Performance of TiO2-Based Tubular Membranes in the Photocatalytic Degradation of Organic Compounds.

This work presents the photocatalytic degradation of organic pollutants in water with TiO2 and TiO2/Ag membranes prepared by immobilising photocatalysts on ceramic porous tubular supports. The permeation capacity of TiO2 and TiO2/Ag membranes was checked before the photocatalytic application, showing high water fluxes (≈758 and 690 L m-2 h-1 bar-1, respectively) and <2% rejection against the model pollutants sodium dodecylbenzene sulfonate (DBS) and dichloroacetic acid (DCA). When the membranes were submerged in the aqueous solutions and irradiated with UV-A LEDs, the photocatalytic performance factors for the degradation of DCA were similar to those obtained with suspended TiO2 particles (1.1-fold and 1.2-fold increase, respectively). However, when the aqueous solution permeated through the pores of the photocatalytic membrane, the performance factors and kinetics were two-fold higher than for the submerged membranes, mostly due to the enhanced contact between the pollutants and the membranes photocatalytic sites where reactive species were generated. These results confirm the advantages of working in a flow-through mode with submerged photocatalytic membranes for the treatment of water polluted with persistent organic molecules, thanks to the reduction in the mass transfer limitations.

Circular economy in hot-dip galvanizing with zinc and iron recovery from spent pickling acids.

The management of spent pickling acids (SPA) is an environmental challenge for the hot-dip galvanizing (HDG) industry. Bearing in mind its elevated content of iron and zinc, SPA can be regarded as a source of secondary materials in a circular economy approach. This work reports the pilot scale demonstration of non-dispersive solvent extraction (NDSX) in hollow fiber membrane contactors (HFMCs) to perform the selective zinc separation and SPA purification, so that the characteristics needed for use as a source of iron chloride are achieved. The operation of the NDSX pilot plant, which incorporates four HFMCs with a 80 m2 nominal membrane area, is carried out with SPA supplied by an industrial galvanizer, and consequently technology readiness level (TRL) 7 is reached. The purification of the SPA requires of a novel feed and purge strategy to operate the pilot plant in continuous mode. To facilitate the further implementation of the process, the extraction system is formed by tributyl phosphate as the organic extractant and tap water as the stripping agent, both easily available and cost-effective chemicals. The resulting iron chloride solution is successfully valorized as a hydrogen sulfide suppressor to purify the biogas generated in the anaerobic sludge treatment of a wastewater treatment plant. Additionally, we validate the NDSX mathematical model using pilot scale experimental data, providing a design tool for process scale-up and industrial implementation.

On the quest of reliable 3D dynamic in vitro blood-brain barrier models using polymer hollow fiber membranes: Pitfalls, progress, and future perspectives.

With the increasing concern of neurodegenerative diseases, the development of new therapies and effective pharmaceuticals targeted to central nervous system (CNS) illnesses is crucial for ensuring social and economic sustainability in an ageing world. Unfortunately, many promising treatments at the initial stages of the pharmaceutical development process, that is at the in vitro screening stages, do not finally show the expected results at the clinical level due to their inability to cross the human blood-brain barrier (BBB), highlighting the inefficiency of in vitro BBB models to recapitulate the real functionality of the human BBB. In the last decades research has focused on the development of in vitro BBB models from basic 2D monolayer cultures to 3D cell co-cultures employing different system configurations. Particularly, the use of polymeric hollow fiber membranes (HFs) as scaffolds plays a key role in perfusing 3D dynamic in vitro BBB (DIV-BBB) models. Their incorporation into a perfusion bioreactor system may potentially enhance the vascularization and oxygenation of 3D cell cultures improving cell communication and the exchange of nutrients and metabolites through the microporous membranes. The quest for developing a benchmark 3D dynamic in vitro blood brain barrier model requires the critical assessment of the different aspects that limits the technology. This article will focus on identifying the advantages and main limitations of the HFs in terms of polymer materials, microscopic porous morphology, and other practical issues that play an important role to adequately mimic the physiological environment and recapitulate BBB architecture. Based on this study, we consider that future strategic advances of this technology to become fully implemented as a gold standard DIV-BBB model will require the exploration of novel polymers and/or composite materials, and the optimization of the morphology of the membranes towards thinner HFs (<50 µm) with higher porosities and surface pore sizes of 1-2 µm to facilitate the intercommunication via regulatory factors between the cell co-culture models of the BBB.

