Cake Layer Thickness Research Articles

Antifouling characteristics and mechanisms in visible-light photocatalytic membrane bioreactor based on g-C3N4 modified membrane

A novel visible-light photocatalytic membrane bioreactor (R3) was constructed for membrane fouling control and effluent quality improvement. Specially, g-C3N4 modified membrane was evaluated for the performance of synergistic separation and photocatalysis. Another two parallel reactors, MBRs with ceramic membrane (R1) and g-C3N4 membrane in dark condition (R2), were operated synchronously for comparison. A satisfactory effluent quality was obtained in R3 with COD and NH4+-N around 22.0 mg/L and 1.02 mg/L during 60-day operation, which was superior to R1 (27.8, 1.42 mg/L) and R2 (29.9, 2.26 mg/L). The thickness of cake layer on membranes in R3 (2.46 μm) was thinner than R1 (3.52 μm) and R2 (4.97 μm) after operation, indicating the introduction of visible light could effectively mitigate membranes fouling. Moreover, microorganism community analysis revealed that visible light increased the relative abundance of Bacteroidetes and Chryseolinea, which not only enhanced the activity of microorganisms in metabolizing organic nutrients, but also improved the transfer and utilization of photogenerated electrons on the semiconductor-microorganism interface. The active aromatic protein metabolism and the upregulated related enzymes further demonstrated the synergistic effect of photocatalysis and microbial communities on the membrane fouling mitigation. This work provides a novel application of photocatalysis into antibiofouling effect in MBRs, and opens a strategy for bacteria inactivation and foulants removal with eco-friendly solar energy.

Unveiling the role of cake layer in coagulation-ultrafiltration on membrane fouling and emerging application as dynamic membrane before ultrafiltration

Cake layer is considered to play a crucial role in membrane fouling during the coagulation-ultrafiltration process. However, the contribution of the cake layer on membrane fouling and probable natural organic matter (NOM) removal in this process is unclear, leading to a limited understanding of cake layer and potential secondary utilization. Here, ultrafiltration (UF) membrane fouling contribution, NOM removal, and dynamic membrane application of the cake layer were investigated. Results showed reversible fouling was dominated by cake layer, whereas irreversible fouling was determined by both cake layer and residual NOM in coagulation effluent. Compared with direct UF, the cake layer improved approximately by 15 % of HA removal with molecular weight (MW) of 2000–4000 Da. By optimizing membrane material, HA removal and membrane fouling alleviation were synchronously achieved by cake layer deposition-UF. According to mechanisms analysis, HA removal was attributed to the adsorption or interception of HA with larger MW by the cake layer. Zeta potential and fractal dimension of flocs, and contact angle of the cake layer were closely related to HA removal by cake layer, whereas reversible and irreversible fouling were positively correlated with cake layer thickness and floc fractal dimension respectively. Compared with other dynamic membranes, the cake layer had the best economic performance, which provided application potential on NOM removal in micro-polluted surface water.

Investigating effective strategies for sustainable operation of a submerged anaerobic membrane bioreactor (SAnMBR) coupled with ceramic ultrafiltration membrane

This study presents a mechanistic approach to explore the key operational parameters governing the flux performance of an SAnMBR system coupled with a ceramic flat-sheet ultrafiltration membrane. Experiments were conducted at mixed liquor suspended solid (MLSS) concentrations of 12, 18, and 24 g/L using biogas sparging, backwashing, and a combination of both to investigate the most effective fouling mitigation strategy by exploring the fouling mechanism at a critical flux regime. To validate the experimental findings, a mathematical model was used to simulate the time-based variation of membrane effective pore radius (m), decrease in membrane porosity (%), thickness of cake layer (m), and membrane resistance (1/m). The study found that at a low biomass concentration, there was a sharp decline in the membrane pore radius leading to an increase in membrane resistance in the absence of any fouling mitigation strategies. However, by implementing these strategies individually and in combination, they maintained a higher pore radius and controlled the increase in membrane resistance even at high biomass concentrations. It was observed that biogas sparging outperformed the conventional backwashing strategy and the SAnMBR system exhibited superior performance attaining higher flux rates for prolonged duration. The advanced spectroscopic analysis confirmed the presence of a higher concentration of polysaccharides responsible for cake layer biofouling, and significant pore blocking due to inorganic foulants at high biomass concentrations. This suggests that the SAnMBR system must be operated at optimised biomass levels below the critical flux for sustained operation. Additionally, the key operational parameters identified using the mathematical model provide a precise assessment of SAnMBR performance, to improve its design efficiency for field applications.

