Effect of intermittent ultrasound on controlling membrane fouling with coagulation pre-treatment: Significance of the nature of adsorbed organic matter

Beneficial impacts of natural biopolymers during surface water purification by membrane nanofiltration

Membrane filtration in various forms has become an increasingly used treatment method worldwide for the supply of safe drinking water. The fouling of membranes is commonly considered to be the major operational limitation to its wider application since it leads to frequent backwashing and a shortening of membrane life, and increased production costs. The components of natural organic matter (NOM) in surface waters have been reported previously to be important foulants of nanofiltration (NF) membranes, however, the potential beneficial effect of particular components of these 'foulants' has not been investigated or demonstrated to date. In this study, we have considered the roles of different organic materials including autochthonous NOM (e.g., biopolymers) and allochthonous NOM (e.g., humic substances) on the fouling of NF membranes by bench-scale tests with samples of two representative source waters (UK) taken in two different seasons (autumn and winter). Microfiltration (MF) and ultrafiltration (UF) were employed to generate two permeates, between which the presence of biopolymers (30 kDa - 90 kDa) is the major difference. We developed sequential filtration (MF/UF-NF) to investigate biopolymers' behaviours in NF process. The results showed that the accumulation of biopolymers on NF membranes can mitigate fouling by providing a protective layer in which medium-low molecular weight (MW) materials (e.g. humic substances) are separated by adsorption and/or size exclusion. The protective layers assisted by biopolymers were seen to be thicker under scanning electron microscope (SEM) observation and characterized by higher roughness (i.e. three-dimensional, spacial structure) and greater adsorptive capacity. Moreover, improvement on NF membrane fouling mitigation could be more significant in autumn, comparing to that in winter. The findings in this study were found to be repeatable in similar tests with samples of comparable raw waters in China, and will be important to the practical application of NF membrane systems in terms of a new approach to combating fouling in long-term operation.

Recent Advancements of UF-Based Separation for Selective Enrichment of Proteins and Bioactive Peptides—A Review

Proteins are one of the primary building blocks that have significant functional properties to be applied in food and pharmaceutical industries. Proteins could be beneficial in their concentrated products or isolates, of which membrane-based filtration methods such as ultrafiltration (UF) encompass application in broad spectra of protein sources. More importantly, selective enrichment by UF is of immense interest due to the presence of antinutrients that may dominate their perspicuous bioactivities. UF process is primarily obstructed by concentration polarization and fouling; in turn, a trade-off between productivity and selectivity emerges, especially when pure isolates are an ultimate goal. Several factors such as operating conditions and membrane equipment could leverage those pervasive contributions; therefore, UF protocols should be optimized for each unique protein mixture and mode of configuration. For instance, employing charged UF membranes or combining UF membranes with electrodialysis enables efficient separation of proteins with a similar molecular weight, which is hard to achieve by the conventional UF membrane. Meanwhile, some proposed strategies, such as utilizing ultrasonic waves, tuning operating conditions, and modifying membrane surfaces, can effectively mitigate fouling issues. A plethora of advancements in UF, from their membrane material modification to the arrangement of new configurations, contribute to the quest to actualize promising potentials of protein separation by UF, and they are reviewed in this paper.

Improving the clarity and sensitization of polysorbate 80 by ultrasonic-assisted ultrafiltration technology

The safety problem of injections caused by clarity has lately become a widely shared concern. Due to the synthesis process, polysorbate 80 had a wide molecular weight distribution, which is also related to the clinical anaphylaxis. In this paper, ultrasonic-assisted ultrafiltration (UAU) technology was firstly applied to regulate colloidal structure and remove macromolecules from polysorbate 80 to improve injection clarity. In the separation process, ultrafiltration molecular weight cut off (MWCO), ultrasonic power and polysorbate 80 concentraion were selected as variables to adjust the separation efficiency. The ultrasonic frequency and power were provided by KQ-700DE ultrasonic system, based on the data analysis by response surface methodology (RSM), the optimal UAU parameters were as follows: ultrafiltration MWCO of 50,000, ultrasonic power of 900 W and polysorbate 80 concentration of 15.00 mg/mL. The experimental transmittance of polysorbate 80 was 87.6% and the qualification rate of clarity was 94.5%, which solved the separation contradiction among yield, clarity and safety. As an innovation in colloidal separation fields, UAU had a vast range of prospects for making use in pharmaceutical area.

