Raquel O. Cristóvão

Application of statistical experimental methodology to optimize reactive dye decolourization by commercial laccase.

Three-level Box-Behnken factorial design with three factors (pH, temperature and enzyme concentration) combined with response surface methodology (RSM) was applied to optimize the dye degradation of reactive red 239 (RR239), reactive yellow 15 (RY15) and reactive blue 114 (RB114) dyes by commercial laccase. Mathematical models were developed for each dye showing the effect of each factor and their interactions on colour removal. The model predicted for RY15 that a decolourization above 90% (after 24h) could be obtained when the enzyme concentration, temperature and pH were set at 109.8U/L, 39.2 degrees C and 6.6, respectively; whilst for RB114 and RR239 the temperature and enzyme concentration did not affect the decolourization (>90%) in the considered range and optimum pH value was found at 5.5-7.0 and 7.0-7.5, respectively. These predicted values were also experimentally validated. Average final values of responses were in good agreement with calculated values, thus confirming the reliability of the models of RY15, RB114 and RR239 decolourization.

Modeling the discoloration of a mixture of reactive textile dyes by commercial laccase.

Degradation of a mixture of three reactive textile dyes (Reactive Black 5, Reactive Yellow 15 and Reactive Red 239), simulating a real textile effluent, by commercial laccase, was investigated in a batch reactor. The discoloration was appraised as a percentage of the absorbance reduction at the wavelength of maximum absorbance for each dye and as total color removal based in all visible spectrum. A significantly high discoloration was achieved in both cases, indicating the applicability of this method for textile wastewater treatment. Mathematical models were developed to simulate the kinetics of laccase catalyzed degradation of reactive dyes in mixtures. Like in single dye degradation, some of the reactions present an unusual kinetic behavior, corresponding to the activation of the laccase-mediator system. The kinetic constants of the models were estimated by minimizing the difference between the predicted and the experimental time courses. Although not perfect, the ability of the models in representing the experimental results suggests that they could be used in design and simulation applications.

Treatment and kinetic modelling of a simulated dye house effluent by enzymatic catalysis

Biocatalytic treatment of a synthetic dye house effluent, simulating a textile wastewater containing various reactive dyestuffs (Reactive Yellow 15, Reactive Red 239 and Reactive Black 5) and auxiliary chemicals, was investigated in a batch reactor using a commercial laccase. A high decolourisation (above 86%) was achieved at the maximum wavelength of Reactive Black 5. The decolourisation at the other dyes wavelengths (above 63% for RY15 and around 41% for RR239) and the total decolourisation based on all the visible spectrum (around 55%) were not so good, being somewhat lower than in the case of a mixture of the dyes (above 89% for RB5, 77% for RY15, 68% for RR239 and above 84% for total decolourisation). Even so, these results suggest the applicability of this method to treat textile dyeing wastewaters. Kinetic models were developed to simulate the synthetic effluent decolourisation by commercial laccase. The kinetic constants of the models were estimated by minimizing the difference between the predicted and the experimental time courses. The close correlation between the experimental data and the simulated values seems to demonstrate that the models are able to describe with remarkable accuracy the simulated effluent degradation. Water quality parameters such as TOC, COD, BOD(5) and toxicity were found to be under the maximum permissible discharge limits for textile industries wastewaters.

OPTIMISATION OF REACTIVE DYE DEGRADATION BY LACCASE USING BOX–BEHNKEN DESIGN

Abstract A three‐level Box–Behnken factorial design with three factors and the Response Surface Methodology were used to optimise the colour removal of the reactive textile dye, Colour Index (C.I.) reactive red 180, by commercial laccase. A mathematical model was developed to study the effect of temperature, pH, enzyme concentration and their interactions on the decolourisation. Enzyme concentration and pH as well as their interaction were the principal factors that affected the decolourisation. The dye degradation was independent of temperature. The model estimated that the highest decolourisation (> 92%) was obtained for 27°C, pH 7.5 and 85 U l−1. This predicted value was experimentally validated, obtaining dye colour removal (540 nm) of 93 ± 1.5%.

Ionic Liquids: Alternative Reactive Media for Oxidative Enzymes

During the last decades, biotechnology has attracted a great interest from academic and industrial environments due to the progress made in the discovery of new and efficient biocatalysts for many different applications. Due to the increasing variety of these applications, the aqueous medium became limiting. Biocatalysis in nonaqueous media offers unique capabilities and thus plays a major role in biotransformation technologies. It is well known that when enzymes are introduced in a non-aqueous medium, a number of factors can alter their native structure (critically at the active centre of the protein) and so alter their biological functions, thus causing reversible or irreversible inactivation of the enzymes. In order to overcome these problems, a high number of papers related to biocatalysis in organic solvents are published every year, in several areas of knowledge, investigating the effects of different organic media in enzyme activity, stability, structure and kinetics. It is important to highlight that good results have been reported for several enzymes, involving many different reaction types and a wide variety of organic solvents (Carrea & Riva, 2000). As in aqueous enzymatic reactions, the enzymology in non-aqueous media also presents specific and unique advantages like: reaction enantioselectivity, resistance to contamination by microorganisms, enhanced thermo-stability of the enzyme. Additionally, the solubility of hydrophobic substrates and/or products can be increased with the right selection of the solvent. The latter decreases diffusional barriers for the reactions, thus improving their yields. The study of enzymatic reactions in non-aqueous media started more than 100 years ago (Halling & Kvittingen, 1999), but did not receive attention until the 1970s with the pioneering works of Berezin and co-workers (Klyosov et al., 1975; Klibanov et al., 1977; Martinek et al., 1981) and today either water and organic solvents are conventional media for enzymes. Klyosov et al. (1975) studied the hydrolysis of p-nitrophenyl esters by means of α-chymotrypsin and related proteins in four different organic solvents (dimethylsulfoxide, dimethylformamide, formamide, and N-methylacetamide). The work of Klibanov et al. (1977) was based on enzymatic reactions in a “water–water-immiscible organic solvent” biphasic system with bovine chymotrypsin using chloroform, benzene, ether, acetone, ethanol, dimethylsulfoxide and dioxane as organic solvents. On the other hand, Martinek et al. (1981) investigated the behaviour of α-chymotrypsin, trypsin, pyrophosphatase,