Presence of iron oxide particles can reduce the cake fouling in UF systems

Ultrafiltration (UF) has been widely used in drinking water treatment. However, the deposition of iron oxide particles on the membrane surface facilitates the formation of cake layers, which limits the application of UF in iron-bearing water treatment. To understand the impact of iron oxides on the membrane fouling of UF, the effects of iron oxide particles on the bio-regulated cake layer and conventional cake layer formed at the flux of 5 and 20 L·m−2·h−1 were investigated, and compared with SiO2 particles. Unlike the SiO2 paticles which tends to increase the cake fouling resistance, iron oxide paticles could significantly reduce the cake fouling resistance. The iron oxide-UF could reduce specific resistance by 65 %～75 % in bio-regulated cake layer and 40%～50% in conventional cake layer. OCT observations revealed that in the presence of iron oxide, the thickness of the conventional cake layer increased significantly, while the thickness of the bio-regulated cake layer remains unchanged. Therefore, the increased resistance was primarily attributed to the formation of a porous cake layer, which could be evidenced by SEM images. Besides, in the presence of iron oxide, the content of polysaccharides and proteins in the cake layer decreased. Particularly, for the bio-regulated cake layer, the content of polysaccharides and proteins decreased by 80.0% and 59.9%, respectively. This may be attributed to the capability of iron oxide to mitigate microbial-induced fouling and selectively adsorb macromolecular organic matters. Consequently, iron oxide exhibits distinct properties compared to traditional particles in mitigating cake fouling. Retaining some iron oxide before UF could facilitate the mitigation of membrane fouling in iron-bearing water treatment

An Experimental on Filtration and Clogging of Geotextile Filters around Drain Pipes in Fine Tailings

Needle-punched nonwoven geotextiles have been used as filters for decades in mine drainage systems. But the physical clogging of geotextiles by fine particles has continued to receive increasing attention. In this study, the permeation characteristics of a drain pipe wrapped with geotextiles were investigated based on a new radial flow experiment apparatus, and particle size distribution (PSD), pore water pressure (PWP), and scanning electron microscopy (SEM) analyses were employed to identify the geotextile clogging mechanism. The geotextile cleaning methods after clogging were also discussed. The results showed that an exponential decay of hydraulic conductivity (K) with time under different flow conditions. Particles less than 30 μm migrated to the drainage pipe under the action of seepage forces, and a dense and thick cake layer was formed upstream of the geotextile filter. According to microscopic analysis, the clogging process of geotextiles was divided into three stages: pore blockage and cake formation, filter cake dynamic growth and cake layer filtration. Backwash cleaning is a good way to remove a filter cake layer on the surface of geotextiles, which can recover 60% of the hydraulic conductivity (K0).

Flux decline in crossflow ultrafiltration-based diafiltration process for lignin recovery from a deep eutectic solvent comprised of lactic acid and choline chloride

This study investigates a continuous ultrafiltration (UF)-based diafiltration (DF) method to separate and purify lignin from a deep eutectic solvent (DES) containing lactic acid and choline chloride after biomass delignification. A crossflow setup with a polyether sulfone UF membrane with a molecular weight cut off of 5000 Da was used to evaluate flux decline and fouling in this process. Under different pressure, feed flowrate, lignin, and DES concentrations, lignin rejection is around 0.90. Higher lignin and DES concentrations increase filtration resistance, and thus decrease flux at constant pressure. On the basis of a previously setup model based on dead-end filtration, a modeling approach was further developed to predict the system size required to implement UF-DF on a large scale. The results shows that at a constant pressure, the membrane system's area increases as the cake layer thickness over the membrane's surface increases.