In-situ ultrasound-assisted control of polymeric membrane fouling

Membrane separation processes have been more widely applied to industrial activities, especially in water and wastewater treatment. However, there are still challenges associated with the use of membranes. Concentration polarization and fouling can cause significant permeate flux decay during the filtration process, hindering its efficiency and increasing cost. Among many strategies, the combination of membrane filtration with ultrasound (US) application has shown promising results in reducing membrane fouling. The main goal of this research was to identify the effect of US frequency, US power intensity and feed solid concentration on permeate flux during ultrafiltration of simulated latex paint effluent. Maximum increase in permeate flux of 19.7% was obtained by applying 20 kHz and 0.29 W cm^-2 to a feed solution containing 0.075 wt% of solid. Overall, the application of US improves permeate flux by reducing fouling of ultrafiltration polymeric membrane.

A critical review on ultrasonic-assisted fouling control and cleaning of fouled membranes

Fouling is one of the most challenging problems impacting the performance of membrane-based separation technology. In recent years, ultrasound have been widely applied as an unconventional method to control membrane fouling, as well as to enhance membrane cleaning. The aim of the present work is to review the current literature and the recent developments related to the use of ultrasound as an innovative and alternative approach to improve the fouling behavior of membrane separation processes. The theory underlying ultrasonic-assisted phenomena is reviewed, together with operational factors that influence the effectiveness of the ultrasound treatment, such as frequency, power intensity, pressure, temperature, pH, and operation mode. Ultrasound irradiation effectively aids the cleaning of contaminated surfaces and enhances the permeate flux, owing to cavitation phenomena and powerful convective currents, associated with secondary phenomena, such as microstreamers, shock waves, and heating. However, the lifetime of the membranes should be carefully evaluated when applying ultrasonication as a technique of cleaning or controlling membrane fouling. Indeed, the integrity of membranes after sonication and the control of erosion produced by high ultrasonic intensities are key issues hindering the scale-up of this approach in the membrane industry. This reviews highlights the topics requiring more investigations, specifically to evaluate the economic aspects of ultrasonic assisted fouling control and cleaning in membrane processes.

The Fe-N-C oxidase-like nanozyme used for catalytic oxidation of NOM in surface water

The removal of natural organic matter (NOM), particularly humic substances (HS) from surface waters during drinking water treatment is necessary to avoid various water quality problems in supply, such as the formation of disinfection by-products. As an alternative to conventional processes (e.g. coagulation), and in the light of the rapidly increasing applications of nanozyme in bio-catalysis, a novel Fe-N-C oxidase-like nanozyme (FeNZ) has been prepared and used to catalyze the oxidative degradation of NOM during simple aeration. Using humic acid (HA) as a model NOM it was found that the HA removal (as TOC) was increased by a factor of 6 with a low dose (10 mg/L) of FeNZ compared to an aerated solution without FeNZ. A variety of analytical methods was used to investigate the oxygen reduction reaction, including cyclic voltammetry, electron spin resonance, and density functional theory (DFT) simulation. Based on these studies, a catalytic oxidation mechanism described as "adsorption-activation-oxidation" was proposed. The enhanced NOM removal performance of FeNZ catalytic oxidation was confirmed with samples of natural surface water in terms of organic mineralization and conversion of hydrophobic to hydrophilic components. The results show great potential for the use of oxidase-like nano catalytic materials in the field of water treatment.

PAC-PDMDAAC pretreatment of typical natural organic matter mixtures: Ultrafiltration membrane fouling control and mechanisms

Precoagulation by polyaluminum chloride-poly dimethyl diallyl ammonium chloride (PAC-PDMDAAC) prior to ultrafiltration (UF) was conducted to evaluate the influence of PAC-PDMDAAC on controlling membrane fouling from typical natural organic matter (NOM) mixtures of humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA). Membrane flux decline and flux recovery after backwashing were investigated to evaluate the membrane fouling. The fouling mechanisms were determined from the floc size, floc structure and membrane resistance. PAC-PDMDAAC effectively alleviated membrane fouling caused by the HA, HA-BSA, HA-SA and HA-BSA-SA mixtures; furthermore, membrane fouling was better mitigated in the HA-SA and HA-BSA-SA mixtures. The untreated HA-SA and HA-BSA-SA mixtures caused much more serious total membrane resistance and fouling due to blocking and adsorption in the membrane pores by particles with sizes similar to those of the pores. The increased membrane flux and decreased irreversible resistance after the PAC-PDMDAAC pretreatment were attributed to the formation of flocs with a large size and small fractal dimension, which mainly formed a cake layer on the membrane surface. However, PAC-PDMDAAC was not particularly effective in reducing the irreversible membrane fouling originating from the HA and HA-BSA mixtures due to the formation of aggregates and pore blocking by microflocs.

