates in only 5 to 30 min, depending on the type of dye to be treated.

Structural modification of eucalypt pulp lignin in a totally chlorine-free bleaching sequence including a laccase-mediator stage

Abstract Structural modification of eucalypt pulp lignin was investigated in a totally chlorine-free (TCF) bleaching sequence including a laccase-mediator stage. This stage was applied after two oxygen delignification stages, and was followed by an alkaline peroxide stage. After two oxygen delignification stages, two more stages with a laccase mediator and alkaline peroxide were applied. The residual lignins were enzymatically isolated from the different pulps and analyzed by spectroscopic techniques and analytical pyrolysis. The latter revealed high amounts of syringyl units (>70%) in the lignins. 13C-1H heteronuclear single quantum correlation (HSQC) NMR indicated high amounts of β-O-4′ inter-unit linkages (>75% side-chains). Changes in lignin composition and inter-unit linkages were demonstrated in the course of the bleaching sequence. Moreover, oxidative modification of the major syringyl units was shown by C2,6-H2,6 HSQC correlations and by the presence of oxidized pyrolysis markers in pyrograms. The existence of both Cα keto and carboxyl groups in the residual lignin, together with normal (Cα-hydroxylated) units, was revealed by heteronuclear multiple bond correlation (HMBC) between aromatic H2,6 and side-chain carbons. These Cα-oxidized structures represent nearly 60% of total units in the lignin isolated from the enzymatically treated pulp. Analysis of residual lignin after the final peroxide stage compared with a simple alkaline treatment revealed that most of the oxidatively altered lignin was removed by the alkali used in the peroxide stage. Thus, the kappa number decreased and the final residual lignin was more structurally related to that found before the oxidative stages, although it contained less resinols and more carboxyl group-bearing units. However, the action of peroxide is necessary to attain the high brightness required (>90% ISO).

Main lipophilic extractives in different paper pulp types can be removed using the laccase–mediator system

Lipophilic extractives in wood and other lignocellulosic materials exert a negative impact in pulp and paper manufacturing causing the so-called pitch problems. In this work, the appropriateness of an enzymatic treatment using the laccase–mediator system for pitch biocontrol is evaluated. With this purpose, three pulp types representative for different raw materials and pulping processes—eucalypt kraft pulping, spruce thermomechanical pulping, and flax soda-anthraquinone pulping—were treated with a high-redox-potential laccase from the basidiomycete Pycnoporus cinnabarinus in the presence of 1-hydroxybenzotriazole as a redox mediator. The gas chromatography and gas chromatography/mass spectrometry analyses of the lipophilic extractives from the enzymatically treated pulps revealed that the laccase–mediator treatment completely or greatly removed most of the pitch-causing lipophilic compounds present in the different pulps including: (1) free and conjugated sitosterol in eucalypt paper pulp; (2) resin acids, sterol esters, and triglycerides in spruce pulp; and (3) sterols and fatty alcohols in the flax pulp. Different amounts of free and conjugated 7-oxosterols were found as intermediate products in the oxidation of pulp sterols. Therefore, the laccase–mediator treatment is reported as an efficient method for removing pitch-causing lipophilic compounds from paper pulps obtained from hardwood, softwood, and nonwoody plants.

Enzymatic deinking of secondary fibers: cellulases/hemicellulases versus laccase-mediator system.

