Herbicides such as atrazine and humus substances such as fulvic acid are widely used in agricultural sector. They can be traced in surface and groundwater around the agriculture field at concentrations beyond the approved limit due to their mobility and persistence. Bismuth-based photocatalysts activated by visible light are potential materials for removing various organic pollutants from water bodies. These photocatalysts can also be suitable candidates for developing a hybrid membrane with anti-fouling properties. In this study, Bi2WO6 nanoparticles were synthesized via the hydrothermal method and integrated into the cellulose acetate (CA), polyetherimide (PEI), polysulfone (PSF) and polyvinylidene fluoride (PVDF) polymers via physical blending approach. The hybrid membranes were then characterized by FTIR, XPS and FESEM to confirm the chemical bonding, chemical composition and surface morphology of Bi2WO6. Thus, the pure water flux of CA (35.6 L m-2 h-1), PEI (46.56 L m-2 h-1), PSF (6.84 L m-2 h-1), and PVDF (68.47 L m-2 h-1) hybrid membranes has significantly enhanced than the pristine CA, PEI, PSF and PVDF membranes. The significant rejection of atrazine-fulvic acid was observed with hybrid membranes in the order of CA (84.1%) > PVDF (72.7%) > PEI (47.8%) > PSF (37.2%), and these membranes have shown an excellent flux recovery ratio than pristine membranes. Further, electrochemical quantification studies were performed to analyze the removal efficiency of atrazine-fulvic acid from water. In this present work, GO-modified SPE was employed for electrochemical sensing studies. The resultant CA hybrid membrane achieved removal efficiency of 84.08% for atrazine. It was observed that the Bi2WO6 established strong bonding with CA, and PVDF membranes, thus showing a significant removal efficiency and FRR than other hybrid and pristine membranes.
Water constitutes one of the basic necessities of life. Around 71% of the Earth is covered by water, however, not all of it is readily available as fresh water for daily consumption. Fresh water scarcity is a chronic issue which poses a threat to all living things on Earth. Seawater, as a natural resource abundantly available all around the world, is a potential water source to fulfil the increasing water demand. Climate-independent seawater desalination has been touted as a crucial alternative to provide fresh water. While the membrane-based desalination process continues to dominate the global desalination market, the currently employed membrane fabrication materials and processes inevitably bring adverse impacts to the environment. This review aims to elucidate and provide a comprehensive outlook of the recent efforts based on greener approaches used for desalination membrane fabrication, which paves the way towards achieving sustainable and eco-friendly processes. Membrane fabrication using green chemistry effectively minimizes the generation of hazardous compounds during membrane preparation. The future trends and recommendations which could potentially be beneficial for researchers in this field are also highlighted.
Our research focuses on developing environmentally friendly biodegradable ultrafiltration (UF) membranes for small-scale water purification in areas lacking infrastructure or during emergencies. To address biofouling challenges without resorting to harmful chemicals, we incorporate bio-based extracts, such as methyl gallate from A. occidentale leaves, a Malaysian ulam herb, known for its quorum sensing inhibition (QSI) properties. The methyl gallate enriched extract was purified by solvent partitioning and integrated into cellulose-based UF membranes (0 to 7.5% w w-1) through phase inversion technique. The resulting membranes exhibited enhanced anti-organic fouling and anti-biofouling properties, with flux recovery ratio (FRR) of 87.84 ± 2.00% against bovine serum albumin and FRRs of 76.67 ± 1.89% and 69.57 ± 1.77% against E. coli and S. aureus, respectively. The CA/MG-5 membrane showed a 224% improvement in pure water flux (PWF) compared to the neat CA membrane. Our innovative approach significantly improves PWF, presenting an environmentally friendly method for biofouling prevention in UF membrane applications.
