Mônica Maria Diniz Leão

Evaluation of photocatalytic activities of supported catalysts on NaX zeolite or activated charcoal

This study aimed to evaluate the photocatalytic activity of ZnO and Nb2O5 catalysts, both supported on NaX zeolite and activated charcoal (AC). The synergistic effect between oxide and support and the influence of solution pH (3, 7 and 9) on photocatalytic degradation of reactive blue 5G (C.I. 222) were analyzed. The catalysts Nb2O5/NaX, Nb2O5/AC and ZnO/NaX, ZnO/AC with 5 and 10% (wt%) were prepared by wet impregnation. The results showed that the catalysts exhibit quite different structural and textural properties. The synergic effect between ZnO and NaX support was higher than that with the activated charcoal, showing that these catalysts were more efficient. The most photoactive catalyst was 10% ZnO/NaX which showed 100% discoloration of the dye solution at pH 3, 7 and 9 after 0.5, 5 and 2h of irradiation, respectively. The hydrolytic nature of zeolite favored the formation of surface hydroxyl radicals, which increased the activity of the photocatalyst. Thus, catalysts supported on NaX zeolite are promising for use in photocatalysis.

Solar energy for wastewater treatment: review of international technologies and their applicability in Brazil

Several studies have reported the adverse effects of recalcitrant compounds and emerging contaminants present in industrial effluents, which are not degradable by ordinary biological treatment. Many of these compounds are likely to accumulate in living organisms through the lipid layer. At concentrations above the limits of biological tolerance, these compounds can be harmful to the ecosystem and may even reach humans through food chain biomagnification. In this regard, advanced oxidation processes (AOPs) represent an effective alternative for the removal of the pollutants. This study focused on the AOP involving the use of ultraviolet radiation in homogeneous and heterogeneous systems. Based on the literature review, comparisons between natural and artificial light were established, approaching photoreactors constructive and operational characteristics. We concluded that the high availability of solar power in Brazil would make the implementation of the AOP using natural solar radiation for the decontamination of effluents feasible, thereby contributing to clean production and biodiversity conservation. This will serve as an important tool for the enforcement of environmental responsibility among public and private institutions.

Textile wastewater reuse after additional treatment by Fenton’s reagent

AbstractThis study verifies textile wastewater reuse treated by the conventional activated sludge process and subjected to further treatment by advanced oxidation processes. Three alternative processes are discussed: Fenton, photo-Fenton, and UV/H2O2. Evaluation of treatments effects was based on factorial experiment design in which the response variables were the maximum removal of COD and the minimum concentration of residual H2O2 in treated wastewater. Results indicated Fenton’s reagent, COD/[H2O2]/[Fe2+] mass ratio of 1:2:2, as the best alternative. The selected technique was applied to real wastewater collected from a conventional treatment plant of a textile mill. The quality of the wastewater before and after the additional treatment was monitored in terms of 16 physicochemical parameters defined as suitable for the characterization of waters subjected to industrial textile use. The degradation of the wastewater was also evaluated by determining the distribution of its molecular weight along with the organic matter fractionation by ultrafiltration, measured in terms of COD. Finally, a sample of the wastewater after additional treatment was tested for reuse at pilot scale in order to evaluate the impact on the quality of dyed fabrics. Results show partial compliance of treated wastewater with the physicochemical quality guidelines for reuse. Removal and conversion of high and medium molecular weight substances into low molecular weight substances was observed, as well as the degradation of most of the organic matter originally present in the wastewater. Reuse tests indicated positive results, confirming the applicability of wastewater reuse after the suggested additional treatment. Graphical abstractTextile wastewater samples after additional treatment by Fenton’s reagent, photo-Fenton and H2O2/UV tested in different conditions

Comparação entre diferentes processos oxidativos avançados para degradação de corante azo

This study aimed at comparing various advanced oxidation processes (H2O2, UV, UV/H2O2, Fe2+/H2O2, UV/Fe2+/H2O2) for textile dye Reactive Red 195 decolorization. The use of blast furnace dust (BFD) was also investigated as an alternative source of iron in catalytic peroxidation with and without UV radiation. The effects of H2O2 and dye concentrations in kinetics of decolorization were studied. Decolorization reactions follow pseudo-first order kinetics. The results indicated greater efficiency of decolorization in the photo-Fenton system with the use of BFD; however, the use of BFD in the Fenton system without irradiation reached the same efficiency with a reaction time only 15 minutes superior. The use of blast furnace dust increased considerably the rates of reactions and is very promising as a source of iron.

Removal of ethylenthiourea and 1,2,4-triazole pesticide metabolites from water by adsorption in commercial activated carbons

This study evaluated the adsorption capacity of ethylenthiourea (ETU) and 1H-1,2,4-triazole (1,2,4-T) for two commercial activated carbons: charcoal-powdered activated carbon (CPAC) and bovine bone-powdered activated carbon (BPAC). The tests were conducted at a bench scale, with ETU and 1,2,4-T diluted in water, for isotherm and adsorption kinetic studies. The removal of the compounds was accompanied by a total organic carbon (TOC) analysis and ultraviolet (UV) reduction analysis. The coals were characterized by their surface area using nitrogen adsorption/desorption, by a scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) and by a zero charge point analysis (pHpcz). The results showed that adsorption kinetics followed a pseudo-second-order model for both coals, and the adsorption isotherms for CPAC and BPAC were adjusted to the Langmuir and Freundlich isotherms, respectively. The CPAC removed approximately 77% of the ETU and 76% of the 1,2,4-T. The BPAC was ineffective at removing the contaminants.