Influence of the properties of different graphene-based nanomaterials dispersed in polycaprolactone membranes on astrocytic differentiation.

Composites of polymer and graphene-based nanomaterials (GBNs) combine easy processing onto porous 3D membrane geometries due to the polymer and cellular differentiation stimuli due to GBNs fillers. Aiming to step forward to the clinical application of polymer/GBNs composites, this study performs a systematic and detailed comparative analysis of the influence of the properties of four different GBNs: (i) graphene oxide obtained from graphite chemically processes (GO); (ii) reduced graphene oxide (rGO); (iii) multilayered graphene produced by mechanical exfoliation method (Gmec); and (iv) low-oxidized graphene via anodic exfoliation (Ganodic); dispersed in polycaprolactone (PCL) porous membranes to induce astrocytic differentiation. PCL/GBN flat membranes were fabricated by phase inversion technique and broadly characterized in morphology and topography, chemical structure, hydrophilicity, protein adsorption, and electrical properties. Cellular assays with rat C6 glioma cells, as model for cell-specific astrocytes, were performed. Remarkably, low GBN loading (0.67 wt%) caused an important difference in the response of the C6 differentiation among PCL/GBN membranes. PCL/rGO and PCL/GO membranes presented the highest biomolecule markers for astrocyte differentiation. Our results pointed to the chemical structural defects in rGO and GO nanomaterials and the protein adsorption mechanisms as the most plausible cause conferring distinctive properties to PCL/GBN membranes for the promotion of astrocytic differentiation. Overall, our systematic comparative study provides generalizable conclusions and new evidences to discern the role of GBNs features for future research on 3D PCL/graphene composite hollow fiber membranes for in vitro neural models.

Coaxial Synthesis of PEI-Based Nanocarriers of Encapsulated RNA-Therapeutics to Specifically Target Muscle Cells.

In this work, we performed a methodological comparative analysis to synthesize polyethyleneimine (PEI) nanoparticles using (i) conventional nanoprecipitation (NP), (ii) electrospraying (ES), and (iii) coaxial electrospraying (CA). The nanoparticles transported antisense oligonucleotides (ASOs), either encapsulated (CA nanocomplexes) or electrostatically bound externally (NP and ES nanocomplexes). After synthesis, the PEI/ASO nanoconjugates were functionalized with a muscle-specific RNA aptamer. Using this combinatorial formulation methodology, we obtained nanocomplexes that were further used as nanocarriers for the delivery of RNA therapeutics (ASO), specifically into muscle cells. In particular, we performed a detailed confocal microscopy-based comparative study to analyze the overall transfection efficiency, the cell-to-cell homogeneity, and the mean fluorescence intensity per cell of micron-sized domains enriched with the nanocomplexes. Furthermore, using high-magnification electron microscopy, we were able to describe, in detail, the ultrastructural basis of the cellular uptake and intracellular trafficking of nanocomplexes by the clathrin-independent endocytic pathway. Our results are a clear demonstration that coaxial electrospraying is a promising methodology for the synthesis of therapeutic nanoparticle-based carriers. Some of the principal features that the nanoparticles synthesized by coaxial electrospraying exhibit are efficient RNA-based drug encapsulation, increased nanoparticle surface availability for aptamer functionalization, a high transfection efficiency, and hyperactivation of the endocytosis and early/late endosome route as the main intracellular uptake mechanism.

Intensified fish farming. Performance of electrochemical remediation of marine RAS waters.

