José Roberto Guimarães

A comparative study on the degradation of RB-19 dye in an aqueous medium by advanced oxidation processes

The effectiveness of photolysis (UV), peroxidation (H(2)O(2)), peroxidation combined with UV light (UV/H(2)O(2)), Fenton reagent (H(2)O(2)/Fe(2+)), and the photo-Fenton process (H(2)O(2)/Fe(2+)/UV) at degrading the textile dye Reactive Blue 19 was evaluated. The efficiency of the photo-Fenton process for degrading raw textiles and biologically pre-treated effluents was also evaluated. H(2)O(2) (100-800 mg L(-1)) and UV light did not degrade dye when used separately. The UV/H(2)O(2) process was effective but slow: 91% of dye degraded within 3 h of reaction at a concentration of 500 mg L(-1) H(2)O(2). Fenton reagent reduced dissolved organic carbon by 36.8% and color was reduced by >98% within a few minutes of reaction. The photo-Fenton process was the most efficient, reducing 94.5% of dissolved organic carbon and 99.4% of color. The combination of a biological system and the photo-Fenton process degraded a high level of textile effluent degradation, reducing dissolved organic carbon by 88%, color by 85%, chemical oxygen demand by 80%, and biochemical oxygen demand by 93%.

Arsenic removal from water employing heterogeneous photocatalysis with TiO2 immobilized in PET bottles.

Arsenic oxidation (As(III) to As(V)) and As(V) removal from water were assessed by using TiO2 immobilized in PET (polyethylene terephthalate) bottles in the presence of natural sunlight and iron salts. The effect of many parameters was sequentially studied: TiO2 concentration of the coating solution, Fe(II) concentration, pH, solar irradiation time; dissolved organic carbon concentration. The final conditions (TiO2 concentration of the coating solution: 10%; Fe(II): 7.0 mg l(-1); solar exposure time: 120 min) were applied to natural water samples spiked with 500 microg l(-1) As(III) in order to verify the influence of natural water matrix. After treatment, As(III) and total As concentrations were lower than the limit of quantitation (2 microg l(-1)) of the voltammetric method used, showing a removal over 99%, and giving evidence that As(III) was effectively oxidized to As(V). The results obtained demonstrated that TiO2 can be easily immobilized on a PET surface in order to perform As(III) oxidation in water and that this TiO2 immobilization, combined with coprecipitation of arsenic on Fe(III) hydroxides(oxides) could be an efficient way for inorganic arsenic removal from groundwaters.

Short-term toxicity test using Escherichia coli: Monitoring CO2 production by flow injection analysis

Abstract Short-term toxicity tests using Escherichia coli were carried out for different stressing agents such as metal ions [Cd(II), Cu(II) and Hg(II)], sediments and one type of antibiotic (Bactrin). Inhibition of the microbial respiration was monitored using flow injection analysis (FIA) with a conductometric detector. Inhibition in the respiration of E. coli suspensions were detected within 20 min for Hg(II) ions and the antibiotic, whereas sediment samples from eutrophic water bodies stimulated CO 2 production.

Degradation of formaldehyde by advanced oxidation processes.

The degradation of formaldehyde in an aqueous solution (400 mg L(-1)) was studied using photolysis, peroxidation and advanced oxidation processes (UV/H(2)O(2), Fenton and photo-Fenton). Photolysis was the only process tested that did not reduce formaldehyde concentration; however, only advanced oxidation processes (AOPs) significantly decreased dissolved organic carbon (DOC). UV/H(2)O(2) and photo-Fenton AOPs were used to degrade formaldehyde at the highest concentrations (1200-12,000 mg L(-1)); the processes were able to reduce CH(2)O by 98% and DOC by 65%. Peroxidation with ultraviolet light (UV/H(2)O(2)) improved the efficiency of treatment of effluent from an anatomy laboratory. The effluents CH(2)O content was reduced by 91%, DOC by 48%, COD by 46% and BOD by 53% in 420 min of testing.

Degradation of flumequine by the Fenton and photo-Fenton processes: evaluation of residual antimicrobial activity.

Flumequine is a broad-spectrum antimicrobial agent of the quinolone class, and it is widely used as a veterinary drug in food-producing animals. The presence of flumequine in the environment may contribute to the development of drug resistant bacterial strains. In this study, water samples fortified with flumequine (500 μg L(-1)) were degraded using the Fenton and photo-Fenton processes. The maximum degradation efficiency for flumequine by the Fenton process was approximately 40% (0.5 mmol L(-1) Fe(II), 2.0 mmol L(-1) H(2)O(2) and 15 min). By applying UV radiation (photo-Fenton process), the efficiency reached more than 94% in 60 min when 0.25 mmol L(-1) Fe(II) and 10.0 mmol L(-1) H(2)O(2) were used. Under these conditions, the Fenton process was able to reduce the biological activity, whereas the photo-Fenton process eliminated almost all of the antimicrobial activity because it was not detected. Four byproducts with an m/z of 244, 238, 220 and 202 were identified by mass spectrometry, and a degradation pathway for flumequine was proposed. The byproducts were derived from decarboxylation and defluorination reactions and from modifications in the alkylamino chain of the fluoroquinolone.

