Lab-scale and pilot-scale fabrication of amine-functional reverse osmosis membrane with improved chlorine resistance and antimicrobial property

Impact of Chlorinated-Assisted Backwash and Air Backwash on Ultrafiltration Fouling Management for Urban Wastewater Tertiary Treatment

To improve membrane fouling management, the NaClO-assisted backwash has been developed to improve permeability maintenance and reduce the need for intensive chemical cleanings. This study is aimed to focus on the efficiency of NaClO-assisted backwash in real UF pilot scale and with periodic classic backwash (CB) and air backwash (AB). The impacts on hydraulic filtration performance, physicochemical properties of membrane material under different addition frequencies of NaClO, and the performance of chlorinated CB and AB will be discussed. In result, 10 mg Cl₂ L⁻¹ NaClO addition in backwash water is confirmed to greatly improve the overall filtration performance and backwash cleaning efficiency. One condition stands out from the other due to better control of irreversible fouling, less NaClO consumption in 10 years prediction, sustainable and adaptable filtration performance, and less potential damage on the physicochemical properties of the membrane. Additionally, it can be inferred from this experiment that frequent contact with NaClO induced some degradation on the PES-made UF membrane surface properties. To retain the best state of UF membrane on anti-fouling and qualified production, the optimized condition with more frequent NaClO contact was not suggested for long-term filtration.

Separation, anti-fouling, and chlorine resistance of the polyamide reverse osmosis membrane: From mechanisms to mitigation strategies

Membrane technology has been widely used in the wastewater treatment and seawater desalination. In recent years, the reverse osmosis (RO) membrane represented by polyamide (PA) has made great progress because of its excellent properties. However, the conventional PA RO membranes still have some scientific problems, such as membrane fouling, easy degradation after chlorination, and unclear mechanisms of salt retention and water flux, which seriously impede the widespread use of RO membrane technology. This paper reviews the progress in the research and development of the RO membrane, with key focus on the mechanisms and strategies of the contemporary separation, anti-fouling and chlorine resistance of the PA RO membrane. This review seeks to provide state-of-the-art insights into the mitigation strategies and basic mechanisms for some of the key challenges. Under the guidance of the fundamental understanding of each mechanism, operation and modification strategies are discussed, and reasonable analysis is carried out, which can address some key technical challenges. The last section of the review focuses on the technical issues, challenges, and future perspective of these mechanisms and strategies. Advances in synergistic mechanisms and strategies of the PA RO membranes have been rarely reviewed; thus, this review can serve as a guide for new entrants to the field of membrane water treatment and established researchers.

Development of high-performance mixed matrix reverse osmosis membranes by incorporating aminosilane-modified hydrotalcite

Thin film nanocomposite (TFN) reverse osmosis (RO) membranes were prepared by dispersing 3-aminopropyltriethoxysilane (APTES) modified hydrotalcite (HT), designated as A-HT, in aqueous solution and incorporating the nanoparticles in polyamide layers during the interfacial polymerization process. Results of Fourier transform infrared spectroscopy and zeta potential characterization showed the successful modification of nanoparticles by APTES. In addition, Fourier transform infrared spectroscopy suggested that amidation would take place between the aminosilane on APTES and trimesoyl chloride in organic solution, providing firm covalent interaction between the nanoparticles and polyamide matrix. Dynamic light scattering and transmission electron microscopy indicated that aminosilane modification improved dispersibility of the nanoparticles in aqueous solution and obtained membranes, which suppressed the aggregation. Both the covalent interaction and aggregation suppression were beneficial to compatibility between nanoparticles and the polyamide matrix. TFN RO membranes incorporated with A-HT demonstrated excellent performance. Compared with the pristine RO membrane, the water flux of A-HT-0.050 prepared with an optimum A-HT concentration of 0.050 wt% was enhanced by 18.6% without sacrificing the salt rejection. Moreover, the selectivity of A-HT-0.050 was superior to that of HT-0.050 prepared with HT of 0.050 wt%, which proved aminosilane modification of hydrotalcite was beneficial to high membrane performance especially to selectivity.

Thin film nanocomposite reverse osmosis membranes were prepared by dispersing 3-aminopropyltriethoxysilane modified hydrotalcite in aqueous solution and incorporating the nanoparticles in polyamide layer during interfacial polymerization process.

Rechargeable polyamide-based N-halamine nanofibrous membranes for renewable, high-efficiency, and antibacterial respirators

Emerging infectious diseases (EIDs) have been acknowledged as a major public health concern worldwide. Unfortunately, most protective respirators used to prevent EID transmission suffer from the disadvantage of lacking antimicrobial activity, leading to an increased risk of cross-contamination and post-infection. Herein, we report a novel and facile strategy to fabricate rechargeable and biocidal air filtration materials by creating advanced N-halamine structures based on electrospun polyamide (PA) nanofibers. Our approach can endow the resultant nanofibrous membranes with powerful biocidal activity (6 log CFU reduction against E. coli), an ultrahigh fine particle capture efficiency of 99.999% (N100 level for masks), and can allow the antibacterial efficacy and air filtration performance to be renewed in a one-step chlorination process, which has never been reported before. More importantly, for the first time, we revealed the synergistic effect involving the intrinsic structure of polymers and the assembling structure of nanofibers on the chlorination capacity. The successful fabrication of such a fascinating membrane can provide new insights into the development of nanofibrous materials in a multifunctional, durable, and renewable form.

In Situ Surface Modification of Thin-Film Composite Polyamide Membrane with Zwitterions for Enhanced Chlorine Resistance and Transport Properties

High-performance chlorine-resistant thin-film composite (TFC) membranes with zwitterions were fabricated by in situ surface modification of polyamide with 2,6-diaminopyridine and the subsequential quaternization with 3-bromopropionic. The successful modification of the TFC polyamide surface with zwitterions was confirmed by various characterizations including surface chemistry, surface hydrophilicity, and surface charge. The transport performance of the membrane was measured in both of the cross-flow reverse osmosis (RO) and forward osmosis processes, and the results showed that the modified TFC membrane improved both of its water permeability and perm-selectivity with the increased A and A/ B ratios upon modification with zwitterions. The chlorination challenging experiments were performed to demonstrate that the modified membrane enhanced its chlorine resistance without affecting its salt rejection upon 16 000 ppm·h chlorination exposure. A chlorination mechanism study illustrated that the modified membrane with zwitterions could prevent the Orton rearrangement of the benzene ring of the polyamide layer. Importantly and excitingly, the optimal chlorinated TFC membrane with zwitterions achieved a very high water flux of 72.15 ± 2.55 LMH with 99.67 ± 0.09% of salt rejection in the cross-flow RO process under 15 bar.

Biguanidine functional chitooligosaccharide modified reverse osmosis membrane with improved anti-biofouling property

The COSG-modified RO membrane with excellent anti-adhesive and antimicrobial properties was successfully fabricated by second interfacial polymerization.