Aquaculture has been the fastest growing agricultural sector in the past few decades and currently supplies about half of the fish market. A range of environmental and management concerns including limited land and water availability have led to intensifying fish production by recirculating aquaculture systems (RAS). Fish's diet contains 30-60 % protein and about 4-10 % nitrogen (N). As fish assimilate only 20-30 % of the feed to produce body mass, the unassimilated N is released in the form of toxic ammonium that deteriorates water quality and compels its degradation. Widely extended biological nitrification is not efficient in the removal of nitrites nor other chemicals and pharmaceuticals used during fish culture. Electrochemical oxidation, a less developed alternative, reports several advantages such as, i) simultaneous degradation of ammonia­nitrogen (TAN) and water disinfection in the same step with considerable simplification of the whole process, ii) easy adaptability to different production scales and periods of fish growth, and iii) no generation of harmful by-products and no use of chemicals, among others. Besides, in the case of marine aquaculture, the technology benefits from the high conductivity of seawater; thus, electrochemical oxidation is positioned in a very good place to satisfy the water treatment needs of the increasing production rate of marine aquaculture fish. Here, we report the analysis of the performance of a RAS demonstration plant aimed at farming gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) and provided with electrochemical remediation of culture water. The performance of the plant, with 20 m3 of seawater operating at a recirculation rate of 0.9-1.4 h-1, has been analysed in terms of TAN removal, water disinfection, make-up water intake and energy consumption and compared to data of conventional RAS provided with biofilters. The benefits and advantages of the innovative electrochemical remediation of RAS water are highlighted.

Life cycle assessment of zinc and iron recovery from spent pickling acids by membrane-based solvent extraction and electrowinning.

In this paper we conducted a life cycle assessment to evaluate the environmental performance of the valorization of spent pickling acid (SPA) generated in the hot-dip galvanizing (HDG) process. We analyzed the environmental impacts of treating one m3 of SPA, comparing the reference treatment consisting of neutralization, precipitation, stabilization, and landfilling of the metallic sludge (scenario #1), with the innovative LIFE2ACID technology (scenario #2) that produces secondary zinc and iron chloride in solution through non-dispersive solvent extraction (NDSX) and electrowinning (EW). The results showed that the materials credits achieved by the implementation of LIFE2ACID technology turned most of the impact categories evaluated (toxicity, acidification, eutrophication, ozone depletion, etc.) into environmental benefits. Scenario #2 was adapted to achieve either zinc-only recovery (#2.1) or simultaneous iron and zinc recovery (#2.2). The abiotic depletion potential (ADP) of fossil fuels increased slightly from scenario #1 to scenario #2.1 because of the higher energy demand and NaOH consumption of EW, and because only zinc was recovered. However, the valorization of both zinc and iron chloride in scenario #2.2 reduced the ADP-fossil by 27%, compared to the reference treatment. Furthermore, the global warming impact was reduced by 20% and 97% in scenarios #2.1 and #2.2, respectively. With the focus on promoting the circular economy concept, we conclude that the LIFE2ACID technology significantly improves the environmental performance of SPA management. Next steps should consider the life-cycle costs analysis in specific scenarios to find out the trade-off between environmental and economic objectives.

Thermodynamic Modeling and Validation of the Temperature Influence in Ternary Phase Polymer Systems.

The effect of the temperature, as a process variable in the fabrication of polymeric membranes by the non-solvent induced phase separation (NIPS) technique, has been scarcely studied. In the present work, we studied the influence of temperature, working at 293, 313 and 333 K, on the experimental binodal curves of four ternary systems composed of PVDF and PES as the polymers, DMAc and NMP as the solvents and water as the non-solvent. The increase of the temperature caused an increase on the solubility gap of the ternary system, as expected. The shift of the binodal curve with the temperature was more evident in PVDF systems than in PES systems indicating the influence of the rubbery or glassy state of the polymer on the thermodynamics of phase separation. As a novelty, the present work has introduced the temperature influence on the Flory-Huggins model to fit the experimental cloud points. Binary interaction parameters were calculated as a function of the temperature: (i) non-solvent/solvent (g12) expressions with UNIFAC-Dortmund methodology and (ii) non-solvent/polymer (χ13) and solvent/polymer (χ23) using Hansen solubility parameters. Additionally, the effect of the ternary interaction term was not negligible in the model. Estimated ternary interaction parameters (χ123) presented a linear relation with temperature and negative values, indicating that the solubility of the polymers in mixtures of solvent/non-solvent was higher than expected for single binary interaction. Finally, PES ternary systems exhibited higher influence of the ternary interaction parameter than PVDF systems.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part I: Membrane Synthesis and Characterization.

