Surface modification of polypropylene microporous membrane to improve its antifouling characteristics in an SMBR: Air plasma treatment

From Basics to Frontiers: A Comprehensive Review of Plasma-Modified and Plasma-Synthesized Polymer Films

This comprehensive review begins by tracing the historical development and progress of cold plasma technology as an innovative approach to polymer engineering. The study emphasizes the versatility of cold plasma derived from a variety of sources including low-pressure glow discharges (e.g., radiofrequency capacitively coupled plasmas) and atmospheric pressure plasmas (e.g., dielectric barrier devices, piezoelectric plasmas). It critically examines key operational parameters such as reduced electric field, pressure, discharge type, gas type and flow rate, substrate temperature, gap, and how these variables affect the properties of the synthesized or modified polymers. This review also discusses the application of cold plasma in polymer surface modification, underscoring how changes in surface properties (e.g., wettability, adhesion, biocompatibility) can be achieved by controlling various surface processes (etching, roughening, crosslinking, functionalization, crystallinity). A detailed examination of Plasma-Enhanced Chemical Vapor Deposition (PECVD) reveals its efficacy in producing thin polymeric films from an array of precursors. Yasuda's models, Rapid Step-Growth Polymerization (RSGP) and Competitive Ablation Polymerization (CAP), are explained as fundamental mechanisms underpinning plasma-assisted deposition and polymerization processes. Then, the wide array of applications of cold plasma technology is explored, from the biomedical field, where it is used in creating smart drug delivery systems and biodegradable polymer implants, to its role in enhancing the performance of membrane-based filtration systems crucial for water purification, gas separation, and energy production. It investigates the potential for improving the properties of bioplastics and the exciting prospects for developing self-healing materials using this technology.

Plasma Surface Engineering of Natural and Sustainable Polymeric Derivatives and Their Potential Applications

Recently, natural as well as synthetic polymers have been receiving significant attention as candidates to replace non-renewable materials. With the exponential developments in the world each day, the collateral damage to the environment is incessant. Increased demands for reducing pollution and energy consumption are the driving force behind the research related to surface-modified natural fibers (NFs), polymers, and various derivatives of them such as natural-fiber-reinforced polymer composites. Natural fibers have received special attention for industrial applications due to their favorable characteristics, such as low cost, abundance, light weight, and biodegradable nature. Even though NFs offer many potential applications, they still face some challenges in terms of durability, strength, and processing. Many of these have been addressed by various surface modification methodologies and compositing with polymers. Among different surface treatment strategies, low-temperature plasma (LTP) surface treatment has recently received special attention for tailoring surface properties of different materials, including NFs and synthetic polymers, without affecting any of the bulk properties of these materials. Hence, it is very important to get an overview of the latest developments in this field. The present article attempts to give an overview of different materials such as NFs, synthetic polymers, and composites. Special attention was placed on the low-temperature plasma-based surface engineering of these materials for diverse applications, which include but are not limited to environmental remediation, packaging, biomedical devices, and sensor development.

Membranes for Oil/Water Separation: A Review

Recent advancements in separation and membrane technologies have shown a great potential in removing oil from wastewaters effectively. In addition, the capabilities have improved to fabricate membranes with tunable properties in terms of their wettability, permeability, antifouling, and mechanical properties that govern the treatment of oily wastewaters. Herein, authors have critically reviewed the literature on membrane technology for oil/water separation with a specific focus on: 1) membrane properties and characterization, 2) development of various materials (e.g., organic, inorganic, and hybrid membranes, and innovative materials), 3) membranes design (e.g., mixed matrix nanocomposite and multilayers), and 4) membrane fabrication techniques and surface modification techniques. The current challenges and future research directions in materials and fabrication techniques for membrane technology applications in oil/water separation are also highlighted. Thus, this review provides helpful guidance toward finding more effective, practical, and scalable solutions to tackle environmental pollution by oils.

