Fouling Model Research Articles

Effect of particle size distribution on filtration performance of cell culture medium.

Cell culture media used in CHO-based biologic processes are typically sterile filtered to prevent microbial contamination prior to inoculation. In this study, the impact of common sterile filter throughput on a different, commercially available cell culture media was evaluated from the intermediate-adsorption fouling model of the filtration model. The key particle size range for optimum filter performance was discussed and identified by measuring the submicron order particle size distribution. It may be possible to predict the performance of filter capacity with size-exclusive separation by understanding the media particle counts and size distribution.

Membrane fouling by mixtures of oppositely charged particles

Membrane fouling persists to be among key obstacles in liquid membrane-based separation processes, and thereby the underlying understanding has actively been pursued. The two gaps attempted to be addressed here are namely, (i) internal fouling, which has limited studies due to limitations of instruments available; and (ii) fouling by mixtures of oppositely charged particles, as an extension to the studies on effect of surface charge of pure foulants on fouling. With the sub-micron pure constituents (namely, negatively charged carboxylated latex particles and positively charged aminated latex particles) as benchmarks, mixtures of three different compositions of the two particle types were investigated. The membrane was polycarbonate track-etched (PCTE) membrane. Surprisingly, the mixtures gave worse flux decline than that by purely positively charged aminated latex, which contradicts electrostatic considerations. The fouling model indicates that the mixtures exhibited higher pore blockage parameters (α) than either of the pure constituents, which agree with the flux decline trends. On the other hand, the mixtures gave internal cake resistance parameters (Rc/Rm) in between that of the pure constituents, which disagree with the fouling trends. Furthermore, optical coherence tomography (OCT) analysis indicates that the mixtures had taller buildups on the membrane as well as heterogenous internal cakes. Therefore, the steepest flux declines for the mixtures seem to be better correlated with the extensive external fouling as manifested in the taller buildups on the membrane pores, rather than internal fouling since the internal cakes were more porous. The contradictory extensive external and mitigated internal fouling phenomena are unexpected based on electrostatic considerations, and thereby highlight that fouling resulting from mixtures may not be readily extrapolated from understanding based on pure particle feeds.

Improved integrated dynamic model for the simulation of submerged membrane bioreactors for urban and hospital wastewater treatment

This article presents the modeling of a submerged membrane bioreactor (SMBR) using experimental values at laboratory and pilot scale for urban and hospital wastewater treatment, respectively. The main objective of this work is to develop an improved model integrating a biological model with a membrane fouling model, with upgraded precision, consistency and calibration in the description of the functioning of SMBR. For this, concerning the biological model, an evolution of the Activated Sludge Model 3 (ASM3), including the simultaneous growth and substrate storage, and the soluble and bound extracellular polymeric substances (EPS) production was proposed. The concentration of EPS and the mixed liquor suspended solids are the variables of connection with the new version of the membrane fouling model that takes into account the influence of EPS on the sludge cake and membrane porosity. A new procedure was developed to calibrate the parameters considering their influence on the model and parameters uncertainty. It allowed the calibration and successful validation of the developed model. The high correspondence obtained between numerical and experimental results evidences the relevance of the phenomena considered in the model.

Optimal Cleaning Cycle Scheduling under Uncertain Conditions: A Flexibility Analysis on Heat Exchanger Fouling

Fouling is a substantial economic, energy, and safety issue for all the process industry applications, heat transfer units in particular. Although this phenomenon can be mitigated, it cannot be avoided and proper cleaning cycle scheduling is the best way to deal with it. After thorough literature research about the most reliable fouling model description, cleaning procedures have been optimized by minimizing the Time Average Losses (TAL) under nominal operating conditions according to the well-established procedure. For this purpose, different cleaning actions, namely chemical and mechanical, have been accounted for. However, this procedure is strictly related to nominal operating conditions therefore perturbations, when present, could considerably compromise the process profitability due to unexpected shutdown or extraordinary maintenance operations. After a preliminary sensitivity analysis, the uncertain variables and the corresponding disturbance likelihood were estimated. Hence, cleaning cycles were rescheduled on the basis of a stochastic flexibility index for different probability distributions to show how the uncertainty characterization affects the optimal time and economic losses. A decisional algorithm was finally conceived in order to assess the best number of chemical cleaning cycles included in a cleaning supercycle. In conclusion, this study highlights how optimal scheduling is affected by external perturbations and provides an important tool to the decision-maker in order to make a more conscious design choice based on a robust multi-criteria optimization.

