Degradation of carbendazim in water via photo-Fenton in Raceway Pond Reactor: assessment of acute toxicity and transformation products.

This study aimed at investigating the degradation of fungicide carbendazim (CBZ) via photo-Fenton reactions in artificially and solar irradiated photoreactors at laboratory scale and in a semi-pilot scale Raceway Pond Reactor (RPR), respectively. Acute toxicity was monitored by assessing the sensibility of bioluminescent bacteria (Aliivibrio fischeri) to samples taken during reactions. In addition, by-products formed during solar photo-Fenton were identified by liquid chromatography coupled to mass spectrometry (UFLC-MS). For tests performed in lab-scale, two artificial irradiation sources were compared (UVλ > 254nm and UV-Visλ > 320nm). A complete design of experiments was performed in the semi-pilot scale RPR in order to optimize reaction conditions (Fe2+ and H2O2 concentrations, and water depth). Efficient degradation of carbendazim (> 96%) and toxicity removal were achieved via artificially irradiated photo-Fenton under both irradiation sources. Control experiments (UV photolysis and UV-Vis peroxidation) were also efficient but led to increased acute toxicity. In addition, H2O2/UVλ > 254nm required longer reaction time (60 minutes) when compared to the photo-Fenton process (less than 1 min). While Fenton's reagent achieved high CBZ and acute toxicity removal, its efficiency demands higher concentration of reagents in comparison to irradiated processes. Solar photo-Fenton removed carbendazim within 15 min of reaction (96%, 0.75 kJ L-1), and monocarbomethoxyguanidine, benzimidazole isocyanate, and 2-aminobenzimidazole were identified as transformation products. Results suggest that both solar photo-Fenton and artificially irradiated systems are promising routes for carbendazim degradation.

Oxidation of ethylenethiourea in water via ozone enhanced by UV-C: identification of transformation products.

Ethylenethiourea (ETU) is a toxic degradation product of one class of fungicide which is largely employed in the world, the ethylenebisdithiocarbamates. In this study, ETU was degraded by ozonation enhanced by UV-C light irradiation (O3/UV-C) in aqueous medium. Degradation experiments were conducted at natural pH (6.8) and neutral pH (7.0, buffered). ETU was promptly eliminated from the reactive medium during ozonation in the presence and absence of light. Within the first few minutes of reaction conducted in natural pH, the pH decreased quickly from 6.8 to 3.0. Results show that ETU mineralization occurs only in the reaction conducted in neutral pH and that it takes place in a higher rate when enhanced by UV-C irradiation. Main intermediates formed during the O3/UV-C experiments in different conditions tested were also investigated and three different degradation mechanisms were proposed considering the occurrence of direct and indirect ozone reactions. At pH 7, ethylene urea (EU) was quickly generated and degraded. Meanwhile, at natural pH, besides EU, other compounds originated from the electrophilic attack of ozone to the sulfur atom present in the contaminant molecule were also identified during reaction and EU was detected within 60 min of reaction. Results showed that ozonation enhanced by UV-C promotes a faster reaction than the same system in the absence of light, and investigation of the toxicity is recommended.

Development of Fe/Nb-based solar photocatalysts for water treatment: impact of different synthesis routes on materials properties.

Semiconductors based on Fe/Nb oxides can present both solar sensitivity and high catalytic activity. However, there is still a lack regarding the comparison between different routes to produce Fe/Nb-based solar photocatalysts and the evaluation of the impact of the synthesis operating conditions on the material properties. In this work, Fe/Nb2O5 ratio, type of precipitating agent, presence/absence of washing stage, and temperature of calcination were verified to be the most relevant parameters in the synthesis by the co-precipitation method. These factors led to remarkable differences in the properties and performance of the photocatalysts produced by each distinct synthesis route. Composition, iron species present in the materials, crystallinity characteristics, and pH of the catalysts were affected, leading to different photocatalytic activities under UV-Vis light. Due to their characteristics, the synthesized materials are potential photocatalysts for application in solar processes. Graphical abstract ᅟ.