Advanced Research and Development of Face Masks and Respirators Pre and Post the Coronavirus Disease 2019 (COVID-19) Pandemic: A Critical Review

The outbreak of the COVID-19 pandemic, in 2020, has accelerated the need for personal protective equipment (PPE) masks as one of the methods to reduce and/or eliminate transmission of the coronavirus across communities. Despite the availability of different coronavirus vaccines, it is still recommended by the Center of Disease Control and Prevention (CDC), World Health Organization (WHO), and local authorities to apply public safety measures including maintaining social distancing and wearing face masks. This includes individuals who have been fully vaccinated. Remarkable increase in scientific studies, along with manufacturing-related research and development investigations, have been performed in an attempt to provide better PPE solutions during the pandemic. Recent literature has estimated the filtration efficiency (FE) of face masks and respirators shedding the light on specific targeted parameters that investigators can measure, detect, evaluate, and provide reliable data with consistent results. This review showed the variability in testing protocols and FE evaluation methods of different face mask materials and/or brands. In addition to the safety requirements needed to perform aerosol viral filtration tests, one of the main challenges researchers currently face is the inability to simulate or mimic true aerosol filtration scenarios via laboratory experiments, field tests, and in vitro/in vivo investigations. Moreover, the FE through the mask can be influenced by different filtration mechanisms, environmental parameters, filtration material properties, number of layers used, packing density, fiber charge density, fiber diameter, aerosol type and particle size, aerosol face velocity and concentration loadings, and infectious concentrations generated due to different human activities. These parameters are not fully understood and constrain the design, production, efficacy, and efficiency of face masks.

Application of zinc oxide and sodium alginate for biofouling mitigation in a membrane bioreactor treating urban wastewater

This research aimed to mitigate fouling in membrane bioreactors (MBR) through concurrent usage of zinc oxide as an antibacterial agent (A) and sodium alginate as a hydrophilic agent (H) within a polyacrylonitrile membrane (PM) structure. The antibacterial polymeric membranes (APM) and antibacterial hydrophilic polymeric membranes (AHPM) synthesized showed a higher porosity, mechanical strength and bacterial inhibition zone, and a lower contact angle in comparison with PM membranes. EDS, SEM and AFM analyses were used to characterize the chemical, structural, and morphological properties of PM, APM, and AHPM. The flux of PM, APM, and AHPM in MBR was 37, 48, and 51 l m^-2 h^-1 and COD removal was 81, 93.5, and 96.7%, respectively. After MBR operation for 35 days in an urban wastewater treatment, only 50% of the flux of PM was recovered, while the antibacterial and hydrophilic agents yielded a flux recovery of 72.7 and 100% for APM and AHPM, respectively.

Fouling-resistant biofilter of an anaerobic electrochemical membrane reactor

Membrane fouling is a considerable challenge for the stable operation of anaerobic membrane-based bioreactors. Membrane used as a cathode is a common measure to retard fouling growth in anaerobic electrochemical membrane bioreactors (AnEMBR), which; however, cannot avoid the fouling growth. Here we report a strategy using the membrane as an anode to resist membrane fouling in an AnEMBR. Although aggravating in the initial stage, the fouling on the anode membrane is gradually alleviated by the anode oxidation with enriching exoelectrogens to finally achieve a dynamic equilibrium between fouling growth and decomposition to maintain the operation stable. A mesh-like biofilter layer composed of cells with less extracellular polymeric substance (EPS) is formed on the membrane surface to lower the trans-membrane pressure and promote the interception of the anode membrane. The membrane has high electron storage and transfer capacities to accelerate the oxidation of the intercepted fouling materials, especially, the redundant EPSs of the biofilter layer.