Membrane-based clarification of banana juice: pre-treatment effect on the flux behaviour, fouling mechanism and juice quality attributes

The processing of banana into clarified juice provides an alternative in the beverages market, but further exploration of the related processing is required. Hence, this study investigated the pre-treatment effect during the membrane-based process on the flux behaviour, fouling mechanism and banana juice quality attributes. Observation on juice viscosity was done after the crude banana juice was pre-treated with 0.1 – 0.5% pectinase. Both pectinase-treated and untreated banana juices were then subjected to an ultrafiltration process using a 100 kDa dead-end polyethersulfone membrane to clarify the juice. This study found a 50-55% viscosity reduction of the banana juice after the pre-treatment, with no significant difference in terms of the pectinase concentrations. Pre-treatment of the banana juice prior to ultrafiltration also have improved the permeate flux by 65.5% compared to the untreated sample. Based on the fitting of several fouling models, cake layer formation on the entire surface of the membrane was identified as the main cause of the membrane fouling and flux deterioration. The ultrafiltration process has significantly improved the juice turbidity, total soluble solid and colour, at a stable pH, indicating the success of the clarification process.

Review of Membrane Separation Models and Technologies: Processing Complex Food-Based Biomolecular Fractions

There is growing interest in the food industry to develop approaches for large-scale production of bioactive molecules through continuous downstream processing, especially from sustainable sources. Membrane-based separation technologies have the potential to reduce production costs while incorporating versatile multiproduct processing capabilities. This review describes advances in membrane technologies that may facilitate versatile and effective isolation of bioactive compounds. The benefits and drawbacks of pressure-driven membrane cascades, functionalized membranes and electromembrane separation technologies are highlighted, in the context of their applications in the food industry. Examples illustrate the separation of functional macromolecules (peptides, proteins, oligo/polysaccharides, plant secondary metabolites) from complex food-based streams. Theoretical and mechanistic models of membrane flux and fouling are also summarized. Overcoming existing challenges of these technologies will provide the food industry with several attractive options for bioprocessing operations.

A novel method for calculating effective thermal conductivity of particulate fouling

The accurate thermal conductivity of fouling plays a very significant role in designing heat exchanger. In this paper, a novel method of calculating the effective thermal conductivity of particulate fouling is put forward by using IMAGE-PRO-PLUS image processing, the finite element method and ANSYS parametric design language. First of all, according to the analysis on the particulate fouling samples features, the particulate fouling is considered as porous media with fractal characteristics, whose microscopic network model is established using the finite element method, and each unit body material properties are randomly assigned by ANSYS parametric design language. Secondly, effective thermal conductivity of particulate fouling model is calculated by the steady-state plate method. Then, the influence of particulate fouling micro-structure on effective thermal conductivity is explored. Last, it is also show that the calculation resulting of effective thermal conductivity agrees well with available experimental data and empirical correlation. Moreover, it has been shown that effective thermal conductivity of particulate fouling is closely associated with the porosity and pore size. The method can be used to research on the thermal conductivity of fouling, discuss the influence of micro-structure on effective thermal conductivity of fouling, and provide the guidelines for designing of heat exchanger on calculating accurate thermal conductivity of fouling.

Fouling Behavior during Sterile Filtration of Different Glycoconjugate Serotypes Used in Conjugate Vaccines.

