A new approach to construct three-dimensional surface morphology of sludge flocs in a membrane bioreactor

Predicting thermodynamic adhesion energies of membrane fouling in planktonic anammox MBR via backpropagation neural network model

Predicting thermodynamic adhesion energies was a critical strategy for mitigating membrane fouling. This study utilized a backpropagation (BP) neural network model to predict the thermodynamic adhesion energies associated with membrane fouling in a planktonic anammox MBR. Acid-base (ΔGAB), electrostatic double layer (ΔGEL), and Lifshitz-van der Waals (ΔGLW) energies were selected as output variables, the training dataset was collected by the advanced Derjaguin-Landau-Verwey-Overbeek (XDLVO) method. Optimization results identified "7-10-3″ as the optimal network structure for the BP model. The prediction results demonstrated a high degree of fit between the predicted and experimental values of thermodynamic adhesion energy (R2 ≥ 0.9278), indicating a robust predictive capability of the model in this study. Overall, the study presented a practical BP neural network model for predicting thermodynamic adhesion energies, significantly enhancing the prediction tool for adhesive fouling behavior in anammox MBRs.

A modeling approach for quantitative assessment of interfacial interaction between two rough particles in colloidal systems

HYPOTHESIS AND BACKGROUND

The simulation of rough particle surface is important to understand and control the interface behavior of particles in colloidal systems. Literature analysis suggested a lack of information for an accurate model simulating the interfacial interaction between two rough particles. It is hypothesized that the total interfacial energy developed between two rough particles would depend on the surface morphologies of particles, and it could be predicted if a mathematical model to represent the interaction of two rough particles were created accurately.

EXPERIMENTS

In this study, mathematical models were developed to determine the interfacial energy created between two particles according to the XDLVO theory by considering the rippled particle theory and surface element integral (SEI) method. Three different scenarios of particle interactions were assumed in the simulation. The present study provides deep insights into particle interactions via considering aspect ratio, size, and surface roughness of two particles in colloidal systems.

FINDINGS

The assessment of the interfacial interaction revealed that an increase in the aspect ratio, surface roughness, and relative surface roughness of particles would weaken the total interaction energy generated between particles and promote particle aggregation. Increased interaction energy was predicted for the interaction of particles by increasing the particle size. The asperity ratio was more effective than the asperity number in controlling the interfacial energy between two particles. The results of this study could be used for foreseeing the interaction of rough particles, which has a significant application in particle coagulation or dispersion in colloidal systems.

Membrane bioreactors and electrochemical processes for treatment of wastewaters containing heavy metal ions, organics, micropollutants and dyes: Recent developments

Research and development activities on standalone systems of membrane bioreactors and electrochemical reactors for wastewater treatment have been intensified recently. However, several challenges are still being faced during the operation of these reactors. The current challenges associated with the operation of standalone MBR and electrochemical reactors include: membrane fouling in MBR, set-backs from operational errors and conditions, energy consumption in electrochemical systems, high cost requirement, and the need for simplified models. The advantage of this review is to present the most critical challenges and opportunities. These challenges have necessitated the design of MBR derivatives such as anaerobic MBR (AnMBR), osmotic MBR (OMBR), biofilm MBR (BF-MBR), membrane aerated biofilm reactor (MABR), and magnetically-enhanced systems. Likewise, electrochemical reactors with different configurations such as parallel, cylindrical, rotating impeller-electrode, packed bed, and moving particle configurations have emerged. One of the most effective approaches towards reducing energy consumption and membrane fouling rate is the integration of MBR with low-voltage electrochemical processes in an electrically-enhanced membrane bioreactor (eMBR). Meanwhile, research on eMBR modeling and sludge reuse is limited. Future trends should focus on novel/fresh concepts such as electrically-enhanced AnMBRs, electrically-enhanced OMBRs, and coupled systems with microbial fuel cells to further improve energy efficiency and effluent quality.

