Flux Decline Research Articles

Removal of natural organic matter fractions by adsorptive asymmetric ceramic membrane functionalized with in situ phytogenic nanoscale zero valent iron: Performance and Fenton cleaning strategy

AbstractExtant literature has demonstrated that conventional water treatment processes especially in developing countries struggle in completely removing detrimental organic loads. Emerging research delineates nanomaterials such as nanoscale zero valent iron (nZVI) to have excellent performance in organic matter removal from aqueous media. In this work, nZVI particles were prepared from the liquor of commercially available green tea and supported on kaolin (K‐nZVI) and investigated as an adsorbent for natural organic matter (NOM) sequestration from aquatic media. Further, the asymmetric ceramic membrane was prepared by incorporating the developed adsorbent on a concrete support for the removal of NOM. A Fenton cleaning strategy was developed to mitigate fouling. The Brunauer–Emmett–Teller (BET) results revealed the developed adsorbent surface area was greater compared to raw kaolin (27.07 and 11.64 m3 g−1, respectively). The scanning electron microscopy (SEM) imagery of the developed adsorbent showed the particle staking was presented as paper slices of varying sizes, an indication of dispersed particles with characteristic plate‐like fragments. The synthesized membrane exhibited a pHZPC value of 4.79 ± 0.03. This meant at pH above 4.79 ± 0.03, the membrane would be negatively charged, and conversely at pH below the pHZPC value. Membrane fouling due to bovine serum albumin (BSA) deposition showed a 50% flux decline in the first 60 min, coinciding with the rapid adsorption capacity within the same time frame. The optimal cleaning parameters of pH (4.5) and H2O2 (5 mM) gave the best flux recovery rates. This work demonstrated an efficient Fenton cleaning strategy to regenerate the developed membrane.

Polyamidoamine and carboxylated cellulose nanocrystal grafted antifouling forward osmosis membranes for efficient leachate treatment via integrated forward osmosis and membrane distillation process

Organic fouling remains an intractable challenge for forward osmosis (FO) and integrated FO-membrane distillation (MD) strategy to treat landfill leachate. To address this challenge, polyamidoamine (PAMAM)/polydopamine (PDA) and carboxylated cellulose nanocrystal (CCN) were grafted gradually on the commercial thin film composite (TFC) FO membranes via chemical coupling to achieve excellent antifouling capacity. PAMAM dendrimers, with abundant terminal amines, hyperbranched structure and open interior cavity, served as a unique intermediate platform for chemically covalent attachment of CCN with high water affinity, then cooperated with CCN to form a hydrophilic and robust antifouling layer. Compared to the raw TFC membrane, the PAMAM/PDA-CCN modified TFC membrane exhibited a similar water flux of 30.6 L m−2 h−1 (LMH) accompanied with a decreased reverse salt flux of 6.9 g m−2 h−1 (gMH) by using 1 M NaCl solution as draw solution (DS) and DI water as feed solution (FS). When actual leachate was used as FS, the modified FO membranes possessed significantly enhanced antifouling capacity with a lower flux decline (≤43.7%) and a higher flux recovery rate (≥94.2%) than the raw TFC membrane (flux decline ≤59.4% and flux recovery rate ≥79.0%, respectively). The improved fouling resistance could be further demonstrated by the reduced thickness of the organic fouling layer. Eventually, the employment of the modified FO membranes improved the compatibility of the FO and MD water fluxes and achieved sustained water production. The construction of synergistic dendritic PAMAM and CCN grafted surface paves a new way for the development of high-performance water treatment membranes.

Evaluation of Ceramics Adsorption Filter as a Pretreatment for Seawater Reverse-Osmosis Desalination.

