Removal of aqueous nC60 fullerene from water by low pressure membrane filtration

Preparation of the titanium-based composite coagulant PTFS and its coagulation performance on nanoparticles

In this study, a titanium-based coagulant, (i.e., PTFS), with a three-dimensional spatial mesh structure was prepared for the coagulation removal of polystyrene (PS) and titanium dioxide (TiO2) nanoparticles in water. The results of scanning electron microscopy, TGA-DSC, Fourier infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy characterization showed that the PTFS was not a simple mixture of raw materials and a chemical reaction occurred, thereby generating new chemically connected bonds. The optimum removal of PS could reach 92.5% at the dosage of 0.6 mg/L, initial concentration of 70 mg/L, pH of 7, stirring intensity of 350 rpm, settling time of 60 min, and kaolin concentration of 70 mg/L. The best removal rate of TiO2 could reach 95.3% when the dosage was 0.8 mg/L, the initial concentration was 70 mg/L, the pH was 7, the stirring intensity was 350 rpm, the settling time was 60 min, and the kaolin concentration was 50 mg/L. The flocs produced by PTFS were large and dense. In the early stage of coagulation, the flocculation mechanism was dominated by electroneutralization, and in the middle and late stages of coagulation, adsorption, bridging, and netting were dominated. This study aims to provide a reference for the removal of nanopollutants by coagulation in the actual water treatment process. PRACTITIONER POINTS: A titanium-based coagulant PTFS with a three-dimensional spatial mesh structure was prepared. PTFS effectively removes nano-PS and nano-TiO2 from water. The flocs produced by PTFS were large and dense flocs. Removal of PS and TiO2 by PFTS has been a combination of multiple coagulation mechanisms.

Mobility and redox transformation of arsenic during treatment of artificially recharged groundwater for drinking water production

In this study we investigate opportunities for reducing arsenic (As) to low levels, below 1 μg/L in produced drinking water from artificially infiltrated groundwater. We observe that rapid sand filtration is the most important treatment step for the oxidation and removal of As at water treatment plants which use artificially recharged groundwater as source. Removal of As is mainly due to As co-precipitation with Fe(III)(oxyhydr)oxides, which shows higher efficiency in rapid sand filter beds compared to aeration and supernatant storage. This is due to an accelerated oxidation of As(III) to As(V) in the filter bed which may be caused by the manganese oxides and/or As(III) oxidizing bacteria, as both are found in the coating of rapid sand filter media grains by chemical analysis and taxonomic profiling of the bacterial communities. Arsenic removal does not take place in treatment steps such as granular activated carbon filtration, ultrafiltration or slow sand filtration, due to a lack of hydrolyzing iron in their influent and a lack of adsorption affinity between As and the filtration surfaces. Further, we found that As reduction to below 1 μg/L can be effectively achieved at water treatment plants either by treating the influent of rapid sand filters by dosing potassium permanganate in combination with ferric chloride or by treating the effluent of rapid sand filters with ferric chloride dosing only. Finally, we observe that reducing the pH is an effective measure for increasing As co-precipitation with Fe(III)(oxyhydr)oxides, but only when the oxidized arsenic, As(V), is the predominant species in water.

Water disinfection processes change the cytotoxicity of C60 fullerene: Reactions at the nano-bio interface

