Maria J. Rivero

Nitrate removal from electro-oxidized landfill leachate by ion exchange

Treatment of landfill leachates by electrochemical oxidation led to the complete removal of chemical oxygen demand and ammonium nitrogen. However, as result of the ammonium oxidation, the partial formation of nitrate ions was observed. Ion exchange technology was investigated as a polishing step in the treatment of landfill leachates. Removal of nitrate from aqueous solutions was studied using two selective anion exchangers: Purolite A 520E and Purolite A 300, under a fixed bed configuration. The following aspects of the ion exchange system were experimentally analyzed: (i) the influence of the presence of other competitive anions in solution, sulfate and chloride, during the loading step, (ii) the breakthrough point and resin saturation as a function of chloride concentration in the feed stream and, (iii) the efficiency of the regeneration step working with NaCl solutions at several concentrations. After a comparison of the experimental results, it was concluded that the resin Purolite A 300 showed a better behavior. Experimental analysis of the equilibrium isotherms made it possible to determine the equilibrium constant (K=3.21) and the maximum capacity (q(max)=183mgg(-1)), important parameters in the design of the treatment process.

TiO2 structures doped with noble metals and/or graphene oxide to improve the photocatalytic degradation of dichloroacetic acid

AbstractNoble metals have been used to improve the photocatalytic activity of TiO2. Noble metal nanoparticles prevent charge recombination, facilitating electron transport due to the equilibration of the Fermi levels. Furthermore, noble metal nanoparticles show an absorption band in the visible region due to a high localized surface plasmon resonance (LSPR) effect, which contributes to additional electron movements. Moreover, systems based on graphene, titanium dioxide, and noble metals have been used, considering that graphene sheets can carry charges, thereby reducing electron-hole recombination, and can be used as substrates of atomic thickness. In this work, TiO2-based nanocomposites were prepared by blending TiO2 with noble metals (Pt and Ag) and/or graphene oxide (GO). The nanocomposites were mainly characterized via transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR), Raman spectroscopy, and photocurrent analysis. Here, the photocatalytic performance of the composites was analyzed via oxidizing dichloroacetic acid (DCA) model solutions. The influence of the noble metal load on the composite and the ability of the graphene sheets to improve the photocatalytic activity were studied, and the composites doped with different noble metals were compared. The results indicated that the platinum structures show the best photocatalytic degradation, and, although the presence of graphene oxide in the composites is supposed to enhance their photocatalytic performance, graphene oxide does not always improve the photocatalytic process. Graphical abstractIt is a schematic diagram. Where NM is Noble Metal and LSPR means Localized Surface Plasmon Resonance

Photocatalytic degradation and mineralization of perfluorooctanoic acid (PFOA) using a composite TiO2 -rGO catalyst

The inherent resistance of perfluoroalkyl substances (PFASs) to biological degradation makes necessary to develop advanced technologies for the abatement of this group of hazardous substances. The present work investigated the photocatalytic decomposition of perfluorooctanoic acid (PFOA) using a composite catalyst based on TiO2 and reduced graphene oxide (95% TiO2/5% rGO) that was synthesized using a facile hydrothermal method. The efficient photoactivity of the TiO2-rGO (0.1gL-1) composite was confirmed for PFOA (0.24mmolL-1) degradation that reached 93±7% after 12h of UV-vis irradiation using a medium pressure mercury lamp, a great improvement compared to the TiO2 photocatalysis (24±11% PFOA removal) and direct photolysis (58±9%). These findings indicate that rGO provided the suited properties of TiO2-rGO, possibly as a result of acting as electron acceptor and avoiding the high recombination electron/hole pairs. The release of fluoride and the formation of shorter-chain perfluorocarboxilyc acids, that were progressively eliminated in a good match with the analysed reduction of total organic carbon, is consistent with a step-by-step PFOA decomposition via photogenerated hydroxyl radicals. Finally, the apparent first order rate constants of the TiO2-rGO UV-vis PFOA decompositions, and the intermediate perfluorcarboxylic acids were found to increase as the length of the carbon chain was shorter.

LCA of greywater management within a water circular economy restorative thinking framework

Greywater reuse is an attractive option for the sustainable management of water under water scarcity circumstances, within a water circular economy restorative thinking framework. Its successful deployment relies on the availability of low cost and environmentally friendly technologies. The life cycle assessment (LCA) approach provides the appropriate methodological tool for the evaluation of alternative treatments based on environmental decision criteria and, therefore, it is highly useful during the process conceptual design. This methodology should be employed in the early design phase to select those technologies with lower environmental impact. This work reports the comparative LCA of three scenarios for greywater reuse: photocatalysis, photovoltaic solar-driven photocatalysis and membrane biological reactor, in order to help the selection of the most environmentally friendly technology. The study has been focused on the removal of the surfactant sodium dodecylbenzenesulfonate, which is used in the formulation of detergents and personal care products and, thus, widely present in greywater. LCA was applied using the Environmental Sustainability Assessment methodology to obtain two main environmental indicators in order to simplify the decision making process: natural resources and environmental burdens. Energy consumption is the main contributor to both indicators owing to the high energy consumption of the light source for the photocatalytic greywater treatment. In order to reduce its environmental burdens, the most desirable scenario would be the use of solar light for the photocatalytic transformation. However, while the technological challenge of direct use of solar light is approached, the environmental suitability of the photovoltaic solar energy driven photocatalysis technology to greywater reuse has been demonstrated, as it involves the smallest environmental impact among the three studied alternatives.