Seawater reverse osmosis (SWRO) is the most energy-efficient process for desalination to produce drinking water from seawater. However, its sustainability is still challenged by membrane fouling. Appropriate feed water quality is one of the crucial prerequisites for SWRO operation. In the current study, a ceramic adsorption filter (CAF), which was predominantly coated with an aluminum-based adsorbent (i.e., Alumina, Al2O3), was employed to enhance the pretreatment performance of SWRO. The fouling performance of SWRO pre-treated with a CAF was evaluated by feeding with real ultrafiltration (UF)-filtrated seawater collected from a seawater desalination R&D facility in Singapore. The flux decline profile showed that the presence of CAF after UF could mitigate around 10-30% of SWRO fouling. Based on the autopsy of the fouled SWRO membranes, it was observed that SWRO with CAF pre-treatment and daily regeneration could alleviate around 77.5% of Ca-induced inorganic fouling as well as 76% of lower biofouling. The present work highlights the potential of applying adsorption technology to enhance pre-treatment performance to extend the lifespan of SWRO membranes. Coupling the adsorbents on a ceramic filter should be a useful way to ease their implementation, i.e., inline adsorption and re-generation.

Antifouling graphene oxide membranes for oil-water separation via hydrophobic chain engineering

Engineering surface chemistry to precisely control interfacial interactions is crucial for fabricating superior antifouling coatings and separation membranes. Here, we present a hydrophobic chain engineering strategy to regulate membrane surface at a molecular scale. Hydrophilic phytic acid and hydrophobic perfluorocarboxylic acids are sequentially assembled on a graphene oxide membrane to form an amphiphilic surface. The surface energy is reduced by the introduction of the perfluoroalkyl chains while the surface hydration can be tuned by changing the hydrophobic chain length, thus synergistically optimizing both fouling-resistance and fouling-release properties. It is found that the surface hydration capacity changes nonlinearly as the perfluoroalkyl chain length increases from C4 to C10, reaching the highest at C6 as a result of the more uniform water orientation as demonstrated by molecular dynamics simulations. The as-prepared membrane exhibits superior antifouling efficacy (flux decline ratio <10%, flux recovery ratio ~100%) even at high permeance (~620 L m−2 h−1 bar−1) for oil-water separation.

Coagulation characteristic and mechanism of Fe(III) salts toward typical Cr(III) complexes in wastewater treatment.

Cr(III) complexes are typical pollutants in various industrial wastewater and pose a serious threat to the ecosystem and humans. The coagulation process is commonly used in water treatment plants, yet its removal characteristic and mechanism toward Cr(III) complexes have been rarely reported. In this study, the Fe(III) coagulation process was adopted for the evaluation of Cr(III) complex removal in terms of Cr residual concentration as well as floc size. The results showed that Fe(III) with a dose of 0.8mM removed more than 80% of total Cr for Cr3+ and Cr(III)-acetate, whereas poor removal rate (~ 50%) was obtained for Cr(III)-citrate under the same conditions. Neutral and alkaline conditions facilitated Cr(III)-acetate removal by Fe(III) coagulation, while limited influence was observed for Cr(III)-citrate with various pH. The main removal mechanism of Cr(III)-acetate was precipitation. Cr(III)-citrate elimination largely relied on the adsorption property and sweeping effect of Fe floc. Moreover, Cr(III)-acetate was easier to be separated from a solution since the generated floc sizes were 270μm. Flocs that formed in the Cr(III)-citrate treatment were only 0.3μm, resulting in separation difficulties during the coagulation process. The presence of Cr(III)-acetate and Cr(III)-citrate caused a significant decline in membrane flux. This study provided fundamental knowledge of Fe coagulation treatment in Cr(III) complex-containing wastewater.

Effects of chlorine disinfection on RO membrane biofouling at low feed water temperature for wastewater reclamation

Abstract Chlorine disinfection has been reported to be ineffective in controlling RO membrane biofouling in some projects. Feed water temperature is a crucial factor in the formation of RO membrane biofouling. It has a positive impact on the wide application of the RO process to ascertain whether chlorine disinfection can alleviate the membrane biofouling at low temperatures. In this study, the effects of chlorination on the RO membrane biofouling at low feed water temperature (10 °C) were investigated by a lab-scale RO apparatus. The final normalized flux was 0.33 and 0.29 with and without chlorination, respectively. According to the normalized flux decline curve, chlorination could not alleviate the RO membrane fouling at low temperature. Based on the intermediate blocking model, chlorination increased the membrane fouling potential of the feed water. At low temperature, the biofilm on the membrane with chlorination was thinner and denser than that without chlorination. In addition, the membrane with chlorination contained more foulants and dissolved organic matter than that without chlorination. Chlorination failed to continuously prevent bacteria accumulation on RO membrane at low temperature, but screened out bacteria that were potentially more suitable for the low-temperature membrane environment.

