Electronic and optical competence of TiO2/BiVO4 nanocomposites in the photocatalytic processes.

Nanocomposites with different ratios of titanium dioxide and bismuth vanadate [TiO2]/[BiVO4] give rise to compatible electronic band structure alignment at their interfaces to ensure enhanced photoactivated charge transfer under visible light. The sol-gel method and suitable post-synthesis thermal treatments were used to synthesize different compositions with stabilized anatase phase of TiO2 and monoclinic scheelite polymorph BiVO4. Structural, electronic and optical characterizations were performed and the results were analysed as a function of the stoichiometry, in which both crystalline structures show a clear junction formation among their characteristic stacking planes. Photocatalytic and (photo) electrochemical responses of the nanocomposites were investigated and tested for the degradation of azo dyes (Acid Blue-113, AB-113) (~ 99%) under visible light radiation. The nanocomposite with a mass ratio of (1:10) shows the highest photocatalytic efficiency compared to the other compositions. HRTEM images showed marked regions in which both crystalline structures form a clear junction and their characteristic planes. However, the increase of BiVO4 content in the network overcomes the photocatalytic activity due to the decrease in the reduction potential of the photo-generated electrons with high recombination rates.

Environmental fate of naproxen, carbamazepine and triclosan in wastewater, surface water and wastewater irrigated soil - Results of laboratory scale experiments.

Lab-scale photolysis, biodegradation and transport experiments were carried out for naproxen, carbamazepine and triclosan in soil, wastewater and surface water from a region where untreated wastewater is used for agricultural irrigation. Results showed that both photolysis and biodegradation occurred for the three emerging pollutants in the tested matrices as follows: triclosan>naproxen>carbamazepine. The highest photolysis rate for the three pollutants was obtained in experiments using surface water, while biodegradation rates were higher in wastewater and soil than in surface water. Carbamazepine showed to be recalcitrant to biodegradation both in soil and water; although photolysis occurred at a higher level than biodegradation, this compound was poorly degraded by natural processes. Transport experiments showed that naproxen was the most mobile compound through the first 30cm of the soil profile; conversely, the mobility of carbamazepine and triclosan through the soil was delayed. Biodegradation of target pollutants occurred within soil columns during transport experiments. Triclosan was not detected either in leachates or the soil in columns, suggesting its complete biodegradation. Data of these experiments can be used to develop more reliable fate-on-the-field and environmental risk assessment studies.

Retention of Escherichia coli, Giardia lamblia cysts and Ascaris lumbricoides eggs in agricultural soils irrigated by untreated wastewater.

In central Mexico, agricultural irrigation reusing Mexico City's municipal wastewater has been occurring for the last century, resulting in the recharge of the local aquifer. However, groundwater of this zone is of good quality, indicating that the microorganisms contained in wastewater are retained by soil after infiltration. This study aims to assess the capacity of three agricultural soils to retain three microorganisms frequently found in wastewater, namely Escherichia coli (E. coli), Giardia lamblia (G. lamblia) cysts and Ascaris lumbricoides (A. lumbricoides) eggs, through batch sorption-desorption assays. The tested soils were: an organic-clayey soil (C-OM), a clayey soil (C-om) and a sandy soil (c-om). For the three soils, sorption equilibrium of E. coli was reached before 1 h, while for G. lamblia cysts and A. lumbricoides eggs, sorption equilibrium took 2.5 h. Sorption of E. coli was better described by the Freundlich model than by the Langmuir one. Higher retention of bacteria was observed in the C-om soil (KF = 4340) than in the C-OM and c-om ones (KF = 1821 and 0.01, respectively). Regarding G. lamblia cysts and A. lumbricoides eggs, data could not be fitted to the tested sorption models. For both organisms, retention was lower in the C-OM soil than in the C-om and c-om ones. In the desorption tests, a sudden liberation of E. coli from soils was observed, probably due to bacterial re-growth. Desorption of G. lamblia was higher in the sandy soil than in the clayey ones; desorption was not increased when a surfactant was applied to the soil, suggesting that hydrophobic interactions are not necessarily responsible for retention of the cysts onto the tested soils. For A. lumbricoides eggs, desorption using NaOCl solution suggested that retention was caused by interactions between the mineral fraction of the soil and the external walls of eggs. This study showed that the three target microorganisms are retained by the tested soils and that mineral domain of soil has an important role in such retention.