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Quantification of interfacial interaction with randomly rough surface is the prerequisite to quantitatively understand and control the interface behaviors such as adhesion, flocculation and membrane fouling. In this study, it was found that membrane surface was randomly rough with obvious fractal characteristics. The randomly rough surface of membrane could be well reconstructed by the fractal geometry represented by a modified Weierstrass-Mandelbrot function. A novel method, which combined composite Simpson’s approach, surface element integration method and approximation by computer programming, was developed. By using this method, this study provided the first realization of quantifying interfacial energy between randomly rough surface of membrane and a foulant particle. The calculated interactions with randomly rough surface of membrane were significantly different from those with smooth surface of membrane, indicating the significant effect of surface topography on interactions. This proposed method could be also potentially used to investigate various natural interface environmental phenomena. [ABSTRACT FROM AUTHOR]

A membrane bioreactor (MBR) was continuously operated to investigate mechanisms of fouling caused by the gel layer in this study. Agar was used as a model foulant for gel layer formation, and filtration resistance of gel layers was systematically assessed. The results showed that gel layer possessed unusually high specific filtration resistance (SFR) and high measured porosity as compared with cake layer. Current knowledge cannot explain the contradiction between high filtration resistance and high porosity of gel layer. A new fouling mechanism based on Flory-Huggins theory was then proposed. Filtration resistance of agar gel layer was found to be independent of pH and ionic strength, but linearly increase with gel thickness. The results are accordant with the mechanism deductions. Simulation of the mechanism model showed that the filtration resistance induced by mixing chemical potential variation was comparable to the experimental data of filtration resistance of agar gel layer, indicating that the proposed mechanism is the predominant mechanism responsible for the high filtration resistance of gel layer. The proposed mechanism was further verified from the bound water viewpoint. [ABSTRACT FROM AUTHOR]

In this paper, fractal reconstruction of rough membrane surface with a modified Weierstrass-Mandelbrot (WM) function was conducted. The topography of rough membrane surface was measured by an atomic force microscopy (AFM), and the results showed that the membrane surface was isotropous. Accordingly, the fractal dimension and roughness of membrane surface were calculated by the power spectrum method. The rough membrane surface was reconstructed on the MATLAB platform with the parameter values acquired from raw AFM data. The reconstructed membrane was much similar to the real membrane morphology measured by AFM. The parameters (including average roughness and root mean square (RMS) roughness) associated with membrane morphology for the model and real membrane were calculated, and a good match of roughness parameters between the reconstructed surface and real membrane was found, indicating the feasibility of the new developed method. The reconstructed membrane surface can be potentially used for interaction energy evaluation. [ABSTRACT FROM AUTHOR]

Concept of hydrophobicity always fails to accurately assess the interfacial interaction and membrane fouling, which calls for reliable parameters for this purpose. In this study, effects of contact angle on interfacial interactions related to membrane fouling were investigated based on thermodynamic analysis. It was found that, total interaction energy between sludge foulants and membrane monotonically decreases and increases with water and glycerol contact angle, respectively, indicating that these two parameters can be reliable indicators predicting total interaction energy and membrane fouling. Membrane roughness decreases interaction strength for over 20 times, and effects of membrane roughness on membrane fouling should consider water and glycerol contact angle on membrane. It was revealed existence of a critical water and glycerol contact angle for a given membrane bioreactor. Meanwhile, diiodomethane contact angle has minor effect on the total interaction, and cannot be regarded as an effective indicator assessing interfacial interactions and membrane fouling. [ABSTRACT FROM AUTHOR]

The interfacial interactions between a foulant particle and rough membrane surface in a submerged membrane bioreactor (MBR) were quantitatively assessed by using a new-developed method. It was found that the profile of total interaction versus separation distance was complicated. There were an energy barrier and two negative energy ranges in the profile. Further analysis showed that roughness scale significantly affected the strength and properties of interfacial interactions. It was revealed that there existed a critical range of roughness scale within which the total energy in the separation distance ranged from 0 to several nanometers was continually repulsive. Decrease in foulant size would increase the strength of specific interaction energy, but did not change the existence of a critical roughness scale range. These findings suggested the possibility to “tailor” membrane surface morphology for membrane fouling mitigation, and thus gave significant implications for membrane selection and fabrication in MBRs. [ABSTRACT FROM AUTHOR]