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.

Scale of Small Particle Population in Activated Sludge Flocs

The light scattering method is a valuable tool for accessing particle size and structure mainly due to fast and the nonintrusive nature of the measurement. The method is based on a scattered intensity pattern and depends on particle volume, particle morphology, the light wavelength and the scattering angle. The light scattering model, for particles characterised by a fractal structure, is enabled with the use of the Rayleigh-Gans-Debye theory under constrained assumptions. The range of validity of the Rayleigh-Gans-Debye is limited when primary particles constituting aggregate have a size close to the wavelength. In this work, a range of particle sizes was characterised in order to achieve a better understanding of the relationship between flocs size and its fractal dimension. Hence, the width of the power law regime is discussed. What is more, a specific fractal dimension value of activated sludge flocs was found for each of the analysed wastewater treatment plant, which suggests that the spatial structure of suspensions constituting the activated sludge is an individual characteristic of each treatment facility. It has been shown that activated sludge consists of microflocs from the range of 1-10 μm, which constitute approximately 90% of all the population.

Impacts of morphology on fouling propensity in a membrane bioreactor based on thermodynamic analyses

Impacts of morphologies of both membrane and foulant on interaction energies related with adhesive fouling in a membrane bioreactor (MBR) were explored by thermodynamic analyses. Interaction energies in three possible interaction scenarios regarding different membrane and foulant morphologies under conditions in this study were quantified according to the thermodynamic methods. It was interestingly found that, strength of total interaction between soluble microbial products (SMPs) and rough membrane was over 20,000 times of that between sludge flocs and rough membrane under same conditions, indicating the extremely higher adhesion ability of SMPs than the large particulate foulants. This result plausibly explained the high fouling propensity of SMPs over sludge flocs. As compared with smooth surfaces, rough surfaces of both membrane and sludge flocs significantly reduced total interaction strength, alleviating adhesive fouling caused by the sludge flocs. Reduce in fractal dimension (D_f) of membrane increased adhesive fouling caused by the SMPs, but alleviated adhesive fouling caused by the sludge flocs. These findings gave important implications to better understand and control membrane fouling in MBRs.

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.

Membrane fouling in a submerged membrane bioreactor: New method and its applications in interfacial interaction quantification

Quantification of interfacial interactions between two rough surfaces represents one of the most pressing requirements for membrane fouling prediction and control in membrane bioreactors (MBRs). This study firstly constructed regularly rough membrane and particle surfaces by using rigorous mathematical equations. Thereafter, a new method involving surface element integration (SEI) method, differential geometry and composite Simpson's rule was proposed to quantify the interfacial interactions between the two constructed rough surfaces. This new method were then applied to investigate interfacial interactions in a MBR with the data of surface properties of membrane and foulants experimentally measured. The feasibility of the new method was verified. It was found that asperity amplitude and period of the membrane surface exerted profound effects on the total interaction. The new method had broad potential application fields especially including guiding membrane surface design for membrane fouling mitigation.

Quantitative evaluation of the interfacial interactions between a randomly rough sludge floc and membrane surface in a membrane bioreactor based on fractal geometry

In this paper, a new method for quantification of interfacial interactions between a randomly rough particle and membrane surface was proposed. It was found that sludge flocs in a membrane bioreactor were of apparent fractal characteristics, and could be modeled by the modified two-variable Weierstrass-Mandelbrot (WM) function. By combining the surface element integration (SEI) method, differential geometry and composite Simpson's rule, the quantitation method for calculating such interfacial interactions was further developed. The correctness and feasibility of the new method were verified. This method was then applied to evaluate the interfacial interactions between a randomly rough particle and membrane surface. It was found that, randomly rough particle possesses stronger interaction strength than regularly rough particle but weaker strength than smooth particle with membrane surface, indicating significant effects of surface morphology and roughness. The proposed method in this study has broad application prospect in membrane fouling study.