Sterile filtration can be a particular challenge when processing very large glycoconjugate vaccines. The objective of this study was to examine the sterile filtration performance of a series of glycoconjugate vaccines produced by coupling different polysaccharide serotypes to an immunogenic protein. Sterile filtration was performed at constant filtrate flux using 0.22μm pore size Durapore® polyvinylidene fluoride membranes. Glycoconjugates were characterized by dynamic light scattering, rheological measurements, and nanoparticle tracking analysis (NTA). Confocal microscopy was used to examine glycoconjugate capture profiles within the membrane. Transmembrane pressure data were analyzed using a recently developed fouling model. All glycoconjugates deposited in a narrow band near the entrance of the Durapore® membranes. The rate of fouling varied significantly for the different serotypes, with the fouling parameter correlated with the fraction of glycoconjugates larger than 200nm in size. The fouling behavior and sterile filter capacity of the different glycoconjugate serotypes are determined primarily by the presence of large species (>200nm in size) as determined by nanoparticle tracking analysis. The modified intermediate pore blockage model provides a framework for predicting the sterile filtration performance for these glycoconjugate vaccines.

Effect of pH on membrane fouling during alcohol dehydrogenase immobilization in PES membrane

Fouling-induced enzyme immobilization is a technique to immobilize enzyme by positively manipulating the knowledge of membrane fouling. In this study, Alcohol dehydrogenase (ADH) (EC 1.1.1.1) was immobilized in the support layer of ultrafiltration PES membrane at different solution pH (acid, neutral and alkaline). ADH catalyses formaldehyde (CHOH) to methanol (CH3OH) and simultaneously oxidised nicotinamide adenine dinucleotide (NADH) to NAD+. The initial feed amount of enzyme is 3.0 mg. The objective of the study aims at the effect of different pH of feed solution during enzyme immobilization, in terms of permeate flux, observed rejection, enzyme loading and fouling mechanism. The results showed that, pH 5 holds the highest enzyme loading which is 65% while pH 7 holds the lowest at 52% out of 3.0 mg as the initial enzyme feed. The permeate flux for each pH decreased with increasing cumulative permeate volume. The observed rejection is inversely correlated with the pH where increase in pH will cause a lower observed rejection. The fouling model predicted that irreversible fouling occurs during enzyme immobilization at pH 7 with standard blocking mechanism while reversible fouling occurs at pH 5 and 9 with intermediate and complete blocking, respectively.

Development of a mechanistic fouling model for predicting deposit formation in a woodchip-fired grate boiler

Currently fouling is still a major issue for the woodchip-fired boilers, which limits the utilization of the woody type fuel. In this work, a mechanistic fouling model considering both ash deposition and removal mechanisms was developed to model ash deposition. New criterions for the sliding and rolling particle detachment were proposed, and the effect of impacts among multiple particles, particle sizes of the deposited particles and surface roughness on ash deposition were considered. Combining with the Discrete Phase Model (DPM), heat transfer model, and dynamic mesh model, and this newly developed fouling model, the simulation tool was applied to predict the growth of ash deposit on a single tube. Good agreement was obtained between the simulation results and the results from a lab-scale experimental setup. By further investigation, it was found to be necessary to consider the removal process even when the flue gas velocity was as low as 1.93 m/s, and increasing the flue gas velocity significantly reduced ash deposition. The Young’s module of ash particles was also identified as an important parameter for ash deposition. The results indicate that the developed mechanistic model is a promising approach for predicting ash deposition behavior in the woodchip-fired grate boilers.

