Physicochemical correlations between membrane surface hydrophilicity and adhesive fouling in membrane bioreactors

Quantifying interfacial interactions for improved membrane antifouling: A novel approach using triangulation and surface element integration method

To gain a thorough understanding of interfacial behaviors such as adhesion and flocculation controlling membrane fouling, it is necessary to simulate the actual membrane surface morphology and quantify interfacial interactions. In this work, a new method integrating the rough membrane morphology reconstruction technology (atomic force microscopy (AFM) combining with triangulation technique), the surface element integration (SEI) method, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the compound Simpson's approach, and the computer programming was proposed. This new method can exactly mimic the real membrane surface in terms of roughness and shape, breaking the limitation of previous fractal theory and Gaussian method where the simulated membrane surface is only statistically similar to the real rough surface, thus achieving a precise description of the interfacial interactions between sludge foulants and the real membrane surface. This method was then applied to assess the antifouling propensity of a polyvinylidene fluoride (PVDF) membrane modified with Ni-ZnO particles (NZPs). The simulated results showed that the interfacial interactions between sludge foulants in a membrane bioreactor (MBR) and the modified PVDF-NZPs membrane transformed from an attractive force to a repulsive force. The phenomenon confirmed the significant antifouling propensity of the PVDF-NZPs membrane, which is highly consistent with the experimental findings and the interfacial interactions described in previous literature, suggesting the high feasibility and reliability of the proposed method. Meanwhile, the original programming code of the quantification was also developed, which further facilitates the widespread use of this method and enhances the value of this work.

High-Performance Novel Polyoxometalate-LDH Nanocomposite-Modified Thin-Film Nanocomposite Forward Osmosis Membranes: A Study of Desalination and Antifouling Performance

Numerous investigations have focused on creating effective membranes for desalination in order to alleviate the water scarcity crisis. In this study, first, LDH nanoplates were synthesized and utilized to alter the surface of thin-film composite (TFC) membranes in the course of this investigation. Following that, a simple technique was used to produce a novel nanocomposite incorporating LDH layers and Na14(P2W18Co4O70)·28H2O polyoxometalate nanoparticles, resulting in the creation of a fresh variety of thin-film nanocomposite (TFN). The performance of all of the membranes acquired was examined in the process of forward osmosis (FO). The impact of the compounds that were prepared was assessed on the hydrophilicity, topology, chemical structure, and morphology of the active layer of polyamide (PA) through analysis methods such as atomic force microscopy (AFM), energy-dispersive X-ray (EDX), FTIR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and water contact angle (WCA) goniometry. After evaluating the outcomes of both modified membrane types, it was observed that the membrane equipped with the nanocomposite modifier at a concentration of 0.01 wt % exhibited the highest water flux, measuring 46.6 LMH and selectivity of 0.23 g/L. This membrane was thus considered the best option. Furthermore, the membrane's ability to prevent fouling was examined, and the findings revealed an enhancement in its resistance to fouling in comparison to the filler-free membrane.

Multi-input multi-output temporal convolutional network for predicting the long-term water quality of ocean ranches

The prediction of water quality parameters is of great significance to the control of marine environments and provides a scientific decision-making basis for maintaining the stability of water environments and ensuring the normal survival and growth of marine aquatic products. However, the water quality in ocean ranches is affected by the complex, dynamic, and changeable environments of open water, which have complex nonlinear relationships, poor accuracy, high time complexity, and poor long-term predictability. Therefore, in this paper, a multi-input multi-output end-to-end prediction model based on a temporal convolutional network (MIMO-TCN) is proposed to predict water quality. A ConvNeXt module and TCN module were used as the model encoder and decoder, respectively. ConvNeXt was used to extract the features of the input data, and the TCN used the extracted feature data to achieve improved prediction accuracy. The model adds skip connections between its modules to solve the gradient disappearance problem as the number of network layers increases. To prove the effectiveness of the proposed method, a model robustness and prediction ability evaluation was conducted in this paper based on the dissolved oxygen in multiple ocean pasture validation samples. Compared with other learning models, the mean absolute error (MAE), root mean square error (RMSE), and mean absolute percentage error (MAPE) of the MIMO-TCN prediction results were reduced by 60.77%, 30.88%, and 52.45% on average, respectively, and the R² improved by 6.07% on average over those of other models. The experimental results show that the proposed method has higher forecasting accuracy than competing approaches.

