Eduardo Bessa Azevedo

Microwave-enhanced UV/H2O2 degradation of an azo dye (tartrazine): optimization, colour removal, mineralization and ecotoxicity

This study optimizes two factors, pH and initial [H2O2], in the ultraviolet (UV)/H2O2/microwave (MW) process through experimental design and assesses the effect of MWs on the colour removal of an azo-dye (tartrazine) solution that was favoured by an acidic pH. The estimated optimal conditions were: initial [H2O2]=2.0 mmol L−1 and pH=2.6, at 30±2°C. We obtained colour removals of approximately 92% in 24 min of irradiation (EDL, 244.2 W), following zero order kinetics: k=(3.9±0.52)×10−2 a.u. min−1 and R 2=0.989. Chemical and biological oxygen demand were significantly removed. On the other hand, the carbon content, biodegradability and ecotoxicity (Lactuca sativa) remained approximately the same. The UV/H2O2/MW process was shown to be eight times faster than other tested processes (MW, H2O2, H2O2/MW, and UV/MW).

Microwaves and their coupling to advanced oxidation processes: Enhanced performance in pollutants degradation

This review assesses microwaves (MW) coupled to advanced oxidation processes (AOPs) for pollutants degradation, as well as the basic theory and mechanisms of MW dielectric heating. We addressed the following couplings: MW/H2O2, MW/UV/H2O2, MW/Fenton, MW/US, and MW/UV/TiO2, as well as few studies that tested alternative oxidants and catalysts. Microwave Discharge Electrodeless Lamps (MDELs) are being extensively used with great advantages over ballasts. In their degradation studies, researchers generally employed domestic ovens with minor adaptations. Non-thermal effects and synergies between UV and MW radiation play an important role in the processes. Published papers so far report degradation enhancements between 30 and 1,300%. Unfortunately, how microwaves enhance pollutants is still obscure and real wastewaters scarcely studied. Based on the results surveyed in the literature, MW/AOPs are promising alternatives for treating/remediating environmental pollutants, whenever one considers high degradation yields, short reaction times, and small costs.

Degradação de corantes ácidos por processos oxidativos avançados usando um reator com disco rotatório de baixa velocidade

Three technologies were tested (TiO2/UV, H2O2/UV, and TiO2/H2O2/UV) for the degradation and color removal of a 25 mg L-1 mixture of three acid dyes: Blue 9, Red 18, and Yellow 23. A low speed rotating disc reactor (20 rpm) and a H2O2 concentration of 2.5 mmol L-1 were used. The dyes did not significantly undergo photolysis, although they were all degraded by the studied advanced oxidation processes. With the TiO2/H2O2/UV process, a strong synergism was observed (color removal reached 100%). Pseudo first order kinetic constants were estimated for all processes, as well as the respective apparent photonic efficiencies.

Color removal of Remazol® dyebaths wastewater by UV/H2O2 does not decrease TOC, BOD/COD, and toxicity of the effluent

AbstractThe present paper aimed at treating the dyebath wastewater of a textile industry by the UV/H2O2 process, mainly to remove color due to reactive Remazol® dyes (Chemical Oxygen Demand [COD]  600 mg O2 L–1; Biochemical Oxygen Demand [BOD]  220 mg O2 L–1; Total Organic Carbon (TOC)  310 mg C L–1). Experimental designs were performed to assess the effects of variables (initial pH, temperature, and initial [H2O2]) and optimize treatment conditions. Those were: initial pH = 11, temperature (T) = 50°C, and initial [H2O2] = 3.1 × 10–4 mol L–1. The response variables were color removal and residual [H2O2]. After two hours of irradiation, color removals of approximately 80 and 75% for UV/H2O2 and direct photolysis were respectively achieved. BOD/COD ratios, TOC, and COD analyses showed no significant changes. Acute ecotoxicity tests, using lettuce (Lactuca sativa) seeds, showed a slight increase in the ecotoxicity of the treated wastewater, for both processes. So, they are not recommended for treating this k...

The response surface methodology speeds up the search for optimal parameters in the photoinactivation of E. coli by photodynamic therapy

Antimicrobial Photodynamic Inactivation (a-PDI) is based on the oxidative destruction of biological molecules by reactive oxygen species generated by the photo-excitation of a photosensitive molecule. When a-PDT is performed with the use of mathematical models, the optimal conditions for maximum inactivation are found. Experimental designs allow a multivariate analysis of the experimental parameters. This is usually made using a univariate approach, which demands a large number of experiments, being time and money consuming. This paper presents the use of the response surface methodology for improving the search for the best conditions to reduce E. coli survival levels by a-PDT using methylene blue (MB) and toluidine blue (TB) as photosensitizers and white light. The goal was achieved by analyzing the effects and interactions of the three main parameters involved in the process: incubation time (IT), photosensitizer concentration (CPS), and light dose (LD). The optimization procedure began with a full 23 factorial design, followed by a central composite one, in which the optimal conditions were estimated. For MB, CPS was the most important parameter followed by LD and IT whereas, for TB, the main parameter was LD followed by CPS and IT. Using the estimated optimal conditions for inactivation, MB was able to inactivate 99.999999% CFU mL-1 of E. coli with IT of 28 min, LD of 31 J cm-2, and CPS of 32 μmol L-1, while TB required 18 min, 39 J cm-2, and 37 μmol L-1. The feasibility of using the response surface methodology with a-PDT was demonstrated, enabling enhanced photoinactivation efficiency and fast results with a minimal number of experiments.

Experimental-design-guided approach for the removal of atrazine by sono-electrochemical-UV-chlorine techniques

ABSTRACT The aim of the present study was to investigate the electrochemical formation of free chlorine species (HOCl/ClO−) and their subsequent use for the degradation of the pesticide atrazine. Initially, the process of electrochemical-free chlorine production was investigated using a bench-scale electrochemical flow-cell. The most significant variables (electrolyte concentration ([NaCl]) and inter-electrode gap) of the process were obtained using a 23 factorial design and the optimum process conditions (1.73 mol L−1 and 0.56 cm) were determined by a central composite design. Following optimization of free chlorine production, three degradation techniques were investigated, individually and in combination, for atrazine degradation: electrochemical, photochemical and sonochemical. The method using the techniques in combination was denominated sono-photo-assisted electrochemical degradation. Constant current assays were performed and the sono-photo-assisted electrochemical process promoted more efficient removal of atrazine, achieving total organic carbon removal of ∼98% and removal of atrazine to levels below the detection limit (>99%) in under 30 min of treatment. Furthermore, the combination of three techniques displayed lower energy consumption, and phytotoxicity tests (Lactuca sativa) showed that there was no increase in toxicity.