Abstract: A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating sewage was used to investigate the membrane fouling mechanism. Characterization of cake layer formed on membrane surface showed that cake layer was hydrated, rich of extracellular polymeric substances (EPS) and negative charged with the charge density of 0.21–0.46meq/kg MLSS. Detailed analysis revealed a new membrane fouling mechanism, osmotic pressure during cake layer filtration process due to the interception of ions. An osmotic pressure model was then developed to elaborate the existence of osmotic pressure and to estimate the contribution of osmotic pressure to membrane fouling. The calculated results showed that osmotic pressure accounted for the largest fraction of total operation pressure, indicating that osmotic pressure generated by the retained ions was one of the major mechanisms responsible for membrane fouling problem in MBRs. These findings provided a new insight into membrane fouling in MBRs. [Copyright &y& Elsevier]

Membrane bioreactor (MBR) technology has been extensively employed for various industrial wastewater treatments due to its distinct advantages over conventional technologies. To provide present state and development trends of MBR technology used for industrial wastewater treatments, the authors reviewed and analyzed more than 300 scientific publications. They present an overview of the most recent development of MBR technology for treatment of industrial wastewaters (e.g., food processing, pulp and paper, textile, tannery, landfill leachate, pharmaceutical, oily and petrochemical wastewaters). Moreover, they discuss the operational characteristics, fouling characteristics, fouling control strategies, and costs of MBRs in industrial wastewater treatments. Based on the present information on MBR technology, the authors discuss further research aspects of MBRs in industrial wastewater treatments. [ABSTRACT FROM PUBLISHER]

Abstract: A laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping whitewater was operated for over 7months to investigate and compare the characteristics of cake sludge and bulk sludge during stable state operation period. Serial analysis showed that cake sludge had a smaller particle size distribution (PSD), much higher specific filtration resistance (1.34×1014 m/kg), 1.5 times higher bound EPS and significantly different microbial community as compared with bulk sludge. Further analysis indicated that small flocs, bound EPS and inorganic materials play important role in cake formation process. The formed cake layer was found to have a heterogeneous structure. The results obtained in this study indicated that cake formation process started from attachment of small flocs and/or specific bacterial clusters which colonize the surface of the membrane and provide enhanced conditions that allow for cake formation to progress. [ABSTRACT FROM AUTHOR]

• BP ANN and GRNN were proposed to quantify interfacial energy related to fouling. • BP ANN and GRNN well captured the relations between interfacial energy and factors. • BP ANN and GRNN showed quick response to quantify interfacial energy and fouling. • this study showed breakthrough of the fundamental methodology in membrane fouling. Interfacial energy between sludge foulants and rough membrane surface critically determines adhesive fouling in membrane bioreactors (MBRs). As a current available method, the advanced extensive Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach cannot efficiently quantify the interfacial energy. In this study, novel methods including back propagation (BP) artificial neural network (ANN) and generalized regression neural network (GRNN) were proposed to quantify the interfacial energy associated with the membrane fouling in an MBR. Different levels of 5 apparent input factors and the resulted interfacial energies were used as training and testing databases for establishment of ANN models. The established BP ANN and GRNN models exhibited high regression coefficients and accuracies, suggesting the high capacity of ANN models to capture the complicated non-linear mapping relations between interfacial energy and various factors. As compared with the advanced XDLVO approach, both BP ANN and GRNN showed remarkably improved quantification efficiency. Meanwhile, BP ANN showed better prediction performance than GRNN model. Case study further demonstrated the robustness and feasibility of BP ANN for interfacial energy quantification. This study provided a new approach to quantify interfacial energy associated with membrane fouling. [ABSTRACT FROM AUTHOR]

While membrane bioreactor (MBR) technology is generally considered as one of the most promising technologies for wastewater treatment and recovery, membrane fouling remains the major obstacle limiting its applications. Interfacial interactions, which critically determine adhesion process and membrane fouling, were investigated in this study. It was found that, natural membrane surface was of a Gaussian surface obeying Gaussian distribution. A Gaussian approach integrating Fourier transform technique, Gaussian distribution and spectrum method was deduced to simulate rough surface topography of membrane. Thereafter, surface element integral (SEI) method, together with composite Simpson rule and triangulation of Gaussian surface was proposed to calculate interfacial interactions. By using the unified method, quantification of interfacial interactions with a Gaussian membrane surface was realized for the first time to date. It was further found that, membrane surface topography had profound impacts on interfacial interactions and adhesive fouling in the MBR. The deduced method can be used to address impacts of various factors on interfacial interactions and adhesive fouling, posing in-depth thermodynamic insights into membrane fouling and pointing towards its widespread potential in fouling research in MBRs. [ABSTRACT FROM AUTHOR]

