1,720,963 research outputs found
Effect of TiO2 nanoparticles on fouling mitigation of ultrafiltration membranes for activated sludge filtration
No full textMembrane bioreactors (MBRs) have been widely used as advanced wastewater treatment process in recent years. However, MBR system has a membrane fouling problem, which makes the system less competitive. Thus there have been great efforts for fouling mitigation. In this study, two types of TiO2 immobilized ultrafiltration membranes (TiO2 entrapped and deposited membranes) were prepared and applied to activated sludge filtration in order to evaluate their fouling mitigation effect. Membrane performances were changed by addition of TiO2 nanoparticles to the casting solution. TiO2 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content, but it reached limit content above which fouling mitigation did not increase. Regardless of polymeric materials, membrane fouling was mitigated by TiO2 immobilization. TiO2 deposited membrane showed greater fouling mitigation effect compared to that of TiO2 entrapped membrane, since larger amount of nanoparticle was located on membrane surface. It can be concluded that TiO2 immobilized membranes are simple and powerful alternative for fouling mitigation in MBR application. (C) 2004 Published by Elsevier B.V.
Interpretation of fouling characteristics of ultrafiltration membranes during the filtration of membrane bioreactor mixed liquor
No full textIn this study, ultrafiltration (UF) membranes with various pore sizes were prepared by the phase inversion method, and their fouling characteristics were investigated with membrane bioreactor (MBR) mixed liquor. MBR sludge was fractionated into three parts, suspended solids, colloids and solutes, and their individual contributions to membrane fouling were quantified in order to asses the mechanisms by which fouling occurs. Cake layer formation on the membrane surface constituted the main fouling mechanism and the incidence of irreversible fouling was so small as to be negligible. The degree of fouling correlated very strongly with membrane permeability. This implies that hydrodynamic conditions are important factors affecting membrane fouling. The fouling contribution of each sludge fraction appeared to depend on particle size, as both permeation drag and back transport velocity are particle size-related functions. Solutes played a significant role in the initiation of cake layer formation, because they were deposited onto the membrane surface and pore wall immediately upon initial filtration, but were dislodged only in small amounts by cross flow. Suspended solids were consistently deposited onto the membrane surface, until flux reached a steady state and colloids exhibited characteristics commensurate with an intermediated state between solutes and suspended solids. Suspended A solids were, in fact, found to be the main contributor to the fouling process. However, the relative contribution of each of the sludge fractions to membrane fouling varied with the permeability of the membrane, and also with the hydrodynamic condition. (c) 2005 Elsevier B.V. All rights reserved.
Preparation of TiO2 self-assembled polymeric nanocomposite membranes and examination of their fouling mitigation effects in a membrane bioreactor system
No full textIn this study, we investigated the ability of TiO2 self-assembled nanocomposite membranes to mitigate fouling effects during the filtration of membrane bioreactor (MBR) mixed liquor. Our results showed that membrane fouling was significantly reduced by the immobilization of TiO2 nanoparticles on the surface of these membranes. The fouling mitigation effect increased with increasing amounts of TiO2 nanoparticles and the initial sharp flux decline observed for neat polymeric membranes was alleviated by TiO2 immobilization. Adsorbed foulants on the surface of nanocomposite membranes were more readily dislodged by shear force than those on neat polymeric membranes due to the increased hydrophilicity of the membrane. Accordingly, the amount and the rate of membrane fouling decreased in the nanocomposite membranes. (c) 2005 Elsevier B.V. All rights reserved.
Preparation and characterization of fouling-resistant TiO2 self-assembled nanocomposite membranes
No full textIn this study, fouling-resistant nanocomposite membranes were prepared via electrostatic self-assembly between TiO2 nanoparticles and sulfonic acid groups on the membrane surface. Sulfonated polyethersulfone (SPES) was prepared by heterogeneous sulfonation with chlorosulfonic acid, and a TiO2 nanoparticle solution was prepared from the controlled hydrolysis of titanium tetraisopropoxide. Then, the SPES ultrafiltration membranes, which were prepared by the phase inversion method, were dipped in the TiO2 nanoparticle solution, thereby producing the TiO2/polymer nanocomposite membranes. The fouling mitigation property of the nanocomposite membrane was examined using membrane bioreactor (MBR) sludge, which contains a great number of various foulants. The results showed that the amount and rate of membrane fouling decreased in the nanocomposite membranes compared to the polymeric membranes. (c) 2006 Elsevier B.V. All rights reserved.
Influence of sludge retention time on membrane fouling and bioactivities in membrane bioreactor system
No full textSludge retention time (SRT) can produce significant effects on biomass properties in a membrane bioreactor (MBR) system. In this study, the membrane separation process was coupled to a sequencing batch reactor (SBR), which is one of the biological nutrient removal (BNR) processes, and the influence of SRT on membrane fouling and biological activity was investigated. Membrane fouling increased with SRT since sludge particles were more severely deposited on the membrane surface at longer SRT. Regardless of SRT change, COD removal efficiency was high and stable (over 92%) throughout the experiment. Nitrogen removal efficiency also attained a high treatment level. However, it was not proportioned to SRT increase and rather decreased at the longest SRT. Phosphorus removal decreased at prolonged SRT since excess sludge was reduced. Biological activity such as specific oxygen uptake rate (SOUR), specific nitrification rate (SNR), and specific denitrification rate (SDNR) did not increase with SRT but decreased at prolonged SRT. (c) 2004 Elsevier Ltd. All rights reserved.
The behavior of membrane fouling initiation on the crossflow membrane bioreactor system
No full textA membrane bioreactor (MBR) system (i.e. an activated sludge system where the clarifier has been replaced with membrane filtration) has many advantages compared with the conventional activated sludge process. However a serious problems that has prevented this technology from reaching its potential is membrane fouling. In this study, the biomass was cultivated under three conditions: normal (high dissolved oxygen, DO); bulking; and normal conditions with low DO concentration. Membrane filtration tests were performed with cellulose acetate (CA), sulfonated polyethersulfone (SPES) and polyethersulfone (PES) membranes, respectively. Relatively hydrophobic PES membranes fouled more seriously than hydrophilic CA membranes. This phenomenon was especially significant under bulking conditions. Ultimate flux was almost equal for all three membrane types however, since the PES and SPES started with higher initial fluxes. Effluent quality was not affected by membrane fouling/flux but did deteriorate at low Dos. (C) 2002 Elsevier Science B.V. All rights reserved.
Fouling control in activated sludge submerged hollow fiber membrane bioreactors
No full textThe goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid-liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH4)(2)SO4 as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate, The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mg/L. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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