Mitigate Membrane Fouling Research Articles

Ballasted flocculation pretreatment for mitigating ultrafiltration membrane fouling: Role of differently charged polyacrylamides at typical coagulant dosages

In this work, ballasted flocculation (without sedimentation) was suggested as a potential pretreatment for ultrafiltration to improve cake layer microstructure and mitigate membrane fouling. First, three representative aluminum sulfate (AS) coagulant dosages (including 1.0, 2.5 and 8.0 mg Al/L) were determined during preliminary testing to produce microfloc aggregates with negative, zero and positive zeta potentials at the coagulation stage of ballasted flocculation. Regardless of the applied coagulant dosage, not only ballasted floc size but also their strength and recovery abilities (following breakage) were dependent upon the selection of differently charged polyacrylamides (PAMs), likely due to the effect of PAM selection on polymer bridging and associated flocculation mechanisms. Second, comparisons of membrane flux decline and resistance distribution were performed to evaluate the importance of coagulant dosage and PAM type to cake layer formation and membrane fouling potential in the ballasted flocculation and ultrafiltration integrated process. The results demonstrated that the ballasted floc aggregates formed by ballasted flocculation pretreatment contributed to diverse structural characteristics of the fouled layer during their accumulation on the membrane surface, thereby affecting the degree of membrane fouling for various combinations of AS dosage and PAM type. Besides, the microsand particles involved in the formed layer could act as a skeleton of the cake layer structure, so their spatial distribution within the layer interior played a critical role in cake layer microstructure improvement, ultrafiltration efficiency enhancement and membrane fouling mitigation. In other words, the extent of steric-hindrance effects by ballasted floc aggregates should be emphasized in the formation of cake layer.

Enabling efficient water desalination and mitigating membrane fouling by the novel two-dimensional fullerene with unlocking its electrostatic forces

Graphene-based two-dimensional (2D) materials are currently a prominent focus in membrane research, yet they face challenges related to precise perforation and regulation of interface activity. Recently, the successful synthesis of 2D fullerene (C60) (Meirzadeh et al., Nature 2023, 613, 71) has expanded the repertoire of available 2D materials. However, its potential for membrane separation remains unexplored until now. In this study, we propose, for the first time, the utilization of 2D C60 for water desalination, leveraging its natural pores to circumvent the perforation challenge and allowing for precise tuning of interface activity. By establishing quantitative relationships between water flux and various operating conditions, this theoretical work can be extrapolated to guide practical desalination processes. Through non-equilibrium molecular dynamics simulations, it demonstrates that pristine 2D C60 exhibits unparalleled water permeance and achieves 100% salt rejection, regardless of operating pressure or the types of salt ions. To enhance desalination performance, we further propose a rational design strategy using endohedral 2D C60 with a positively charged surface, which improves water permeance up to 29.3 L⋅cm−2⋅day−1⋅MPa−1 and simultaneously reduces crystallization and colloidal fouling on the membrane surface by unlocking electrostatic attraction and repulsion forces, respectively. The mechanism behind this exceptional performance is attributed to the existence of well-endowed nanopores that form a connected hydrogen bond network, enabling swift vertical flow of water through the channels. Our findings showcase the exciting prospects of the novel 2D C60 material and provide a compelling new approach to membrane-based desalination, with the potential to revolutionize membrane materials.

Recent Advances in Organic Fouling Control and Mitigation Strategies in Membrane Separation Processes: A Review

Membrane separation processes have become increasingly popular in many industries because of their ability to treat wastewater and purify water. However, one of the main problems related to the processes is organic fouling, which can significantly reduce their efficiency and cause membrane damage. This review provides a summary of the various forms of organic fouling that can occur in membrane separation methods and examines the factors that lead to their development. The article evaluates the progress made in different techniques designed to manage and reduce organic fouling, such as physical cleaning methods, chemical cleaning agents, and modifications to the membrane surface, including ultrasonic and membrane vibration methods. The review also highlights recent advances in emerging 3D printing technology to mitigate membrane fouling. Finally, the review provides a brief summary of the conclusions and future directions for research in the field of organic fouling control and mitigation in membrane separation processes.