In this work, polymeric membranes functionalized with ionic liquids (ILs) and exfoliated graphene nanoplatelets (xGnP) were developed and characterized. These membranes based on graphene ionanofluids (IoNFs) are promising materials for gas separation. The stability of the selected IoNFs in the polymer membranes was determined by thermogravimetric analysis (TGA). The morphology of membranes was characterized using scanning electron microscope (SEM) and interferometric optical profilometry (WLOP). SEM results evidence that upon the small addition of xGnP into the IL-dominated environment, the interaction between IL and xGnP facilitates the migration of xGnP to the surface, while suppressing the interaction between IL and Pebax®1657. Fourier transform infrared spectroscopy (FTIR) was also used to determine the polymer-IoNF interactions and the distribution of the IL in the polymer matrix. Finally, the thermodynamic properties and phase transitions (polymer-IoNF) of these functionalized membranes were studied using differential scanning calorimetry (DSC). This analysis showed a gradual decrease in the melting point of the polyamide (PA6) blocks with a decrease in the corresponding melting enthalpy and a complete disappearance of the crystallinity of the polyether (PEO) phase with increasing IL content. This evidences the high compatibility and good mixing of the polymer and the IoNF.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part II: Gas Separation Properties toward Fluorinated Greenhouse Gases.

Membrane technology can play a very influential role in the separation of the constituents of HFC refrigerant gas mixtures, which usually exhibit azeotropic or near-azeotropic behavior, with the goal of promoting the reuse of value-added compounds in the manufacture of new low-global warming potential (GWP) refrigerant mixtures that abide by the current F-gases regulations. In this context, the selective recovery of difluorometane (R32, GWP = 677) from the commercial blend R410A (GWP = 1924), an equimass mixture of R32 and pentafluoroethane (R125, GWP = 3170), is sought. To that end, this work explores for the first time the separation performance of novel mixed-matrix membranes (MMMs) functionalized with ioNanofluids (IoNFs) consisting in a stable suspension of exfoliated graphene nanoplatelets (xGnP) into a fluorinated ionic liquid (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate ([C2C1py][C4F9SO3]). The results show that the presence of IoNF in the MMMs significantly enhances gas permeation, yet at the expense of slightly decreasing the selectivity of the base polymer. The best results were obtained with the MMM containing 40 wt% IoNF, which led to an improved permeability of the gas of interest (PR32 = 496 barrer) with respect to that of the neat polymer (PR32= 279 barrer) with a mixed-gas separation factor of 3.0 at the highest feed R410A pressure tested. Overall, the newly fabricated IoNF-MMMs allowed the separation of the near-azeotropic R410A mixture to recover the low-GWP R32 gas, which is of great interest for the circular economy of the refrigeration sector.

Hollow Fiber Membranes of PCL and PCL/Graphene as Scaffolds with Potential to Develop In Vitro Blood-Brain Barrier Models.

There is a huge interest in developing novel hollow fiber (HF) membranes able to modulate neural differentiation to produce in vitro blood-brain barrier (BBB) models for biomedical and pharmaceutical research, due to the low cell-inductive properties of the polymer HFs used in current BBB models. In this work, poly(ε-caprolactone) (PCL) and composite PCL/graphene (PCL/G) HF membranes were prepared by phase inversion and were characterized in terms of mechanical, electrical, morphological, chemical, and mass transport properties. The presence of graphene in PCL/G membranes enlarged the pore size and the water flux and presented significantly higher electrical conductivity than PCL HFs. A biocompatibility assay showed that PCL/G HFs significantly increased C6 cells adhesion and differentiation towards astrocytes, which may be attributed to their higher electrical conductivity in comparison to PCL HFs. On the other hand, PCL/G membranes produced a cytotoxic effect on the endothelial cell line HUVEC presumably related with a higher production of intracellular reactive oxygen species induced by the nanomaterial in this particular cell line. These results prove the potential of PCL HF membranes to grow endothelial cells and PCL/G HF membranes to differentiate astrocytes, the two characteristic cell types that could develop in vitro BBB models in future 3D co-culture systems.