The use of enzymes has been suggested as an environmentally friendly alternative to complement conventional chemical deinking in the recycling of recovered paper. This study compares the use of cellulases/hemicellulases versus the laccase-mediator system for deinking printed fibers from newspapers and magazines. For this purpose, two commercial enzyme preparations with endoglucanase and endoxylanase activities (Viscozyme Wheat from Aspergillus oryzae and Ultraflo L from Humicola insolens, Novozymes) and a commercial laccase (NS51002 from Trametes villosa, Novozymes), the latter in the presence of synthetic or natural (lignin-related) mediators, were evaluated. The enzymatic treatments were studied at the laboratory scale using a standard chemical deinking sequence consisting of a pulping stage; an alkaline stage using NaOH, sodium silicate and fatty acid soap; and a bleaching stage using hydrogen peroxide. The handsheets were then prepared and their brightness, residual ink concentration, and strength properties were measured. Among the different enzymatic treatments assayed, both carbohydrate hydrolases were found to deink the secondary fibers more efficiently. Brightness increased up to 3–4% ISO on newspaper fibers, being Ultraflo 20% more efficient in the ink removal. Up to 2.5% ISO brightness increase was obtained when magazine fibers were used, being Viscozyme 9% more efficient in the ink removal. Regarding the laccase-mediator system, alone or in combination with carbohydrate hydrolases, it was ineffective in deinking both newspaper and magazine fibers, resulting in pulps with worse brightness and residual ink concentration values. However, pulp deinking by the laccase-mediator system was displayed when secondary fibers from printed cardboard were used, obtaining up to 3% ISO brightness increase and lower residual ink concentrations.

Exploring enzymatic treatments for the production of dissolving grade pulp from different wood and non-wood paper grade pulps 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract The feasibility of producing dissolving grade pulps for viscose production from different fiber raw materials, such as paper grade pulps from wood and non-woody plants, was investigated. Commercial dried bleached hardwood kraft pulps from eucalypt, and bleached non-wood soda/AQ pulps from flax, hemp, sisal, abaca, and jute, were subjected to enzymatic and chemical pre-treatments in order to improve the accessibility and reactivity of cellulose and to reduce their hemicellulose content. A commercial monocomponent endoglucanase and a commercial xylanase were employed for biochemical treatment. The chemical treatment consisted of cold alkaline extraction. The effects of these pre-treatments on pulps were studied by reactivity, according to Focks method, and viscosity measurements, determination of hemicellulose content, and recording of molecular weight distributions. The results were compared to those of commercial bleached eucalypt dissolving pulp. Eucalypt and sisal pulps showed high improvement in reactivity, reaching levels near or even higher than that of the eucalypt dissolving pulp (65%–70%), and a low hemicellulose content (2%–4%), when both were submitted to a sequence of treatments consisting of an initial xylanase treatment followed by cold alkaline extraction, and a final endoglucanase treatment. However, the viscosity decreased considerably. A uniform and narrow molecular weight distribution was observed in both eucalypt and sisal pulps after this sequential pre-treatment.

Evaluating Lignin-Rich Residues from Biochemical Ethanol Production of Wheat Straw and Olive Tree Pruning by FTIR and 2D-NMR

Lignin-rich residues from the cellulose-based industry are traditionally incinerated for internal energy use. The future biorefineries that convert cellulosic biomass into biofuels will generate more lignin than necessary for internal energy use, and therefore value-added products from lignin could be produced. In this context, a good understanding of lignin is necessary prior to its valorization. The present study focused on the characterization of lignin-rich residues from biochemical ethanol production, including steam explosion, saccharification, and fermentation, of wheat straw and olive tree pruning. In addition to the composition and purity, the lignin structures (S/G ratio, interunit linkages) were investigated by spectroscopy techniques such as FTIR and 2D-NMR. Together with the high lignin content, both residues contained significant amounts of carbohydrates, mainly glucose and protein. Wheat straw lignin showed a very low S/G ratio associated with p-hydroxycinnamates (p-coumarate and ferulate), whereas a strong predominance of S over G units was observed for olive tree pruning lignin. The main interunit linkages present in both lignins were β-O- ethers followed by resinols and phenylcoumarans. These structural characteristics determine the use of these lignins in respect to their valorization.