36 membrane material cases used in membrane bioreactors (MBRs) covering wide range of hydrophilicity/hydrophobicity were used to calculate thermodynamic interactions between membranes and foulants. It was found that adhesive fouling can be represented by the total interaction energy at minimum separation distance ( h 0 ). No functional relationship between membrane hydrophilicity and adhesive fouling can be deduced. However, membrane hydrophilicity, in terms of water contact angle or interaction energy between two identical surfaces at h 0 in water (Δ G sws ), had high statistical correlations with adhesive fouling. This statistical correlations should be attributed to the major role of acid-base interaction in total interaction associated with adhesion in most of membrane cases. Moreover, the statistical correlations were independent of the changes in membrane surface roughness or hydrophilicity/hydrophobicity of foulants. These findings satisfactorily explained the inconsistent conclusions in the literature regarding effects of membrane hydrophilicity on adhesive fouling, giving implications for membrane fouling mitigation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, polyvinylidene fluoride (PVDF) microfiltration membrane was coated by dipping the membrane alternatingly in solutions of the polyelectrolytes (poly-diallyldimethylammonium chloride (PDADMAC) and polystyrenesulfonate (PSS)) via layer-by-layer (LBL) self-assembly technique to improve the membrane antifouling ability. Filtration experiments showed that, sludge cake layer on the coated membrane could be more easily washed off, and moreover, the remained flux ratio (RFR) of the coated membrane was obviously improved as compared with the control membrane. Characterization of the membranes showed that a polyelectrolyte layer was successfully coated on the membrane surfaces, and the hydrophilicity, surface charge and surface morphology of the coated membrane were changed. Based on the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approaches, quantification of interfacial interactions between foulants and membranes in three different scenarios was achieved. It was revealed that there existed a repulsive energy barrier when a particle foulant adhered to membrane surface, and the enhanced electrostatic double layer (EL) interaction and energy barrier should be responsible for the improved antifouling ability of the coated membrane. This study provided a combined solution to membrane modification and interaction energy evaluation related with membrane fouling simultaneously. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach to construct three-dimensional (3D) surface morphology of sludge flocs in a membrane bioreactor (MBR) was proposed. The new approach combined the static light scattering method for fractal dimension ( D f ) determination with the modified two-variable Weierstrass-Mandelbrot (WM) function based on fractal geometry and coordinate transformation for spherical surface construction. It was found that the sludge flocs in the MBR showed apparent fractal characteristics. Results showed that the constructed 3D morphology of sludge flocs was very sensitive to D f , and higher D f induced a more compact and smoother surface morphology. With a set of proper parameter data, the constructed 3D surface morphology of sludge flocs could be quite similar to the real floc surface morphology, showing the feasibility of the proposed approach. The proposed solution to floc surface construction could be potentially used in interfacial interaction assessment, giving important implications for membrane fouling research. [ABSTRACT FROM AUTHOR]

Effects of both membrane and sludge foulant surface zeta potentials on interfacial interactions between membrane and sludge foulant in different interaction scenarios were systematically investigated based on thermodynamic methods. Under conditions in this study, it was found that zeta potential had marginal effects on total interfacial interaction between two infinite planar surfaces, and the total interfacial interaction between foulant particles and membrane would be more repulsive with increase of absolute value of zeta potential. Adhesion of foulant particles on membrane surface should overcome an energy barrier. There exists a critical zeta potential below which energy barrier would disappear. Results also showed that rough surface membrane corresponded to significantly low strength of interfacial interactions. This study not only provided a series of methods to quantitatively assess the interfacial interactions between membrane and sludge foulants, but also reconciled the contradictory conclusions regarding effects of zeta potential in literature, giving important implications for membrane fouling mitigation. [ABSTRACT FROM AUTHOR]

The interfacial interactions between sludge foulants and four different types of membranes were assessed based on a new combined calculation method. Effects of membrane surface hydrophilicity/hydrophobicity on the interfacial interactions were investigated. It was found that, membrane surface hydrophilicity/hydrophobicity was not directly relevant to the interfacial interactions with sludge particles. Increasing membrane surface zeta potential could significantly increase the strength of the electrostatic double layer (EL) interaction and the energy barrier. For membrane with a surface roughness of 300 nm, the total interaction was continuously repulsive in the separation distance coverage of 0–4 nm in this study. The results suggest that, under conditions in this study, designing membranes with a high zeta potential and certain roughness can significantly mitigate membrane fouling, whereas, the strategy of improving membrane surface hydrophilicity cannot alleviate sludge adhesion in the membrane bioreactor. [ABSTRACT FROM AUTHOR]