Scale-Up of Membrane-Based Zinc Recovery from Spent Pickling Acids of Hot-Dip Galvanizing.

Zinc recovery from spent pickling acids (SPAs) can play an important role in achieving a circular economy in the galvanizing industry. This work evaluates the scale-up of membrane-based solvent extraction technology aimed at the selective separation of zinc from industrial SPAs as a purification step prior to zinc electrowinning (EW). The experiments were carried out at a pilot scale treating SPAs batches of 57 to 91 L in a non-dispersive solvent extraction (NDSX) configuration that simultaneously performed the extraction and backextraction steps. The pilot plant was equipped with four hollow fiber contactors and 80 m2 of total membrane area, which was approximately 30 times higher than previous bench-scale studies. Tributylphosphate diluted in Shellsol D70 and tap water were used as organic and stripping agents, respectively. Starting with SPAs with high Zn (71.7 ± 4.3 g·L-1) and Fe (82.9 ± 5.0 g·L-1) content, the NDSX process achieved a stripping phase with 55.7 g Zn·L-1 and only 3.2 g Fe·L-1. Other minor metals were not transferred, providing the purified zinc stripping with better quality for the next EW step. A series of five consecutive pilot-scale experiments showed the reproducibility of results, which is an indicator of the stability of the organic extractant and its adequate regeneration in the NDSX operation. Zinc mass transfer fluxes were successfully correlated to zinc concentration in the feed SPA phase, together with data extracted from previous laboratory-scale experiments, allowing us to obtain the design parameter that will enable the leap to the industrial scale. Therefore, the results herein presented demonstrate the NDSX technology in an industrially relevant environment equivalent to TRL 6, which is an essential progress to increase zinc metal resources in the galvanizing sector.

An optimization model for the treatment of perfluorocarboxylic acids considering membrane preconcentration and BDD electrooxidation.

Treatment of persistent perfluorocarboxylic acids in water matrixes requires of strong oxidation conditions, as those achieved by boron doped diamond (BDD) electrooxidation (ELOX). However, large scale implementation of ELOX is still hindered by its high energy consumption and economical investment. In this work, we used process systems engineering tools to define the optimal integration of a membrane pre-concentration stage followed by the BDD electrolysis of the concentrate, to drastically reduce the costs of treatment of perfluorohexanoic acid (PFHxA, 100 mg L-1) in industrial waste streams. A multistage membrane cascade system using nanofiltration (NF90 and NF270 membranes) was considered to achieve more sophisticated PFHxA separations. The aim was to minimize the total costs by determining the optimal sizing of the two integrated processes (membrane area per stage and anode area) and the optimal process variables (pre-concentration operating time, electrolysis time, input and output concentrations). The non-linear programming model (NLP) was implemented in the General Algebraic Modelling System (GAMS). The results showed that for a 2-log PFHxA abatement (99% removal), the optimal two membrane stages using the NF90 membrane obtains a 75.8% (6.4 $ m-3) reduction of the total costs, compared to the ELOX alone scenario (26.5 $ m-3). The optimized anode area and the energy savings, that were 85.3% and 88.2% lower than in ELOX alone, were the major contributions to the costs reduction. Similar results were achieved for a 3-log and 4-log PFHxA abatement, pointing out the promising benefits of integrating electrochemical oxidation with membrane pre-concentration through proper optimization for its large-scale application to waters impacted by perfluorocarboxylic acids.

Evidences of the Effect of GO and rGO in PCL Membranes on the Differentiation and Maturation of Human Neural Progenitor Cells.