Strategies to reduce mass and photons transfer limitations in heterogeneous photocatalytic processes: Hexavalent chromium reduction studies

The current work presents different approaches to overcome mass and photon transfer limitations in heterogeneous photocatalytic processes applied to the reduction of hexavalent chromium to its trivalent form in the presence of a sacrificial agent. Two reactor designs were tested, a monolithic tubular photoreactor (MTP) and a micro-meso-structured photoreactor (NETmix), both presenting a high catalyst surface area per reaction liquid volume. In order to reduce photon transfer limitations, the tubular photoreactor was packed with transparent cellulose acetate monolithic structures (CAM) coated with the catalyst by a dip-coating method. For the NETmix reactor, a thin film of photocatalyst was uniformly deposited on the front glass slab (GS) or on the network of channels and chambers imprinted in the back stainless steel slab (SSS) using a spray system. The reaction rate for the NETmix photoreactor was evaluated for two illumination sources, solar light or UVA-LEDs, using the NETmix with the front glass slab or/and back stainless steel slab coated with TiO2-P25. The reusability of the photocatalytic films on the NETmix walls was also evaluated for three consecutive cycles using fresh Cr(VI) solutions. The catalyst reactivity in combination with the NETmix-SSS photoreactor is almost 70 times superior to one obtained with the MTP.

Pollution prevention and wastewater treatment in fish canning industries of Northern Portugal

High concentrations of particulate matter (PM) in the atmosphere have been associated with degradation of human health. Auckland is the most populous city in New Zealand, with a humid subtropical climate (characterised by hot and humid summers and mild winters) and is one of the most remote cities in the world. Analysis of the weather conditions and PM10 concentrations in Auckland can provide an understanding of how weather conditions impact PM10 concentrations in isolated systems. This study looks at the impacts of Temperature and Relative Humidity (RH) on localised PM10 concentrations in an urban area of Auckland over the winter period. This study has shown that the ratios of PM1:PM10 and PM2.5:PM10 were 64% and 87% over the study period. Temperature was observed to have a negative correlation with PM10 over a diurnal timescale. RH generally showed a positive correlation with PM10 up to a threshold value of 75% RH, beyond which the correlation ceased. RH affects the natural deposition process of PM, whereby moisture particles adhere to PM, accumulating atmospheric PM concentration. With increasing humidity, moisture particles eventually grow in size to a point where ‘dry deposition’ occurs, reducing PM10 concentrations in the atmosphere. There were a number of occasions where PM10 remained low even while RH increased and further investigation showed these events coincided with periods of rainfall.Soybean milk is a kind of highly perishable Asian traditional soy product, and this study was envisaged to extend its shelf-life through the application of hurdle technology. Twelve strains of bacteria were isolated from samples of spoilage soybean milk and were identified as Klebsiella oxytoca (S 5,S 7,S 8), Serratia marcescens (S 9, S 10,S 14, S 15, S 17), Klebsiella ozena (S 16, S 18), and Serratia plymuthica (S 21, S 25, S 28). To control these spoilage microorganisms, eight commonly used food preservatives were tested by Oxford Cup inhibition method. Results showed that sodium dehydroacetate, nipagin complex esters and nisin significantly inhibited the growth of the isolated strains with their MIC (minimum inhibition concentration) values ranging from 0.004% to 0.05%. Levels of heat treatment duration, together with concentrations of sodium dehydroacetate, nipagin complex esters, and nisin were employed as hurdle factors. The optimum conditions for improvement of the sshelf-life were gained from orthogonal tests as follows: heat treatment at 100°C for 10 minutes, and nisin 0.004%, nipagin complex esters 0.008%, dehydroacetate 0.002%. The fresh soybean milk applied with the optimum formula could be maintained under upper limit of the microbial count (100 CFU/mL, DB44/425-2007 China) for more than 6 days at 25°C, and 11 days at 4°C. Here in our study, hurdle technology approach significantly improved the shelf-life of soybean milk.The main environmental problems of fish canning industries are high water consumption and high organic matter, oil and grease and salt content in their wastewaters. This work aims to analyze the situation (water consumption, wastewater production, wastewater characterization, etc.) of different plants located north of Douro river, in Portugal, in order to propose various solutions to their problems. Thus, initially it was made an identification and implementation of prevent and control pollution measures within the industrial units in order to reduce water consumption, minimize the wastewater production and reduce the pollutant load to treat. Then, the evaluation of wastewater treatability was started through a sedimentation and coagulation-flocculation process, with two organic coagulants (RIPOL 070 and RIFLOC 1815), commonly used in wastewater treatment. Sedimentation experiments showed that the flotation of 54% of oils and greases occurred, and 36% of total suspended solids were removed. The coagulation-flocculation process gave good results, especially in terms of oil and grease and total suspended solids removal. The best suspended solids removal efficiencies were 53% and 79%, using 400 mg/L of RIPOL 070 and 150 mg/L of RIFLOC 1815, respectively. At these dosages, both coagulants demonstrated excellent oil and grease removals, about 99% for RIFLOC 1815 and 88% for RIPOL 070.Liana Dalcantara Ongouya Mouekouba, Zhen-Zhu Zhang, Erinle Kehinde Olajide, Ai-Jie Wang, and Ao-Xue Wang