Cellulose Triacetate Forward Osmosis Membranes Research Articles

Metal-phenolic network as precursor complex coating for forward osmosis membrane with enhanced antifouling property.

In this study, a multi-functional layer was developed based on the commercially available cellulose triacetate (CTA) forward osmosis (FO) membrane to improve its antifouling property. Tannic acid/ferric ion (TA/Fe3+) complexes were firstly coated as a precursor layer on the membrane surface via self-assembly. Afterwards, the tannic acid/diethylenetriamine (TA/DETA) hydrophilic functional layer was further coated, following Ag/polyvinylpyrrolidone (PVP) anti-bacterial layer was formed in situ through the reducibility of TA to obtain TA/Fe3+-TA/DETA-Ag/PVP-modified membrane. The optimized precursor layer was acquired by adjusting the buffer solution pH to 8, TA/Fe3+ ratio to 4 and the number of self-assembled layers to 5. The permeability testing results illustrated that the functional layer had an insignificant effect on the membrane transport parameters. The TA/Fe3+-TA/DETA-Ag/PVP-modified membrane simultaneously exhibited excellent physical and chemical stability. The coated membrane also demonstrated enhanced anti-bacterial properties, achieving 98.63 and 97.30% inhibition against Staphylococcus aureus and Escherichia coli, respectively. Furthermore, the dynamic fouling experiment showed a 12% higher water flux decrease for the TA/Fe3+-TA/DETA-Ag/PVP CTA membrane compared to the nascent CTA membrane, which proved its excellent antifouling performance. This work provides a feasible strategy to heighten the antifouling property of the CTA FO membrane.

Improving antifouling performance of FO membrane by surface immobilization of silver nanoparticles based on a tannic acid: diethylenetriamine precursor layer for municipal wastewater treatment.

In this study, a facile method for multifunctional surface modification on forward osmosis (FO) membrane was constructed by surface immobilization of AgNPs based on tannic acid (TA)/diethylenetriamine (DETA) precursor layer. The cellulose triacetate (CTA) FO membranes modified by TA and DETA with different co-deposition time (6 h, 12 h, 24 h) were investigated. Results indicated that the TA/DETA (24)-Ag CTA membrane with a TA/DETA co-deposition time of 24 h was identified to be optimal, which attained more hydrophilic. And it had the bacterial mortality of Escherichia coli and Staphylococcus aureus reaching 98.23% and 99.83% respectively and possessed excellent physical and chemical binding stability. Meanwhile, the coating layer resulted in the antifouling ability without damaging the membrane intrinsic transport characteristics. As for synthetic municipal wastewater treatment, the water flux of CTA FO membrane decreased approximately 49% of the initial flux after running for 14 days. In contrast, the flux decline rate of TA/DETA (24)-Ag CTA membrane was about 37%. Furthermore, less foulant deposition and higher recovery rate of water flux was observed for TA/DETA (24)-Ag CTA membrane, implying that the modified membrane effectively alleviated membrane fouling and processed a lower flux decline during municipal wastewater treatment. It was attributed to the enhanced surface hydrophilicity and antibacterial property of the coating layer, which improved antifouling property.

Performance of photopolymerized active layer forward osmosis membrane in the osmotic microbial fuel cell

Osmotic microbial fuel cell (OMFC) is evolved by substituting the proton exchange membrane (PEM) by forward osmosis (FO) membrane in a microbial fuel cell (MFC). This study tried to mitigate the dependency on commercial FO membranes to enhance the mutual benefits between MFC and FO. We investigated the performance of photo-polymerized active layer FO membranes in OMFC with feed as a synthetic wastewater and draw solution as 35 g/L NaCl solution and compared by commercial HTI cellulose triacetate (CTA) membrane. Poly (ethylene glycol) phenyl ether acrylate (PPEA) monomer and methacrylic acid (MAA) monomer was used in different ratio i.e., 100/0, 75/25, 50/50, 25/75 and 0/100 for preparation of active layer on our earlier work’s optimized substrate. Effect of the concentration of MAA had a significant effect on ion exchange capacity, water uptake, and oxygen and proton mass transfer. Among all prepared membranes, the 75/25 FO membrane showed the highest power density of 237.23 ± 0.90 mW/m 2 and average water flux 0.95 ± 0.71 LMH. • Photo-polymerized active layer FO membranes were investigated in OMFC. • PPEA and MAA were used as monomers to prepared FO membranes. • The concentration of MAA was found a significant parameter. • 75/25 FO membrane showed highest performance than CTA FO membrane.