Enhanced photocatalytic activity using GO/TiO 2 catalyst for the removal of DCA solutions

This work aimed to optimize high-performance photocatalysts based on graphene oxide/titanium dioxide (GO/TiO2) nanocomposites for the effective degradation of aqueous pollutants. The catalytic activity was tested against the degradation of dichloroacetic acid (DCA), a by-product of disinfection processes that is present in many industrial wastewaters and effluents. GO/TiO2 photocatalysts were prepared using three different methods, hydrothermal, solvothermal, and mechanical, and varying the GO/TiO2 ratio in the range of 1 to 10%. Several techniques were applied to characterize the catalysts, and better coupling of GO and TiO2 was observed in the thermally synthesized composites. Although the results obtained for DCA degradation showed a coupled influence of the composite preparation method and its composition, promising results were obtained with the photocatalysts compared to the limited activity of conventional TiO2. In the best case, corresponding to the composite synthesized via hydrothermal method with 5% of GO/TiO2 weight ratio, an enhancement of 2.5 times of the photocatalytic degradation yield of DCA was obtained compared to bare TiO2, thus opening more efficient ways to promote the application of photocatalytic remediation technologies.

Kinetic Modeling of the Photocatalytic Oxidation of Sodium Dodecylbenzenesulphonate

Abstract This work reports the experimental and theoretical analysis of the kinetics of degradation of the surfactant dodecylbenzenesulphonate (DBS) using TiO2 photocatalysis. Experimental data were obtained working with DBS concentrations of 50 mg L-1 and 200 mg L-1 and TiO2 concentrations from 0.5 g L-1 to 10 g L-1 in aqueous suspensions under UV irradiation. After having analysed the dark-adsorption equilibrium, kinetic data for DBS degradation were fitted to the Langmuir-Hinshelwood (L-H) expression. Three different approaches were used to correlate experimental data and to determine the characteristic parameters, i) correlation between the initial rates and initial concentrations of DBS, ii) approaching to a pseudo-first order model and, iii) fitting of kinetic data to the integrated L-H equation Best results were obtained with the integrated L-H expression being the corresponding parameters k = 2.24 10-3 mM min-1 and 3.41 mM-1 < Kads < 13.22 mM-1 .

Integration of Electrochemical Advanced Oxidation With Membrane Separation and Biodegradation

Abstract This chapter evaluates process integration as a strategy to boost the effectiveness of electrochemical advanced oxidation processes (EAOPs) by their combination with other technologies in search of synergies to overcome EAOP limitations. In the first case, EAOPs will be shown as a powerful tool to increase the biodegradability of organic contaminants contained in recalcitrant landfill leachates. Our second approach consists of using membrane separation aimed at the increase of the concentration of pollutants before the application of electrochemical degradation as a way to increase the kinetics of diffusion-limited electrooxidation.

Role of reactive oxygen species on the activity of noble metal-doped TiO 2 photocatalysts

Modified TiO2 catalysts are of interest in environmental water remediation since they can lead to efficient electron-hole separation and greatly enhance the photocatalytic properties of TiO2. Reactive oxygen species (ROS), such as the superoxide radical (O2-), hydroxyl radical (OH), and positive valence band holes (h+VB), have been reported as the main oxidative species involved in photocatalytic degradation processes. In this work, the role of these species using TiO2, TiO2/Pt 0.5 wt%, and TiO2/Ag 10 wt% has been examined in order to clarify the oxidation pathways. For this purpose, the contribution of the main oxidative species was analyzed in the photocatalytic degradation of dichloroacetic acid (DCA) solutions using specific scavengers (benzoquinone, tert-butyl alcohol, and formic acid). Moreover, the hydroxyl radicals were quantitatively determined in order better understand the results. Regardless of the catalyst used, it is concluded that OH radicals are the major reactive species responsible for DCA degradation and no significant degradation is due to O2- radicals. Nevertheless, different OH generation pathways were found, depending on the nature of the catalysts. Degradation using TiO2 was conducted mainly via OH radicals generated in the positive holes, while noble metal-doped TiO2 catalysts generated OH radicals through the transformation of O2- radicals.