Electro-membrane processes for organic acid recovery

With an increase in the organic acid requirement, the production of organic acids has been increased over the years. To achieve cost-effective production of organic acids, efficient recovery processes are needed. Electro-membrane processes, including electrodialysis (ED), electrometathesis (EMT), electro-ion substitution (EIS), electro-electrodialysis (EED), electrodialysis with bipolar membrane (EDBM), and electrodeionization (EDI), are promising technologies for the recovery of organic acids. In the electro-membrane processes, organic acids are separated from water and other impurities based on the electro-migration of ions through ion-exchange membranes. These processes can recover various types of organic acids from the fermentation broth with high recovery yield and low energy consumption. In addition, the integration of fermentation and the electro-membrane process can improve the acid recovery with lower byproduct concentration and energy consumption.

With an increase in the organic acid requirement, the publication of organic acids recovery has been increased over the years.

Surface grafting techniques on the improvement of membrane bioreactor: State-of-the-art advances

Membrane bioreactor (MBR) is regarded as the state-of-the-art technology in separation processes. Surface modification techniques play a critical role in improving the conventional membrane system which is mostly hydrophobic in nature. The hydrophobic nature of membranes is known to cause fouling, resulting in high maintenance costs and shorter lifespan of MBR. Thus, surface grafting aims to improve the hydrophilicity of bio-based membrane systems. This review describes the major surface grafting techniques currently used in membranes, including photo induced grafting, plasma treatment and plasma induced grafting, radiation induced grafting, thermal induced grafting and ozone induced grafting. The advantages and disadvantages of each method is discussed along with their parametric studies. The potential applications of MBR are very promising, but some integral membrane properties could be a major challenge that hinders its wider reach. The fouling issue could be resolved with the surface grafting techniques to achieve better performance of MBRs.

Highly fouling-resistant brominated poly(phenylene oxide) membranes using surface grafted diethylenetriamine

Composite BPPO/DETA ultrafiltration membranes show decreased membrane fouling and enhanced protein rejection with very high flux recovery ratios.

Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling

The membrane bioreactor (MBR) has emerged as an efficient compact technology for municipal and industrial wastewater treatment. The major drawback impeding wider application of MBRs is membrane fouling, which significantly reduces membrane performance and lifespan, resulting in a significant increase in maintenance and operating costs. Finding sustainable membrane fouling mitigation strategies in MBRs has been one of the main concerns over the last two decades. This paper provides an overview of membrane fouling and studies conducted to identify mitigating strategies for fouling in MBRs. Classes of foulants, including biofoulants, organic foulants and inorganic foulants, as well as factors influencing membrane fouling are outlined. Recent research attempts on fouling control, including addition of coagulants and adsorbents, combination of aerobic granulation with MBRs, introduction of granular materials with air scouring in the MBR tank, and quorum quenching are presented. The addition of coagulants and adsorbents shows a significant membrane fouling reduction, but further research is needed to establish optimum dosages of the various coagulants/adsorbents. Similarly, the integration of aerobic granulation with MBRs, which targets biofoulants and organic foulants, shows outstanding filtration performance and a significant reduction in fouling rate, as well as excellent nutrients removal. However, further research is needed on the enhancement of long-term granule integrity. Quorum quenching also offers a strong potential for fouling control, but pilot-scale testing is required to explore the feasibility of full-scale application.

Advances in preparation, modification, and application of polypropylene membrane

Polypropylene (PP) is one of the most used polymers for microporous membrane fabrication due to its good thermal stability, chemical resistance, mechanical strength, and low cost. There have been numerous studies reporting the developments and applications of PP membranes. However, PP membrane with high performance is still a challenge. Thus, this article presents a comprehensive overview of the advances in the preparation, modification and application of PP membrane. The preparation methods of PP membrane are firstly reviewed, followed by the modification approaches of PP membrane. The modifications includes hydrophilic and superhydrophobic modification so that the PP membranes become more suitable to be applied either in aqueous applications or in non-aqueous ones. The fouling resistant of hydrophilized PP membrane and the wetting resistant of superhydrophobized PP membrane are then reviewed. Finally, special attention is given to the various potential applications and industrial outlook of the PP membranes.