Nitrification stability and membrane performance under different water permeation intensity of an osmotic membrane bioreactor

The effects of water permeation intensity on nitrifying bacterial activity, forward osmosis (FO) membrane performance, and bacterial community structure were investigated in an osmotic membrane bioreactor (OMBR). Ammonia was partially oxidized by controlling acidification buffer concentration. Then, the FO module was externally integrated with a nitrifying bioreactor to examine nitrifying bacterial activity in response to the increased salinity. The salinity gradually increased from 2.7 to 45.7 g.L−1 total dissolved solids (TDS). Inhibition of nitrite-oxidizing activity was initiated at a salt concentration of 36.2 g.L−1 TDS. Complete ammonia-oxidizing bacteria inhibition occurred at 45.7 g.L−1 TDS. Illumina high-throughput sequencing revealed that the bacterial community responded to the operational conditions such as the ammonia loading rate and salt concentration. Only two species, Nitrosomonas eutropha and Nitrobacter winogradskyi, were responsible for nitrification in the OMBR. The cellulose triacetate FO membrane showed poor rejection efficiencies for ammonia, nitrite, and nitrate. The FO module was capable to maximally recover 107.8% water in the OMBR. However, the water permeation intensity should be appropriately adjusted to avoid nitrification failure by maintaining the optimal salinity as lower than 35 g.L−1 TDS, which is equivalent to water permeation efficiency of 107.8% in this study.

Fouling and transport of organic matter in cellulose triacetate forward-osmosis membrane for wastewater reuse and seawater desalination

Forward osmosis (FO) can extract water from a solution with a low chemical potential (feed solution, FS) and transport it to a solution with a high chemical potential (draw solution, DS) through natural osmotic pressure. For wastewater reuse via FO, an identifying the foulants and understanding the fouling and transport mechanisms are important. An element-scale spiral-wound FO (SWFO) system and a laboratory-scale FO module tests were conducted with a cellulose triacetate-based FO membrane. Secondary wastewater effluent was used as the FS. To determine the main foulants in FO, the element-scale SWFO was operated at a wastewater plant for 36 d, and a detailed characterization of the foulants (particularly organic matters; OMs) and a membrane autopsy were conducted. The results were verified via a laboratory-scale demonstration. Hydrophilic and large-molecular-weight OMs was the main foulant. It was transported to the DS from the FS through the membrane. The water flux, reverse solute flux, and related parameters (type, concentration, and valence of the draw solute) affected the transport of OMs through the FO membrane. Therefore, further study is needed to develop strategies for reducing the transportation of OMs through the membrane in the wastewater reuse by selecting a suitable draw solute or properly arranging the elements.

Synthesis of asymmetrical cellulose acetate/cellulose triacetate forward osmosis membrane: Optimization

Abstract This study aims at identifying asymmetric cellulose acetate (CA)/cellulose triacetate (CTA) forward osmosis (FO) membranes that have high water flux (Jv) and low reverse salt diffusion flux (Js) with acetic acid to replace the 1,4-dioxane for the mixed solvent for CA/CTA dissolution. The optimum fabrication parameters for the CA/CTA FO membranes are determined by using response surface methodology with a 43 Box-Behnken design. Effects of weight fraction of CA (at CA/CTA = 2), spinning speed, annealing temperature and annealing time on the Jv and Js are investigated. The optimum conditions to maximize the Jv to 6.4 L/m2/h and minimize Js to 0.47 g/m2/h together are: 6%/3% CA/CTA, 2993 rpm spinning speed, 87.8 °C annealing temperature and 180 s annealing time. The fabricated FO membranes can reject over 99.9% heavy metal ions from feed wastewater and can be used as an effective barrier for alginate gels with easy flux recovery by ultrasound cleaning.

