Effect of protein fouling on filtrate flux and virus breakthrough behaviors during virus filtration process.

Virus filtration process is used to ensure viral safety in the biopharmaceutical downstream processes with high virus removal capacity (i.e., >4 log10 ). However, it is still constrained by protein fouling, which results in reduced filtration capacity and possible virus breakthrough. This study investigated the effects of protein fouling on filtrate flux and virus breakthrough using commercial membranes that had different symmetricity, nominal pore size, and pore size gradients. Flux decay tendency due to protein fouling was influenced by hydrodynamic drag force and protein concentration. As the results of prediction with the classical fouling model, standard blocking was suitable for most virus filters. Undesired virus breakthrough was observed in the membranes having relatively a large pore diameter of the retentive region. The study found that elevated levels of protein solution reduced virus removal performance. However, the impact of prefouled membranes was minimal. These findings shed light on the factors that influence protein fouling during the virus filtration process of biopharmaceutical production.

Tannic acid-assisted in-situ interfacial formation of Prussian blue-assembled adsorptive membranes for radioactive cesium removal.

There is a growing interest in advanced materials that can effectively treat wastewater contaminated with radioactive cesium (137Cs), which is an extremely hazardous material. Here, we report a new class of Cs-adsorptive membranes compactly assembled with Cs-adsorptive Prussian blue (PB) particles. The PB particle assembly was formed via an in-situ interfacial reaction between two PB precursors in the presence of tannic acid (TA) as a binder on a porous support. While the interfacial reaction enabled the formation of a defect-less PB network, TA enhanced the PB-PB and PB-support compatibilities, consequently producing a uniform, densely packed PB assembly near the support surface. The fabricated TA-assisted PB membrane (PB/TA-M) synergistically rejected Cs via a combination of adsorption and membrane filtration, although adsorption predominantly determined Cs rejection initially. Hence, the PB/TA-M membrane showed considerably higher Cs removal performance than commercial nanofiltration (NF) and reverse osmosis (RO) polyamide (PA) membranes for a sufficiently long operation time. Furthermore, the PB/TA-M membrane displayed excellent radioactive 137Cs removal performance, significantly exceeding those of commercial NF and RO PA membranes due to its higher radiation stability, indicating its viability for application in treating actual radioactive wastewater.

Investigation of the performance behavior of a forward osmosis membrane system using various feed spacer materials fabricated by 3D printing technique.

Recently, feed spacer research for improving the performance of a membrane module has adopted three-dimensional (3D) printing technology. This study aims to improve the performance of membrane feed spacers by using various materials and incorporating 3D printing. The samples were fabricated after modeling with 3D computer-aided design (CAD) software to investigate the mechanical strength, water flux, reverse solute flux, and fouling performances. This research was performed using acrylonitrile butadiene styrene (ABS), polypropylene (PP), and natural polylactic acid (PLA) as printing material, and the spacer model was produced using a diamond-shaped feed spacer, with a commercially available product as a reference. The 3D printed samples were initially compared in terms of size and precision with the 3D CAD model, and deviations were observed between the products and the CAD model. Then, the spacers were tested in terms of mechanical strength, water flux, reverse solute flux, and fouling (alginate-based waste water was used as a model foulant). Although there was not much difference among the samples regarding the water flux, better performances than the commercial product were obtained for reverse solute flux and fouling resistance. When comparing the prominent performance of natural PLA with the commercial product, PLA was found to have approximately 10% less fouling (based on foulant volume per unit area and root mean square roughness values), although it showed similar water flux. Thus, another approach has been introduced for using bio-degradable materials for membrane spacers.

Alginate fouling reduction of functionalized carbon nanotube blended cellulose acetate membrane in forward osmosis.

Functionalized multi-walled carbon nanotube blended cellulose acetate (fCNT-CA) membranes were synthesized for forward osmosis (FO) through phase inversion. The membranes were characterized through SEM, FTIR, and water contact angle measurement. AFM was utilized to investigate alginate fouling mechanism on the membrane. It reveals that the fCNT contributes to advance alginate fouling resistance in FO (57% less normalized water flux decline for 1% fCNT-CA membrane was observed than that for bare CA membrane), due to enhanced electrostatic repulsion between the membrane and the alginate foulant. Furthermore, it was found that the fCNT-CA membranes became more hydrophilic due to carboxylic groups in functionalized carbon nanotube, resulting in approximately 50% higher water-permeated flux than bare CA membrane. This study presents not only the fabrication of fCNT-CA membrane and its application to FO, but also the quantification of the beneficial role of fCNT with respect to alginate fouling in FO.