Membrane-based separation is an appealing solution to mitigate CO2 emission sustainably due to its energy efficiency and environmental friendliness. Attributed to its excellent separation endowed by nanomaterial incorporation, nanocomposite membrane is rigorously developed. This study explored the feasibility of boron nitride (BN) embedment and changes to formation mechanism of ultrathin selective layer of thin film nanocomposite (TFN) are investigated. The effects of amine-functionalization on nanosheet-polymer interaction and CO2 separation performance are also identified. Participation of nanosheets during interfacial polymerization reduced the crosslinking of selective layer, hence, improved TFN permeance while the formation of contorted diffusion paths by the nanosheets favors transport of small gases. Amine-functionalization enhanced the nanosheet-polymer interaction and elevated the membrane affinity towards CO2 which led to enhanced CO2 selectivity. The best TFN prepared in this study exhibited 37% and 20% increment in permeability and selectivity, respectively with respect to neat thin film composite (TFC). It is found that the CO2 separation performance of BN incorporated TFN is on par with many non-porous nanosheet-incorporated TFNs reported in literatures. The transport and barrier effects of BN and functionalized BN are discussed in detail to provide further insights into the development of commercially attractive CO2 selective TFN membranes.
In this study, fouling mechanism and modelling analysis of synthetic lignocellulose biomass and agricultural palm oil effluent was studied using polyethersulfone (PES) ultrafiltration (UF) 10 kDa membrane. The impact of process variables (transmembrane pressure (TMP), pH and concentration of feed solution) on lignocellulosic flux was analysed using pore blocking model. The feasible approaches on utilising deep learning artificial neural network (ANN) to predict smaller flux datasets are studied. Among the input variables, pH of lignin feed solution has significant control towards flux and lignin rejection coefficient for both lignin and lignocellulosic solution. Alteration in the structure of lignin at different pH conditions contributed in the improvement of lignin rejection coefficient to 0.98 at the feed pH of 9. A maximum steady state flux of 52.03 L/m2h was observed at the lower lignin concentration (0.25 g/L), TMP of 200 kPa and feed pH of 3. At high TMP and concentration, lignin rejection decreased due to enhancement of feed concentration on membrane surface. The mechanistic model exhibited that cake layer phenomena was dominant in both lignin and lignocellulosic solution. The proposed ANN model showed good correlation (R2-1.00) with experimental non-linear flux dynamic data of both lignin and synthetic lignocellulosic solution. In ANN analysis, activation function, algorithm and neuron effect have significant effect in design of accurate model for prediction of small flux datasets. Aerobically-treated palm oil mill filtration analysis also showed that cake layer phenomenon was dominant. A water recovery of 82 % was achieved even at low TMP under short durations.
Membranes are a promising technology for bulk CO2 separation from natural gas mixtures due to their numerous advantages. Despite the numerous fundamental studies on creating better quality membrane efficiency, scaling up the research work for field testing requires huge efforts. The challenge is to ensure the stability of the membrane throughout the operation while maintaining its high performance. This review addresses the key challenges in the application of polymeric technology for CO2 separation, focusing on plasticization and aging. A brief introduction to the properties and limitations of the current commercial polymeric membrane is first deliberated. The effect of each plasticizer component in natural gas towards membrane performance and the relationship between operating conditions and the membrane efficiency are discussed in this review. The recent technological advancements and techniques to overcome the plasticization and aging issues covering polymer modification, high free-volume polymers, polymer blending and facilitated transport membranes (FTMs) have been highlighted. We also give our perspectives on a few main features of research related to polymeric membranes and the way forwards. Upcoming research must emphasize mixed gas with CO2 including minor condensable contaminants as per real natural gas, to determine the competitive sorption effect on CO2 permeability and membrane selectivity. The effects of pore blocking, plasticization and aging should be given particular attention to cater for large-scale applications.
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.