Durable photocatalytic membrane of PAN/TiO2/CNT for methylene blue removal through a cross-flow membrane reactor

ABSTRACT PAN/TiO2/CNT and PAN/TiO2/CNT-PVA composite nanofibrous membranes with photocatalytic activity were successfully synthesized using electrospinning. The effect of CNT concentration and PVA coating on the membrane surface toward the membrane performances was investigated. TiO2 anatase phase was exist on the respective membranes. SEM morphological investigation revealed the random orientation of the nanofibers with beads decorated in each strand. The PAN/TiO2/CNT composite nanofiber membrane exhibited high performance for the removal of cationic organic dye methylene blue (MB) in a cross-flow photocatalytic membrane reactor under low power visible light of LED lamp (14.5 W) and a constant pollutant flow rate of 0.21 L/min. The presence of TiO2/CNT photocatalyst was proven to prolong the lifetime of the photocatalytic membrane and retard membrane fouling to the maximum extent. PAN/TiO2/CNT membrane has displayed 100% MB rejection for the first 8 h of operation. Both, PAN/TiO2/CNT and PAN/TiO2/CNT-PVA maintained their membrane performances and did not show major flux decline even after five recycling uses. The incorporation of TiO2/CNTs on PAN nanofibers has resulted in a durable photocatalytic membrane for the effective removal of dye waste using a cross-flow membrane reactor.

Fouling evolution of extracellular polymeric substances in forward osmosis based microalgae dewatering

Membrane fouling was still a challenge for the potential application of forward osmosis (FO) in algae dewatering. In this study, the fouling behaviors of Chlorella vulgaris and Scenedesmus obliquus were compared in the FO membrane filtration process, and the roles of their soluble-extracellular polymeric substances (sEPS) and bound-EPS (bEPS) in fouling performance were investigated. The results showed that fouling behaviors could be divided into two stages including a quickly dropped and later a stable process. The bEPS of both species presented the highest flux decline (about 40.0%) by comparison with their sEPS, cells and broth. This performance was consistent with the largest dissolved organic carbon losses in feed solutions, and the highest interfacial free energy analyzed by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The chemical characterizations of algal foulants further showed that the severe fouling performance was also consistent with a proper ratio of carbohydrates and proteins contents in the cake layer, as well as the higher low molecular weight (LMW) components. Compared with the bEPS, the sEPS was crucial for the membrane fouling of S. obliquus, and an evolution of the membrane fouling structure was found in both species at the later filtration stage. This work clearly revealed the fundamental mechanism of FO membrane fouling caused by real microalgal suspension, and it will improve our understanding of the evolutionary fouling performances of algal EPS.

Influence of Membrane Fouling and Reverse Salt Flux on Membrane Impedance of Forward Osmosis Microbial Fuel Cell.

The forward osmosis membrane (FO membrane) is an emerging wastewater treatment technology in bioelectricity generation, organic substrate removal and wastewater reclamation. Compared with traditional membrane materials, the FO membrane has a more uniform water content distribution and internal solution concentration distribution. In the past, it was believed that one of the important factors restricting power generation was membrane fouling. This study innovatively constructed a mass transfer model of a fouling membrane. Through the analysis of the hydraulic resistance coefficient and the salt mass transfer resistance coefficient, the driving force and the tendency of reverse salt flux during membrane fouling were determined by the model. A surprising discovery was that the fouling membrane can also achieve efficient power generation. The results showed that the hydraulic resistance coefficient of the fouling membrane increased to 4.97 times the initial value, while the salt mass transfer resistance coefficient did not change significantly. Meanwhile, membrane fouling caused concentration polarization in the FO membrane, which enhanced the reverse trend of salt, and the enhancement effect was significantly higher than the impact of the water flux decline caused by membrane pollution. This will make an important contribution to research on FO membrane technology as sustainable membrane technology in wastewater treatment.