Crossflow-induced membrane vibration and its effects on fouling and scaling in direct contact membrane distillation

Membrane distillation (MD) is driven by vapor pressures rather than hydraulic pressures. Consequently, certain regions of the membrane may be in an unrestrained state, which potentially lead to membrane vibrations due to the turbulence caused by crossflow. However, this crossflow-induced membrane vibration has been largely overlooked in the previous studies. Here, we made the first attempt to investigate the crossflow-induced membrane vibration through the observation using optical coherence tomography (OCT), and explore the effect of this vibration on membrane fouling and scaling. The experimental results revealed that the vibration exhibited a self-excited vibration mode, with amplitudes reaching tens of micrometers. Moreover, the amplitude could be readily adjusted through changing crossflow velocity, transmembrane pressure, and the mesh size of spacer. For humic acid (HA) fouling, the membrane vibration could effectively reduce the thickness of HA cake layer, thereby stabilizing the specific flux at a constant level of 0.85, in contrast to the continuous decline of the flux under non-vibration condition. For gypsum scaling, the membrane vibration allowed the MD under low crossflow velocity (5 cm/s) to achieve comparable scaling occurrence concentration and scaling layer thickness as those under high crossflow velocity (10 cm/s). Our findings emphasized the potential of crossflow-induced membrane vibration as an effective strategy to mitigate membrane fouling and scaling in MD and other non-pressure driven membrane systems.

Membrane clarification of pomegranate and carrot juices using scraped surface membrane unit, a comparative study

The membrane processes are used for clarification of fruit juices, but fouling is a limiting phenomenon. The blade rotation in scraped surface membrane unit can increase flow turbulence and thus reduce fouling phenomenon. This unit was used to clarify the carrot juice (which has a cloudy texture) and pomegranate juice (which has a non-cloudy texture) to compare the effect of juice texture on the efficiency of process. The process was performed at three transmembrane pressures (1, 1.5 and 2 bar), three feed flow rates (5, 10 and 15 ml/s) and three blade rotation speeds (0, 147.5 and 222.5 RPM) and changes in permeate flux and volume concentration factor (VCF) and fouling mechanism were studied. The results showed that the rotation of the blade, especially at 222.5 RPM, increased the permeate flux and VCF during clarification of both juices. Also, reduction of feed flow rate increases the effectiveness of blade rotation during membrane clarification of juices. Comparison between two juices showed that the increase in permeate flux and VCF after blade rotation for pomegranate juice was higher than the increase value for carrot juice, especially in the early stages of the process. But, decreasing the transmembrane pressure makes the effect of blade rotation on carrot juice that has a cloudy texture more than pomegranate juice that has a non-cloudy texture, especially when the blade rotation speed is low. The cake formation is the main fouling mechanism in the most tests and SEM images confirm that blade rotation has a significant effect on reduction of cake layer thickness.

Microfiltration of concentrated albumin solutions and the role of processing conditions on membrane fouling

Membrane processing is a subject of growing scientific and industrial interest as a valuable technology to replace conventional energy-intensive operations, but is hindered by the progressive decrease of permeate flux caused by membrane fouling. Although physico-chemical factors affecting membrane fouling have been widely investigated, less is known concerning the effects of processing conditions. Here, we focus on microfiltration of aqueous bovine serum albumin (BSA) solutions by using a novel miniaturized modular unit allowing to study both dead-end (DE) and crossflow (CF) filtration. Pure water flux measurements and Computational Fluid Dynamics (CFD) simulations were firstly performed to characterize the flow field inside the module. In presence of BSA, at the same transmembrane pressure (TMP) of 20 mbar and average pore size of 0.45 μm, a remarkable decrease in the fouling progression with time was found for CF with a peristaltic pump as compared to pressure-driven DE filtration. Furthermore, BSA concentration in the permeate was the same as in the feed for peristaltic CF, while negligible for DE. By either increasing transmembrane pressure or lowering membrane pore size, a stronger decay of permeate flux with time was observed. Scanning electron microscopy images of the membrane showed the presence of a thick surface cake layer under peristaltic CF, which became thinner by increasing TMP or reducing membrane pore size. Overall, the better performance of peristaltic CF can be interpreted in terms of reduced BSA residence time in the membrane, membrane deformability and formation of a permeable cake layer at lower TMP and larger membrane pore size. The innovative design of our filtration module and the combination of permeate flux and concentration measurements with CFD results and microscopy observations constitute the most significant aspects of this research work, which provides a multiscale picture of membrane fouling. The insight emerging from results aims to provide qualitative guidelines towards an optimal setting of processing conditions in membrane operations, which is highly needed to improve the membrane innovation pipeline.