Feasibility study of the use of basic oxygen furnace sludge in a permeable reactive barrier.

In this study, the steel manufacturing waste Basic Oxygen Furnace Sludge (BOFS) was tested as permeable reactive material for the remediation of soil contaminated with chromium. The material presents a high content of elemental iron and iron oxides typical of the steel manufacturing process. Here we propose a scheme of the chemical reactions responsible for remediation process including BOFS dissolution, Cr(VI) reduction and Cr(III) precipitation. Batch reactors showed that Cr(VI) removal increases as the pH decreases. Column tests demonstrated that the simulated PRB with BOFS as the reactive media was quite effective for removing Cr(VI) from groundwater, with a sorption capability of 0.213 mg Cr per gram of BOFS at an initial Cr(VI) concentration of 50 mg L-1 at pH 5.5. A long-term test lasting 71 days confirmed the proposed mechanisms and the suitability of using BOFS in a permeable reactive barrier.

Optimized treatment conditions for textile wastewater reuse using photocatalytic processes under UV and visible light sources.

In this study, photo-Fenton systems using visible light sources with iron and ferrioxalate were tested for the DOC degradation and decolorization of textile wastewater. Textile wastewaters originated after the dyeing stage of dark-colored tissue in the textile industry, and the optimization of treatment processes was studied to produce water suitable for reuse. Dissolved organic carbon, absorbance, turbidity, anionic concentrations, carboxylic acids, and preliminary cost analysis were performed for the proposed treatments. Conventional photo-Fenton process achieved near 99 % DOC degradation rates and complete absorbance removal, and no carboxylic acids were found as products of degradation. Ferrioxalate photo-Fenton system achieved 82 % of DOC degradation and showed complete absorbance removal, and oxalic acid has been detected through HPLC analysis in the treated sample. In contrast, photo-peroxidation with UV light was proved effective only for absorbance removal, with DOC degradation efficiency near 50 %. Treated wastewater was compared with reclaimed water and had a similar quality, indicating that these processes can be effectively applied for textile wastewater reuse. The results of the preliminary cost analysis indicated costs of 0.91 to 1.07 US$ m-3 for the conventional and ferrioxalate photo-Fenton systems, respectively. Graphical Abstract ᅟ.

Multistage ozone and biological treatment system for real wastewater containing antibiotics.

In this study, a multistage treatment system was proposed to treat real pharmaceutical wastewater containing the antibiotic amoxicillin. Ozonation (O3), and ozonation combined with aerobic biodegradation, were performed. The real pharmaceutical wastewater presented a high concentration of organic matter (TOC: 803 mg C·L-1 and COD: 2775 mg O2·L-1), significant amoxicillin content (50 mg L-1) and acute ecotoxicity (Aliivibrio fischeri aTU: 48.22). Ozonation proved to be effective for amoxicillin degradation (up to 99%) and the results also indicated the removal of the original colour of the wastewater, with average consumption of 1 g of ozone. However, the ozonation system alone could not achieve complete mineralization. Therefore, a combination of ozonation and biodegradation in a multistage system was proposed in order to improve cost and treatment efficiency. The multistage treatment system presented promising results, achieving degradation of more than 99% of the amoxicillin, more than 98% of the original chemical oxygen demand (COD), and 90% of initial toxicity, with the consumption of approximately 500 mg of ozone. This indicates that this system could prevent dangerous and biorecalcitrant antibiotics from entering water resources.

Application of solar photo-Fenton toward toxicity removal and textile wastewater reuse.