This study focused on developing a hydrophilic hybrid polyvinylidene fluoride (PVDF)-polyethylene glycol (PEG) hollow membrane by incorporating Nano-magnesium oxide (NMO) as a potent antifouling mediator. The Nano-hybrid hollow fibers with varied loading of NMO (0 g; 0.25 g; 0.50 g; 0.75 g and 1.25 g) were spun through phase inversion technique. The resultants Nano-hybrid fibers were characterized and compared based on SEM, EDX, contact angle, surface zeta-potential, permeability flux, fouling resistance and color rejection from palm oil mill effluent (POME). Noticeably, the permeability flux, fouling resistance and color rejection improved with the increase in NMO loading. PVDF-PEG with 0.50 g-NMO loading displayed an outstanding performance with 198.35 L/m2·h, 61.33 L/m2·h and 74.65% of water flux, POME flux and color rejection from POME, respectively. More so, a remarkable fouling resistance were obtained such that the flux recovery, reversible fouling percentage and irreversible fouling percentage remains relatively steady at 90.98%, 61.39% and 7.68%, respectively, even after 3 cycles of continuous filtrations for a total period of 9 h. However, at excess loading of 0.75 and 1.25 g-NMO, deterioration in the flux and fouling resistance was observed. This was due to the agglomeration of nanoparticles within the matrix structure at the excessive loading.
Forward osmosis (FO) has been recognized as the preferred alternative membrane-based separation technology for conventional water treatment technologies due to its high energy efficiency and promising separation performances. FO has been widely explored in the fields of wastewater treatment, desalination, food industry and bio-products, and energy generation. The substrate of the typically used FO thin film composite membranes serves as a support for selective layer formation and can significantly affect the structural and physicochemical properties of the resultant selective layer. This signifies the importance of substrate exploration to fine-tune proper fabrication and modification in obtaining optimized substrate structure with regards to thickness, tortuosity, and porosity on the two sides. The ultimate goal of substrate modification is to obtain a thin and highly selective membrane with enhanced hydrophilicity, antifouling propensity, as well as long duration stability. This review focuses on the various strategies used for FO membrane substrate fabrication and modification. An overview of FO membranes is first presented. The extant strategies applied in FO membrane substrate fabrications and modifications in addition to efforts made to mitigate membrane fouling are extensively reviewed. Lastly, the future perspective regarding the strategies on different FO substrate layers in water treatment are highlighted.
A unique method for determining chlorophyll content in microalgae is devised employing a gold interdigitated electrode (G-IDE) with a 10-µm gap, augmented by a nano-molecularly imprinted polymer (nano-MIP) and a titanium dioxide/multiwalled carbon nanotube (TiO2/MWCNT) nanocomposite. The nano-MIP, produced using chlorophyll template voids, successfully trapped chlorophyll, while the TiO2/MWCNT nanocomposite, synthesized by the sol-gel technique, exhibited a consistent distribution and anatase crystalline structure. The rebinding of procured chlorophyll powder, which was used as a template for nano-MIP synthesis, was identified with a high determination coefficient (R2 = 0.9857). By combining the TiO2/MWCNT nanocomposite with nano-MIP, the G-IDE sensing method achieved a slightly better R2 value of 0.9892 for detecting chlorophyll in microalgae. The presented G-IDE sensor showed a significant threefold enhancement in chlorophyll detection compared with commercially available chlorophyll powder. It had a detection limit of 0.917 mL (v/v) and a linear range that spanned from 10-6 to 1 mL. The effectiveness of the sensor in detecting chlorophyll in microalgae was confirmed through validation of its repeatability and reusability.