Analysis of zwitterionic membrane fouling mechanism caused by HPAM in the presence of electrolytes

Membrane fouling has always been a tough issue that is urgent to solve. Electrolytes which are prevalent in wastewater have a major influence on membrane fouling. Therefore, it is of great significance to understand the role and fouling mechanism of electrolytes in the membrane fouling process. In this work, the zwitterionic membrane is used to process hydrolyzed poly(acrylamide) (HPAM) with the addition of electrolytes (CaCl₂, NaCl). Meanwhile, the effect of different electrolytes on the zwitterionic membrane fouling process by hydrolyzed poly(acrylamide) (HPAM) is systematically investigated. It was found that the flux recovery ratio (FRR) of the zwitterionic membrane is nearly 100% after treating HPAM with the addition of electrolytes. Therefore, molecular dynamics (MD) simulations were applied to illustrate the impact of electrolytes on the change of foulant structures and confirm the consequent effect of electrolytes on membrane fouling. According to the experiment and MD simulation results, it is found that the positive ion layer which exists between the HPAM and zwitterionic surface results in the excellent fouling resistance performance of the zwitterionic membrane. The zwitterionic membrane fouling mechanism is analyzed, which is helpful to the understanding of zwitterionic membrane fouling in high salinity wastewater.

Cyclic on-chip bacteria separation and preconcentration

Nanoparticles and biological molecules high throughput robust separation is of significant interest in many healthcare and nanoscience industrial applications. In this work, we report an on-chip automatic efficient separation and preconcentration method of dissimilar sized particles within a microfluidic platform using integrated membrane valves controlled microfiltration. Micro-sized E. coli bacteria are sorted from nanoparticles and preconcentrated on a microfluidic chip with six integrated pneumatic valves (sub-100 nL dead volume) using hydrophilic PVDF filter with 0.45 μm pore diameter. The proposed on-chip automatic sorting sequence includes a sample filtration, dead volume washout and retentate backflush in reverse flow. We showed that pulse backflush mode and volume control can dramatically increase microparticles sorting and preconcentration efficiency. We demonstrate that at the optimal pulse backflush regime a separation efficiency of E. coli cells up to 81.33% at a separation throughput of 120.45 μL/min can be achieved. A trimmed mode when the backflush volume is twice smaller than the initial sample results in a preconcentration efficiency of E. coli cells up to 121.96% at a throughput of 80.93 μL/min. Finally, we propose a cyclic on-chip preconcentration method which demonstrates E. coli cells preconcentration efficiency of 536% at a throughput of 1.98 μL/min and 294% preconcentration efficiency at a 10.9 μL/min throughput.

Employing magnetism of Fe3O4 and hydrophilicity of ZrO2 to mitigate biofouling in magnetic MBR by Fe3O4-coated ZrO2/PAN nanocomposite membrane

The aim of this research is benefiting from the synergistic effect of the simultaneous presence of Fe₃O₄ and ZrO₂ in the form of Fe₃O₄-coated ZrO₂ (Fe₃O₄@ZrO₂) nanoparticles within the structure of PAN membrane to reduce membrane fouling. The role of Fe₃O₄ nanoparticles in increasing the pore size and magnetic saturation as well as the role of ZrO₂ in decreasing surface roughness and hydrophobicity can mitigate membrane fouling in magnetic-assisted membrane bioreactors. For this purpose, Fe₃O₄, ZrO₂, and Fe₃O₄@ZrO₂ nanoparticles were embedded into PAN membrane structure and magnetic (M _nM), hydrophilic (H _nM), and magnetic-hydrophilic (HM _nM) membranes were synthesized. H ₁M (1ZrO₂/PAN) membrane with a contact angle of 31 degrees, M ₁N (1Fe₃O₄/PAN) with a pore size of 90 nm, and H ₃M (3ZrO₂/PAN) membrane with an RMS roughness of 13.5 nm were the most hydrophilic, porous, and smoothest membranes, respectively. High sensitivity to magnetic field along with high porosity, high hydrophilicity and low surface roughness simultaneously exist within the structure of MHMs membranes, such that MH ₁M (1Fe₃O₄@ZrO₂/PAN) indicated 116% greater flux, 121% greater flux recovery, and 85% less total filtration resistance in comparison with the blank membrane in magnetic membrane bioreactor, at a magnetic field intensity of 120 mT and MLSS = 10,000 mg/l. As an overall conclusion, the output of this research was compared with other research in term of normalized flux. Results reveal that at MLSS = 10,000 mg/l, HRT = 8 h and TMP = 0.3 bar, MH ₁M membrane has normalized flux equal to 1.56 g/m² h bar which is an acceptable value compared to normalized flux reported by other researchers.

