Intermediate Blocking Model Research Articles

The pre-coated photocatalytic ceramic membrane with Bi2O3–TiO2/powdered activated carbon nanoparticles to alleviate ultrafiltration fouling caused by intracellular organic matter of Microcystis aeruginosa

Algal intracellular organic matter (IOM), released during algae's normal growth phase and water treatment processes, has long been a source of significant membrane fouling, considerably limiting the effective use of ultrafiltration(UF) technology. In this study, a Bi-doped TiO2 composite with powdered activated carbon (Bi2O3–TiO2/PAC) was loaded on ceramic UF membranes by vacuum filtration, and the prepared photocatalytic modified ceramic membranes (MCMs) were investigated for the removal of IOM and the mitigation of membrane fouling at different loading levels and under three operating conditions: Dark, Dark-UV, and UV. The results showed that the photocatalytic MCMs were able to remove the protein and humic acid fluorescent components of IOM and decompose or mineralize organic matter with molecular weights of 10–50 kDa. Under the Dark, Dark-UV, and UV conditions, the final normalized flux of MCM-2.88 was significantly increased by 22.6 %, 82.1 %, and 108.0 %, respectively. The hydrophilicity of MCMs not only transformed the interactions between IOM and the membrane into repulsive forces, but also the composite material on the membrane surface transforms the membrane fouling mechanism from intermediate blocking model to cake layer formation. Furthermore, the application of photocatalytic oxidation under the Dark-UV and UV conditions yielded a reduction in both reversible and irreversible fouling. This action led to an increased hydrophilicity and elevated free energy of adhesion with IOM during the filtration process. Moreover, the main fouling mechanism changed into complete or intermediate blocking. These outcomes collectively underscore the capability of MCMs to alleviate membrane fouling induced by IOM. This advancement holds substantial promise for the advancement and widespread implementation of photocatalytic ceramic membrane filtration techniques.

Evaluation and optimization of reverse osmosis pretreatment technology using the modified intermediate blocking model

Membrane fouling is the unavoidable obstruction that occurs during reverse osmosis (RO), the use of pretreatment technology is highly effective for mitigating membrane fouling. In this study, the modified intermediate blocking model was applied to fit the data from literature about RO pretreatment, getting good fitting performance, over 86% of the determination coefficient (R2) exceeding 0.90. The working law of RO pretreatment on model parameters (final permeate flux (Jpss) and fouling velocity (k)) was systematically studied. The result showed that pretreatment works by three pathways: enhancing Jpss and reducing k, reducing both k and Jpss, and increasing both k and Jpss; it exerts more of an effect by improving k rather than Jpss. Furthermore, ultrafiltration exhibits a 10% higher effect on Jpss compared to ozonation while its effect on k is about 20% better than that of ozonation. Additionally, ultrafiltration demonstrates greater stability than ozonation. We further analyzed and found that the improvement in Jpss or k does mitigate membrane fouling, however, it does not necessarily produce more volume of clean water than without pretreatment. With the aim of obtaining more volume of permeate water, a new model, the Normalized Total Permeate Water Volume (VN) model is proposed, which enables pretreatment efficiency comparable and has been applied to optimize the application of pretreatment, achieving great application results.

Synthesis and Characterisation of Self-Cleaning TiO2/PES Mixed Matrix Membranes in the Removal of Humic Acid.

Membrane application is widespread in water filtration to remove natural organic matter (NOM), especially humic acid. However, there is a significant concern in membrane filtration, which is fouling, which will cause a reduction in the membrane life span, a high energy requirement, and a loss in product quality. Therefore, the effect of a TiO2/PES mixed matrix membrane on different concentrations of TiO2 photocatalyst and different durations of UV irradiation was studied in removing humic acid to determine the anti-fouling and self-cleaning effects. The TiO2 photocatalyst and TiO2/PES mixed matrix membrane synthesised were characterised using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), contact angle, and porosity. The performances of TiO2/PES membranes of 0 wt.%, 1 wt.%, 3 wt.%, and 5 wt.% were evaluated via a cross-flow filtration system regarding anti-fouling and self-cleaning effects. After that, all the membranes were irradiated under UV for either 2, 10, or 20 min. A TiO2/PES mixed matrix membrane of 3 wt.% was proved to have the best anti-fouling and self-cleaning effect with improved hydrophilicity. The optimum duration for UV irradiation of the TiO2/PES mixed matrix membrane was 20 min. Furthermore, the fouling behaviour of mixed matrix membranes was fitted to the intermediate blocking model. Adding TiO2 photocatalyst into the PES membrane enhanced the anti-fouling and self-cleaning properties.