The development of wearable artificial kidney demands an efficient dialysate recovery, which relies upon the adsorption process. This study proposes a solution to solve the problem of competitive adsorption between the uremic toxins by employing two adsorptive components in a membrane separation process. Dual-layer hollow fiber (DLHF) membranes, which are composed of a polysulfone (PSf)/activated carbon (AC) inner layer and a PSf/poly(methyl methacrylate) (PMMA) outer layer, were prepared for co-adsorptive removal of creatinine and urea from aqueous solution. The DLHF membranes were characterized in terms of morphological, physicochemical, water transport, and creatinine adsorption properties. The membrane was then subjected to an ultrafiltration adsorption study for performance evaluation. The incorporation of AC in membrane, as confirmed by microscopic and surface analyses, has improved the pure water flux up to 25.2 L/(m2 h). A membrane with optimum AC loading (9 wt %) demonstrated the highest maximum creatinine adsorption capacity (86.2 mg/g) based on the Langmuir adsorption isotherm model. In the ultrafiltration adsorption experiment, the membrane removed creatinine and urea with a combined average percent removal of 29.3%. Moreover, the membrane exhibited creatinine and urea uptake recoveries of 98.8 and 81.2%, respectively. The combined action of PMMA and AC in the PSf DLHF membrane has made the adsorption of multiple uremic toxins possible during dialysate recovery.
Poly (citric acid)-grafted-MWCNT (PCA-g-MWCNT) was incorporated as nanofiller in polyethersulfone (PES) to produce hemodialysis mixed matrix membrane (MMM). Citric acid monohydrate was polymerized onto the surface of MWCNTs by polycondensation. Neat PES membrane and PES/MWCNTs MMMs were fabricated by dry-wet spinning technique. The membranes were characterized in terms of morphology, pure water flux (PWF) and bovine serum albumin (BSA) protein rejection. The grafting yield of PCA onto MWCNTs was calculated as 149.2%. The decrease of contact angle from 77.56° to 56.06° for PES/PCA-g-MWCNTs membrane indicated the increase in surface hydrophilicity, which rendered positive impacts on the PWF and BSA rejection of the membrane. The PWF increased from 15.8Lm(-2)h(-1) to 95.36Lm(-2)h(-1) upon the incorporation of PCA-g-MWCNTs due to the attachment of abundant hydrophilic groups that present on the MWCNTs, which have improved the affinity of membrane towards the water molecules. For protein rejection, the PES/PCA-g-MWCNTs MMM rejected 95.2% of BSA whereas neat PES membrane demonstrated protein rejection of 90.2%. Compared to commercial PES hemodialysis membrane, the PES/PCA-g-MWCNTs MMMs showed less flux decline behavior and better PWF recovery ratio, suggesting that the membrane antifouling performance was improved. The incorporation of PCA-g-MWCNTs enhanced the separation features and antifouling capabilities of the PES membrane for hemodialysis application.
A novel approach in the design of a safe, high performance hemodialysis membrane is of great demand. Despite many advantages, the employment of prodigious nanomaterials in hemodialysis membrane is often restricted by their potential threat to health. Hence, this work focusses on designing a biocompatible polyethersulfone (PES) hemodialysis membrane embedded with poly (citric acid)-grafted-multi walled carbon nanotubes (PCA-g-MWCNTs). Two important elements which could assure the safety of the nanocomposite membrane, i.e. (i) dispersion stability and (ii) leaching of MWCNTs were observed. The results showed the improved dispersion stability of MWCNTs in water and organic solvent due to the enriched ratio of oxygen-rich groups which subsequently enhanced membrane separation features. It was revealed that only 0.17% of MWCNTs was leached out during the membrane fabrication process (phase inversion) while no leaching was detected during permeation. In terms of biocompatibility, PES/PCA-g-MWCNT nanocomposite membrane exhibited lesser C3 and C5 activation (189.13 and 5.29ng/mL) and proteins adsorption (bovine serum albumin=4.5μg/cm2, fibrinogen=15.95μg/cm2) as compared to the neat PES membrane, while keeping a normal blood coagulation time. Hence, the PES/PCA-g-MWCNT nanocomposite membrane is proven to have the prospect of becoming a safe and high performance hemodialysis membrane.
