Removal of TiO 2 nanoparticles from water by low pressure pilot plant filtration

Rising use of nanoparticles in manufacturing as well as in commercial products bring issues related to environmental release and human exposure. A large amount of TiO2 nanoparticles will eventually reach wastewater treatment plants. Low pressure membrane filtration has been suggested as a feasible treatment of water streams. This study investigated first at laboratory scale the influence of: i) membrane material, ii) pore size and iii) water chemistry on nTiO2 removal. TiO2 retention was governed by the cake layer formation mechanism and significant retention of nanoparticles was observed even for filters having considerably larger pores than nTiO2. PVDF showed a great potential for nTiO2 rejection. Additionally, filtration pilot plant experiments were carried out using PVDF membranes (0.03 and 0.4 μm pore size). The release of nTiO2 in the pilot scale filtration system was always above the instrumental detection limit (> 1.5 μg/L) and in most cases below 100 μg/L regardless of the pore size and applied conditions. The nTiO2 membrane breakthrough predominantly occurred in the first few minutes after backwashes and ceased when the cake layer was formed. Ultrafiltration and microfiltration were comparable with rejection of nTiO2 above 95% at similar permeate flow rates. Nevertheless, ultrafiltration is more promising than microfiltration because it allowed longer operation times between backwash cycles.This work was funded by the Provincial Government of Bizkaia (6-12-TK-2010-0013)

Evaluation of photocatalytic nanoparticle release to the aquatic environment

Publisher Copyright: © 2013 TANGER Ltd.Nanotechnology creates possibilities to produce new products with novel functionalities and improved characteristics. Therefore the incorporation of engineered nanoparticles (ENP) in commercial products is progressively increasing and so is the potential for release of these novel materials into the environment. In fact, the occurrence and release of titanium nanomaterials in a wastewater treatment plant has already been proven. This implies that nanomaterials will reach the aquatic environment and that they could represent a risk to aquatic organisms and humans. We have studied the discharge of nano-TiO2 (nTiO2) to water for two case studies related to photocatalytic nanomaterials: A- The release of nTiO2 from two photocatalytic coatings under accelerated aging under a water flow and B- The release of nTiO2 though a filtration pilot plant from tap water containing 2 mg/L nanoparticles. Case A. The influence of environmental parameters (water matrix, UV-light) was investigated while the consequences of aging were evaluated under different endpoints, among them, the release of TiO2 nanoparticles. Despite that TiO2 emissions were observed for both coatings, only one of them presented mechanical damages. TiO2 concentrations up to 150.5 μg/L were detected in the aging water. Case B. Preliminary experiments were conducted at laboratory scale to determine optimum polymeric material as well as pore size. Among the common commercial materials PVDF showed the best performance. Two different industrial hollow fiber cartridges were tested with a pore size of 0.45 μm (microfiltration) and 0.03 μm (ultrafiltration). TiO2 was detected at an average concentration of 51 μg/L in the filtered water.Peer reviewe

Aging of photocatalytic coatings under a water flow: Long run performance and TiO 2 nanoparticles release

Although photocatalytic coatings may experience severe wearing in most of their application, little work has been done to investigate their aging in a comprehensive way. In this article, we present an original experimental protocol to simulate an accelerated aging of photocatalytic coatings under a water flow, and test it on two materials: a well-known commercial product, Pilkington Activ™, and an experimental coating. The influence of intrinsic properties of the coatings (chemical nature, thickness) as well as environmental parameters (water matrix, UV-light) is investigated while the consequences of aging are evaluated under three different endpoints, related either to the long run performance of photocatalytic coatings or their environmental impact: (i) loss of the photocatalytic activity, (ii) degradation of mechanical properties, and (iii) release of TiO 2 nanoparticles. It is observed that both photocatalytic coatings experienced a deactivation of their active sites upon prolonged immersion. The extent of deactivation varies depending on the coating, being around 20% for experimental coatings and 65% for Pilkington Activ™ but shows little dependency on water matrix or illumination. An alteration of mechanical properties is seen on experimental coatings, which was accompanied by TiO 2 emissions as high as 150.5μgL -1. Although no reduction in film hardness or adhesion could be evidenced for Pilkington Activ™, TiO 2 concentrations up to 30.8μgL -1 was detected in the aging water showing that some release of TiO 2 nanoparticles also took place on this material. Interestingly, a common mechanism of release, triggered by an interaction between TiO 2, NaCl and UVA could be identified. Most severe damages were observed in presence of sodium chloride. These results suggest that the use of photocatalytic coatings with surface-bound nanoparticles in environmental applications may entail new entries of nanomaterials into the aqueous medium. They also prove that aging assays are an effective way of assessing the emissions.This work was jointly funded by Cantabria Government in the framework of the AquaNAN project and TECNALIA Foundation under its internal Nanotechnology Programme. Great thanks are due to Txomin Laburu for his determining help in the design and elaboration of the aging flumes and Carmen del Río for ICP-OES measurements.Peer reviewe

Stacked wire-mesh monoliths for VOCs combustion: Effect of the mesh-opening in the catalytic performance

Structured reactors based on low cost metallic wire-mesh substrates of highly enhanced transport properties can be an interesting alternative to parallel channel monolithic reactors. In this work stacked wire-mesh monoliths were studied for volatile organic compounds elimination. Monoliths of different mesh-opening were homogeneously and adherently dip-coated with Pt/Manganese Octahedral Molecular Sieve (OMS-2) bifunctional catalyst. The catalytic activity was tested in toluene and methanol complete oxidation reactions. Catalytic activity increases using stacked wire-mesh monoliths instead of parallel channel monoliths and decreases when increasing the wire-mesh opening, showing the importance of the mass-transfer phenomena (contact between the gas phase and the solid catalyst).Fil: Sanz, Oihane. Universidad del País Vasco; EspañaFil: Banus, Ezequiel David. Universidad del País Vasco; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Goya, Aintzane. Universidad del País Vasco; EspañaFil: Larumbe, Haizea. Universidad del País Vasco; EspañaFil: Delgado, Juan José. Universidad de Cádiz; EspañaFil: Monzón, Antonio. Universidad de Cádiz; EspañaFil: Montes, Mario. Universidad del País Vasco; Españ