Effects of organic acids on the performance of cellulose triacetate forward osmosis membrane

Forward osmosis (FO) membrane performance was improved using different organic acids (formic acid, acetic acid, lactic acid) for the addition of the casting solution. Scanning electron microscope (SEM) images of all the FO CTA membranes exhibited essentially the membranes have a structure of looking like two dense skin layers and a sponge‐like supporting layer. Additionally, based on the surface roughness values analysis of Atomic Force Microscope (AFM), the membranes with lactic acid, with similar roughness to the membranes without any acid, have bigger roughness than the membranes with formic acid or acetic acid. Furthermore, the water flux of membranes with acids has been improved and the reverse salt flux decreased. The membranes with lactic acid, with an outstanding penetration performance, were utilized to test the performance when 1 mol/L sodium chloride (NaCl), magnesium chloride (MgCl2), magnesium sulfate (MgSO4), and sodium sulfate (Na2SO4) were, respectively, as the draw solutions. The results revealed that the membranes have a higher rejection ratio for MgSO4. Besides, in the process of separating oil–water mixture, the membranes with the organic acids have a better separation efficiency than the membrane without any acid during FO process and the water flux recovery rate could achieve above 90% insuring the membrane anti‐fouling. POLYM. ENG. SCI., 59:E138–E145, 2019. © 2018 Society of Plastics Engineers

Biofouling Mitigation by Chloramination during Forward Osmosis Filtration of Wastewater.

Pre-concentration is essential for energy and resource recovery from municipal wastewater. The potential of forward osmosis (FO) membranes to pre-concentrate wastewater for subsequent biogas production has been demonstrated, although biofouling has also emerged as a prominent challenge. This study, using a cellulose triacetate FO membrane, shows that chloramination of wastewater in the feed solution at 3–8 mg/L residual monochloramine significantly reduces membrane biofouling. During a 96-h pre-concentration, flux in the chloraminated FO system decreased by only 6% and this flux decline is mostly attributed to the increase in salinity (or osmotic pressure) of the feed due to pre-concentration. In contrast, flux in the non-chloraminated FO system dropped by 35% under the same experimental conditions. When the feed was chloraminated, the number of bacterial particles deposited on the membrane surface was significantly lower compared to a non-chloraminated wastewater feed. This study demonstrated, for the first time, the potential of chloramination to inhibit bacteria growth and consequently biofouling during pre-concentration of wastewater using a FO membrane.

Enhancement of nonwoven cellulose triacetate forward-osmosis membranes by surface coating modification

Enhancement of nonwoven cellulose triacetate forward-osmosis membranes by surface coating modification

Interforce initiated by magnetic nanoparticles for reducing internal concentration polarization in CTA forward osmosis membrane

ABSTRACTThe interforce between the magnetic composite forward osmosis (FO) membranes and the magnetic draw solution was proposed to reduce the internal concentration polarization (ICP) of FO process, and realized the synergetic permeability improvement of resultant FO membranes. The key factor was the successful fabrication of the Fe3O4 magnetic nanoparticles (MNPs) with small‐size and narrow distribution via co‐precipitation method. The cellulose triacetate (CTA) magnetic composite FO membranes were fabricated using Fe3O4 as additive via in situ interfacial polymerization, and named CTA‐Fe3O4. Dynamic light scattering (DLS) and zeta results showed that the coated sodium oleate on the MNPs explained their reducing aggregation and the stability of various pHs. The MNPs' surface segregation during demixing process resulted in the improvement of hydrophilicity, Fe content and roughness of resultant CTA‐Fe3O4 composite FO membranes. Furthermore, the in situ interfacial polymerization resulted in the formation of the polyamide selective layer, and the CTA‐Fe3O4 membrane's N content was 11.02% to 11.12%. The permeability properties (FO and pressure retarded osmosis modules) were characterized using 1.0M NaCl and 100 mg/L Fe3O4 as draw solutions, respectively. The results indicated that the higher concentration of MNPs supplied more interforce and better FO permeability properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44852.

Preparation of cellulose triacetate forward osmosis membranes for treating esterification wastewater

Preparation of cellulose triacetate forward osmosis membranes for treating esterification wastewater

Characterization and antifouling performance of cellulose triacetate forward osmosis membranes modified with graphene oxide

Characterization and antifouling performance of cellulose triacetate forward osmosis membranes modified with graphene oxide

Enhanced performance of cellulose triacetate membranes using binary mixed additives for forward osmosis desalination