The black soldier fly larvae (BSFL) have been widely extolled for the application in managing various solid organic wastes. Owing to the saprophagous nature of BSFL, a rapid valorization of solid organic wastes can be accomplished with the simultaneous production of valuable biochemical compounds derived from larval biomass. In the present works, the mixed waste coconut endosperm (w-CE) and soybean curd residue (SC-r) substrates with increasing protein nutritional constituent were administered to BSFL. The correlations between protein from larval feed substrates and nutritional profiles of BSFL biomasses were ultimately unveiled. The protein from larval feed substrates could be increased by increasing of SC-r portion against w-CE. At the w-CE:SC-r ratio of 3:2, the highest larval total weight gained and growth rate were attained; indicating an optimum protein nutritional constituent in mixed organics (12.4%) that could enhance the BSFL palatability. Further increment of protein nutritional constituent in mixed organics was found acidifying the residual larval feed substrate progressively, undermining the growth of BSFL. By feeding the BSFL with optimum mixed organics, the maximum accumulations of larval lipid and protein could be achieved. Transesterification of extracted lipid had demonstrated high in monounsaturated fatty acids (73%) which was suitable for biodiesel. The BSFL palatability was finally confirmed from the bioconversion viewpoint of mixed organic wastes. Again, achieving the highest bioconversion efficiency of 14% into larval biomass after accounting the metabolic loss of 54%. Therefore, a total of 68% of mixed w-CE and SC-r could be successfully bioconverted.
Portable dialysis is a need to implement daily and nocturnal hemodialysis. To realize portable dialysis, a dialysate regeneration system comprising superior adsorbents is required to regenerate the used dialysate. This study aims to develop a nano-adsorbent, derived from corn starch for urea removal. Oxidized starch nanoparticles (oxy-SNPs) were prepared via liquid phase oxidation, followed by chemical dissolution and non-solvent precipitation. The oxy-SNPs possessed Z-average size of 177.7 nm with carbonyl and carboxyl contents of 0.068 and 0.048 per 100 glucose units, respectively. The urea adsorption achieved the equilibrium after 4 h with 95% removal. The adsorption mechanism fitted Langmuir isotherm while the adsorption kinetics obeyed pseudo-second-order model. This new material has a maximum adsorption capacity of 185.2 mg/g with a rate constant of 0.04 g/mg.h. Moreover, the oxy-SNPs exhibited the urea uptake recovery of 91.6%. Oxy-SNPs can become a promising adsorbent for dialysate regeneration system to remove urea.
Polyurethane (PU) with three different functional groups: carboxyl, hydroxyl and sulphonyl group on its molecular structure were synthesised in this work. The synthesised material suppresses blood clotting and exhibits anticoagulant characteristics due to the presence of the important anionic groups. The synthesised PU was blended with polyethersulphone (PES) and fabricated into flat-sheet membrane to study the physico-chemical and biocompatibility properties of the PES membrane for blood purification application. PES-PU flat-sheet membranes were fabricated via the dry-wet phase separation technique. Different loading of PU (0, 1, 2, 3, 4, and 5%) blended with PES was studied and compared. Based on the in-vitro biocompatibility analysis of the membrane, it can be suggested that the membrane incorporated with PU has better anticoagulant properties compared to the pristine PES membrane. PU incorporation prolonged the clotting time, decreased the formation of thrombin, decreased soluble complement component 3a (C3a) generation and suppressed platelet adhesion and aggregation. The anionic groups on the membrane surface might bind to coagulation factors (antithrombin) and the calcium ions, Ca2+ and thus improve anticoagulant ability. Based on both physico-chemical and in-vitro studied, 4% loading of PU is the optimum loading for incorporation with PES membrane. These results suggested that the blended PES-PU membranes with good haemocompatibility allowed practical application in the field of blood purification.