Obtainment and Characterization of Hydrophilic Polysulfone Membranes by N-Vinylimidazole Grafting Induced by Gamma Irradiation

Polysulfone (PSU) film and N-vinylimidazole (VIM) were used to obtain grafted membranes with high hydrophilic capacity. The grafting process was performed by gamma irradiation under two experiments: (1) different irradiation doses (100-400 kGy) and VIM 50% solution; (2) different concentration of grafted VIM (30-70%) and 300 kGy of irradiation dose. Characteristics of the grafted membranes were determined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), contact angle, swelling degree, desalination test, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Both experiments indicated that the absorbed dose 300 kGy and the VIM concentration, at 50% v/v, were effective to obtain PSU grafted membranes with 14.3% of grafting yield. Nevertheless, experimental conditions, 400 kGy, VIM 50% and 300 kGy, VIM 60-70% promoted possible membrane degradation and VIM homopolymerization on the membrane surface, which was observed by SEM images; meanwhile, 100-200 kGy and VIM 30-50% produced minimal grafting (2 ± 0.5%). Hydrophilic surface of the grafted PSU membranes by 300 kGy and VIM 50% v/v were corroborated by the water contact angle, swelling degree and desalination test, showing a decrease from 90.7° ± 0.3 (PSU film) to 64.3° ± 0.5; an increment of swelling degree of 25 ± 1%, and a rejection-permeation capacity of 75 ± 2%. In addition, the thermal behavior of grafted PSU membranes registered an increment in the degradation of 20%, due to the presence of VIM. However, the normal temperature of the membrane operation did not affect this result; meanwhile, the glass transition temperature (T_g) of the grafted PSU membrane was found at 185.4 ± 0.5 °C, which indicated an increment of 15 ± 1%.

Polymeric Membranes Incorporated With ZnO Nanoparticles for Membrane Fouling Mitigation: A Brief Review

Due to the flexibility of operation, high removal ability, and economic cost, separation membranes have proved to be one of the most significant technologies in various aspects including water treatment. However, membrane fouling is a predominant barrier which is severely limiting the whole membrane industry. To mitigate membrane fouling, researchers have carried out several modification strategies including the incorporation of hydrophilic inorganic components. Zinc oxide (ZnO) nanoparticles, known as a low-cost, environment-friendly, and hydrophilic inorganic material, have been used by worldwide researchers. As claimed by the scientific literatures, ZnO nanoparticles can not only endow the polymeric membranes with antifouling performance but also supply a photocatalytic self-cleaning ability. Therefore, polymer-ZnO composite membranes were considered to be an attractive hot topic in membrane technology. In the last decades, it has been significantly matured by a large mass of literature reports. The current review highlights the latest findings in polymeric membranes incorporated with ZnO nanoparticles for membrane fouling mitigation. The membrane fouling, ZnO nanoparticles, and modification technology were introduced in the first three sections. Particularly, the review makes a summary of the reports of polyvinylidene fluoride (PVDF)-ZnO composite membranes, polyethersulfone (PES)-ZnO composite membranes, and other composite membranes incorporated with ZnO nanoparticles. This review further points out several crucial topics for the future development of polymer-ZnO composite membranes.

Synergistic oxidation - filtration process analysis of catalytic CuFe2O4 - Tailored ceramic membrane filtration via peroxymonosulfate activation for humic acid treatment

This work synthesized catalytic CuFe₂O₄ tailored ceramic membrane (CuFeCM), and systematically investigated the intercorrelated oxidation - filtration mechanism of peroxymonosulfate (PMS)/CuFeCM catalytic filtration for treating humic acid (HA). PMS/CuFeCM filtration exhibited enhanced HA removal efficiency while reduced the irreversible fouling resistance as compared with the conventional CM filtration. Results from HA characterizations showed that PMS/CuFeCM catalytic filtration oxidized HA into conjugated structures of smaller molecular weight. The unsaturated bonds further caused the re-agglomeration of HA, hence enhancing the size exclusion of CuFeCM. Meanwhile, oxidized HA particles with changing physicochemical properties reduced the total attractive interaction energy between CuFeCM and HA, mainly attributed to the reduced acid-base interaction energy according to the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) analysis. The changing of HA properties and HA-CuFeCM physicochemical interactions rendered more re-agglomerated HA particles retained above membrane with less attachment, which induced decreasing irreversible fouling resistance and facilitated easier external fouling removal by hydraulic cleaning. Overall, the PMS/CuFeCM configuration demonstrated in this study could provide a new insight into the synergistic oxidation - filtration interaction mechanism of hybrid catalytic ceramic membrane filtration process.

