M. T. Pessoa de Amorim

Use of laccase together with redox mediators to decolourize Remazol Brilliant Blue R

A pure fungal laccase, obtained from a commercial formulation used in the textile industry, did not decolourize Remazol Brilliant Blue R (RBBR). Decolourization was only observed when a small molecular weight redox mediator was added together with the laccase. Under the conditions specified, violuric acid (5.7 mM) was the most effective mediator studied and almost complete decolourization was observed within 20 min. In contrast, 1-hydroxybenzotriazole (HOBT, 11 mM) decolourized RBBR at about a two-fold slower rate and to a lesser extent. Also, higher concentrations of HOBT were inhibitory which could be due to inactivation of laccase by the toxic HOBT radical. The commercial laccase formulation that contained phenothiazine-10-propionic acid as the mediator was least effective, giving 30% decolourization under equivalent conditions. We suggest that similar laccase plus mediator systems could be used for the detoxification of related anthraquinone textile dyes.

Decolorization of an anthraquinone-type dye using a laccase formulation

Decolorization of the dye Remazol Brilliant Blue R (RBBR) was studied, as it is representative of an important class of recalcitrant anthraquinone-type dyes. For this purpose a commercial laccase formulation (CLF) containing laccase, a redox mediator and a non-ionic surfactant was used. Small molecular weight components were removed from the CLF by gel filtration, which made it possible to compare the effect of its laccase alone. Apart from slightly better thermostability of the CLF as compared with the laccase alone, the pH and temperature profiles were similar regardless of the presence of the small molecular weight components. The laccase alone did not decolorize RBBR. A small molecular weight redox mediator (HBT) was necessary for decolorization to occur. A comparison of the kinetics of RBBR decolorization using the CLF and its laccase alone is reported. Provided that a redox mediator is included, it is suggested that laccase may be suitable for the wastewater treatment of similar anthraquinone dyes.

Specificity of phenolic disazo dyes in relation to transformation by laccase

Four novel disazo dyes were synthesized and characterized using FTIR and NMR spectroscopy. These water-soluble dyes had a hydroxyl group in the para position of the phenolic ring in relation to the azo bond, whereas the other substituents on the phenolic ring and/or between the two azo bonds varied. The transformation of the dyes was studied using purified fungal laccase. The rank order in which the dyes were transformed was IV > III ≫ I. Dye II was not a laccase substrate. As both dye I and II had a carboxylic substituent on the phenolic ring but the ring structures between the two azo linkages were different, we suggest that the latter also influenced laccase catalysis. Both of the redox mediators tested, violuric acid and N-hydroxybenzotriazole, enhanced the laccase reaction with violuric acid, being generally more effective. The results show that the chemical structure of both the phenolic ring as well as the ring distal to the phenolic moiety affect the reaction kinetics.

Cotton Dyeing with Extract from Renewable Agro Industrial Bio-resources: A Step Towards Sustainability

The massive consumption of synthetic dyes and subsequent discharge into the aquatic ecosystem is a major environmental issue. Consumer’s demand for natural textile products is driving research and development efforts to partially replace synthetic dye products for those based in renewable materials. In the growing concerns for environmental and human health issues, natural dyes are now being seen as promoters of “green chemistry” in textile dyeing, due to its non-toxic and biocompatibility properties. Colour-fastness of natural dyes may not always fulfil the usual standard requirements, but it can be improved by an inorganic or organic mordant. However, as defended by several authors, high standards on colour-fastness may not to be a top priority, mainly for environmentally aware consumers. The aim of this work was to obtain natural dyeing extracts for cellulosic fibres from Olea europaea pruning wastes, a native species from the Mediterranean basin, and from Acacia dealbata tree, a species native to south-eastern Australia introduced in Europe as ornamental, that become invasive in Mediterranean-climate regions. Dyeing conditions were studied in terms of pH, electrolyte and mordants. Colours of dyed cotton samples were measured for CIELab and LCh colour space values; colour-fastness of dyed samples was assessed by wet rubbing and washing tests according to ISO standards.

Application of modified membranes in drinking water treatment

This paper presents filtration results obtained with commercial acetate membrane with a pore diameter of 0.45 μm, unmodified and modified with TiO2, bearing in mind drinking water treatment. The experimental filtration set-up that was used consisted in the gravitational filtration system, whereas the accomplished tests that were endured consisted of hydraulic permeability of the modified and unmodified membranes, treatment of polluted water with E. coli bacterium, color removal, turbidity and free chlorine. The results of hydraulic permeability showed similar flux for all membranes at the end of the experiments, between 25 and 30 kg·m· h. The retention results for color, turbidity and E.coli bacteria are comparable.

Coagulation/flocculation/flotation/nanofiltration processes using Moringa Oleifera as coagulant of Eutrophized river

This study investigated the efficiency of Moringa oleifera (MO) seeds as natural coagulant in coagulation/flocculation/dissolved air flotation (C/F/DAF), followed by nanofiltration (NF) for Microcystis protocystis and microcystin-LR removal. The methodology adopted in this work was performed in two steps: 1) coagulation/flocculation/dissolved air flotation (C/F/DAF) process using the MO extracted in saline solution of potassium chloride (KCl-1M) and sodium chloride (NaCl-1M) in optimum dosage 50 mg·L -1 ; 2) nanofiltration process using NF90 and NF270 membrane provided Dow Chemical Company®. A working pressure of 8 bar was applied. In all samples were analyzed color, turbidity, pH, cyanobacterial cells count and microcystin concentration. The use of MO seeds as natural coagulant, obtained satisfactory results in the M. protocystis, color and turbidity removal. NF was able to completely remove cyanobacterial cells and microcystins (100 %) from M. protocystis (always under the quantification limit). Therefore, C/F/DAF+NF sequence is a safe barrier against M. protocystis and microcystins in drinking water.

Recovery of Polyvinyl Alcohol from Textile Wastewaters: A Case Study

The reduction of pollution, the energy crisis and the shortage of water are the incentives for the recovery of chemicals, recycling and reuse of water. The application of ultrafiltration technology in the recovery of polyvinyl alcohol size materials has been studied. Several grades of polyvinyl alcohol were tested and recoverability was determined.