The high investment cost required by modern treatment technologies of hazardous sewage sludge such as incineration and anaerobic digestion have discouraged their application by many developing countries. Hence, this review elucidates the status, performances and limitations of two low-cost methods for biological treatment of hazardous sewage sludge, employing vermicomposting and black soldier fly larvae (BSFL). Their performances in terms of carbon recovery, nitrogen recovery, mass reduction, pathogen destruction and heavy metal stabilization were assessed alongside with the mature anaerobic digestion method. It was revealed that vermicomposting and BSFL were on par with anaerobic digestion for carbon recovery, nitrogen recovery and mass reduction. Thermophilic anaerobic digestion was found superior in pathogen destruction because of its high operational temperature. Anaerobic digestion also had proven its ability to stabilize heavy metals, but no conclusive finding could confirm similar application from vermicomposting or BSFL treatment. However, the addition of co-substrates or biochar during vermicomposting or BSFL treatment may show synergistic effects in stabilizing heavy metals as demonstrated by anaerobic digestion. Moreover, vermicomposting and BSFL valorization had manifested their potentialities as the low-cost alternatives for treating hazardous sewage sludge, whilst producing value-added feedstock for biochemical industries.
Membrane technology is a sustainable method to remove pollutants from petroleum wastewater. However, the presence of hydrophobic oil molecules and inorganic constituents can cause membrane fouling. Biomass derived biopolymers are promising renewable materials for membrane modification. In this study, fouling resistant biopolymer N-phthaloylchitosan (CS)- based polythersulfone (PES) mixed matrix membranes (MMMs) incorporated with nanocrystalline cellulose (NCC) was fabricated via phase inversion method and applied for produced water (PW) treatment. The morphological and Fourier-transform infrared spectroscopy (FTIR) analyses of the as-prepared NCC evidenced the formation of fibrous sheet-like structure and the presence of hydrophilic group. The membrane morphology and AFM analysis showed that the NCC altered the surface and cross-sectional morphology of the CS-PES MMMs. The tensile strength of NCC-CS-PES MMMs was also enhanced. 0.5 wt% NCC-CS-PES MMMs displayed a water permeability of 1.11 × 10-7 m/s.kPa with the lowest contact angle value of 61°. It affirmed that its hydrophilicity increased through the synergetic interaction between CS biopolymer and NCC. The effect of process variables such as transmembrane pressure (TMP) and synthetic produced water (PW) concentration were evaluated for both neat PES and NCC-CS-PES MMMs membranes. 0.5 wt% NCC-CS-PES MMMs exhibited the highest PW rejection of 98% when treating 50 mgL-1 of synthetic PW at a transmembrane pressure (TMP) of 200 kPa. The effect of nano silica and sodium chloride on the long-term PW filtration of NCC-CS-PES MMMs was also investigated.
Current study had made a significant progress in microalgal wastewater treatment through the implementation of an economically viable polyethylene terephthalate (PET) membrane derived from plastic bottle waste. The membrane exhibited an exceptional pure water flux of 156.5 ± 0.25 L/m2h and a wastewater flux of 15.37 ± 0.02 L/m2h. Moreover, the membrane demonstrated remarkable efficiency in selectively removing a wide range of residual parameters, achieving rejection rates up to 99%. The reutilization of treated wastewater to grow microalgae had resulted in a marginal decrease in microalgal density, from 10.01 ± 0.48 to 9.26 ± 0.66 g/g. However, this decline was overshadowed by a notable enhancement in lipid production with level rising from 181.35 ± 0.42 to 225.01 ± 0.11 mg/g. These findings signified the membrane's capacity to preserve nutrients availability within the wastewater; thus, positively influencing the lipid synthesis and accumulation within microalgal cells. Moreover, the membrane's comprehensive analysis of cross-sectional and surface topographies revealed the presence of macropores with a highly interconnected framework, significantly amplifying the available surface area for fluid flow. This exceptional structural attribute had substantially contributed to the membrane's efficacy by facilitating superior filtration and separation process. Additionally, the identified functional groups within the membrane aligned consistently with those commonly found in PET polymer, confirming the membrane's compatibility and efficacy in microalgal wastewater treatment.