Fouling and cleaning of plate heat exchangers: Dairy application

Plate heat exchangers (PHEs) used in milk thermal treatments are subject to rapid fouling, while Cleaning-in-Place (CIP) produces large amounts of wastes. Up to 80% of production costs in the dairy industry have been attributed to the effects of fouling and cleaning.In spite of decades of research, a detailed model for simulation, monitoring, control and optimisation of full heating and cleaning cycles for PHEs is still not available. Mechanistic simulation models based on differential equations typically address only fouling but not cleaning. More detailed models based on Computational Fluid Dynamics (CFD) are computationally very expensive and impractical to use for optimization, scheduling and control of complete PHEs.Here, a dynamic 2D model of PHEs is presented that enables optimizing milk thermal treatment operations, taking into account both fouling and cleaning. The model balances predictive accuracy and computational feasibility.It integrates: (i) various mechanisms and kinetics for fouling and cleaning; (ii) a detailed moving boundary model of deposit growth that captures its spatial distribution; (iii) a dynamic thermo-hydraulic model of mass and heat transfer in a single PHE channel; (iv) the flexible assembly of channels into a variety of PHE configurations, and (v) the flexible definition of heating-cleaning cycles.The fouling model has been validated for two PHE configurations against experimental data, with excellent results. Alternative fouling mechanism (due to aggregate proteins or denatured proteins, and with/without deposit re-entrainment) have been explored. Results show that the fouling observed in the two arrangements is best fitted by distinct fouling models, and that the performance of the two PHE arrangements is quite different.Dynamic cleaning models have been integrated with the deposit moving boundary model and validated. This has enabled for the first time the seamless, detailed simulation of individual and multiple heating-cleaning cycles, where each phase starts from the detailed deposit distribution at the end of the previous phase. The models detail enables the introduction of sophisticated condition-based logic in the operation of each phase and overall cycle. Using such condition-based logic it is shown that cleaning time could potentially be reduced by ∼50%. Finally, it is shown that the heating/cleaning cycle can be optimized for maximum productivity, balancing fouling and cleaning trade-offs. This is demonstrated for one of the PHE arrangements.

Effect of boron-doped diamond anode electrode pretreatment on UF membrane fouling mitigation in a cross-flow filtration process

In this study, ultrafiltration coupled with electrochemical oxidation using a boron-doped diamond (BDD) electrode prior to reverse osmosis was employed to treat the simulated sea water. It was found that BDD based anodic pre-oxidation effectively improved the removal efficiency of dissolved organic matters especially enhance the rejection of fluorescent substances when prolong the oxidation time. Based on the analysis of XAD resin adsorption, the fraction of hydrophilic components significantly increased after the electro-oxidation pretreatment. In addition, the BDD based oxidation pretreatment was found to reduce the disinfection byproduct formation potential. A two-stage fouling model and the interfacial free energy were employed to investigate the fouling mitigation mechanisms via electrochemical oxidation pretreatment. The results show that membrane fouling was mitigated with increasing repulsive interactions and decreasing attractive interactions between humic acid molecules and the membrane surface after electrochemical oxidation. With longer electrochemical oxidation time, the dominant mechanism of membrane fouling shifted from complete pore blocking and cake filtration, mainly caused by hydrophobic humic acid compounds with higher molecular weight, to standard blocking and pore blocking, caused by hydrophobic humic acid compounds with low molecular weight.

A biofouling thermal resistance model with a growth term of surface biofilm on heat transfer surface

To study the occurrence of biofouling phenomenon on heat exchanger surfaces, a new biofouling thermal resistance model for heat exchanger surface was developed. Considering the effect of microbial activity on fouling resistance, a growth term of surface biofilm was introduced into the Kern–Seaton model. The microbial growth dynamics was described by using a modified Gompertz model. The occurrence of fouling process due to iron bacteria in a tube and an alternating elliptical axis tube were considered as examples to validate the fouling model. The results showed that the relative error between the calculated data obtained from new microbial fouling resistance model and experimental data was less than 10%, in addition to the induction phase.

A heat‐transfer model for tube fouling in the radiant section of once‐through steam generators

AbstractOnce‐through steam generators (OTSGs) produce steam by recycling produced water in the steam‐assisted‐gravity‐drainage (SAGD) process for extracting Alberta's oil sands via in situ recovery of bitumen. The industry's specifications for water quality, steam quality, and water recycle ratio, as well as high temperature and pressure operations, lead to the fouling of OTSG tubes, which has important economic, safety, and environmental consequences. The roles and mechanisms of inorganic and organic impurities on tube fouling also complicate the study of heat transfer in OTSGs. Heat transfer in OTSGs involves radiation, convection, conduction, forced convection, and boiling. In this investigation on OTSG fouling, a steady‐state mathematical model was built in Microsoft Excel, incorporating industry design data, to demonstrate the impact of tube fouling on heat transfer and tube‐wall temperature. The model predictions indicate that tube fouling introduces a significant thermal resistance that not only decreases the rate of heat transfer but also causes an increase in the tube‐wall temperature such that it could exceed the safe operating limits of the tube material, leading to potential tube failures. Predictions are provided for the average tube‐wall temperature exceeding the recommended operating limit of 700 K over a range of foulant thermal conductivity (ie, 0.05‐2 W m−1 K−1) and foulant thickness (ie, 0.4‐11 mm corresponding to 0.1%‐30% of the tube radius).