In this study, on a basis of the single additive optimization experiments of the cellulose triacetate (CTA) forward osmosis (FO) membranes, the CTA FO membranes with binary mixed pore-forming additives were designed and fabricated to retrofit the membrane structure and separation performance for FO desalination. The binary mixed additives such as acetic acid-lactic acid (AA-LA), acetic acid-maleic acid (AA-MA) as well as zinc chloride-lactic acid (ZnCl2-LA) were selected via combining a single additive with the capacity to improve the salt rejection with another single additive with the capacity to improve the water flux. The effectiveness of the binary mixed additives on the FO performance was extensively evaluated and confirmed. For example, with the ZnCl2-LA as binary additive, the resulting CTA membrane exhibited a much improved water flux of ~11.5L/m2h and an excellent salt rejection of ~98.3% under the fixed FO operating condition (0.1M NaCl solution as feed, 2M glucose solution as draw solution, FO mode, 2h), which were increased by approximately 51.3% and 8.1% compared to the commercial CTA membrane from HTI, respectively. Compared to the single additives, the binary mixed additives could significantly enhance the water flux for the CTA membranes with an insignificant reduction in salt rejection, which might depend on the interaction between two additives as well as the interaction between additives and solvent during the phase inversion. It indicated that the trade-off effect between the selectivity and permeability of a polymer membrane was partially broken for our membranes with binary mixed additives. This study helps us to pave the way to design highly efficient additives for high-performance FO membranes.

Integration of forward osmosis process and a continuous airlift nitrifying bioreactor containing PVA/alginate-immobilized cells

Forward osmosis (FO) and biological nitrification processes were integrated in this study. High strength ammonia wastewater of 2500mg-N/L was partially nitrified at an ammonia conversion rate of 1.34±0.25kg-N/m3-d under the limitation of an acidification buffer, i.e., HCO3−-C/NH4+-N=1, as a control factor. Direct contact between biomass and a cellulose triacetate FO membrane was avoided by employing PVA/alginate-immobilized nitrifiers in the bioreactor. The simultaneous FO process concentrated the wastewater at concentration factors (CFs) of up to 2.34 during the partial nitritation (PN) reaction. As a result, the concentration of total dissolved solids (TDS) ranged from 13.6g/L to 35.7g/L. It was found that salinity higher than 17g-TDS/L inhibited the activity of the nitrite-oxidizing bacteria, but not the ammonia-oxidizing bacteria. Scanning electron microscopy and fluorescence excitation–emission matrix and liquid chromatography-organic carbon detection analysis revealed the existence of hydrophilic organic fouling including biopolymers and low molecular weight neutrals on the surface of the FO active layer. However, the FO fouling was successfully controlled by air scouring for 15min.

The improvement of CTA forward osmosis membrane performance by hydrophilic modification on interface between support layer and non-woven fabric

Cellulose triacetate (CTA) forward osmosis (FO) membrane was fabricated with a polyvinyl alcohol (PVA)-modified nonwoven fabric (NWF) as a support material, which helps achieve a significant improvement in membrane performance. First, a surface modification was performed on the NWF by attaching PVA and glutaraldehyde to the fabric by cross-linking. Second, a CTA membrane was cast on the surface of the surface-modified NWF by phase inversion process. Then, the modified NWF and the modified CTA membrane were characterized by infrared spectroscopy, scanning electron microscopy (SEM), and the contact angle. It was found from the infrared spectroscopy that large quantities of hydroxyl group on the surface made the NWF more hydrophilic. It was also found from the SEM that, the PVA was not only attached on the surface of the fabric, but also embedded in the fabric. With the PVA content of the modified CTA membrane increased, the small sponge-like pores in the support layer were changed gradually into bigger finger-like pores. After the PVA modification, the contact angle of the NWF decreased from 116.9° to 38.5°, and that of the modified CTA membrane decreased from 114.1° to 55.8°, leading to a significant improvement in hydrophilicity. As a result, the water flux of the PVA-modified CTA FO membrane in FO mode was greatly improved up to 55 LMH. And the same time the Js/Jw was only 0.25. It has been calculated that the modified CTA membrane has a porosity of 0.51, and a tortuosity of 0.48, and a structural parameter of 93.65 μm. Compared the PVA-modified CTA membrane with several other FO membranes, it was found that the former has a smaller structural parameter and which can effectively reduce the internal concentration polarization in the support layer, thereby resulting in a significant improvement in membrane performance.