Pressure drop model of DPF considering ash factor at different capture stages

In this paper, a pressure drop model of diesel particulate filter (DPF) is established on diesel bench loading tests and simulation studies. A proposed DPF soot loading prediction model takes into account the different factors and calculation methods of pressure drop formation in different capture stages, including deep bed capture stage, transitional capture stage and soot cake capture stage. Further, a pressure drop model of DPF is improved, and the model for different filter wall permeability in different capture stages is discussed. The calculated results of the model are verified with the experimental results. Finally, the influence of ash factor on the modification of DPF pressure drop model was investigated.The results show that, when the ash layer is 0.05 mm–0.15 mm in the deep bed capture stage, the modified values of filtration wall permeability are 8.2%–43.8% of the original values. In the transitional capture stage, the ash layer with thickness of 0.01 mm–0.05 mm needs to modify 0.75 g/L∼1.5 g/L soot loading. The DPF pressure drop and the particle soot cake layer thickness increase linearly with time in the soot cake capture stage. When the ash layer changes in the range of 0.05 mm–0.15 mm, the soot loading is modified to 13.4%–36.8% of the original value. When the axial scale of the ash plug is 1/5,1/4 and 1/3 of the DPF length, the soot loading is corrected to 33.3%, 37.3% and 45.1%.

Modification of Thin Film Composite Membrane by Chitosan-Silver Particles to Improve Desalination and Anti-Biofouling Performance.

Reverse osmosis (RO) desalination is a technology that is commonly used to mitigate water scarcity problems; one of its disadvantages is the bio-fouling of the membranes used, which reduces its performance. In order to minimize this problem, this study prepared modified thin film composite (TFC) membranes by the incorporation of chitosan–silver particles (CS–Ag) of different molecular weights, and evaluated them in terms of their anti-biofouling and desalination performances. The CS–Ag were obtained using ionotropic gelation, and were characterized by Fourier transform infrared spectroscopy (FTIR), high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and dynamic light scattering (DLS). The modified membranes were synthetized by the incorporation of the CS–Ag using the interfacial polymerization method. The membranes (MCS–Ag) were characterized by Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and contact angle. Bactericidal tests by total cell count were performed using Bacillus halotolerans MCC1, and anti-adhesion properties were confirmed through biofilm cake layer thickness and total organic carbon (%). The desalination performance was defined by permeate flux, hydraulic resistance, salt rejection and salt permeance by using 2000 and 5000 mg L−1 of NaCl. The MCS–Ag-L presented superior permeate flux and salt rejection (63.3% and 1% higher, respectively), as well as higher bactericidal properties (76% less in total cell count) and anti-adhesion capacity (biofilm thickness layer 60% and total organic carbon 75% less, compared with the unmodified membrane). The highest hydraulic resistance value was for MCS–Ag-M. In conclusion, the molecular weight of CS–Ag significantly influences the desalination and the antimicrobial performances of the membranes; as the molecular weight decreases, the membranes’ performances increase. This study shows a possible alternative for increasing membrane useful life in the desalination process.