Prediction of interfacial interactions related with membrane fouling in a membrane bioreactor based on radial basis function artificial neural network (ANN)

It is of great importance to propose effective methods to quantify interfacial interaction since it directly determines foulant adhesion and membrane fouling process in membrane bioreactors (MBRs). This study developed a radial basis function (RBF) artificial neural network (ANN) to predict the interfacial interactions with randomly rough membrane surface. The interaction data quantified by the advanced extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach were used as the training samples for the RBF networks. It was found that, the computing time consumption for the RBF network prediction was only about 1/50 of that for the advanced XDLVO approach under same conditions, indicating the high efficiency of the RBF ANN method. Meanwhile, the calculation accuracy of the method was acceptable to get reliable results. This study demonstrated the breakthrough of the fundamental methodology related with membrane fouling. The proposed RBF ANN method has broad application prospects in membrane fouling and interface behavior research.

A facile method to modify polypropylene membrane by polydopamine coating via inkjet printing technique for superior performance

Membrane surface functionalization based on mussel-inspired polydopamine (PDA) deposition for enhancing antifouling ability has attracted considerable attention. However, high cost of dopamine (DA) and long-time of reaction during self-polymerization of DA in aqueous solution remain the major problems impeding its practical application. This study provided a first report on a low-cost and facile membrane modification approach based on inkjet printing of DA and sodium periodate (SP) to rapidly deposit PDA on polypropylene (PP) membrane. Compared with the pristine PP membrane and DA printed PP membrane, the PDA-SP coated PP membrane demonstrated superior hydrophilicity (67.2°), high pure water permeability (2156.8 L·m^-2·h^-1) and antifouling property, due to the improved oxidation degree of PDA. Moreover, the modified membrane possesses good chemical stability in aqueous solution over the wide range of pH 2-9. The inkjet printing integrated oxidant-induced mussel-inspired modification proposed in this study is substrate-independent, and can be applied to various geometries and materials, showing broad application prospects in membrane fabrication.

Enhancing Morphology and Separation Performance of Polyamide 6,6 Membranes By Minimal Incorporation of Silver Decorated Graphene Oxide Nanoparticles

Nanomaterials can be incorporated in the synthesis of membrane to obtain mixed-matrix membrane with marked improvement in properties and performance. However, stability and dispersion of the nanomaterials in the membrane matrix, as well as the need to use high ratio of nanomaterials for obvious improvement of membrane properties, remain a major hurdle for commercialization. Hence, this study aims to investigate the improvement of polyamide 6,6 membrane properties with the incorporation of silver nanoparticles decorated on graphene oxide (Ag-GO) nanoplates and at the same time focus is given to the issues above. Graphene oxide nanoplates were synthesized using the modified Hummers’ method and decorated with silver before embedded into the polyamide 6,6 matrix. Physicochemical characterizations were conducted on both nanoplates and the mixed-matrix Ag-GO polyamide 6,6 membrane. The issues of Ag agglomeration and leaching were not observed, which could be attributed to the decoration of Ag on GO that helped to disperse the nanomaterials and provided a better anchor point for the attachment of Ag nanoparticles. The synthesized membrane showed marked improvement regarding flux (135% increment) and antifouling (40% lower irreversible fouling), which could be ascribed to the more negative charge of membrane surface (−14 ± 6 to −31 ± 3.8 mV) and hydrophilicity (46% enhancement) of the membranes. With minimal embedment of Ag nanoparticles, the membrane showed superior antibacterial property where the E. coli bacteria could not form a single colony on the membrane surface. Overall, the decoration of Ag on GO nanoplates could be a promising approach to resolve the agglomeration and leaching issues as well as reduce the amount of precious Ag in the synthesis of Ag-GO polyamide 6,6 membrane.

Quorum sensing and quenching in membrane bioreactors: Opportunities and challenges for biofouling control

Membrane biofouling, due to biofilm growth after planktonic bacteria attachment to a membrane, is a major bottleneck limiting the energy-efficient operation and maintenance of membrane bioreactors (MBRs). Microbial communications, known as quorum sensing (QS), are responsible for this biofouling behavior. Novel strategies for stopping this communication, known as quorum quenching (QQ), appear to be successful for biofouling control in MBRs used for wastewater treatment. This review describes recent information regarding the signal molecules and mechanisms responsible for QS behaviors, promising approaches for QQ (enzymatic, bacterial, fungal, photocatalytic, mimicking, and biostimulating methods), and efficient fabrication and use of QQ media for MBR applications. We discuss the opportunities and challenges of QQ techniques for their further improvement and practical use in MBRs.