Tratamento de águas contaminadas por diesel/biodiesel utilizando processo Fenton

A contaminacao de aguas por misturas diesel/biodiesel pode causar grandes impactos ambientais, relacionados a presenca de compostos orgânicos recalcitrantes e toxicos, inviabilizando o uso de processos biologicos de tratamento. A avaliacao da biodegradabilidade, nas proporcoes B0, B25, B50, B75 e B100 (os numeros especificam o percentual em massa de biodiesel na mistura), indicou que a adicao de biodiesel em teores acima de 50% aumenta a biodegradabilidade, alcancando 60 e 80% para B50 e B75, respectivamente. Na aplicacao do processo Fenton, a remocao da materia orgânica foi superior a 80% em todas as misturas, exceto para B0, que apresentou remocao maxima de 50%. A oxidacao por Fenton se ajustou a um modelo cinetico de pseudo-segunda ordem em relacao a concentracao de materia orgânica, e resultou em aumento da biodegradabilidade de ate 150%.

Degradation of ethylenethiourea pesticide metabolite from water by photocatalytic processes

In this study, photocatalytic (photo-Fenton and H2O2/UV) and dark Fenton processes were used to remove ethylenethiourea (ETU) from water. The experiments were conducted in a photo-reactor with an 80 W mercury vapor lamp. The mineralization of ETU was determined by total organic carbon analysis, and ETU degradation was qualitatively monitored by the reduction of UV absorbance at 232 nm. A higher mineralization efficiency was obtained by using the photo-peroxidation process (UV/H2O2). Approximately 77% of ETU was mineralized within 120 min of the reaction using [H2O2]0 = 400 mg L−1. The photo-Fenton process mineralized 70% of the ETU with [H2O2]0 = 800 mg L−1 and [Fe2+] = 400 mg L−1, and there is evidence that hydrogen peroxide was the limiting reagent in the reaction because it was rapidly consumed. Moreover, increasing the concentration of H2O2 from 800 mg L−1 to 1200 mg L−1 did not enhance the degradation of ETU. Kinetics studies revealed that the pseudo-second-order model best fit the experimental conditions. The k values for the UV/H2O2 and photo-Fenton processes were determined to be 6.2 × 10−4 mg L−1 min−1 and 7.7 × 10−4 mg L−1 min−1, respectively. The mineralization of ETU in the absence of hydrogen peroxide has led to the conclusion that ETU transformation products are susceptible to photolysis by UV light. These are promising results for further research. The processes that were investigated can be used to remove pesticide metabolites from drinking water sources and wastewater in developing countries.

Use of tar pitch as a binding and reductant of BFD waste to produce reactive materials for environmental applications

In this work, a new approach is presented for the modification of the hazardous steel industry waste BFD (Blast Furnace Dust) into a versatile material for application in environmental remediation processes. Tar pitch, another waste, was used to agglomerate the very fine (submicrometric) dust particles to produce a compact and robust pelletized material that under simple thermal treatment produces notably reactive reduced Fe phases. SEM, TG/DTA, Mössbauer, XRD, Raman, BET and elemental analyses indicated that the tar/BFD composite (1:1wt ratio) pellets treated at 400, 600 and 800°C lead to tar decomposition to form a carbon binding coat concomitant with the reduction of the Fe oxides to produce primarily Fe3O4 (magnetite), FeO (wüstite) and Fe(0). Preliminary reactivity studies indicated that these treated composites, especially at 800°C, are active for the reduction of Cr(VI)aq and for the elimination of textile dye via reduction and the Fenton reaction.

Tratamento de dados censurados em estudos ambientais

Due to the inherent limitations of the analytical methods of measurement, environmental exposure data often present observations described as below a certain detection limit, also called left-censored data. Censored data directly interferes in almost all types of statistical analyzes, including descriptive parameters, hypothesis testing, confidence intervals, correlations and regressions. In this work, we investigated the performance of the main classes of methods from major publications available in the literature, considering their advantages and limitations. Some criteria for selecting the best method of dealing with censored data are presented.

Risk estimate of water contamination by pesticides used in coffee crops

ABSTRACT A study was conducted in Manhuacu city, Minas Gerais, aiming to study the effects of pesticides used incoffee crops on surface and ground waters. Manhuacu is located in an important Brazilian region ofagricultural production. Moreover, the city possesses many different water sources directed to the publicwater supply, and 13 points of surface and groundwater pumping. There have also been severaloccurrences of cancer in the local population. A survey conducted among cities of Minas Gerais identified122 cities with high occurrences of death due to cancer, among which was Manhuacu. The physico-chemical properties and applied mass of the active ingredients of each pesticide studied were surveyed.Goss and GUS algorithms were applied to estimate the risk of surface and ground water contamination,respectively. Some of the most widely used pesticides in the region, whose contamination potential wasestimated as high, were later detected in surface waters through LC/MS-MS. This study can helpagriculturists and officials of environmental organizations select and control, respectively, less harmfulproducts to the water.