Fluorescence-assisted real-time study of magnetically immobilized enzyme stability in a crossflow membrane bioreactor

The detailed structures and distribution of enzymatically active magnetic-responsive dynamic layers (EnzSP) were investigated for the first time in a crossflow superparamagnetic biocatalytic membrane reactor (XF-BMRSP). The trade-off between a higher mass transfer rate, lower fouling tendency, and preventing washout of the dynamic layer, highly depends on the balance of the various forces that act on the EnzSP. The real-time visual inspection of the biointerface was realized through the design and fabrication of an adapted crossflow system, guided by computational fluid dynamics (CFD) simulations. Time-resolved images of the dynamic layer under a broad range of operational conditions was obtained using fluorescence microscopy.The deposition, dispersion and stability of the dynamic layer was mainly governed by the external magnetic force. The shear force did not cause significant particle washout when a buffer solution was recirculated without permeation even under a turbulent flow regime (6.4 cm/s ∼ Re = 5200). The removal of the external magnetic force after initial magnetic immobilization of the EnzSP, or the substitution of a smooth flow velocity by the propagation of an impulse flow, significantly affected the stability of the dynamic layer.Although membrane fouling occurs at the membrane-solution interface, where a laminar flow regime prevails, most membrane fouling models are based on turbulent flow. Therefore, the detailed, time-resolved images obtained here can provide solid foundation for the development of theoretical models that can describe the membrane fouling under the more representative laminar flow regime.

A comprehensive analysis of membrane fouling in microfiltration of complex linear macromolecules based on theoretical modeling and FESEM images

AbstractBACKGROUNDMembrane technology is an attractive alternative to conventional water/wastewater treatment technologies as it is sustainable and can be used as an independent process as well as being a part of integrated systems with other treatment technologies. Notwithstanding the abundant benefits that membrane‐based systems offer, their commercial application is overshadowed by the ubiquitous fouling. However, accurate prediction and identification of membrane fouling mechanisms can help to open new doors in recognition of appropriate arrangements for developing more effective membrane synthesis methods and fundamental strategies to achieve better performance, especially in large‐scale production.RESULTSIn this study, three fouling models, namely resistance‐in‐series (RIS), Hermia's and combined cake filtration–pore blockage models, were applied to precisely analyze fouling behavior in dead‐end microfiltration (MF) of collagen solution, as model foulant, using pure high‐density polyethylene and modified high‐density polyethylene membranes. The RIS model was shown to be not representative of the real fouling mechanism in MF membrane units. Similarly, none of the classical models were able to accurately predict fouling in the entire MF process. However, the combined cake–intermediate blockage model provided excellent fits for the membranes.CONCLUSIONSObtained results also demonstrated that physical cleaning was not enough for organic fouling elimination in MF processes. Finally, computational results were validated with experimental observations of collagen rejection and field emission scanning electron microscopy analyses as well. © 2020 Society of Chemical Industry

Effect of initial particle deposition rate on cake formation during dead-end microfiltration

The relationships between various parameters and membrane fouling are generally well-established in microfiltration. Surprisingly, a non-monotonic correlation between initial particle deposition rate and extent of flux decline was observed during dead-end microfiltration. To understand the underlying mechanism, a fouling model and three-dimensional optical coherence tomography (OCT) scanning were employed. Four different initial deposition rates were imposed using latex particles (3 μm) as the model foulant and polycarbonate track-etched membrane (pore size = 2 μm). The network fouling model revealed that, as the initial deposition rate increased, (i) the probability of deposition on the non-porous part of the membrane (β) increased then decreased; (ii) the initial cake resistance (Rc0) increased monotonically; and (iii) the specific cake resistance (R'c) decreased then increased. The OCT image analysis further informed that (i) the deposited foulants tended to form larger clusters at the lowest and highest initial deposition rates of 12.5 and 31.25 g/m2/h, respectively, but tended to be more dispersed at the intermediate initial deposition rate of 25 g/m2/h; and (ii) the more significant specific cake resistances (R'c) at the lowest and highest initial deposition rates were due to denser cakes stemming from greater particle rearrangement within the cake and greater particle concentration near the membrane, respectively. The network fouling model and experimental OCT characterization served to explain the counter-intuitive flux decline trends, and the insights are valuable towards better understanding of the inevitable membrane fouling phenomena.