The effect of doping graphene oxide (GO) and reduced graphene oxide (rGO) into poly(ε-caprolactone) (PCL) membranes prepared by solvent induced phase separation is evaluated in terms of nanomaterial distribution and compatibility with neural stem cell growth and functional differentiation. Raman spectra analyses demonstrate the homogeneous distribution of GO on the membrane surface while rGO concentration increases gradually toward the center of the membrane thickness. This behavior is associated with electrostatic repulsion that PCL exerted toward the polar GO and its affinity for the non-polar rGO. In vitro cell studies using human induced pluripotent cell derived neural progenitor cells (NPCs) show that rGO increases marker expression of NPCs differentiation with respect to GO (significantly to tissue culture plate (TCP)). Moreover, the distinctive nanomaterials distribution defines the cell-to-nanomaterial interaction on the PCL membranes: GO nanomaterials on the membrane surface favor higher number of active matured neurons, while PCL/rGO membranes present cells with significantly higher magnitude of neural activity compared to TCP and PCL/GO despite there being no direct contact of rGO with the cells on the membrane surface. Overall, this work evidences the important role of rGO electrical properties on the stimulation of neural cell electro-activity on PCL membrane scaffolds.

Factors Affecting Mass Transport Properties of Poly(ε-caprolactone) Membranes for Tissue Engineering Bioreactors.

High porosity and mass transport properties of microfiltration polymeric membranes benefit nutrients supply to cells when used as scaffolds in interstitial perfusion bioreactors for tissue engineering. High nutrients transport is assumed when pore size and porosity of the membrane are in the micrometric range. The present work demonstrates that the study of membrane fouling by proteins present in the culture medium, though not done usually, should be included in the routine testing of new polymer membranes for this intended application. Two poly(ε-caprolactone) microfiltration membranes presenting similar average pore size (approximately 0.7 µm) and porosity (>80%) but different external surface porosity and pore size have been selected as case studies. The present work demonstrates that a membrane with lower surface pore abundance and smaller external pore size (approximately 0.67 µm), combined with adequate hydrodynamics and tangential flow filtration mode is usually more convenient to guarantee high flux of nutrients. On the contrary, having large external pore size (approximately 1.70 µm) and surface porosity would incur important internal protein fouling that could not be prevented with the operation mode and hydrodynamics of the perfusion system. Additionally, the use of glycerol in the drying protocols of the membranes might cause plasticization and a consequent reduction of mass transport properties due to membrane compaction by the pressure exerted to force perfusion. Therefore, preferentially, drying protocols that omit the use of plasticizing agents are recommended.

Hydrolytic Degradation and Mechanical Stability of Poly(ε-Caprolactone)/Reduced Graphene Oxide Membranes as Scaffolds for In Vitro Neural Tissue Regeneration.

The present work studies the functional behavior of novel poly(ε-caprolactone) (PCL) membranes functionalized with reduced graphene oxide (rGO) nanoplatelets under simulated in vitro culture conditions (phosphate buffer solution (PBS) at 37 °C) during 1 year, in order to elucidate their applicability as scaffolds for in vitro neural regeneration. The morphological, chemical, and DSC results demonstrated that high internal porosity of the membranes facilitated water permeation and procured an accelerated hydrolytic degradation throughout the bulk pathway. Therefore, similar molecular weight reduction, from 80 kDa to 33 kDa for the control PCL, and to 27 kDa for PCL/rGO membranes, at the end of the study, was observed. After 1 year of hydrolytic degradation, though monomers coming from the hydrolytic cleavage of PCL diffused towards the PBS medium, the pH was barely affected, and the rGO nanoplatelets mainly remained in the membranes which envisaged low cytotoxic effect. On the other hand, the presence of rGO nanomaterials accelerated the loss of mechanical stability of the membranes. However, it is envisioned that the gradual degradation of the PCL/rGO membranes could facilitate cells infiltration, interconnectivity, and tissue formation.

BDD anodic treatment of 6:2 fluorotelomer sulfonate (6:2 FTSA). Evaluation of operating variables and by-product formation.