3D nano-structured sepiolite dynamic membranes for enhanced ultrafiltration treatment and membrane fouling mitigation

The construction of replaceable dynamic membranes (DMs) on membrane surfaces is a promising strategy to effectively mitigate membrane fouling. Nevertheless, the efficiency of DMs in mitigating membrane fouling remains low due to the lack of microstructural configurations. Herein, we report a natural sepiolite (SEP) DM with a three-dimensional (3D) network structure for mitigating PES ultrafiltration (UF) membrane fouling. The abundant oxygen-containing groups on the surface of SEP nanofibers endowed SEP DM with good organic adsorption capacity, hindering the migration of contaminants such as humic acid (HA) and bovine serum albumin (BSA). Owing to the porous 3D network structure, SEP DM prevented the formation of a dense filter cake layer, which effectively mitigated the sharp rise in membrane resistance when filtering ideal HA and BSA solutions. For the actual secondary wastewater, SEP DM improved the removal of UV254 and DOC by 29.8% and 22.5%, respectively, over the pristine PES membrane. The decrease in membrane-specific flux was mitigated by about 20%. Notably, the dynamic nature of SEP DM allowed the contaminated DM layer to be replaced by hydraulic cleaning, resulting in 99% flux recovery (only 89% for the pristine PES membrane). These findings are beneficial in providing new ideas for the mitigation and control of UF membranes.

Activation of peroxymonosulfate with biochar-supported CuO (CuO@BC) for natural organic matter removal and membrane fouling control

To achieve excellent activation efficiency of peroxymonosulfate (PMS), this work prepared a biochar-supported CuO (CuO@BC) catalyst, and the CuO@BC/PMS system was proposed to remove the organic matter in natural surface water and reduce the fouling of ultrafiltration membrane. The successful synthesis of CuO@BC was demonstrated through characterization of its microscopic morphology and chemical composition by various techniques. The prepared heterogeneous catalyst showed a strong catalytic effect on PMS, which significantly removed natural organic matter through the production of active substances (•OH, SO4•−, O2•− and 1O2) from water. With respective degradation rates of 39.4% and 59.4%, the concentrations of DOC and UV254 dropped to 1.702 mg/L and 0.026 cm−1, respectively. Additionally, the CuO@BC/PMS oxidation displayed potent oxidation capabilities for contaminants and fluorescent organics with various molecular weights. The system effectively decreased the amount of organic matter that caused reversible and irreversible fouling of polyethersulfone membranes in natural water by 85.8% and 56.3%, respectively. The main fouling mechanisms changed as well, with standard and complete blocking dominating the entire filtration process. The results demonstrated the capacity of the CuO@BC/PMS system to remove contaminants in natural water and mitigate membrane fouling.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics.

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

Utilizing ultrasonic vibrations to mitigate membrane fouling in domestic wastewater membrane bioreactors: a mini review

AbstractDespite their compact design and superior effluent quality, resulting from the smart integration of separation processes with biodegradation, the widespread adoption of membrane bioreactors is limited due to the persistent issue of membrane fouling. This mini review encapsulates research on using ultrasound‐induced vibration to mitigate membrane fouling in domestic wastewater systems. It discusses the dual physical and chemical mechanisms behind the use of ultrasound and highlights its limitations. Moreover, it proposes several future research directions, including further examination of operating conditions such as ultrasound power and frequency, combining ultrasound with other cleaning strategies scaling up the process, and the need for long‐term experiments, where additional emphasis must be given (i) to the influence of ultrasound irradiation on membrane integrity and efficiency and (ii) estimating the cost of sonochemical integration and operation Finally, it underscores the need for a holistic assessment that considers energy and environmental issues and discusses a proposed roadmap toward implementing ultrasound technology in membrane bioreactor systems. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Fenton pretreatment to mitigate membrane distillation fouling during treatment of landfill leachate membrane concentrate: Performance and mechanism