Influence of two phase flow on cake layer resistance and flux enhancement in spiral wound and submerged flat sheet microfiltration membrane modules

<p>Gas sparging has emerged as an effective technique for control of particle fouling in different microfiltration membrane processes. However most of the research work carried out has been pertinent to hollow fiber and tubular membrane geometries. A little attention has been paid to evaluate the potentails of gas-liquid two-phase for control of particle fouling in spiral wound and submerged flat sheet microfiltration membranes. This study focuses on control of particle fopuling by gas sparging in open channel spiral wound and submerged flat sheet microfiltration membranes. Commercial yeast was used as test suspension. The Effect of gas sparging on membrane fouling and permeate flux was studied by analysing the cake layer characteristics like cake mass deposition, cake layer thickness and cake porosity. The filtration flux and cake properties under various operating conditions, such as cross-flow velocity, filtration pressure, particle concentration, and sparging intensity are analyzed based on hydrodynamics. The results of this study show that gas sparging is very effective in control of particle fouling for both membrane module geometries. It was found that gas bubbling reduced the deposition of particles on the membrane surface due to which cake layer thickness decreases and resultantly permeate flux increased substantially. The permeate flux increased with increase in gas sparging intensity. A maximum flux enhancement of 170 % and 284 % were observed for spiral wound and flat sheet membranes respectively when gas sparging was applied to the process.</p>

Spatial evolution of membrane fouling along a multi-stage integrated membrane system: A pilot study for steel industry brine recycling

The establishment of a multi-stage membrane system that integrates different membrane technologies has been regarded as an essential process in industry brine recycling. Although membrane fouling has been intensively studied, in particular, on single membrane unit at the lab-scale, the actual fouling behavior in multi-stage integrated pilot systems has not yet been fully understood. In this study, membrane fouling was systematically investigated in a pilot-scale RO-NF process by monitoring the surface properties of fouling layer and the deposition behavior of foulants. Distinct spatial fouling variation along the flow direction of the multi-stage integrated system was observed. At the first stage of the RO process, severe fouling occurred on the membrane surface under the synergistic interaction of several organic and inorganic foulants, resulting in a rough and thick cake layer. The membrane fouling at the second RO stage became less severe. During the following NF process, the amounts of metal oxides/hydroxides and organic foulants depositing on the membrane surface decreased. The results indicated that the foulants firstly deposited on the front stage of the integrated RO-NF process. Overall, the observations for spatially varied membrane fouling help to advance understanding of membrane technologies to achieve zero liquid discharge in the steel industry.

Modeling of forward osmosis for microalgae harvesting

In this study, a transport-based model capable of predicting water flux in microalgae harvesting in forward osmosis (FO) system was developed. Based on Carman-Kozeny resistance model, steady state hydraulic resistance of cake layer comprised of microalgae cells was calculated; by means of control volume approach growth rate of the cake layer was also quantitatively obtained at transient state. Cake-enhanced concentration polarization (CECP), which arises from cells, along with dissolved compounds, deposited on membrane surface and acts to degrade FO performance, was estimated in real time. Model parameters related to a feed solution of microalgae cells were evaluated on the basis of empirical and theoretical data. It was found that deposition rate constant of microalgal cells was at least two orders of magnitude higher than diffusion rate constant under the experimental condition. Among microalgae related parameters, the porosity and thickness of cake layer were found to be the most influential on the water flux according to sensitivity analysis; and therefore they were calibrated by a statistical technique to improve model accuracy. Based on the estimated parameters, the developed model was validated through batch FO operations, and it was in good alignment with quasi-steady state data. There have been quite a few FO modeling studies thus far; and yet to the best of our knowledge, this study is the first one that elucidates actual fouling phenomenon with an actual feed solution, which may offer both theoretical and practical understandings needed for the development of FO-based microalgae harvesting process.