The concerns about the undesired impacts on human health and the environment of long chain perfluorinated alkyl substances (PFASs) have driven industrial initiatives to replace PFASs by shorter chain fluorinated homologues. 6:2 fluorotelomer sulfonic acid (6:2 FTSA) is applied as alternative to PFOS in metal plating and fluoropolymer manufacture. This study reports the electrochemical treatment of aqueous 6:2 FTSA solutions on microcrystalline BDD anodes. Bench scale batch experiments were performed, focused on assessing the effect of the electrolyte and the applied current density (5-600 A m-2) on the removal of 6:2 FTSA, the reduction of total organic carbon (TOC) and the fluoride release. Results showed that at the low range of applied current density (J = 50 A m-2), using NaCl, Na2SO4 and NaClO4, the electrolyte exerted a minimal effect on removal rates. The formation of toxic inorganic chlorine species such as ClO4- was not observed. When using Na2SO4 electrolyte, increasing the applied current density to 350-600 A m-2 promoted a notable enhancement of the 6:2 FTSA removal and defluorination rates, pointing to the positive contribution of electrogenerated secondary oxidants to the overall removal rate. 6:2 FTSA was transformed into shorter-chain PFCAs, and eventually into CO2 and fluoride, as TOC reduction was >90%. Finally, it was demonstrated that diffusion in the liquid phase was controlling the overall kinetic rate, although with moderate improvements due to secondary oxidants at very high current densities.

Electrochemical mineralization and detoxification of naphthenic acids on boron-doped diamond anodes.

Electrochemical oxidation (ELOX) with boron-doped diamond (BDD) anodes was successfully applied to degrade a model aqueous solution of a mixture of commercial naphthenic acids (NAs). The model mixture was prepared resembling the NA and salt composition of oil sands process-affected water (OSPW) as described in the literature. The initial concentration of NAs between 70 and 120 mg/L did not influence the electrooxidation kinetics. However, increasing the applied current density from 20 to 100 A/m2 and the initial chloride concentration from 15 to 70 and 150 mg/L accelerated the rate of NA degradation. At higher chloride concentration, the formation of indirect oxidative species could contribute to the faster oxidation of NAs. Complete chemical oxygen demand removal at an initial NA concentration of 120 mg/L, 70 mg/L of chloride and applied 50 A/m2 of current density was achieved, and 85% mineralization, defined as the decrease of the total organic carbon (TOC) content, was attained. Moreover, after 6 h of treatment and independently on the experimental conditions, the formation of more toxic species, i.e. perchlorate and organochlorinated compounds, was not detected. Finally, the use of ELOX with BDD anodes produced a 7 to 11-fold reduction of toxicity (IC50 towards Vibrio fischeri) after 2 h of treatment.

Dioxins and furans legacy of lindane manufacture in Sabiñánigo (Spain). The Bailín landfill site case study.

Lindane (γ-hexachlorocyclohexane) manufacture in Spain generated nearly 200,000tonnes of HCH wastes; near 160,000tonnes were originated by the Inquinosa factory located in Sabiñánigo (northern Spain) and were deposited in unlined landfill sites. This study reports for the first time the content of polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/Fs) in non-recycled HCH wastes that had been disposed in the Bailín landfill site in Sabiñánigo. Samples from solid HCH powder residues (white HCH and δ-paste wastes) and the dense non-aqueous phase liquids (DNAPLs), as well as landfill leachates, soil and sediments have been characterized. White HCH wastes exhibited a toxicity of 1488ngWHO-TEQ2005·kg-1 (Σ17 PCDD/Fs), while δ-paste wastes presented a noticeable higher toxicity (12,094ngWHO-TEQ2005·kg-1). Nevertheless, the maximum toxicity value was found for DNAPLs (37,353ngWHO-TEQ2005·L-1). Dioxins were predominant in the DNAPL waste whereas furans predominated in the landfill leachates, soil and sediments. However, in solid HCH wastes, PCDD and PCDFs contributed in a similar proportion. The PCDD/Fs congener profiles in landfill leachates, soil and sediments do not resemble the PCDD/Fs profiles found for the HCH wastes. These preliminary results will be of paramount importance in order to estimate the total quantities of PCDD/Fs disposed to the landfill site and to assess the potential mobility of PCDD/Fs, especially to groundwater and landfill leachates. Besides, this information is of great value to design periodical monitoring plans to evaluate the presence of PCDD/Fs in the impacted groundwater and leachates and finally, to evaluate the risk of PCDD/Fs for the environment and human health.

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.