Membrane distillation (MD) is regarded as a promising technology for treatment of landfill leachate membrane concentrate (LLMC) due to its merits of low cost and high rejection of non-volatile components. However, the high concentration of pollutants in the wastewater will cause severe membrane fouling, resulting in costly cleaning and maintenance. In this study, Fenton pretreatment was applied to alleviate membrane fouling during MD treatment of LLMC. Compared to rapid flux decline of 88.2% at concentration factor (CF) of 3 for raw LLMC, MD flux only decreased by 17.4% at CF = 6 for treating acidic Fenton effluent without subsequent pH adjustment (Fe2+ and H2O2 concentration were 600 mg/L and 1457 mg/L, respectively). The pH neutralization of Fenton effluent or merely acidification of LLMC could not achieve such excellent fouling mitigation. It was concluded that both oxidation and acidification were critical and the collaboration mechanism was revealed to explain low membrane fouling. Firstly, Fenton oxidation removed organic contaminants, reduced the hydrophobicity of organic substances and increased the percentage of carboxylic group within LLMC. Thus, hydrophobic (HP) attraction was weakened but multivalent cation bridging became dominant fouling mechanism for neutral Fenton effluent. Then, acidification weakened multivalent cation bridging by inhibiting the deprotonation of carboxylic group, further mitigating membrane fouling. However, acidification of LLMC caused more severe organic fouling due to decrease in electrostatic (EL) repulsion. In addition to low membrane fouling, satisfactory total organic carbon (TOC) rejection rate of 96.23% was achieved during combined Fenton-MD process. This study demonstrated that Fenton pretreatment without pH neutralization could effectively alleviate MD fouling and elucidated the synergistic mechanism between oxidation and acidification for fouling mitigation.

Peroxymonosulfate based in situ chemical oxidation: An efficient strategy for mitigation of membrane fouling in real seawater reverse osmosis desalination

Persulfate based advanced oxidation processes (AOPs) is an emerging method to assist the pretreatment to prevent membrane fouling for seawater desalination. However, the present strategies which adopt activators (e.g., UV, heat, Fe) to generate kinds of free radicals, are energy-consuming and enhance the concerns of disinfection by-products (DBPs). Here, peroxymonosulfate (PMS) is adopted as a green, effective and economical pretreatment chemical for simultaneous microorganic pollutants degradation and microorganism inactivation in seawater reverse osmosis (SWRO) desalination without any external energy input. After adding into the seawater, 53% PMS could be activated by Cl- in situ to generate HClO at most with no other active species generated, which is verified by stoichiometric analysis and quenching experiments. Benefited from the residual PMS, not only could up to 89.6% of total organic carbon be removed in the real seawater, but also nearly 80% of DBPs could be degraded by simply adjusting pH from neutral to alkaline conditions. Meanwhile, all bacteria could be killed completely and hardly any regrowth appeared, which further proved the anti-fouling ability of the PMS/Cl- system. Consequently, the addition of PMS could maintain the flux for a long time in the practical SWRO application with significantly reducing the RO membrane fouling. Moreover, the operating cost of PMS is only 0.024 $/ton, which is comparable to NaClO. This study demonstrated the excellent performance of PMS in SWRO pretreatment, supplying a promising scheme in practical desalination processes.

Ultrafiltration of digestate liquid fraction by hollow-fiber membranes: Influence of digestate pre-treatment on hydraulic capacity and nutrient removal efficiency

With the growing interest in anaerobic digestion as a processing method of agro-food waste, proper disposal of digestate has become a prominent problem. In the study, ultrafiltration of the sugar beet pulp digestate was conducted using hollow-fiber membranes with a cut-off of 150 kDa operating in an outside-in system. The effect of different pre-treatment strategies of digestate i.e. centrifugation alone or in combination with coagulation with polyaluminium chloride, biocoagulation with chitosan and flocculation with polyacrylamide on mitigation of membrane fouling and permeate quality was investigated. High ultrafiltration performance was obtained using centrifugation followed by flocculation with 416 mg/dm3 of polyacrylamide as digestate pre-treatment. Removal efficiencies of chemical oxygen demand (COD), total solids, phosphorus and nitrogen were 89.80, 90.08, 88.37 and 64.12%, respectively. Permeate flux and total membrane resistance averaged 22.33 dm3/m2/h and 5.32 • 1011 m−1. Hydraulic parameters and removal rates determined during ultrafiltration preceded by centrifugation and biocoagulation with 100 mg/dm3 of chitosan did not differ significantly from the values mentioned above for the pre-treatment consisting of centrifugation and flocculation with polyacrylamide. The results indicate the possibility of filtering the liquid fraction obtained by centrifugation, coagulation or flocculation of the digestate, and using natural auxiliary agents during its pre-treatment.