Solar photo-Fenton represents an innovative and low-cost option for the treatment of recalcitrant industrial wastewater, such as the textile wastewater. Textile wastewater usually shows high acute toxic and variability and may be composed of many different chemical compounds. This study aimed at optimizing and validating solar photo-Fenton treatment of textile wastewater in a semi-pilot compound parabolic collector (CPC) for toxicity removal and wastewater reclamation. In addition, treated wastewater reuse feasibility was investigated through pilot tests. Experimental design performed in this study indicated optimum condition for solar photo-Fenton reaction (20 mg L-1 of Fe2+ and 500 mg L-1 of H2O2; pH 2.8), which achieved 96 % removal of dissolved organic carbon (DOC) and 99 % absorbance removal. A toxicity peak was detected during treatment, suggesting that highly toxic transformation products were formed during reaction. Toxic intermediates were properly removed during solar photo-Fenton (SPF) treatment along with the generation of oxalic acid as an ultimate product of degradation and COS increase. Different samples of real textile wastewater were treated in order to validate optimized treatment condition with regard to wastewater variability. Results showed median organic carbon removal near 90 %. Finally, reuse of treated textile wastewater in both dyeing and washing stages of production was successful. These results confirm that solar photo-Fenton, as a single treatment, enables wastewater reclamation in the textile industry. Graphical abstract Solar photo-Fenton as a revolutionary treatment technology for "closing-the-loop" in the textile industry.

Steel wastes as versatile materials for treatment of biorefractory wastewaters.

Recent research on novel cost-effective adsorbent materials suggests potential use of industrial wastes for effluent treatment, with the added benefit of reuse of the wastes. Waste steel materials, including blast oxygen furnace sludge (BOFS), blast furnace sludge (BFS), and blast furnace dust (BFD), were investigated as low-cost adsorbents for removal of an oil emulsion and RR195 dye. The residues were characterized by X-ray diffraction, Brunauer-Emmett-Teller area, volume and distribution of pore diameters, Mössbauer spectroscopy, X-ray fluorescence, granulometry, scanning electron microscopy/energy dispersive spectroscopy, and pHpzc. Adsorption kinetics data were obtained by UV-vis spectrophotometry at the maximum absorption wavelength of the dye solution and crude oil emulsion. The use of waste as an adsorbent was more efficient for treatment of the oil emulsion than the dye solution. BOFS had higher total organic carbon (TOC) removal efficiency than the other waste materials. For the RR195 dye, good color removal was observed for all adsorbents, >90 % within 24 h. TOC removal was poor, <10 % for BFD and BFS and a maximum of 37 % for BOFS. For the oil emulsion, 97 % TOC removal was obtained by adsorption onto BOFS and 87 % onto BFS.

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 [Fe(2+)] = 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.

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.

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.

Mortality by neoplasia and cellular telephone base stations in the Belo Horizonte municipality, Minas Gerais state, Brazil.

Pollution caused by the electromagnetic fields (EMFs) of radio frequencies (RF) generated by the telecommunication system is one of the greatest environmental problems of the twentieth century. The purpose of this research was to verify the existence of a spatial correlation between base station (BS) clusters and cases of deaths by neoplasia in the Belo Horizonte municipality, Minas Gerais state, Brazil, from 1996 to 2006 and to measure the human exposure levels to EMF where there is a major concentration of cellular telephone transmitter antennas. A descriptive spatial analysis of the BSs and the cases of death by neoplasia identified in the municipality was performed through an ecological-epidemiological approach, using georeferencing. The database employed in the survey was composed of three data banks: 1. death by neoplasia documented by the Health Municipal Department; 2. BSs documented in ANATEL ("Agência Nacional de Telecomunicações": 'Telecommunications National Agency'); and 3. census and demographic city population data obtained from official archives provided by IBGE ("Instituto Brasileiro de Geografia e Estatística": 'Brazilian Institute of Geography and Statistics'). The results show that approximately 856 BSs were installed through December 2006. Most (39.60%) of the BSs were located in the "Centro-Sul" ('Central-Southern') region of the municipality. Between 1996 and 2006, 7191 deaths by neoplasia occurred and within an area of 500 m from the BS, the mortality rate was 34.76 per 10,000 inhabitants. Outside of this area, a decrease in the number of deaths by neoplasia occurred. The greatest accumulated incidence was 5.83 per 1000 in the Central-Southern region and the lowest incidence was 2.05 per 1000 in the Barreiro region. During the environmental monitoring, the largest accumulated electric field measured was 12.4 V/m and the smallest was 0.4 V/m. The largest density power was 40.78 µW/cm(2), and the smallest was 0.04 µW/cm(2).