Surface functionalization of nanofiltration membrane by catechol-amine codeposition for enhancing antifouling performance

Self-cleaning foulant attachment on near-infrared responsive photocatalytic membrane for continuous dynamic removing antibiotics in sewage effluent environment

Bifunctional photocatalytic nanofiltration (PNF) membrane has become a reliable frontier technique for removing refractory organic micropollutants. However, the active mitigated fouling mechanism from the microscopic perspective during its long-term operation of purifying real micro-polluted water is rarely studied. Herein, with an integrated use of QSense Explorer and confocal laser scanning microscope techniques, self-cleaning foulant attachment on an activated and customized near-infrared responsive polymeric PNF (termed as nPNF) membrane with good service performance for continuous dynamic removing antibiotics in sewage effluent environment was firstly elucidated. Time-dependent changes in dissipation oscillation frequency, sensed mass and the visualized foulant spatial distribution all indicated that there were only sporadic foulant attachment, an extremely low fouling layer thickness and irreversible fouling rate on/of the activated nPNF membrane top surface, thereby endowing it with excellent self-cleaning characteristic. This is probably because the reactive oxygen species (mainly •O2- and •OH) concurrently destroys the integrity of fouling layer and its internal adhesion structure, transforming part of the irreversible fouling on nPNF membrane surface into reversible one that is easy to wash off. These new horizons provided useful insight on the fate of selected antibiotics in the to-be-removed stage and self-cleaning foulant attachment of PNF membrane.

Occurrence of aflatoxins in water and decontamination strategies: A review

Aflatoxins are highly carcinogenic metabolites produced by some Aspergillus species and are the most prevalent mycotoxins. Although aflatoxins are commonly synthesized during fungal colonization in preharvest maize, cereals, and nuts, they can be transported by rainfall to surface water and are a common toxin found in wastewater from some food industries. Here, the occurrence of aflatoxins in bodies of water is reviewed for the first time, along with the decontamination methods. Aflatoxins have been detected in surface, wastewater and drinking water, including tap and bottled water. The specific sources of water contamination remain unclear, which is an important gap that must be addressed in future research. Two main kinds of decontamination methods have been reported, including degradation and adsorption. The best degradation rates were observed using gamma and UV irradiations, oxidoreductases and ozone, while the best adsorption abilities were observed with minerals, polyvinyl alcohol, durian peel and activated carbon. Synthetic polymers could be used as membranes in pipes to remove aflatoxins in water flows. Although most decontamination methods were screened using AFB₁, the other commonly found aflatoxins were not used in the screenings. Overall, the occurrence of aflatoxins in water could be a significant emerging public health concern largely ignored by local and international legislation. Numerous advances have been reported for the decontamination of aflatoxins in water; however, there is still a long way to go to put them into practice.

Removal of natural organic matter from surface water sources by nanofiltration and surface engineering membranes for fouling mitigation - A review

Given that surface water is the primary supply of drinking water worldwide, the presence of natural organic matter (NOM) in surface water presents difficulties for water treatment facilities. During the disinfection phase of the drinking water treatment process, NOM aids in the creation of toxic disinfection by-products (DBPs). This problem can be effectively solved using the nanofiltration (NF) membrane method, however NOM can significantly foul NF membranes, degrading separation performance and membrane integrity, necessitating the development of fouling-resistant membranes. This review offers a thorough analysis of the removal of NOM by NF along with insights into the operation, mechanisms, fouling, and its controlling variables. In light of engineering materials with distinctive features, the potential of surface-engineered NF membranes is here critically assessed for the impact on the membrane surface, separation, and antifouling qualities. Case studies on surface-engineered NF membranes are critically evaluated, and properties-to-performance connections are established, as well as challenges, trends, and predictions for the field's future. The effect of alteration on surface properties, interactions with solutes and foulants, and applications in water treatment are all examined in detail. Engineered NF membranes containing zwitterionic polymers have the greatest potential to improve membrane permeance, selectivity, stability, and antifouling performance. To support commercial applications, however, difficulties related to material production, modification techniques, and long-term stability must be solved promptly. Fouling resistant NF membrane development would be critical not only for the water treatment industry, but also for a wide range of developing applications in gas and liquid separations.

Study on Spacing Regulation and Separation Performance of Nanofiltration Membranes of GO

Graphene oxide (GO) membranes have attracted significant attention in the field of water processing in recent years due to their unique characteristics. However, few reports focus on both membrane stability and the “trade-off” effect. In this study, a series of aliphatic diamines (1, 2-ethylenediamine, 1, 4-butanediamine, and 1, 6-hexamethylenediamine) of covalent crosslinked GO were used to prepare diamine-modified nanofiltration membranes, BPPO/AX-GO, with adjustable layer spacing using the vacuum extraction−filtration method. Moreover, Ax-GO-modified nanofiltration membranes modified with adipose diamine had higher layer spacing, lower mass-transfer resistance, and better stability. When the number of carbon atoms was 5, the best layer spacing was reached, and when the number of carbon atoms was greater than 4, the modified membrane nanosheets more easily accumulated. With the increase in layer spacing, the water flux of the composite film increased to 26.27 L/m2·h·bar. Meanwhile, adipose diamine crosslinking significantly improved the stability of GO films. The interception sequence of different valence salts in the composite membrane was NaCl > Na2SO4 > MgSO4, and the rejection rate of bivalent salts was higher than that of monovalent salts. The results can provide some experimental basis and research ideas for overcoming the “trade-off” effect of a lamellar GO membrane.