This study proposed a novel approach for quantitative evaluation of the physicochemical interactions between a particle and rough surface. The approach adopts the composite Simpson’s rule to numerically calculate the double integrals in the surface element integration of these physicochemical interactions. The calculation could be achieved by a MATLAB program based on this approach. This approach was then applied to assess the physicochemical interactions between rough membrane surface and sludge foulants in a submerged membrane bioreactor (MBR). The results showed that, as compared with smooth membrane surface, rough membrane surface had a much lower strength of interactions with sludge foulants. Meanwhile, membrane surface morphology significantly affected the strength and properties of the interactions. This study showed that the newly developed approach was feasible, and could serve as a primary tool for investigating membrane fouling in MBRs. [ABSTRACT FROM AUTHOR]

Abstract: Extracellular polymeric substances (EPSs) are key biological substances, which largely determine properties of sludge flocs, including hydrophobicity, adhesion, flocculation, settling and dewatering properties, and therefore significantly affect membrane fouling in membrane bioreactors (MBRs). Much progress has been achieved in understanding of EPSs and their interrelations with membrane fouling due to a large number of systematic papers published in the last three decades. In this paper, the fundamentals of EPSs including definitions, compositions and properties are summarized. The interrelations of EPSs with other foulants in MBRs are clarified. Roles of EPSs in membrane fouling mechanisms in MBRs are critically assessed. Furthermore, factors affecting EPSs production and characteristics are summarized, and based on which, EPSs control towards membrane fouling mitigation in MBRs are comprehensively discussed. Finally, future research perspectives regarding EPSs and membrane fouling are proposed. [Copyright &y& Elsevier]

Highlights: [•] A new fouling mechanism: osmotic pressure mechanism was identified in MBR. [•] Functional groups were abundant in the surface of cake layer. [•] SMP and BPC in supernatant played key roles in osmotic pressure mechanism. [•] The formed cake layer was much hydrated and elastic. [ABSTRACT FROM AUTHOR]

Highlights: [•] AB interactions predominated in the total interactions of membrane-foulants combination. [•] Proteins play an essential role in adhesion process. [•] Sludge adhesion to membrane encountered a repulsive interaction energy barrier. [•] Small flocs possessed higher attractive interaction energy per unit mass. [•] Initial sludge adhesion reduced energy barrier, facilitating the following adhesion. [Copyright &y& Elsevier]

Abstract: In the last years, anaerobic membrane bioreactor (AnMBR) technology is being considered as a very appealing alternative for wastewater treatment due to the significant advantages over conventional anaerobic treatment and aerobic membrane bioreactor (MBR) technology. Many articles have touted the diverse potential applications of AnMBR in various stream treatment, and membrane fouling issues. In current review, the fundamentals of AnMBR (including advantages and configurations, membrane materials and modules, and history development), application development in various stream treatment, and membrane fouling researches are summarized and critically assessed. The characteristics of AnMBR and aerobic MBR for wastewater treatment are also compared. AnMBR technology appears to be suitable for treatment of various streams, especially for food industrial wastewater and municipal wastewater. AnMBR treatment usually encounters more serious membrane fouling problem. This, however, can be remedied through various conventional and novel membrane fouling control or cleaning measures. Based on the review, future research perspectives relating to its application and membrane fouling research are proposed. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate the feasibility of PAC-MBR process treating municipal secondary effluent. Two laboratory-scale submerged MBRs (SMBR) with and without PAC addition were continuously operated in parallel for secondary effluent treatment. Approximately 63%TOC, 95% NH4 +–N and 98% turbidity in secondary effluent were removed by the PAC-MBR process. Most organics in the secondary effluent were found to be low molecular weight (MW) substances, which could be retained in the reactor and then removed to some extent by using PAC-MBR process. Parallel experiments showed that the addition of PAC significantly increased organic removal and responsible for the largest fraction of organic removal. Membrane fouling analysis showed the enhanced membrane performance in terms of sustainable operational time and filtration resistances by PAC addition. Based on these results, the PAC-MBR process was considered as an attractive option for the reduction of pollutants in secondary effluent. [Copyright &y& Elsevier]