Inactivation of Escherichia coli in water by TiO2-assisted disinfection using solar light

TiO2-assisted heterogeneous photocatalysis and photolysis were evaluated for the disinfection of water samples using a glass reactor with immobilized TiO2 (catalyst), solar light and E. coli as an indicator microorganism of the efficiency of disinfection. Parameters such as color and turbidity of the water, level of coliform bacteria (by the Colilert® method), inclination angle of the solar reactor, solar light intensity, flow rate and retention time were controlled during the experiments. Two different operational modes were used for the solar reactor: single pass mode and recirculation mode. First, synthetic water was used in the disinfection tests as a model system; second, tests were conducted using natural samples specifically groundwater collected from a lake and a well. In bacterial suspensions in synthetic water in the absence of color and turbidity, heterogeneous photocatalysis was responsible for the reduction of approximately 100% of the initial concentration of E. coli. Only a 56.5% reduction was obtained by photolysis during the same solution recirculation time, which indicated a better efficiency using the catalyst. From the natural samples, total inactivation was not achieved in the studied cases. However, photocatalysis using TiO2/solar light was shown to be quantitatively efficient in the destruction of the total coliforms in water, reaching values up to around 80% inactivation in natural waters with initial levels of total coliforms ranging from 16.6 to 22.2´103 MPN per 100 mL.

Measuring the CO2 flux at the air/water interface in lakes using flow injection analysis

The carbon dioxide flux at the air/water interface in lakes was calculated after the determination of H2CO3* (free CO2) and atmospheric CO2 using flow injection analysis (FIA) coupled to a conductometric detector. The method is based on the diffusion of CO2 through a hydrophobic membrane into a flow of deionized water, generating a gradient of conductivity proportional to the concentration of CO2 in the sample. Using one experimental set-up, the speciation of the inorganic carbon (H2CO3* and dissolved inorganic carbon) was accomplished by simply adjusting the sample pH. The determination of CO2 in the atmosphere was carried out by direct injection of the gaseous samples. The FIA apparatus was taken into the field and CO2 fluxes were evaluated in several Brazilian lakes. In these lakes, representing different eutrophic stages, the CO2 flux varied from -242 (invasive) up to 3227 (evasive) mumol CO2 m-2 h-1.

Photocatalytic inactivation of Clostridium perfringens and coliphages in water

This study presents results of the photocatalytic inactivation of two groups of microorganisms: spores of the anaerobic bacterium Clostridium perfringens and coliphage. A cylindrical reactor impregnated with titanium dioxide and irradiated with ultraviolet light (15 W) was used. Parameters such as color, turbidity, hydraulic detention time (HDT) and initial concentration of microorganisms were evaluated in relation to the efficiency of the inactivation process. According to the experiments with the bacterium C. perfringens, the reduction in number of microorganisms was higher than 98% after an irradiation time of 152 seconds, independent of color and turbidity. For solutions with low turbidities efficiency of the coliphage inactivation reached approximately 100% between 89 and 104 HDT, while this value was 98% for solutions with higher turbidities.

Environmental behavior of arsenic(III) and (V) in soils

This paper presents an evaluation of the environmental behavior of arsenic species in soils (F. F. Dias, Master Thesis, University of Delaware, 1997). The results obtained were used to determine adsorption constants that were incorporated in mathematical models using forward and backward stepwise linear regression to correlate data. The amount of adsorption was significantly different depending on soil properties, such as organic matter, iron oxide content, and surface area. Arsenic speciation on the soil surface was deduced from desorption data, with As(V) being more strongly retained in the soil. As(III) was oxidized on the soil surface and desorbed as As(V); an important factor since As(V) is less toxic. In order to develop an adequate adsorption model, Langmuir and Freundlich isotherms were obtained for each soil without pH alteration. Results indicated that the maximum amount of As(V) adsorbed was greater than the amount of As(III) adsorbed. Adsorption edges for As(III) and As(V), with pH varying from 3 to 10, were obtained at concentrations that ranged from 0.1 to 200 mg L(-1). The soils studied exhibited an L-type Langmuir isotherm. Maximum As(III) adsorption occurred around pH 6 to 9, while maximum As(V) adsorption occurred in the 4 to 5 pH range. Experiments to determine arsenic kinetics were carried out and showed that adsorption and desorption equilibrium was reached within 48 hours for both species.

Ocorrência e degradação de quinolonas por processos oxidativos avançados

In this review, the presence of quinolones in the environment, their risks and the available processes for water decontamination were addressed. Their occurrence in surface waters and also in soil raises concerns about the risk of the development of resistant bacteria and other potential chronic effects. AOPs (UV/H2O2, Fenton, photo-Fenton, and UV/TiO2) and ozonation proved effective for degrading these emerging contaminants due to hydroxyl radical formation, surpassing the efficacy of conventional methods. In addition, the main degradation mechanisms of these drugs as well as data on residual biological activity were analyzed.