Fulvic and alginic acid separation during pressure retarded osmosis: Governing effects and fouling mechanisms

In this study, the performance of model foulant (alginate and fulvic acid) separation by pressure retarded osmosis (PRO) was systematically studied. At the various operating conditions tested, fulvic acid had a greater flux decline and power density loss than alginate. The results of membrane resistance test, SEM-EDX images, and the solute diffusion coefficient K demonstrated that fulvic acid was more likely to clog the inside of the porous support layer of the PRO membrane, which would exacerbate the internal concentration polarization (ICP) phenomena. Although model foulants were successfully removed by PRO (with a retention rate of about 95.0%), the presence of either calcium or magnesium ions was detrimental to the fouling process of PRO membranes. According to the XDLVO theory analysis results, the presence of calcium or magnesium ions increased foulant adhesion to the PRO membrane, thereby resulting in membrane fouling. In addition, Pearson correlation coefficient also showed that the hydrodynamic conditions (effective osmotic pressure difference as well as operating hydraulic pressure acting vertically to the membrane and parallel to the membrane cross-flow shear force) had an important effect on the degree of membrane fouling. This is attributed to the influence of the hydrodynamic conditions on the initial influence water flux and thus on the fouling of the PRO membrane.

Advanced thin-film composite polyamide membrane for precise trace short-chain PFAS sieving: Solution, environment and fouling effects

Membrane separation technology has been favorably applied to acquire non-polluting permeate in conditions of contaminative aqueous environment. However, some emerging contaminants with critical impacts on human health and environmental safety such as poly- and perfluoroalkyl (PFAS) compounds composed of various molecular chains are frequently found in water treatment process steps. Especially, short-chain PFASs remain poorly understood in nanofiltration membrane. A thin-film composite membrane with a hyaluronic acid interlayer (TFCi) had been finely tailored to simultaneously gain ameliorative permeate and rejection. Experiments were performed on a small-scale installation to investigate the correlation between operating parameters and short-chain PFASs removal performances. Results showed effectual trace short-chain PFASs rejection during various pressure, temperature, pH, concentration and fouling conditions. Alginate fouling micelles increased PFAS retention and generated a rapid flux decline; nevertheless, the pollutant could be largely removed by washing. Furthermore, molecular dynamics simulations were utilized to reveal the mechanism of the trace short-chain PFASs rejection competence. The hyaluronic acid interlayer was able to suppress the diffusion rate toward the reaction boundary, facilitating the formation of fast water transport pores with good rejection performance for PFAS in polyamides. These results provide important insights into the mechanism of trace hydrophobic contaminants removal system and the interlayer design approach for efficient short-chain PFAS removal using nanofiltration membranes.

Non-Fourier pseudoplastic nanofluidic transport under the impact of momentum slip and thermal radiation

In this modern era of research, fluid mechanics and particularly nanofluids flowing on the stretching surfaces are considered to be occurring more often due to their faster heat transfer mechanism. Mostly, the theoretical research related to nanofluids including this one contributed in studying the performance and reaction of nanomaterials against different physical constraints so that they have wide applications in several developed engineering industries like, atomic receptacles, transportation, microchip technology as well as biomedicine industry and food industry. Several fluids permeating in industrial and biological processes are pseudo-plastics. Their non-Newtonian behavior is usually related to structural reorganizations of the fluid molecules due to their flow. Keeping this in view, this study is an effort to investigate two-dimensional steady incompressible Cattaneo–Christov heat flux model of Carreau–Yasuda nanofluid in the presence of thermal radiation and velocity slip. The governed model is presented through partial differential equations which are transformed into ordinary differential equations by using similarity transformation. The final system of equations are solved numerically and the results are expressed through graphs and tables for fluid’s velocity temperature, concentration and physical quantities like heat and mass flux. It is observed that skin friction as well as local heat and mass flux decline with velocity slip parameter and heat transfer rises but mass flux at surface declines through increment in radiation parameter.