Characterization of natural organic matter treated by iron oxide nanoparticle incorporated ceramic membrane-ozonation process.

In this study, changes in the physical and structural properties of natural organic matter (NOM) were observed during hybrid ceramic membrane processes that combined ozonation with ultrafiltration ceramic membrane (CM) or with a reactive ceramic membrane (RM), namely, an iron oxide nanoparticles (IONs) incorporated-CM. NOM from feed water and NOM from permeate treated with hybrid ceramic membrane processes were analyzed by employing several NOM characterization techniques. Specific ultraviolet absorbance (SUVA), high-performance size exclusion chromatography (HPSEC) and fractionation analyses showed that the hybrid ceramic membrane process effectively removed and transformed relatively high contents of aromatic, high molecular weight and hydrophobic NOM fractions. Fourier transform infrared spectroscopy (FTIR) and 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy revealed that this process caused a significant decrease of the aromaticity of humic-like structures and an increase in electron withdrawing groups. The highest removal efficiency (46%) of hydroxyl radical probe compound (i.e., para-Chlorobenzoic acid (pCBA)) in RM-ozonation process compared with that in CM without ozonation process (8%) revealed the hydroxyl radical formation by the surface-catalyzed reaction between ozone and IONs on the surface of RM. In addition, experimental results on flux decline showed that fouling of RM-ozonation process (15%) was reduced compared with that of CM without ozonation process (30%). These results indicated that the RM-ozonation process enhanced the destruction of NOM and reduced the fouling by generating hydroxyl radicals from the catalytic ozonation in the RM-ozonation process.

As(III) removal by hybrid reactive membrane process combined with ozonation.

The removal of arsenite (As(III)) was investigated using a combined ozonation-reactive ceramic membrane incorporated with iron oxide nanoparticles (IONs). A disk-type γ-Al(2)O(3) ultrafiltration membrane (CM) was covered with IONs using an annealing method. The reactive ceramic membrane (RM) was then characterized using SEM, zeta potential measurements, and pure water permeability tests. The results showed that IONs were well attached on the RM surface. In addition, doped IONs had no significant effects on the pure water permeability and the isoelectric point (IEP) of RM. Laboratory-scale experiments were subsequently conducted to investigate the impact of combined RM and ozonation processes on As(III) rejection. The experimental results revealed that As(III) rejection rate of RM with an ozonation process (92%) significantly enhanced compared with that of CM (63%). The influence of operating parameters (i.e., pH, NOM, co-existing ions and temperature) revealed that an increase of pH, a decrease of temperature and presence of NOM led to a higher As(III) rejection, whereas the presence of co-existing ions in the feed water significantly reduced the As(III) rejection; divalent counter-ions were the greatest inhibitors for As(III) rejection. Finally, a comparison of As(III) rejection in synthetic water and real groundwater confirmed the importance of real conditions in the hybrid reactive membrane process with continuous ozonation.

Carbon nanotube blended polyethersulfone membranes for fouling control in water treatment.

Multi-walled carbon nanotube/polyethersulfone (C/P) blend membranes were synthesized via the phase inversion method. The resultant membranes were then characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle. The C/P blend membranes appeared to be more hydrophilic, with a higher pure water flux than the polyethersulfone (PES) membranes. It was also found that the amount of multi-walled carbon nanotubes (MWCNTs) in the blend membranes was an important factor affecting the morphology and permeation properties of the membranes. After 24 h of surface water filtration with 7 mgC/L TOC content, the C/P blend membranes displayed a higher flux and slower fouling rate than the PES membranes. Subsequent analyses of the desorbed foulants showed that the amount of foulant on bare PES membranes was 63% higher than the C/P blend membrane for 2% MWCNTs content. Thus, the carbon nanotube content of the C/P membranes was shown to alleviate the membrane fouling caused by natural water.