Poly(ethylene oxide) functionalized polyimide-based microporous films to prevent bacterial adhesion

Preventing microbial adhesion onto membranes is a crucial issue that determines the durability of the membrane. In this Research Article, we prepared aromatic polyimides (extensively employed for the elaboration of ultrafiltration membranes) containing PEO branches. Four polyimide-g-PEO copolymers were prepared from 6F dianhydride and a novel aromatic diamine containing PEO-550 side groups. The copolymers were designed to have variable PEO content, and were characterized by their spectroscopic and physical properties. The Breath Figure technique was successfully applied to create an ordered surface topography, where the PEO chains were preferentially located on the surface of the micrometer size holes. These unique features were explored to reduce bacterial adhesion. It was established that surface modified polyimide membranes have a high resistance to biofouling against Staphylococcus aureus. In particular, we observed that an increase of the PEO the content in the copolymer produced a decrease in the bacterial adhesion.

Polymeric membranes: surface modification for minimizing (bio)colloidal fouling

This paper presents an overview on recent developments in surface modification of polymer membranes for reduction of their fouling with biocolloids and organic colloids in pressure driven membrane processes. First, colloidal interactions such as London-van der Waals, electrical, hydration, hydrophobic, steric forces and membrane surface properties such as hydrophilicity, charge and surface roughness, which affect membrane fouling, have been discussed and the main goals of the membrane surface modification for fouling reduction have been outlined. Thereafter the recent studies on reduction of (bio)colloidal of polymer membranes using ultraviolet/redox initiated surface grafting, physical coating/adsorption of a protective layer on the membrane surface, chemical reactions or surface modification of polymer membranes with nanoparticles as well as using of advanced atomic force microscopy to characterize (bio)colloidal fouling have been critically summarized.

Graft polymerization and plasma treatment of polymer membranes for fouling reduction: a review

This article presents a review of recent developments in surface modification of polymer membranes via graft polymerization and plasma treatment for reduction of fouling with organic compounds and microorganisms in pressure driven membrane processes. The factors affecting membrane fouling, such as membrane hydrophilicity, charge and surface roughness are discussed. The recent studies in which the reduction of organic fouling and biofouling by the modification of the membrane surface via ultraviolet/redox initiated surface grafting of hydrophilic polymers and low temperature plasma treatment are reviewed.

Immobilization of silver in polypropylene membrane for anti-biofouling performance

In this study, a method was developed to immobilize silver onto polypropylene (PP) membrane surfaces for improved anti-biofouling performance. A commercial PP membrane was first grafted with the thiol functional groups, and then silver ions were immobilized onto the PP membrane surface through coordinating with the thiol groups. The immobilized silver was found to be very stable, with only ~1.1% of the immobilized silver being leached out during a leaching test. The surface of the modified membrane (PPS-Ag) was examined with ATR-FTIR and XPS analysis, which verified the successful grafting of the thiol groups and the coordination of silver ions on the membrane surface. The surface properties of the membrane were also characterized by SEM, AFM and water contact angle measurements. The PPS-Ag membrane was found to have a smoother and more hydrophilic surface than the PP membrane. Both Gram-negative bacteria, Escherichia coli, and Gram-positive bacteria, Staphylococcus aureus, were used to evaluate the antibacterial and anti-biofouling performance of the PPS-Ag membrane. From disk diffusion experiments, the PPS-Ag membrane exhibited the capability of inhibiting the growth of both the Gram-negative and Gram-positive bacteria tested. The anti-biofouling performance of the membrane was assessed by immersion in a mixed suspension of E. coli and S. aureus and filtration tests. The PPS-Ag membrane showed a stable and significantly enhanced anti-biofouling performance as compared with the PP membrane. The results in this study demonstrate that biofouling of a PP membrane can be sufficiently overcome through immobilizing silver onto the membrane surface.