Effect of ferrous-activated calcium peroxide oxidation on forward osmosis treatment of algae-laden water: Membrane fouling mitigation and mechanism

Forward osmosis (FO) is a high-efficiency and low-energy consumption way for algae-laden water treatment, whereas membrane fouling is still an unavoidable problem in its practical application. In this work, a strategy of ferrous-activated calcium peroxide (Fe(II)/CaO2) was proposed to control FO membrane fouling in the purification of algae-laden water. With the treatment of Fe(II)/CaO2, the aggregation of algal contaminants was promoted, the cell viability and integrity were well preserved, and the fluorescent organics were efficiently removed. With respect to the fouling of FO membrane, the flux decline was generally alleviated, and the flux recovery was promoted to varying degrees under different process conditions. It could be revealed through the extended Derjaguin-Landau-Verwey-Overbeek theory that the adhesion of contaminants and membrane surfaces was reduced by Fe(II)/CaO2 treatment. The interface morphologies and functional groups of membrane verified that Fe(II)/CaO2 could mitigate the fouling by reducing the amount of algal contaminants adhering to the FO membrane. The co-coagulation of in-situ Fe(III) together with Ca(OH)2, as well as the oxidation of •OH were the main mechanisms for fouling mitigation. In sum, the Fe(II)/CaO2 process could effectively improve the efficiency of FO for algae-laden water treatment, and has broad application prospects.

Choice of DLVO approximation method for quantifying the affinity between latex particles and membranes

The Derjaguin-Landau-Verwey-Overbeek (DLVO) model, as well as the extended model (XDLVO), is popularly employed to quantify the interfacial interactions underlying membrane fouling. However, disagreements between membrane fouling extent and the interaction energies derived from DLVO or XDLVO models have been reported, which suggests gaps in the understanding. This study demonstrates that the DLVO approximation methods for predicting the interfacial foulant-membrane interaction are sensitive to the boundary condition assumptions (e.g., constant charge versus constant potential). In particular, while both the Poisson-Boltzmann (P–B) and linear superposition approximation (LSA) equations can quantify the electrostatics (EL) interaction energy component, the former assumes constant potential, while the latter additionally considers constant charge scenarios. The relative accuracy of these two equations were evaluated here. For dead-end filtration tests, flux decline trends, OCT analysis results and fouling model parameters were obtained. Regarding fouling of pristine PCTE membrane by latex particles of opposite charge signs, both the P–B and LSA equations contribute to predict relative fouling extents correctly. However, for the case of the BPEI-coated membrane, the P–B equation failed whereas the LSA equation gave good agreements. For cross-flow filtration tests in organic solvents, LSA also out-performed the P–B equation in providing more accurate predictions of membrane fouling. The results here highlight the shortcomings in the commonly used P–B equation and are expected to be potentially valuable in the development of better approximations for quantifying interfacial interaction energies.

Solar-Driven Evaporators with Thin-Film-Composite Architecture Inspired by Plant Roots for Treating Concentrated Nano-/Submicrometer Emulsions.

Oil/water separation by porous materials has received growing interest over the past years since the ever-increasing oily wastewater discharges seriously threaten our living environment. Purification of nano-sized and concentrated emulsions remains a big challenge because of the sharp flux decline by blocking the pores and fouling the surfaces of those porous materials. Herein, we propose a solar-driven evaporator possessing thin-film-composite architecture to deal with these two bottlenecks. Inspired by plant roots, our evaporator composes of a large-pore sponge wrapped by a thin hydrogel film, which is constructed by the contra-diffusion and cross-linking of alginate and calcium ions at the sponge surface. The dense superoleophobic hydrogel layer serves as a selective barrier that prevents oil emulsions but allows water permeation, while the inner sponge with large pores facilitates water transport within the evaporator, ensuring sufficient water supply for evaporation. By splitting the single evaporator into an array, the evaporator performs a high evaporation rate of ∼3.10 kg·m-2·h-1 and oil removal efficiency above 99.9% for a variety of oil emulsions. Moreover, it displays a negligible decline in the evaporation rate when treating concentrated emulsions for 8 h.

