• Energy Research

Three Kraft lignins isolated from black liquors of several paper pulp mills of the North of Spain and Portugal were structurally characterized by using monodimensional (1H and 13C) and bidimensional Nuclear Magnetic Resonance (NMR) spectrometry. From the latter, 13C–1H heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) were employed. Lignins from black liquors are usually burned for power generation. Nevertheless, they could become high value added products within a biorefinery context. In that case, a good understanding of their structure is a prior step to transform them. From all the NMR techniques studied, HSQC has risen as the most powerful tool in lignin characterization. Kraft cooking conditions and the type of wood seem to be the main factors that determine the differences observed in the lignins. All the samples have shown an important decrease in the number of β–O–4′ linkages, due to the Kraft process, and resinol has become the most resistant linkage to the process. Moreover, all samples seem to be mainly linked to a one polysaccharide: xylan. Several parameters like S/G ratio, portion of phenolic and aliphatic hydroxyls, amount of aromatic protons and other structural aspects were also estimated.

Laccase is a promising biocatalyst with many possible applications, including bioremediation, chemical synthesis, biobleaching of paper pulp, biosensing, textile finishing and wine stabilization. The immobilization of enzymes offers several improvements for enzyme applications because the storage and operational stabilities are frequently enhanced. Moreover, the reusability of immobilized enzymes represents a great advantage compared with free enzymes. In this work, we discuss the different methodologies of enzyme immobilization that have been reported for laccases, such as adsorption, entrapment, encapsulation, covalent binding and self-immobilization. The applications of laccase immobilized by the aforementioned methodologies are presented, paying special attention to recent approaches regarding environmental applications and electrobiochemistry.

An expanding number of human activities are contributing to the rising levels of aromatic compounds, which pose a major threat to the ecosystem. However, readily available microbial enzymes might be used to remediate contaminated wastewater in an economical and environmentally benign manner. In this study, an efficient method of laccase-oriented immobilization on modified Immobead 150P was proposed. The oriented immobilization technique using aminated laccase exceeds in both protein loading onto the carrier (4.26 mg/g) and immobilization yield (93.57%) due to the availability of more active sites. The oriented aminated laccase preserves 100% and 95% of its original activity after six and ten cycles of operation, respectively. The thermal stability performance of the oriented enzyme was the best among both free and random immobilized forms, since it was able to conserve 79% and 44% of its initial activity after 6 h at 50 °C and 60 °C, respectively. The ideal pH of oriented immobilized laccase was altered from 3.0 to 4.0, and it was more stable than both free and random immobilized laccases at pH 7.0. Finally, the integration of the adsorption capacity of Immobead 150P and the biodegradation ability of laccase promises the efficient removal of aqueous phenolics. Oriented immobilized laccase may provide a significant new approach for wastewater treatment, according to these findings.

The great amount of pollutants released from kraft pulp processes, mainly from cooking and bleaching stages, is one of the most relevant environmental problems in this type of industry. New bleaching sequences are being studied based on the use of oxidative enzymes from fungal cultures. In this study, the bleaching systems consisting of Laccase and different mediators such as 1-hydroxybenzotriazole, violuric acid, syringaldehyde and methyl syringate in the bleaching sequence of Eucalyptus globulus kraft pulp were applied. The main objective of this study is to evaluate the aerobic and anaerobic biodegradability and toxicity to Vibrium fischeri of generated L-stage and total bleaching sequence effluents. The highest levels of aerobic and anaerobic degradation of the generated effluents were achieved for treatments with laccase plus violuric acid, with 80% of aerobic degradation and 68% of anaerobic biodegradation. V. fischeri toxicity was remarkably reduced for all the effluents after aerobic degradation.