Biofouling behavior and performance of forward osmosis membranes with bioinspired surface modification in osmotic membrane bioreactor

Forward osmosis (FO) has received considerable interest for water and energy related applications in recent years. Biofouling behavior and performance of cellulose triacetate (CTA) forward osmosis membranes with bioinspired surface modification via polydopamine (PD) coating and poly (ethylene glycol) (PEG) grafting (PD-g-PEG) in a submerged osmotic membrane bioreactor (OMBR) were investigated in this work. The modified membranes exhibited lower flux decline than the pristine one in OMBR, confirming that the bioinspired surface modification improved the antifouling ability of the CTA FO membrane. The result showed that the decline of membrane flux related to the increase of the salinity and MLSS concentration of the mixed liquid. It was concluded that the antifouling ability of modified membranes ascribed to the change of surface morphology in addition to the improvement of membrane hydrophilicity. The bioinspired surface modifications might improve the anti-adhesion for the biopolymers and biocake.

Application of forward osmosis membrane technology for oil sands process-affected water desalination.

The extraction process used to obtain bitumen from the oil sands produces large volumes of oil sands process-affected water (OSPW). As a newly emerging desalination technology, forward osmosis (FO) has shown great promise in saving electrical power requirements, increasing water recovery, and minimizing brine discharge. With the support of this funding, a FO system was constructed using a cellulose triacetate FO membrane to test the feasibility of OSPW desalination and contaminant removal. The FO systems were optimized using different types and concentrations of draw solution. The FO system using 4 M NH4HCO3 as a draw solution achieved 85% water recovery from OSPW, and 80 to 100% contaminant rejection for most metals and ions. A water backwash cleaning method was applied to clean the fouled membrane, and the cleaned membrane achieved 77% water recovery, a performance comparable to that of new FO membranes. This suggests that the membrane fouling was reversible. The FO system developed in this project provides a novel and energy efficient strategy to remediate the tailings waters generated by oil sands bitumen extraction and processing.

Preparation and Characterization of Graphene Oxide / Cellulose Triacetate Forward Osmosis Membranes

Forward osmosis (FO) is an emerging membrane separation technology in environmental and industrial process. This paper presents cellulose triacetate (CTA) membrane containing graphene oxide (GO) nanosheets via blending to enhance membrane performance in forward osmosis (FO) process. GO nanosheets with various loading were added into the casting solution to prepare the modified FO membranes. The prepared membranes were characterized by morphology analysis and permeability measurement. The result showed that the GO nanosheets effectively improved the performance of the CTA membranes. The CTA-0.2GO membrane had the highest water flux, reached 1.5 times as high as that of CTA membrane.

Comparison of biofouling mechanisms between cellulose triacetate (CTA) and thin-film composite (TFC) polyamide forward osmosis membranes in osmotic membrane bioreactors

There are two types of popular forward osmosis (FO) membrane materials applied for researches on FO process, cellulose triacetate (CTA) and thin film composite (TFC) polyamide. However, performance and fouling mechanisms of commercial TFC FO membrane in osmotic membrane bioreactors (OMBRs) are still unknown. In current study, its biofouling behaviors in OMBRs were investigated and further compared to the CTA FO membrane. The results indicated that β-d-glucopyranose polysaccharides and microorganisms accounted for approximately 77% of total biovolume on the CTA FO membrane while β-d-glucopyranose polysaccharides (biovolume ratio of 81.1%) were the only dominant biofoulants on the TFC FO membrane. The analyses on the biofouling structure implied that a tighter biofouling layer with a larger biovolume was formed on the CTA FO membrane. The differences in biofouling behaviors including biofoulants composition and biofouling structure between CTA and TFC FO membranes were attributed to different membrane surface properties.

Effects of membrane orientation on fouling characteristics of forward osmosis membrane in concentration of microalgae culture

Application of forward osmosis (FO) membrane to microalgae cultivation processes enables concentration of microalgae and nutrients with low energy consumption. To understand fouling characteristics of FO membrane in concentration of microalgae culture, we studied flux decline, flux recovery by cleaning, and foulants characteristics, in different membrane orientation of active-layer-facing-feed-solution (AL-FS) and active-layer-facing-draw-solution (AL-DS) modes. Batch concentration of Chlorella vulgaris was conducted with a cellulose-triacetate FO membrane. Rapid flux decline and lower flux recovery was observed in AL-DS mode because of inner-membrane fouling including internal pore clogging, adsorption and internal concentration polarization in the support layer. A proportion of polysaccharides in extracellular polymeric substances to soluble microbial products were larger in chemical cleaning effluent than physical one in AL-DS mode, although those were not significantly different in AL-FS mode. Excitation-emission matrix analysis revealed that proteins and humic-like substances were also possible irreversible foulants both in AL-DS and AL-FS modes.