Fabrication of robust ceramic supported polymeric composite nanofiltration membrane for heavy metal contaminated wastewater treatment

Nanofiltration (NF) membranes with positive charge are essential for efficient removal of heavy metals and salts from waste water. In this work surface modified positively charged novel ‘ceramic-supported-polymeric’ (CSP) composite NF membranes were fabricated with the copper ions embedded crosslinked polyethyleneimine polymer matrix over tubular ceramic substrate using facile dipcoating method. EDX, ATR-FTIR, XPS, FESEM, AFM and contact angle analyses were performed to characterize the chemical structures and morphologies of the prepared membranes. The composite NF membrane exhibited satisfactory pure water permeability (PWP) of 8.1 L.m−2.h−1.bar−1 and promising salt (87.19 % and 74.41 % for Mg2+ and Ca2+, respectively) and heavy metal ion rejections (91.73 %, 83.15 % and 75.50 % for Zn2+, Ni2+ and Cd2+, respectively). Activation energy and overall size-exclusion-dehydration phenomena along with steric hindrance and Donnan electrostatic exclusion plays an important role for heavy metals and salts rejection. In addition, the membrane showed excellent antifouling properties (>99 % humic acid removal) with high flux recovery ratio (77.6 %) and low flux decline ratio (33 %) for 5 h operations (3rd cycle) together with outstanding antibiofouling ability towards Brevibacillusagri and Leclerciaadecarboxylata. Furthermore, excellent chemical stability of the membrane suggests its potential application for waste water treatment under critical conditions.

Selective and high-efficient removal of tetracycline from antibiotic-containing aqueous solution via combining adsorption with membrane pre-concentration

The antibiotics in the livestock sewerage are responsible for antimicrobial resistance, causing a global public health crisis and necessitating high-efficient and environmental-friendly antibiotic treatment processes. Herein, one membrane pre-concentration and MOF-based selective adsorption hybrid system is proposed to high-efficiently remove tetracycline (TC) from the aqueous solution containing other two representative antibiotics (sulfamethoxazole (SMZ), and trimethoprim (TMP)) in the livestock sewage. In this work, two common MOFs-based materials (MIL-101-Fe and NH2-MIL-101-Fe) are employed as the adsorbents to selectively remove TC from the solution. Adsorption experiments showed that the selective coefficient of NH2-MIL-101-Fe for TC could reach up to 95 %, because of stronger interaction between TC and MIL-101s calculated via the theoretical simulation. Also, experimental results demonstrated that the desired operating conditions necessitated thermal input and pre-concentration operation. Accordingly, temperature-enhanced forward osmosis (T-FO) and temperature-enhanced osmotic membrane distillation (T-OMD) were proposed to concentrate the solution containing these three antibiotics in the cost-effective way where the fertilizer solution (KCl in this work) was used as the draw solution (DS) and diluted DS solution could be used in agricultural fertigation. Membrane pre-concentration experiments showed that TC, TMP, and SMZ could be theoretically concentrated in T-FO, but high TC and KCl leakage and inevitable water flux decline behavior significantly sacrificed the concentration efficiency, thereby initiating the application of T-OMD. Higher and more stable water flux occurred in T-OMD, and 99.76 % of antibiotic and KCl leakage could be mitigated compared to T-FO, thereby providing one option to high-efficiently remove antibiotics in livestock sewerage and achieve agricultural fertigation.

Recovery of water and valuable metals using low pressure nanofiltration and sequential adsorption from acid mine drainage

Acid mine drainage (AMD) contains an array of valuable resources such as Rare Earth Elements (REE) and Copper (Cu) which can be recovered along with fresh water. Low pressure nanofiltration with NF90 membrane was first studied to recover fresh water from synthetic AMD and concentration of dissolved metals for subsequent efficient selective recovery. Organic matter (OM) present in AMD was found to cause membrane fouling which resulted in significant flux decline. Powdered eggshell was investigated as a low-cost adsorbent for OM removal. The study showed that a 0.2 mg/l dose of powdered eggshell adsorbed 100% of OM and Fe with no significant loss of other dissolved metals. A steady permeate flux of 15.5 ± 0.2 L/m 2 h (LMH) was achieved for pre-treated AMD with a solute rejection rate of more than 98%. A chromium-based metal organic framework (MOF) modified with N - (phosphonomethyl) iminodiacetic acid (PMIDA) and an amine-grafted mesoporous silica (SBA15) material was synthesized for selective recovery of REE and Cu, respectively. The two adsorbents were used sequentially to selectively adsorb REE (91%) and Cu (90%) from pH adjusted concentrated feed. The formation of coordinating complexes with carboxylate and phosphonic groups on MOF was found to be the primary driving force for selective REE adsorption. Selective uptake of Cu onto amine-grafted SBA15 was due to the formation of strong chelating bonds between Cu and amine ligands. Both adsorbents remained structurally stable over 5 regeneration cycles. The findings here highlight the practical potential of membrane/adsorption hybrid systems for water and valuable metal (REE) recovery from AMD. • Low pressure NF achieved 80% permeate recovery while concentrating dissolved ions. • Modified MOF and SBA15-NH 2 selectively adsorbed 91% of REE and 90% of Cu. • REE show high affinity to deprotonated phosphonic and carboxyl groups in MOF. • Chelating bonds between Cu and amine groups in SBA15 promotes high selectivity. • High reuse capacity over multiple cycles recorded for both adsorbents.

