Maria Cristina Canela

Gas-phase destruction of H2S using TiO2/UV-VIS

Photocatalytic destruction of H2S using TiO2/UV-VIS was conducted in the gas-phase. This process showed high efficiency, reaching degradation yields of 99% at concentration ranges of 33 to 855 ppmv. Oxygen was shown to be necessary for the photodestruction of H2S. Conversion rates were small in experiments conducted under nitrogen atmosphere (17%) compared with experiments in the presence of oxygen (99%). The photocatalytic activity of TiO2 showed that at 217 ppmv, there was no loss of the activity over extended operation periods. Deactivation of the catalyst was observed only when working at higher H2S concentrations (such as 600 ppmv), and is assumed to be caused by the adsorption of the byproducts produced onto the catalyst surface. The main product in the photocatalytic destruction of H2S in gasphase detected by FTIR and for turbidimetric analysis was sulfate ions. A mass balance showed that H2S is oxidized to SO4poststaggered−2 (95% of SO4poststaggered−2 were easily recovered from the catalyst surface), and that only 0.02% of this ion was detected at the reactor effluent. Experiments carried out using the photocatalytic process to minimize noxious emission of H2S stripped from a raw sewage sample showed that this process is viable for the elimination of odor in wastewater treatment plants.

Catalyst deactivation in the gas phase destruction of nitrogen-containing organic compounds using TiO2/UV–VIS

Possible application of the TiO2/UV‐VIS photocatalytic process in the destruction of nitrogen-containing malodorous compounds was evaluated. Pyridine (C5H5N), propylamine (C3H7NH2) and diethylamine (C4H10NH) were photodegraded in the presence and in the absence of oxygen. Degradation of nitrogen-containing organic compounds was confirmed by mass balance taking into consideration NH4 C and NO3 ions trapped at the TiO2 surface. Photocatalytic deactivation was observed in all cases. Online mass spectrometry was used to identify byproducts in the gas phase formed during the degradation process. GC‐MS analysis of the dichloromethane-extract of aqueous species leached from the surface of deactivated catalyst, as well as pre-concentration in a Tenax column were used to identify intermediates in the gas phase. These byproducts are considered to be the major ones responsible for deactivation of TiO2.

Photocatalysis for Continuous Air Purification in Wastewater Treatment Plants: From Lab to Reality

The photocatalytic efficiency of TiO(2)-SiMgO(x) plates to oxidize H(2)S was first evaluated in a flat laboratory reactor with 50 mL min(-1) synthetic air containing 100 ppm H(2)S in the presence of humidity. The use of the photocatalyst-adsorbent hybrid material enhanced the photocatalytic activity in terms of pollutant conversion, selectivity, and catalyst lifetime compared to previous H(2)S tests with pure TiO(2) because total H(2)S elimination was maintained for more than 30 operating hours with SO(2) appearing in the outlet as reaction product only after 18 h. Subsequently, the hybrid material was successfully tested in a photoreactor prototype to treat real polluted air in a wastewater treatment plant. For this purpose, a new tubular photocatalytic reactor that may use solar radiation in combination with artificial radiation was designed; the lamp was turned on when solar UV-A irradiance was below 20 W m(-2), which was observed to be the minimum value to ensure 100% conversion. The efficient distribution of the opaque photocatalyst inside the tubular reactor was achieved by using especially designed star-shaped structures. These structures were employed for the arrangement of groups of eight TiO(2)-SiMgO(x) plates in easy-to-handle channelled units obtaining an adequate flow regime without shading. The prototype continuously removed during one month and under real conditions the H(2)S contained in a 1 L min(-1) air current with a variable inlet concentration in the range of tens of ppmv without release of SO(2).

A preliminary nationwide survey of the presence of emerging contaminants in drinking and source waters in Brazil

This is the first nationwide survey of emerging contaminants in Brazilian waters. One hundred drinking water samples were investigated in 22 Brazilian state capitals. In addition, seven source water samples from two of the most populous regions of the country were evaluated. Samples were collected from June to September of 2011 and again during the same period in 2012. The study covered emerging contaminants of different classes, including hormones, plasticizers, herbicides, triclosan and caffeine. The analytical method for the determination of the compounds was based on solid-phase extraction followed by analysis via liquid chromatography electrospray triple-quadrupole mass spectrometry (LC-MS/MS). Caffeine, triclosan, atrazine, phenolphthalein and bisphenol A were found in at least one of the samples collected in the two sampling campaigns. Caffeine and atrazine were the most frequently detected substances in both drinking and source water. Caffeine concentrations in drinking water ranged from 1.8ngL-1 to values above 2.0μgL-1 while source-water concentrations varied from 40ngL-1 to about 19μgL-1. For atrazine, concentrations were found in the range from 2.0 to 6.0ngL-1 in drinking water and at concentrations of up to 15ngL-1 in source water. The widespread presence of caffeine in samples of treated water is an indication of the presence of domestic sewage in the source water, considering that caffeine is a compound of anthropogenic origin.

Acute toxicity of Hg0 and Hg2+ ions to Escherichia coli

AbstractAcute toxicity tests using mercuric ions (Hg2+) at the concentration of 10 and 50 μg L−1 were carried out using Escherichia coli as the organism test. Toxicity was evaluated by measuring the inhibition in the microbial respiration, at 37°C, within 60 min after the metal spike. It has been shown that mercuric ions are reduced to the much less toxic form of elemental mercury (Hg0) by the glucose, which is usually present in the microbial culture medium as a carbon source. Based on this evidence, inhibition in the microbial respiration caused by the presence of 5,000 μg L−1 of Hg0 were predicted to be similar to the effect caused by 10 μ L−1 of Hg2+ ions. This hypothesis has been proved to be true under the experimental conditions used in the bioassays.

Evaluation of volatile organic compounds coupled to seasonality effects in indoor air from a commercial office in Madrid (Spain) applying chemometric techniques

Volatile organic compounds (VOCs) concentrations depend on several sources and factors, such as temperature, ventilation, and humidity. Sources can be external atmospheric pollution or indoor release from furniture, coatings or occupants. In this context, this study focused on quantification of VOCs present in a confined atmosphere in a commercial office in downtown Madrid, Spain. The influence of seasonal changes in VOCs concentrations was evaluated using chemometric approaches. Indoor air was systematically monitored for one year using stainless steel tubes filled with Tenax® TA. Sampling was conducted one week a month, for three days during that week (Monday, Wednesday and Friday) for 60 min, every 2 h, totaling 24 h, using an autosampler carousel. The analyses were performed using thermal desorption, and compounds were analyzed by a gas chromatograph coupled with a mass spectrometer. The correlation between these compounds and their concentrations, climatic variations, seasons, among others, were explained by multivariate statistics. Considering the current legislation in Spain, only benzene was present above the maximum permissible concentration (threshold value < 1 μg/m3) from all analyzed compounds. The results indicate that concentrations are related to significant environmental changes, such as ventilation, the number of occupants in the office and types of activity undertaken in the environment. The chemometric analyses allowed the identification of structure analyses correlations between multiple variables for the one-year study. These results underscore the importance of indoor atmosphere studies and chronic exposure to these contaminants.