Peroxymonosulfate enhanced Fe(III) coagulation coupled with membrane distillation for ammonia recovery: Membrane fouling control process and mechanism

Membrane fouling limited the application of membrane distillation (MD) process in resource recovery. In this research, the peroxymonosulfate (PMS) enhanced Fe(III) coagulation process was proposed and proved its effectiveness in eliminating natural organic matter (NOM) and emerging organic contaminants (EOCs). Fe(III)/PMS process significantly enhanced the removal of dissolved organic carbon (DOC), turbidity, and UV254, compared to conventional Fe(III) coagulation. Thiamphenicol (TAP) represented the EOCs in the digestate, and Fe(III)/PMS could significantly degrade TAP (86 % degradation). In this course, phenols/quinones served as electron shuttles to induce the Fe(III)/Fe (II) redox cycle. The activation of PMS was boosted, generating the primary reactive substance sulfate (SO4−) radical with intense oxidative properties. In addition, membrane distillation achieved recovery of 93 % of TAN from coagulation effluent without membrane fouling. No tryptophan-like, tyrosine-like, xanthate, and other soluble microbial byproducts were detected on the membrane surface following Fe(III)/PMS pretreatment. The innovation of this study was revealing that the complexation of Fe(III) with NOM could promote Fe (II) regeneration and enhance PMS activation, active substance formation and contaminants degradation. New insights into the role of NOM in the Fe(III)/Fe(II) redox cycle were gained and the development of advanced oxidation process (AOP) coupled membrane technology was promoted to mitigate membrane fouling.

Emulsified oily wastewater treatment via fertilizer drawn forward osmosis using a corrugated thin film composite membrane

Membrane fouling and draw solution recycle are two important challenges faced by forward osmosis (FO) process in treating wastewater. In this study, we innovatively designed a corrugated TFC FO membrane(#FO-C) by conducting interfacial polymerization (IP) on a commercial corrugated polyvinylidene fluoride (PVDF) substrate and utilized fertilizer as the draw solution to treat emulsified oily wastewater for mitigating membrane fouling and recovering draw solution simultaneously. The corrugated-pattern membrane, #FO-C, had a similar separation performance compared with conventional flat TFC membrane (#FO-F), demonstrating that the corrugated pattern makes a little difference on IP process. Inspiringly, compared with #FO-F, #FO-C tested at parallel and vertical modes exhibited lower decrease of water flux in oily wastewater treatment when used 1 M (NH4)2SO4 (SOA) and three different types of oily wastewater (prepared by neutral and negatively/positively charged surfactants) as draw and feed solutions, respectively. In addition, the declined permeability of #FO-C could easily recover with performing surfactant cleaning and osmosis backwashing, which that of #FO-F only recovered partially. The result of computational fluid dynamics (CFD) simulation illustrated that the corrugated pattern of #FO-C would bring about vortex and higher shear stresses, which effectively alleviate the foulant deposition of on the membrane surface. Moreover, the diluted fertilizer draw solution was utilized to irrigate the plants directly and presented a promising result, readily achieving the recovering of draw solution. This work provides a promising strategy for meeting the challenges in FO process, having an important reference value.

Evaluation and optimization of reverse osmosis pretreatment technology using the modified intermediate blocking model

Membrane fouling is the unavoidable obstruction that occurs during reverse osmosis (RO), the use of pretreatment technology is highly effective for mitigating membrane fouling. In this study, the modified intermediate blocking model was applied to fit the data from literature about RO pretreatment, getting good fitting performance, over 86% of the determination coefficient (R2) exceeding 0.90. The working law of RO pretreatment on model parameters (final permeate flux (Jpss) and fouling velocity (k)) was systematically studied. The result showed that pretreatment works by three pathways: enhancing Jpss and reducing k, reducing both k and Jpss, and increasing both k and Jpss; it exerts more of an effect by improving k rather than Jpss. Furthermore, ultrafiltration exhibits a 10% higher effect on Jpss compared to ozonation while its effect on k is about 20% better than that of ozonation. Additionally, ultrafiltration demonstrates greater stability than ozonation. We further analyzed and found that the improvement in Jpss or k does mitigate membrane fouling, however, it does not necessarily produce more volume of clean water than without pretreatment. With the aim of obtaining more volume of permeate water, a new model, the Normalized Total Permeate Water Volume (VN) model is proposed, which enables pretreatment efficiency comparable and has been applied to optimize the application of pretreatment, achieving great application results.