Influences of cross-linking agents with different MW on the structure of GO/CNTs layers, membrane performances and fouling mechanisms for dissolved organic matter

This study evaluated the impacts of cross-linking agents with different molecular weight (MW) on the structure of graphene oxide (GO)/carbon nanotubes (CNTs) layers and fouling mechanisms. The GO/CNTs-modified membrane was fabricated by chemical activation and vacuum filtration methods and exhibited excellent stability in antifouling performance and rejection rates. Increasing the external diameter of CNTs and MW of cross-linking agents improved the water flux through enlarging the interlayer spacing of GO/CNTs layers, showing the highest water flux of about 1280 kg/m2h. The large external diameter of CNTs deteriorated the antifouling performance and removal efficiency. The small cross-linking agents, i.e. ethanediamine with 60.1 Da or polyethyleneimine with 600 Da, maintained the regular lamellar structure of GO/CNTs layers, causing the high flux and DOC rejection. However, polyethyleneimine with 1800 Da promoted GO/CNTs aggregation and created non-uniform lamellar structure with high surface roughness, resulting in the severest flux decline and the lowest DOC rejection. The fouling model was also influenced by the MW of cross-linking agents; the small agents caused complete blocking while the large agent caused intermediate fouling for humic acid (HA) solution. The bridging effect of Ca2+ resulted in intermediate fouling for all the membranes in the case of HA + Ca2+ solution.

Evaluating the impacts of a high concentration of powdered activated carbon in a ceramic membrane bioreactor: Mixed liquor properties, hydraulic performance and fouling mechanism

Owing to the lack of comprehensive studies on the impacts of a high concentration of powdered activated carbon (PAC) in a ceramic membrane bioreactor (MBR), its performance (at 20 g/L) in terms of mixed liquor properties, hydraulic performance and fouling mechanism was elucidated in this study. In addition to the increase in floc size by 29%, zeta potential of the mixed liquor in PAC-MBR increased (from −19 ± 2 mV to −11 ± 2 mV), which was due to the sorption of soluble microbial products on PAC. Importantly, even at a high dose of 20 g/L, membrane fouling was reduced by 33% in PAC-MBR and was attributed to the membrane scouring by PAC and reduced SMP and EPS concentration in the mixed liquor. The viability of the four single and five combined fouling models was assessed to explain the membrane fouling mechanisms in ceramic MBRs for the first time. The intermediate-standard and cake-intermediate models well explained the fouling mechanism in the ‘control’ and PAC-MBR, respectively, and the intermediate fouling was the major component of the combined models. This study clarifies that MBR could be operated at a high PAC concentration without compromising the effluent quality, mixed liquor properties and membrane hydraulic performance.

Revisiting Threshold Fouling Models for Crude Oil Fouling

Threshold crude oil fouling models use activation energy in the deposition rate term to predict the initial fouling rates. It has been reported in the literature that fluid velocity has a strong influence on activation energy, which does not agree well with the principles of chemical reaction engineering. Besides, the existing threshold fouling models always predict an increase in the fouling rate with an increase in film temperature. Several studies reported in the literature reveal that many test crude oils exhibited a decrease in fouling rate with an increase in film temperature caused by an increase in bulk temperature. It is, therefore, necessary to develop a threshold fouling model that is free from the use of activation energy in the model, and that predicts the initial fouling rates correctly for all types of crude oils and fouling mechanisms. In the present study, a modified threshold fouling model has been proposed by introducing a bulk temperature-dependent constant in the place of activation energy and validated with experimental data from our laboratory and data from the literature.