The environmental transformation of nanoparticles results in significant changes in their structure, properties, and toxicity, which are imperative for assessing their environmental impact and health risks. Little is known about the toxicity alteration of fullerene nanoparticles (C₆₀) after water disinfection processes considering their potential application in antimicrobial control in water treatment ultimately ending in sewage treatment plants. We showed that C₆₀ aggregates (nC₆₀) were converted to more oxidized forms via commonly used water disinfection processes (i.e., phototransformation and photochlorination treatment). The light-irradiated nanoparticles (UV_nC₆₀) exhibited mitigated cytotoxicity relative to nC₆₀, whereas photochlorinated nC₆₀ (UV/Cl_nC₆₀) showed an exacerbated outcome. We revealed a distinct toxic mechanism occurring at the nano-bio interface, for which electrons were shuttled by C₆₀ nanoparticles from membrane-bound NADPH oxidase to extracellular molecular oxygen, resulting in the production of various extracellular reactive oxygen species (ROS). UV/Cl_nC₆₀ showed the highest electron-shuttling activity due to its high carbonyl content, and more than 2.4-fold higher level of extracellular hydroxyl radicals were detected relative to that in untreated cells. Although UV_nC₆₀ possessed a somewhat higher carbonyl content than nC₆₀, it showed a weaker adhesion to the cell membrane, which compromised the electron-transfer process. The intrinsic ROS generation/quenching capabilities and oxidative potentials of the various nanoparticles were also systematically compared. Overall, this report highlights the importance of understanding environmental transformations in risk assessment and uncovers an overlooked mechanism through which nC₆₀/derivatives can modulate the electron transfer process at the nano-bio interface via acting as electron shuttles.

Characteristics of Fe and Mn bearing precipitates generated by Fe(II) and Mn(II) co-oxidation with O2, MnO4 and HOCl in the presence of groundwater ions

In this work, we combined macroscopic measurements of precipitate aggregation and chemical composition (Mn/Fe solids ratio) with Fe and Mn K-edge X-ray absorption spectroscopy to investigate the solids formed by co-oxidation of Fe(II) and Mn(II) with O₂, MnO₄, and HOCl in the presence of groundwater ions. In the absence of the strongly sorbing oxyanions, phosphate (P) and silicate (Si), and calcium (Ca), O₂ and HOCl produced suspensions that aggregated rapidly, whereas co-oxidation of Fe(II) and Mn(II) by MnO₄ generated colloidally stable suspensions. The aggregation of all suspensions decreased in P and Si solutions, but Ca counteracted these oxyanion effects. The speciation of oxidized Fe and Mn in the absence of P and Si also depended on the oxidant, with O₂ producing Mn(III)-incorporated lepidocrocite (Mn/Fe = 0.01-0.02 mol/mol), HOCl producing Mn(III)-incorporated hydrous ferric oxide (HFO) (Mn/Fe = 0.08 mol/mol), and MnO₄ producing poorly-ordered MnO₂ and HFO (Mn/Fe > 0.5 mol/mol). In general, the presence of P and Si decreased the crystallinity of the Fe(III) phase and increased the Mn/Fe solids ratio, which was found by Mn K-edge XAS analysis to be due to an increase in surface-bound Mn(II). By contrast, Ca decreased the Mn/Fe solids ratio and decreased the fraction of Mn(II) associated with the solids, suggesting that Ca and Mn(II) compete for sorption sites. Based on these results, we discuss strategies to optimize the design (i.e. filter bed operation and chemical dosing) of water treatment plants that aim to remove Fe(II) and Mn(II) by co-oxidation.

Removal of TiO2 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 0.4μm pore size). The release of nTiO₂ in the pilot scale filtration system was always above the instrumental detection limit (>1.5μg/L) and in most cases below 100μg/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.

Risk analysis and technology assessment in support of technology development: Putting responsible innovation in practice in a case study for nanotechnology

Governments invest in "key enabling technologies," such as nanotechnology, to solve societal challenges and boost the economy. At the same time, governmental agencies demand risk reduction to prohibit any often unknown adverse effects, and industrial parties demand smart approaches to reduce uncertainties. Responsible research and innovation (RRI) is therefore a central theme in policy making. Risk analysis and technology assessment, together referred to as "RATA," can provide a basis to assess human, environmental, and societal risks of new technological developments during the various stages of technological development. This assessment can help both governmental authorities and innovative industry to move forward in a sustainable manner. Here we describe the developed procedures and products and our experiences to bring RATA in practice within a large Dutch nanotechnology consortium. This is an example of how to put responsible innovation in practice as an integrated part of a research program, how to increase awareness of RATA, and how to help technology developers perform and use RATA. Integr Environ Assess Manag 2018;14:9-16. © 2017 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).