Host-Guest Polypyrrole Nanocomplex for Three-Stimuli-Responsive Drug Delivery and Imaging-Guided Chemo-Photothermal Synergetic Therapy of Refractory Thyroid Cancer

Despite the good prognosis of the low-risk thyroid cancer, there are no truly effective treatments for radioactive iodine-refractory thyroid cancer. Herein, a novel theranostic nanoplatform, as well as a smart doxorubucin (DOX) delivery system is fabricated. Gelatin-stabilized polypyrrole nanoparticles are reported for the first time. The combination of gelatin-stabilized polypyrrole and cyclodextrin-DOX complexes enabling three-stimuli-controlled drug delivery, including the enzyme-sensitive, pH-sensitive and photothermal-sensitive drug release, exhibiting a new way to equip photothermal agents with precisely controlled drug delivery. Anti-galectin-3 antibodies are utilized as the targeting molecules of nanoparticles in the first time, which surprisingly increase intracellular DOX uptake by enhanced clathrin-mediated endocytosis, showing galectin-3 can be employed as a highly efficient target of drug delivery systems. The nanoparticles achieve excellent photoacoustic imaging effect, enabled chemo-photothermal combined therapy with pinpointed drug delivery. Compared to free DOX, these multifunctional nanoparticles decrease the heart damage, but greatly increase the tumor/heart ratio of DOX concentration by 12.9-fold. The tumors are completely eradicated without any recurrence after the in vivo combined therapy. To the best of the authors' knowledge, this is also the first report to apply photoacoustic imaging-guided chemo-photothermal therapy for thyroid cancer, showing great potential to solve the dilemma in thyroid cancer therapy.

Optimization of coagulation pre-treatment for alleviating ultrafiltration membrane fouling: The role of floc properties on Al species

This study investigated membrane fouling in a coagulation/ultrafiltration (C-UF) process by comparing the floc properties and humic acid (HA) removal efficiency of three hydrous Al(III) species (Al_a, Al_b, and Al_c). The results indicated that the coagulation and membrane mechanisms were different for all three Al species because of the differences in floc properties. The HA removal efficiency increased with increasing Al dosage until an equilibrium was reached at the optimal dosage of 6 mg L^-1. In addition, membrane fouling gradually decreased as the Al dosages increased. Regardless of coagulant type, the OH and COOH functional groups of HA reacted with the Al species. Both external and internal membrane fouling were strongly dependent on the porosity of the cake layer and on the size distribution of the floc particulates, respectively. The pore area of the cake layer formed by the Al_a-coagulated effluent was large because of the strong charge neutralization. Moreover, Al_a generated large and loose flocs with a porous cake layer that mitigated external fouling. However, the internal fouling with the Al_c coagulant was significant because the concentration of residual aggregates in the membrane pores was high.

Wastewater treatment by membrane ultrafiltration enhanced with ultrasound: Effect of membrane flux and ultrasonic frequency

Membrane ultrafiltration is increasingly applied for wastewater treatment and reuse, even though membrane fouling still represents one of the main drawbacks of this technology. In the last years, innovative strategies for membrane fouling control have been developed, such as the combination of membrane processes with ultrasound (US). In present work, the application of membrane ultrafiltration and its combination with US were studied, evaluating the influence on the performance of the treatment and membrane fouling formation of two membrane fluxes, 75 and 150L/m²h, along with two US frequencies, 35 and 150kHz. The results observed showed that the combination of membrane ultrafiltration with US, respect to the filtration process alone, reduced membrane fouling rates to a greater extent at the higher membrane flux and lower US frequency applied, reaching a reduction of 57.33% at 150L/m²h and 35kHz. Furthermore, higher organic matter and turbidity removals were observed at higher frequency (130kHz). The results obtained highlights the applicability of this combined process for the upgrading of membrane ultrafiltration and as an alternative option to conventional tertiary wastewater treatments.