Investigation of factors affecting sodium alginate fouling mechanisms in a microfiltration process under non-constant-flux and non-constant-pressure conditions.

Variations in transmembrane pressure and permeate flux are closely related to membrane fouling. In this study, a laboratory-scale submerged microfiltration system was used to investigate the influence of sodium alginate (SA) concentration and peristaltic pump rotation speed on the fouling under the conditions of (1) the same driving force and non-aerated-PAC, (2) different driving forces and non-aerated-PAC, and (3) different driving forces and aerated-PAC. The results showed that the normalized transmembrane pressure (TMP') increased linearly with decreasing normalized permeate flux (J') during the early microfiltration stage regardless of the operating conditions, indicating that the SA microfiltration process controlled by the peristaltic pump was non-constant-flux and non-constant-pressure. The latter filtration stage was considered constant-pressure filtration when 200-1,200 mg/L of SA was filtrated at the same rotation speed. During filtration of 800 mg/L of SA under the non-aerated-PAC condition, the later filtration stage was considered constant-pressure filtration when the peristaltic pump rotated at slower speeds of 15 and 30 rpm. This approached constant-flux filtration when the peristaltic pump rotated at faster speeds of 60 and 90 rpm, and PAC-aeration scouring was an effective measure for mitigating membrane fouling by SA.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Role of visible light photocatalysis in alleviation and mechanism transformation of ultrafiltration membrane fouling caused by natural organic matter

In this study, a novel composite based on bismuth oxide, reduced graphene oxide and titanium dioxide (labeled as BRGT) was utilized for visible light photocatalysis to mitigate ultrafiltration membrane fouling caused by natural organic matter (NOM). The results show that the coexistence of NOM and the BRGT composite (without photocatalysis) did not aggravate membrane fouling, and the membrane preferentially retained a high molecular weight, hydrophobic component of NOM that formed a dense cake layer with BRGT composite. As the photocatalysis time increased, the extent of membrane fouling was alleviated. The maximum specific flux recovered from 0.21 to 0.73 at 60 min, and the hydraulic reversible and irreversible resistances ere 1.15 × 1010 and 4.23 × 1010 m−1, respectively. The reduction of NOM in the feed water, especially the removal of UV254, played a significant role in the alleviation of membrane fouling. Additionally, the changes in the properties of NOM, including the reduction of fluorescent humic and protein/polyphenol components corresponding to reversible and irreversible fouling, respectively, the photo-degradation of high molecular weight NOM into low molecular weight NOM (such as low molecular weight-acids), and the conversion of hydrophobic fractions into hydrophilic fractions, contributed to the mitigation of membrane fouling. We also found a strong negative correlation between the roughness of the cake layer and irreversible fouling. Overall, the changes in the properties of NOM in feed water can hinder or even inhibit the formation of the cake layer, and the use of visible light photocatalysis of the BRGT composite has great potential to alleviate ultrafiltration membrane fouling caused by natural organic matter.

Microbial Electrochemical Systems and Membrane Bioreactor Technology for Wastewater Treatment

AbstractMembrane bioreactors (MBRs) and microbial electrochemical systems (MESs) are promising technologies for wastewater treatment and generation of electricity from organic matter. The application of MBRs is limited due to membrane fouling and high energy consumption. The novel design of the coupling system of microbial fuel cell and membrane bioreactor (MFC‐MBR), which efficiently combines microbial degradation in MFCs and uses the microelectric field to reduce and mitigate membrane fouling in MBR. The fundamentals of extracellular electron transport, the performance of MFCs, different types of MBR systems, and the novelty of the MFC‐MBR coupling system for wastewater treatment are reviewed.