Real-time membrane fouling analysis for the assessment of reclamation potential of textile wastewater processed by membrane distillation

Understanding the factors that specify the fouling development in membrane distillation (MD) plays a key role to develop effective control strategies with the aim of providing its widespread use in industrial applications, such as textile industry. The present study investigated the fouling mechanisms in textile wastewater treatment by direct contact MD (DCMD), employing an advanced in-situ optical coherence tomography (OCT) technology allowing to monitor MD fouling in real-time. The OCT analysis enabled evaluating the effect of feed temperature, flow rate, dye concentration on the membrane fouling and the long-term performance of MD operation that includes a periodical water flushing. The permeate flux decrease during the initial stages of experiments was attributed to the existence of attractive hydrophobic-hydrophobic interaction between the membrane and dye molecules as no cake fouling was observed at the early stages. Then, a flat and homogeneous cake layer was developed with time in all the fouled membranes regardless of the cake layer thickness. The long-term experiment resulted in both reversible and irreversible fouling and showed that water flushing had limited efficacy against reversible fouling. Additionally, electrostatic repulsive forces occurring between the membrane and textile dye molecules influenced the permeate flux depending on the dye concentration. Finally, among all the operating parameters, feed temperature had the highest impact on the membrane fouling and process performance, changed the heat transfer activity at the membrane-liquid frontier zone, in turn, leading to variations in the flux.

Membrane fouling performance of Fe-based coagulation-ultrafiltration process: Effect of sedimentation time

Pre-coagulation is commonly used with ultrafiltration (UF) to alleviate the membrane fouling. Compared to conventional coagulation-sedimentation-UF (CSUF) processes, the direct coagulation-UF (CUF) processes are widely believed to perform better due to the formation of a looser cake layer. It is however shown in this study that not only the density of a cake layer, but also its thickness as well, can affect the membrane fouling behavior, which therefore are influenced by both the sedimentation time and flocs characteristics. Herein, the membrane fouling performance of Fe-based coagulation-UF process was systematically investigated with different sedimentation times. A critical threshold of 30 min was observed at the lab-scale: if shorter than that, the membrane fouling depended mainly on the cake layer density, and thus CUF outperformed CSUF; but when the sedimentation time was over 30 min, the cake layer thickness turned to be the dominant factor, thereby resulting in CSUF performing better. Furthermore, it was shown that the critical sedimentation time was decided by flocs characteristics. A lower water temperature induced the formation of irregular flocs with a lower fractal dimension, and the corresponding cake layer exhibited an almost identical density with increasing sedimentation time. In this regard, CSUF processes were constantly superior to CUF as the cake layer thickness decreased. On the other hand, a critical sedimentation time reappeared because of the higher floc fractal dimension under acidic conditions. This work showed for the first time that the membrane fouling of CSUF was up to the sedimentation time, and it was possible to outperform CUF if the sedimentation time exceeded a critical threshold. Such a finding is crucial to the future development of coagulation integrated UF processes.

Performance and foulants characterization of the industrial integrated membrane system

In order to objectively elucidate the state of the membrane after long-term operation, the performance of a full-scale microfiltration-reverse osmosis (MF-RO) integrated membrane system with production capacity of 20,000 m3/d for wastewater reclamation was evaluated by collecting 10 years performance data. The foulants on 1 MF membrane and 12 RO membranes along the feed channel also were analyzed by membrane autopsy. The results indicate that the water quality of the system can still meet the customer requirements while the mechanical and desalting properties of the membranes were close to the abandoned standards. In terms of foulants distribution, the MF membrane surface was covered by a thick cake layer and the leading RO membrane suffered the highest fouling load. The predominate organic foulants on the membrane surface were protein and polysaccharide, and the main inorganic foulants were Fe and Ca, and their distribution showed two different trends along the feed channel. Regarding bio-foulants, the compositions of bacterial colonies on 12 RO membranes were basically the same, but the relative abundance of the dominant bacteria was different and the microbial diversity increased gradually from the leading element to the terminal one in both the two stages.