Calcium carbonate scaling and seeding induced precipitation in FO treating textile reverse osmosis concentrate

Forward osmosis (FO) technology has been applied in the treatment and reclamation water from reverse osmosis concentrate. The performance of treating simulated textile reverse osmosis (sROC) was investigated with a focus upon the effect of calcium carbonate scaling and seeding induced precipitation on flux behavior. The effects of DS dilution & reverse salt flux (α), FS concentration & concentration polarization (β) and carbonate calcium scaling (γ) on flux decline were quantified based on the same water recovery at different DS (NaCl) concentration and FS salinity. The calcium carbonate scaling was found to contribute more to the flux decline when the FS salinity was 5000 ± 500 mg/L TDS at higher DS concentration. When the salinity of FS was increased to 10,000 ± 500 and 15,000 ± 500 mg/L TDS, the water flux was found higher under the situation of scaling than those of no scaling due to the fact that CaCO3 precipitation could inhibit the increase of osmosis pressure in FS in some degree. CaCO3 seeding induced precipitation in FO process promoted water flux and thus alleviated the calcium carbonate scaling on FO membrane. This work proposed a new view on the membrane scaling in FO process treating feed solution like reverse osmosis concentrate (ROC), and the seeding induced precipitation turned out to be an efficient strategy to alleviate calcium scaling in FO process and improve performance.

Photocatalytic thin film composite forward osmosis membrane for mitigating organic fouling in active layer facing draw solution mode

As a high-flux operation mode of thin film composite-forward osmosis (TFC-FO) membrane, active layer facing draw solution (AL-DS) mode suffers from the severe membrane fouling tendency, which is not addressed well. Here, we introduced a photocatalyst (Anatase titanium dioxide, A-TiO2) onto the support layer of TFC-FO membrane via the bonding of polydopamine (PDA) and polytetrafluoroethylene (PTFE), and prepared two photocatalytic membranes, A-TiO2/PDA@TFC and A-TiO2/PTFE@TFC. Compared with the pristine TFC-FO membrane, both A-TiO2/PDA @TFC and A-TiO2/PTFE@TFC had an improved water permeability (10.5 L m−2h−1 and 9.5 L m−2 h−1, respectively) and reduced reverse NaCl flux salt (0.8 g m−2 h−1 and 0.7 g m−2 h−1, respectively) in the AL-DS mode using 1 mol/L NaCl as draw solution and pure water as feed solution. Moreover, in the 16 h fouling experiment using 200 ppm bovine serum albumin (BSA) solution as a representative pollutant, the flux decline rate of both photocatalytic membranes was dramatically alleviated from 39.7% and 21.7% in the darkness to 8.5% and 9.7% under UV irradiation, respectively, indicating a significant anti-fouling capacity of photocatalytic effect. In all, the presence of A-TiO2 endowed membrane with high permeability, high rejection efficiency and excellent anti-fouling capacity under UV spotlight. As bonding agent, PTFE provided the modified membrane with a high photocatalytic effect and high self-cleaning capacity, while PDA increased the membrane permeability and protected membrane against photocatalytic damage. This work provides a simple and feasible method to improve the anti-fouling capacity of TFC-FO membrane in AL-DS mode.