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Rapid industrialization has become one of the root causes of environmental problems, particularly heavy metal pollution. Numerous methods, including chemical precipitation and ion exchange, have been used to remove heavy metal ions from aqueous solutions, but all of them have drawbacks, such as low metal removal effectiveness, significant reagent loss, excessive energy use, and the need for further development of the current techniques. Membrane-based technologies such as reverse osmosis (RO) and nanofiltration (NF) are gaining popularity in the removal of heavy metals due to their high rejection and low formation of secondary pollutants. Among the methods under consideration, the membrane-based approach holds the most promise for wastewater treatment with a focus on heavy metal ion removal due to its ease of manufacture, superior qualities, and increased separation effectiveness. Since membrane performance is typically hampered by fouling, low permeability, and significant contaminant permeation when compared to strict selectivity criteria, the development of novel membrane materials has emerged as an important area of research for academia, industry, and national laboratories. We have therefore reviewed previous initiatives and technological developments in order to achieve more effective heavy metal removal and recovery from industrial wastewater. HIGHLIGHTS Wastewater treatment technologies and existing methods in heavy metal removal are reviewed.; Five types of membranes are discussed on their strengths and weakness.; Table of summary from previous research that used TFN membrane in heavy metal removal is included.; Crucial challenges associated with TFN membrane production are discussed.; Strategies to overcome the limitation of TFN are discussed in detail.;

High organic materials in palm oil mill effluent (POME) can result in serious water pollution. To date, biological treatment has been used to reduce the environmental risks of these effluents prior of their discharge into water streams. However, the effluents’ dark brownish colour remains as a significant issue that must be addressed, as it affects the overall quality of water. Although membrane technology has been frequently used to address these difficulties, membrane fouling has become a serious limitation in POME treatment. On the other hand, zwitterions with balanced charge groups have received growing interest in the fabrication of antifouling membranes due to their hydrated nature. The development of a simple and efficient covalent bonding technique to improve the stability of zwitterions on membrane surfaces remains a challenge. By grafting and co-depositing polyethylenimine (PEI)-based zwitterion (Z-PEI) with super hydrophilic polydopamine (PDA) on the surface of a commercial polysulfone (PSf) ultrafiltration membrane at ambient temperature, a new zwitterionic surface with a neutral surface charge was created (PDA/Z-PEI). This study aims to investigate the effect of different loading ratios of PDA/Z-PEI (1:1, 1:2, and 1:3) and evaluate their performance on treating brownish coloured anaerobically treated POME (AT-POME). SEM and FTIR analysis showed the successful incorporation of the PDA/Z-PEI membrane while the zwitterionic feature is indicated by zeta potential analysis. Water flux analysis demonstrated that a lower water flux was achieved for M-ZPEI membranes as compared to the PSf and PSf-MDPA membranes, attributed by the tight skin layer of PDA-ZPEI. In the development of a tight hydration layer on the membrane surface by zwitterions, zwitterionic membranes demonstrated excellent antifouling capabilities, particularly PDA/Z-PEI with a loading ratio of (1:2) with a flux recovery ratio of around 84% and colour rejection of 81.75%. Overall, this research contributes to the development of a unique coating with improved stability and antifouling properties by altering the membrane surface in a simple and reliable manner.

Modifying polymeric membranes using nanofiller is a promising method to enhance gas permeability and selectivity performance. This work used two types of ZIF-8 functionalized-2D nanofillers to fabricate polyethersulfone mixed matrix membranes. The rGO/ZIF-8 and MoS2/ZIF-8 nanofillers were first synthesised and characterised using FTIR and XRD. Then, 10 wt% of each nanofillers was added to the PES solution. TGA analysis indicates that MMMs containing rGO/ZIF-8 and MoS2/ZIF-8 exhibit improved thermal stability. No additional peaks in FTIR and XRD were observed in the MMMs, indicating that the 2D nanofillers were compatible with the PES matrix. The MMMs show significantly enhanced gas separation properties where the highest selectivity was observed for 10 wt%PRG/Pebax membrane of 35.71 with CO2 permeability of 611 barrer and CH4 permeability of 17.11 barrer. These results confirm the possibility of using 2D nanofillers to develop highperformance membranes for gas separation. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (NP) was successfully immobilized on polydopamine (PDA) supported polyethersulfone (PES) membrane via a redox reaction. Polyvinylpyrrolidone (PVP) was added into membrane dope solution as a pore-forming agent. Four pieces of membranes (M1, M2, M3 and M4) were fabricated with different active layer coatings to compare their morphological and performance properties. The differences between each sample were highlighted as follow: M1 (pristine PES), M2 (PES+PVP), M3 (PDA/PES+PVP) and M4 (Ag/PDA/PES+PVP). All membranes were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and contact angle analysis. The membrane performance was examined using pure water permeability (PWP) test, antibacterial test and humic acid (HA) rejection test. Pristine M1 membrane showed that PWP of 27.16 LMH/bar and HA rejection of 84 %. In this study, it was found that the addition of PVP as a pore agent into the membrane M2 increased water flux but slightly deteriorated HA rejection. Coating of PDA on M3 and immobilizing silver NP on M4 membrane surface have improved HA rejection but compromised PWP. The results showed that membrane M4 carried excellent antibacterial property and highest HA rejection among all fabricated membranes.