Dynamic regulation of Al-based floc cake layers by spiral rotation during ultrafiltration in drinking water treatment

Integrated ultrafiltration (UF) membrane-based processes are promising drinking water treatment technologies. However, the membrane module always remains static, resulting in membrane fouling through the gradual formation of a thick cake layer. As floc-based cake layers are loose, in the present study, a membrane module spiral rotation was introduced with the aim of regulating the cake layers. The cake layer thickness readily decreased and the UF membrane fouling was alleviated. The results showed that Al-based flocs were not easily removed from the membrane surface during rotation due to its low density; as a result, the likelihood of humic acid (HA) reaching the membrane surface was low. Computational fluid dynamics indicated that a strong shearing force was generated with high rotation height. Thus, the cake layer thickness was easily regulated, and the UF membrane fouling was further alleviated. However, the floc-based cake layer could be broken by strong shearing forces, thereby allowing HA molecules to directly reach the membrane surface and further aggravating membrane fouling. In comparison to alkaline condition, the UF membrane performed better under acidic conditions, particularly in terms of HA removal, due to the smaller floc size and higher positive charge. Additionally, excellent UF membrane performance was also observed when treating raw water, indicating the potential application.

A Role of NO <sub>2</sub> on Soot Oxidation in DPFs and Effect of Soot Cake Thickness in Catalyzed DPFs Using Temperature-Programmed Oxidation and Electron Microscopic Visualization

<div class="section abstract"><div class="htmlview paragraph">Development of the diesel particulate filter (DPF) aims to attain fast oxidation of accumulated soot at low temperature. Numerous researchers have explored the characteristics of soot oxidation under ambient conditions of simulated exhaust gas using thermogravimetric analysis or a flow reactor. In this study, temperature programmed oxidation (TPO) experiments were carried out for soot entrapped in miniaturized DPFs, cut-out from practical particulate filters, yielding wall-flow features typically encountered in real-world DPFs. Furthermore, when using the miniaturized samples, highly accurate lab-scale measurements and investigations can be facilitated. Examining different temperature ramping rates used for the TPO experiments, we propose a rate of 10°C/min as the most effective in analyzing soot oxidation in the practical filter substrates. Then, wash-coated catalyzed filters (CDPFs) were benchmarked with bare-type DPFs to clarify their effects on soot oxidation in a practical wall-flow system. According to the Arrhenius expression, differences in soot cake thickness in CDPFs reflect various values of estimated activation energy. This is due to the soot-catalyst proximity. With presence of 450 ppm nitrogen dioxide (NO<sub>2</sub>) in a reactant gas mixture, the soot oxidation range was extent to a lower temperature. Moreover, a reduction in the estimated activation energy was achieved, even in the case of using bare-type DPFs. The thick soot cake layers in bare-type DPF result in a significant amount of soot mass remaining after treatment at 600°C, a typical active regeneration temperature. Subsequently, soot residuals were traced and characterized after a complete active regeneration process. For these reasons, thickness of a soot cake layer was proposed to be a new factor to define an updated regeneration strategy.</div></div>

A simple reaction-diffusion model for initial stages of biofouling in reverse osmosis membranes

Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes and consequently increases operational and maintenance costs. It is difficult to control this operational challenge, so the development of effective biofouling monitoring and control methods and strategies is a critical issue for membrane technology and applications. In this work, we develop a simulation approach for evaluating the operational time of reverse osmosis (RO) membranes based on a reaction-diffusion (RD) type of model. This approach would help to understand different factors involved in the formation of biofilms including microbial population dynamics (replication and death rates of microbial cells) and nutrient consumption. The model is focused on the initial stages of the membrane biofouling that is initiated by attachment of microbial species to the membrane leading to pore blocking followed by the formation of thick cake layer. We applied this approach to study the RO membrane biofouling by Picochlorum algae, the most common biofouling agent in the seawater of the Arabian Gulf, at known contents of total organic carbon and essential nutrients. We found that the biofilm growth dynamics on an RO membrane is mainly defined by the ratio of the replication and death rates of microbial cells. The proposed approach should be useful for fast evaluation of the RO membrane performance in different environmental conditions without using significant computational resources. This methodology allows generalization for multi-microbial and multi-nutrient systems. The establishment of effective fouling control strategies should decrease operational and maintenance costs of RO membrane systems.