Chemoenzymatic Cascade Reaction for Green Cleaning of Polyamide Nanofiltration Membrane

Chemical cleaning is indispensable for the sustainable operation of nanofiltration (NF) in wastewater treatment. However, the common chemical cleaning methods are plagued by low cleaning efficiency, high chemical consumption, and separation performance deterioration. In this work, a chemoenzymatic cascade reaction is proposed for pollutant degradation and polyamide NF membrane cleaning. Glucose oxidase (GOD) enzymatic reaction in this cascade system produces hydrogen peroxide (H₂O₂) and gluconic acid to trigger the oxidation of foulants by Fe₃O₄-catalyzed Fenton reaction. By virtue of the microenvironment (pH and H₂O₂ concentration) engineering and substrate enrichments, this chemoenzymatic cascade reaction (GOD-Fe₃O₄) exhibits a favorable degradation efficiency for bisphenol A and methyl blue (MB). Thanks to the strong oxidizing degradation, the water flux of the NF10 membrane fouled by MB is almost completely recovered (∼95.8%) after a 3-cycle fouling/cleaning experiment. Meanwhile, the chemoenzymatic cascade reaction improves the applicability of the Fenton reaction in polyamide NF membrane cleaning because it prevents the membrane from damaging by high concentration of H₂O₂ and inhibits the secondary fouling caused by ferric hydroxide precipitates. By immobilizing GOD on the aminated Fe₃O₄ nanoparticles, a reusable cleaning agent is prepared for highly efficient membrane cleaning. This chemoenzymatic cascade reaction without the addition of an acid/base/oxidant provides a promising candidate for sustainable and cost-effective cleaning for the polyamide NF membrane.

Functionalised electrospun membranes (TETA-PVC) for the removal of lead(ii) from water

Driven by the need for delivering sustainable water purification solutions for the removal of heavy metals from water, electrospun PVC membranes were functionalised with triethylenetetramine (TETA) and were used to remove lead(ii) ions selectively from water. The membranes were characterised and their adsorption behavior towards the removal of lead from water was investigated. The incorporation of TETA on the membrane's surface significantly improved the removal efficiency of lead(ii) up to 99.8% in 30 minutes and under ambient conditions, with the lowest concentration of 50 ppm. The adsorption mechanism was investigated and kinetic data showed a better correlation with the pseudo-second-order model. Similarly, the equilibrium data best fitted with the Langmuir adsorption isotherm model with a relatively high maximum adsorption capacity of 1250 mg g⁻¹ for lead(ii) ions, larger than recently reported adsorption capacities for similar membranes. The functionalised membrane also showed high selectivity to lead(ii) in a mixed solution containing lead(ii), mercury(ii), cadmium(ii), arsenic(iii), copper(ii), and zinc(ii). The functionalised membrane was regenerated, where desorption of lead(ii) was achieved, under mildly acidic conditions. The removal efficiency of the regenerated membrane after six cycles of adsorption/desorption was maintained at a high level of 98%. The proposed design offers a simple yet effective, sustainable, and environmentally friendly solution for water treatment.

Driven by the need for delivering sustainable water purification solutions for the removal of heavy metals from water, TETA functionalised electrospun PVC membranes were fabricated and used to remove lead(ii) ions selectively from water.

Progress in Research and Application of Nanofiltration (NF) Technology for Brackish Water Treatment

Brackish water is a potential fresh water resource with lower salt content than seawater. Desalination of brackish water is an important option to alleviate the prevalent water crisis around the world. As a membrane technology ranging between UF and RO, NF can achieve the partial desalination via size exclusion and charge exclusion. So, it has been widely concerned and applied in treatment of brackish water during the past several decades. Hereon, an overview of the progress in research on and application of NF technology for brackish water treatment is provided. On the basis of expounding the features of brackish water, the factors affecting NF efficiency, including the feed water characteristics, operating conditions and NF membrane properties, are analyzed. For the ubiquitous membrane fouling problem, three preventive fouling control strategies including feed water pretreatment, optimization of operating conditions and selection of anti-fouling membranes are summarized. In addition, membrane cleaning methods for restoring the fouled membrane are discussed. Furthermore, the combined utilization of NF with other membrane technologies is reviewed. Finally, future research prospects are proposed to deal with the current existing problems. Lessons gained from this review are expected to promote the sustainable development of brackish water treatment with NF technology.