Gradual PVP leaching from PVDF/PVP blend membranes and its effects on membrane fouling in membrane bioreactors

© 2018 Elsevier B.V. Improving the hydrodynamics on the membrane surface in a magnetically induced membrane vibration system (MMV) has been proven efficient for membrane fouling control in membrane bioreactors. This advantage can be further extended by using an optimized membrane. This was realized in this study by preparing porous polyvinylidene fluoride membranes via polyvinylpyrrolidone (PVP) blending and later by leaching out the PVP from the membrane matrix via post-treatment using NaOCl. Results show that increasing the PVP content in the casting solution increases membrane fouling resistance. Slowly leaching of PVP after several periodic NaOCl cleanings increased membrane permeance. No advantage of NaOCl post-treatment was observed. The long-term filtration confirmed the superiority of the highly porous membrane that complemented the advantages offered by the MMV system. This suggests that despite the small quantity of the remaining PVP, its leaching offered a substantial gain to improve membrane filterability.status: publishe

New Concept for Dual-Layer Hydrophilic/Hydrophobic Composite Membrane for Membrane Distillation

This study presents a new concept of a simple method for the synthesis of dual layer hydrophilic/hydrophobic composite membranes for membrane distillation (MD). The membranes were prepared of poly(vinylidenefluoride) (PVDF) by phase inversion. The synthesis was realized by allowing a full or partial penetration of the polymer solution through one or two non-woven support (NWS) layers. This was achieved by proper selection of a thin NWS having high stiffness, high porosity and low surface tension, in combination with a runny polymer solution and sufficient time gap between casting and coagulation. The applied preparation method was effective in yielding dual layer composite membranes. The first layer atop the NWS was a hydrophilic or slightly hydrophobic one (contact angle (CA) of 88-92º), while the bottom layer beneath the NWS was highly hydrophobic (CA=132-140º). The difference in surface energy between the top and bottom layers originated from a difference in morphology. A smooth and dense top layer is formed as a result of an instantaneous demixing, while a porous and multi-scale network with some degrees of spherulitical structure was formed on the bottom by a delayed demixing mechanism. Direct contact MD (DCMD) results showed that the obtained flux was comparable to other composite MD membranes with high salt rejection. Membrane alignment inside the MD module is a critical element in determining the membrane performance and is shown to significantly increase flux when a top facing feed configuration is used

Poly(vinylidene fluoride)-Based Membranes for Microalgae Filtration

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Two poly(vinylidene fluoride) (PVDF) membrane modification approaches, i.e., poly(vinylpyrrolidone) (PVP) modification and sulfonation, were applied and investigated to produce a fouling-resistant membrane for microalgae filtration. Both methods were able to alter the membrane surface to become more hydrophilic. However, clean water permeance increased only for the PVP-modified membranes, while the sulfonated membranes underwent a significant morphology transformation to a denser membrane and thus lower permeance. Microalgae filtration with PVP-modified membranes showed less fouling compared to the pristine one, particularly in the beginning of the filtration, indicating that fouling reduction on these membranes mainly occurs in the initial fouling stage. Fouling is also found to be influenced by the microalgae species, possibly due to the different properties of the formed cake layer.status: publishe

Study of PVDF asymmetric membranes in a high-throughput membrane bioreactor (HT-MBR): Influence of phase inversion parameters and filtration performance

© 2016 Elsevier B.V. All rights reserved. Porous polyvinylidene fluoride (PVDF) membranes with different morphology were prepared via phase inversion followed by comprehensive screening for use in activated sludge filtration applying new type of lab-scale high-throughput membrane reactor (HT-MBR). First, the validation of the HT-MBR was performed involving multiple filtration tests of PVDF membrane samples, either in the same or in different positions in the reactor to verify reproducibility of the measurements in the HT-MBR and to check the homogeneity of the feed liquor hydrodynamics in the reactor. The validated set-up was then used for an accelerated screening of a systematic set of membranes with varying structure. Sixteen PVDF-membranes with mean pore size ranging from 0.05 to 0.37 μm and surface porosity from 2.8% to 13.9% were prepared via non-solvent induced phase separation by varying some phase-inversion parameters. The results showed that lowering the polymer concentration in the membrane casting solution, increasing the exposure time to the air of the cast membrane before solidification, and the use of additives (polyvinylpyrrolidone, PVP) to the casting solution resulted in more porous membranes, larger average pore sizes and higher surface porosities, thus offering higher clean water permeability. Activated sludge filtrations were evaluated implementing two different tests: a flux-stepping and a long-term filtration test. The more porous membranes were superior over the less porous ones, as higher critical fluxes and (slightly) higher permeance was maintained during the 37-day long-term test, although a sharp permeance decrease was observed in the first 7 days. However, for long-term application, these porous membranes should still be improved in order to have more sustained high permeability.publisher: Elsevier articletitle: Study of PVDF asymmetric membranes in a high-throughput membrane bioreactor (HT-MBR): Influence of phase inversion parameters and filtration performance journaltitle: Separation and Purification Technology articlelink: http://dx.doi.org/10.1016/j.seppur.2016.02.008 content_type: article copyright: Copyright © 2016 Elsevier B.V. All rights reserved.status: publishe

Two-way switch: Maximizing productivity of tilted panel in membrane bioreactor

Membrane fouling is a major challenge in membrane bioreactors (MBRs) and its effective handling is the key to improve their competitiveness. Tilting panel system offers significant improvements for fouling control but is strictly limited to one-sided panel. In this study, we assess a two-way switch tilting panel system that enables two-sided membranes and project its implications on performance and energy footprint. Results show that tilting a panel improves permeance by up to 20% to reach a plateau flux thanks to better contacts between air bubbles and the membrane surface to scour-off the foulant. A plateau permeance could be achieved at aeration rate of as low as 0.90 l min−1, a condition untenable by vertical panel even at twice of the aeration rate. Switching at short periods (<5min) can maintain the hydraulic performance as in no-switch (static system), enables application of a two-sided switching panel. A comparison of vertical panel under 1.80 l min−1 aeration rate with a switching panel at a half of the rate, switched at 1 min period shows ≈10% higher permeance of the later. Since periodic switching consumes a very low energy (0.55% of the total of 0.276 kWh m−3), with reduction of aeration by 50%, the switching tilted panel offers 41% more energy efficient than a referenced full-scale MBR (0.390 kWh m−3). Overall results are very compelling and highly attractive for significant improvements of MBR technologies