Novel insights into membrane fouling in a membrane bioreactor: Elucidating interfacial interactions with real membrane surface

While governing adhesion/deposition of various foulants on membrane surface and membrane fouling in membrane bioreactors (MBRs), interfacial interactions with real membrane surface have not yet been fully quantified. In this study, theoretical deduction and experiments were carried out to numerically elucidate interfacial interactions in a MBR. A continuous real membrane morphology was reconstructed based on atomic force microscopy (AFM) characterization and triangulation technique. Thereafter, a method to calculate those interactions was established by incorporating the spatial relationship between a foulant and the reconstructed morphology into surface element integration (SEI) method. A case study of the proposed method was conducted. With surface characterization of the foulants and membrane, the interfacial interactions with real membrane morphology were approximated for the first time by computer programming according to composite Simpson's rule. The results showed that rough morphology prolonged the interfacial interactions, indicating the profound role of morphology in the interfacial interactions related with membrane fouling. The new method would provide significant insights into membrane fouling in MBRs.

Quantitative Analysis of Membrane Fouling Mechanisms Involved in Microfiltration of Humic Acid–Protein Mixtures at Different Solution Conditions

A systematical quantitative understanding of different mechanisms, though of fundamental importance for better fouling control, is still unavailable for the microfiltration (MF) of humic acid (HA) and protein mixtures. Based on extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) theory, the major fouling mechanisms, i.e., Lifshitz–van der Waals (LW), electrostatic (EL), and acid–base (AB) interactions, were for the first time quantitatively analyzed for model HA–bovine serum albumin (BSA) mixtures at different solution conditions. Results indicated that the pH, ionic strength, and calcium ion concentration of the solution significantly affected the physicochemical properties and the interaction energy between the polyethersulfone (PES) membrane and HA–BSA mixtures. The free energy of cohesion of the HA–BSA mixtures was minimum at pH = 3.0, ionic strength = 100 mM, and c(Ca2+) = 1.0 mM. The AB interaction energy was a key contributor to the total interaction energy when the separation distance between the membrane surface and HA–BSA mixtures was less than 3 nm, while the influence of EL interaction energy was of less importance to the total interaction energy. The attractive interaction energies of membrane–foulant and foulant–foulant increased at low pH, high ionic strength, and calcium ion concentration, thus aggravating membrane fouling, which was supported by the fouling experimental results. The obtained findings would provide valuable insights for the quantitative understanding of membrane fouling mechanisms of mixed organics during MF.

Mechanism analyses of high specific filtration resistance of gel and roles of gel elasticity related with membrane fouling in a membrane bioreactor

In this study, mechanisms and roles of gel elasticity in extremely high specific filtration resistance (SFR) were investigated. It was found that, as compared with cake layer in a membrane bioreactor (MBR), real gel layer in the MBR and agar gel possessed extremely high SFR. Foulant characterization showed that foulants were easy to bind water, and agar gel possessed a network structure. Mechanisms based on Flory-Huggins and Flory-Rehner models were deduced to describe the high SFR of agar gel. Model simulation showed that sum of SFR induced by the mixing chemical potential and the elastic chemical potential change is close to that of the agar gel, suggesting feasibility of the deduced models. Gel elasticity accounted for about 13% of total SFR of agar gel under conditions in this study. This study satisfactorily explained the extremely high SFR of gel, and addressed roles of gel elasticity in gel SFR.

Effects of fractal roughness of membrane surfaces on interfacial interactions associated with membrane fouling in a membrane bioreactor

Fractal roughness is one of the most important properties of a fractal surface. In this study, it was found that, randomly rough membrane surface was a fractal surface, which could be digitally modeled by a modified two-variable Weierstrass-Mandelbrot (WM) function. Fractal roughness of membrane surfaces has a typical power function relation with the statistical roughness of the modeled surface. Assessment of interfacial interactions showed that an increase in fractal roughness of membrane surfaces will strengthen and prolong the interfacial interactions between membranes and foulants, and under conditions in this study, will significantly increase the adhesion propensity of a foulant particle on membrane surface. This interesting result can be attributed to that increase in fractal roughness simultaneously improves separation distance and interaction surface area for adhesion of a foulant particle. This study gives deep insights into interfacial interactions and membrane fouling in MBRs.