Microscopy studies reveal delignification and sterol removal from eucalypt kraft pulps by laccase–HBT

Fungal laccases in the presence of mediators are powerful biocatalysts to degrade lignin. Pycnoporus cinnabarinus laccase and 1-hydroxybenzotriazole (HBT) have been successfully used to delignify eucalypt kraft pulp once integrated in a totally chlorine-free bleaching sequence. Real time delignification of kraft pulp by laccase–HBT was verified in situ by monitoring the loss of lignin autofluorescence during the enzymatic treatment using confocal laser scanning microscopy. The highest delignification of pulp fibers occurred over a very short time-span (5 min). Moreover, we demonstrate the removal of sterols, responsible for pitch deposits in hardwood kraft pulps, as an additional effect of laccase-HBT. Spherical structures between pulp fibers localized by low temperature scanning electron microscopy were removed by laccase–HBT. The use of filipin, a specific stain, revealed the sterol nature of many of these structures. At the end of the enzyme-aided bleaching sequence, the fluorescent sterols–filipin signals were almost completely absent.

Relating the near field noise of passenger cars with the driving behavior

Road traffic noise amounts to roughly half of the overall ambient noise. Usual emission (vehicle emission limits) and immission (barriers, sound-reducing windows) noise control techniques have not been enough to decrease significantly the annoyance by road traffic over the last three decades. The positive effect of these control techniques has been counteracted by the increase of traffic density. Moreover, the traffic noise annoyance is highly correlated with the maximum noise levels usually produced by aggressive drivers. However, current traffic noise measurement systems are based upon an overall assessment, so that they are unable to discriminate between quiet and noisy drivers. Therefore, a near field noise measuring system is proposed in this paper that is able to measure the contribution of each vehicle to the road traffic noise, allowing the detection of noisy drivers. The system is based on two onboard microphones, one for the engine noise and other for the rolling noise. Experimental results are provided that demonstrate the performance of the proposed system on five drivers, along suburban and urban courses of a large city, with petrol and diesel vehicles. The analysis of concurrent acoustical and driving condition data reveals that the system is capable of discriminating clearly those vehicles generating the maximum noise levels

Relationship between the noise radiated by a vehicle to the near and the far fields

Driving style can have a significant contribution to the noise radiated by individual vehicles. It has been reported that noisy drivers can radiate maximum noise levels which exceed the noise level of the mean traffic stream by 10 dB. Since regulations in most countries are based on averaged overall levels, it is rather difficult to discriminate and control the contribution of noisy drivers to the road traffic noise. In previous studies, an on-board measurement system was developed to evaluate engine and rolling noise levels in the vehicle near field. This system proved to be able to discriminate the noisiest vehicles in different environments and for different driving behaviors. We demonstrated that vehicles with aggressive drivers radiate to the near field noise levels 5-9 dB higher than the average of vehicles with normal drivers. However, most noise regulations are based on noise levels measured in the far field. Thus, we propose here a complete procedure for the extrapolation of the near field noise levels to the far field with a combination of analytical predictions and experimental measurements. Near and far field noise levels were concurrently measured on several trials including vehicle pass-by runs at constant velocities, and under aggressive acceleration and deceleration. An excellent agreement is obtained between the noise levels measured in the far field and these extrapolated from the near field.

Extrapolation of Maximum Noise Levels From Near-Field Measurements to Far-Field Positions

The goal of this work is to propose a new strategy for the attenuation of the traffic noise, which constitutes one of the main sources of acoustic pollution in urban and suburban areas. This strategy is based on the measurement of the noise radiated by each individual vehicle using an electro-acoustic system, composed of two microphones for the acquisition of the engine and of the rolling noise. These microphones have been situated inside the engine hood and close to the right back tire respectively. The signals have been recorded for diesel and petrol engines and through typical urban and suburban courses with different persons. Using this procedure, we aim to characterise the drivers responsible of the highest noise levels producing maximum annoyance. The near-field measurements have been then extrapolated to far field positions using an analytical filter that takes into account absorbing properties of the propagation floor. For the internal signal it has been necessary to characterise the acoustic properties of the engine hood experimentally using an array of microphones surrounding the vehicle. The propagated noise is calculated considering the absorption due to the geometrical divergence, the absorption by the air, and the effect of the propagating surface. The signals extrapolated to the receiver position could be compared with the current normative to propose recommendations concerning noise control actions.Copyright