Pesticides have been identified as major contaminants of various waterways. Being classified as potential endocrine disrupting compounds, pesticides in aqueous system are highly hazardous to aquatic organisms and the ecosystem. The treatment of pesticide-containing wastewater can be performed through several means, but a wastewater treatment strategy which emphasizes both treatment efficiency and sustainability is a necessity of current time. In this context, bioremediation has been increasingly promoted as an alternative technique for the remediation of diverse pollutants. Particularly, bioremediation which involves the utilization of microalgae for the removal or conversion of pesticides to the harmless or less harmful compounds is becoming a trend. Exploiting microalgae as a tool for wastewater treatment presents multiple advantages over conventional treatment technologies, which include an opportunity to simultaneously treat pesticide-containing wastewater and nutrient recovery for microalgae cultivation as well as less formation of toxic sludge. This review discusses the roles of microalgae in mitigating pesticide pollution issue, while offering an opportunity for nutrient recovery from various wastewater sources. Based on the current laboratory studies, the use of microalgae bioremediation as a promising strategy for pesticide treatment has been rationalized. The establishment of more pilot scale studies is highly encouraged to further facilitate the implementation of this treatment approach for practical application. [ABSTRACT FROM AUTHOR]

The increase in the global population has caused an increment in energy demand, and therefore, energy production has to be maximized through various means including the burning of natural gas. However, the purification of natural gas has caused CO2 levels to increase. Hollow fiber membranes offer advantages over other carbon capture technologies mainly due to their large surface-to-volume ratio, smaller footprint, and higher energy efficiency. In this work, hollow fiber mixed matrix membranes (HFMMMs) were fabricated by utilizing cellulose triacetate (CTA) as the polymer and amine-functionalized metal-organic framework (NH2-MIL-125(Ti)) as the filler for CO2 and CH4 gas permeation. CTA and NH2-MIL-125(Ti) are known for exhibiting a high affinity towards CO2. In addition, the utilization of these components as membrane materials for CO2 and CH4 gas permeation is hardly found in the literature. In this work, NH2-MIL-125(Ti)/CTA HFMMMs were spun by varying the air gap ranging from 1 cm to 7 cm. The filler dispersion, crystallinity, and functional groups of the fabricated HFMMMs were examined using EDX mapping, SEM, XRD, and FTIR. From the gas permeation testing, it was found that the NH2-MIL-125(Ti)/CTA HFMMM spun at an air gap of 1 cm demonstrated a CO2/CH4 ideal gas selectivity of 6.87 and a CO2 permeability of 26.46 GPU. [ABSTRACT FROM AUTHOR]

Most researchers focused on developing highly selective membranes for CO2/CH4 separation, but their developed membranes often suffered from low permeance. In this present work, we aimed to develop an ultrahigh permeance membrane using a simple coating technique to overcome the trade-off between membrane permeance and selectivity. A commercial silicone membrane with superior permeance but low CO2/CH4 selectivity (in the range of 2–3) was selected as the host for surface modification. Our results revealed that out of the three silane agents tested, only tetraethyl orthosilicate (TEOS) improved the control membrane's permeance and selectivity. This can be due to its short structural chain and better compatibility with the silicone substrate. Further investigation revealed that higher CO2 permeance and selectivity could be attained by coating the membrane with two layers of TEOS. The surface integrity of the TEOS-coated membrane was further improved when an additional polyether block amide (Pebax) layer was established atop the TEOS layer. This additional layer sealed the pin holes of the TEOS layer and enhanced the resultant membrane's performance, achieving CO2/CH4 selectivity of ~19 at CO2 permeance of ~2.3 × 105 barrer. This performance placed our developed membrane to surpass the 2008 Robeson Upper Boundary. [ABSTRACT FROM AUTHOR]

Recently, a thermally-driven membrane process known as membrane distillation (MD) has emerged as an alternative to the high-pressure membrane process for contaminants removal from water. The driving force for MD is a vapor pressure gradient produced by a temperature differential across a hydrophobic porous membrane, which results in the transfer of water vapor from hot to cold side. However, the feasibility of MD for industry adoption is hampered by several issues such as temperature polarisation effects, low permeate flux, membrane wetting, and fouling. The membrane properties are known to have a significant role in controlling the final performances of MD. This review first looks into the feature of ideal MD membrane properties. Then, the use of graphenebased materials for the development of high performances MD membrane is discussed. Besides enhancing the water permeability and selectivity of MD, the incorporation of graphene offers additional properties such as anti-fouling, antibacterial, and photodegradation. The future direction of using graphene-based photothermal material in MD for heat generation under solar irradiation is also reviewed. It is found that the localised heating at membrane surfaces by photothermal material can minimise temperature polarisation effects and subsequently enhance the driving force for effective vapour transport. Thus, a more energy-efficient MD system can be developed. [ABSTRACT FROM AUTHOR]