Electrochemically activated peroxymonosulfate (PMS) pretreatment for fouling remediation during membrane distillation of surface water: Role of PMS concentration and dosing mode

Membrane distillation (MD) provides a potential method to supply large volumes of good quality potable water from surface water resources, avoiding the risk of long-term water shortages. However, the high abundance of dissolved natural organic matter (DOM) in surface water induces severe membrane fouling, which reduces productivity and increases energy consumption. Therefore, for the first time, electrochemically activated peroxymonosulfate (PMS) treatment was applied prior to the direct contact (DC)-MD process with the aim of reducing the deposition of organics and inorganics on the membrane and reducing membrane fouling. Results showed that supplying PMS continuously at a rate of 0.10 mM/min, eliminated 30.4% of dissolved organic carbon (DOC). Furthermore, fluorescence parallel factor (PARAFAC) analysis showed that >60% of two fluorescent substances were removed after 60 min of the electrochemically activated PMS pretreatment at a current density of 5 mA/cm2. Electrochemical activation of PMS generated •OH directly, facilitating the removal and degradation of DOM. In terms of the DCMD performance, almost no normalized flux decline was observed for the DCMS process after 0.01 mM/min pre-oxidation, while 44.8% flux decay occurred in the standalone DCMD treating raw surface water. Compared with continuous dosing, the use of a one-time dosing mode achieved a better outcome, as more small organic molecules generated in continuous dosing mode are not conducive to membrane fouling control. Therefore, electrochemically activated PMS could be an effective tool to mitigate membrane fouling in MD processes, although the characteristics of membrane and feed should be considered.

Janus C-PAN/PH membrane for simulated shale gas wastewater (SGW) treatment in membrane distillation: Integrating surface property and catalytic degradation for anti-fouling

Membrane distillation (MD) is an effective method for treating shale gas wastewater (SGW), but membrane fouling remains a significant obstacle. To mitigate membrane fouling, we developed a dual-layer nanofibrous catalytic membrane (C-PAN/PH) that includes a hydrophilic polyacrylonitrile (PAN) layer with Co-TPML nano-catalysts and a hydrophobic poly(vinylidene fluoride-hexafluoropropylene) (PH) layer. This novel membrane can effectively treat feed solutions containing kerosene or aniline due to its surface hydration and peroxymonosulfate (PMS) activation. The water flux of the C-PAN/PH membrane was 38% higher than that of the PH membrane due to the higher thermal conductivity of hydrophilic layer. The C-PAN/PH membrane also exhibited stable flux for 10 h in treating 3,000 mg/L oil/water emulsion due to its hydration capability. Moreover, the C-PAN/PH membrane removed over 92% of the aniline within 2 min, and electron paramagnetic resonance (EPR) analysis indicated that reactive species (•OH and SO4•-) played a primary role in the degradation process. Density functional theory (DFT) simulations suggested that PMS was strongly adsorbed on Co with an adsorption energy of −3.77 eV. This study aimed to design a novel membrane specifically for MD in SGW treatment.

Surfactant pretreatment as a novel fouling mitigation strategy for membrane distillation

Membrane distillation (MD) has emerged as a promising thermal desalination technology for hypersaline wastewater reclamation. However, the practical implementations of MD face a critical challenge of membrane fouling. Conventional strategy to address membrane fouling is to emphasize the progress in developing composite MD membranes, but these membranes are commercially unavailable. In this study, we introduce a new operation strategy to mitigate fouling by using surfactant pretreatment. We demonstrate that after being pretreated by 0.05 mM Triton X-100 feed solution for 10 min, a commercial polyvinylidene fluoride (PVDF) membrane can exhibit outstanding fouling resistance in MD process. Further, we elucidate the underlying working mechanism using quartz crystal microbalance (QCM) experiments, oil contact angle measurements, and force spectroscopy determinations. Specifically, in the pretreatment process, the amphiphilic surfactant adsorbs onto the hydrophobic membrane, altering the membrane surface to be hydrophilic. During the MD operations, a hydration layer forms on the hydrophilic surface, eliminating the foulant-membrane interaction and thereby achieving fouling mitigation. For effective fouling mitigation, a surfactant exhibiting a moderate hydrophilic-lipophilic balance (HLB) value (e.g., Triton X-100 with an HLB of ∼14) is required. As an easy-to-implement but effective strategy to mitigate membrane fouling, surfactant pretreatment can substantially improve the fouling resistances of commercial hydrophobic membranes, greatly facilitating the practical applications of MD and membrane contactor technologies.