Comparative mathematical and data-driven models for simulating the performance of forward osmosis membrane under different draw solutions

Mathematical models have frequently been used to simulate system performance, including forward osmosis (FO)-related processes. More recently, Industry 4.0 has increased in importance, and artificial intelligence (AI) technology has proven to be effective at assisting decision-making across a range of industries, including membrane processes. This study, for the first time, proposes a comparison of the accuracy of predictions for water permeability under various types of draw solutions using conventional models and AI-based models. The results showed that the AI-based models, including artificial neural networks (NN) (2 layers; 10 neurons) and adaptive neuro-fuzzy inference system (NFIS) (with grid partition; membership functions = 5) performed significantly better than the conventional mathematical intermediate blocking (CIB) model, with the coefficient values (R) of 0.974, 0.994, and 0.963, respectively. The corresponding errors of these simulations were 0.04, 0.70, and 0.97 LMH, indicating that the AI technique was better suited than the mathematical CIB model for simulating FO-related system performance. Additionally, using AI to forecast system performance is timely (i.e., considerably quicker than developing a sophisticated mathematical model) and cost-effective (i.e., reducing the expense for analysis of environmental factors for CIB model construction). The authors also successfully constructed an application for end-users for better and simpler experiences with modeling and simulation, even for those with varying knowledge in the field.

Efficient selective methylene blue adsorption by polyurethane/montmorillonite‐based antifouling electrospun composite membranes

AbstractA robust antifouling membrane with pollutant‐removing capacity is in high demand for industrial wastewater treatment. Here, we report a new multifunctional polyurethane/montmorillonite‐oxidized multi‐walled carbon nanotube (PU/MMT) nanofibrous composite membrane, beneficial for both water filtration and selective methylene blue adsorption. It was observed that oxidized multi‐walled carbon nanotube (o‐MWCNT) imparted high flexibility with a high percentage elongation (318%–405%) to the composites, whereas montmorillonite (Mt) improved the hydrophilicity, antifouling property, and dye adsorption capacity of the fibrous PU membrane. The sample with 20 wt% Mt (PU/20‐MMT) showed a minimum water contact angle of 57°. It showed a high water flux, oil rejection, and flux recovery ratio compared to the pristine electrospun PU membrane. The Hermia fouling mechanism suggested that electrospun PU obeyed an intermediate blocking model, whereas PU/20‐MMT was best fitted with a cake formation model. During adsorption, the cationic dye methylene blue (MB) was selectively adsorbed on the sample from a methyl orange/methylene blue (MO/MB) mixture. It showed a maximum adsorption capacity (qm) of 112.35 mg/g. The anionic dye methyl orange, on the other hand, remained unadsorbed. The adsorption kinetics and the adsorption isotherm were pseudo‐second‐order kinetics and the Langmuir adsorption isotherm, respectively. The developed, robust electrospun composite membrane opens a new avenue for the selective adsorption of MB from dye mixtures and contaminated water.

Effects of chlorine disinfection on RO membrane biofouling at low feed water temperature for wastewater reclamation

Abstract Chlorine disinfection has been reported to be ineffective in controlling RO membrane biofouling in some projects. Feed water temperature is a crucial factor in the formation of RO membrane biofouling. It has a positive impact on the wide application of the RO process to ascertain whether chlorine disinfection can alleviate the membrane biofouling at low temperatures. In this study, the effects of chlorination on the RO membrane biofouling at low feed water temperature (10 °C) were investigated by a lab-scale RO apparatus. The final normalized flux was 0.33 and 0.29 with and without chlorination, respectively. According to the normalized flux decline curve, chlorination could not alleviate the RO membrane fouling at low temperature. Based on the intermediate blocking model, chlorination increased the membrane fouling potential of the feed water. At low temperature, the biofilm on the membrane with chlorination was thinner and denser than that without chlorination. In addition, the membrane with chlorination contained more foulants and dissolved organic matter than that without chlorination. Chlorination failed to continuously prevent bacteria accumulation on RO membrane at low temperature, but screened out bacteria that were potentially more suitable for the low-temperature membrane environment.

Biofouling initiation on a microfiltration membrane related to deposition and adhesion of bacteria from the perspective of interface interactions

Inhibition of bacteria deposition and adhesion is an effective strategy to control biofouling in membrane applications. In this study, the deposition and adhesion characteristics of individual bacteria (Pseudomonas aeruginosa) on a polyvinylidene fluoride microfiltration membrane were systematically investigated from the perspective of interface interactions. Preliminary results demonstrated that the deposition process was compatible with and dominated by the intermediate blocking model and cake filtration model However, the adhesion process analyzed by thermodynamic analysis revealed that bacteria should, in theory, not adhere to the virgin membrane, which was inconsistent with the experimental results. Further experiments and theoretical analysis suggested that organic matter in feed water, bovine serum albumin (BSA), or sodium alginate (SA) increased the adhesion capacity of the membrane by changing the properties of the membrane, and the thermodynamic relationship resulted in a reduction in the total interface interaction energy, Lewis acid–base component, and repulsive force. Therefore, biofouling can be controlled by reducing BSA-like or SA-like organics and inhibiting protein secretion by bacteria. This study furthers the understanding of the bacterial attachment process, and provides new insights into the adhesion mechanism from the perspective of interface interactions and thermodynamic analysis.

Comparison of the formation, filtration performance, and structural characteristic of self-forming dynamic membranes under constant transmembrane pressure and constant filtration flux

The formation and filtration of self-forming dynamic membranes (SFDMs) can be affected by multiple factors, such as the operating conditions and sludge properties in membrane bioreactors. There has been limited research on the effects of the constant transmembrane pressure and constant filtration flux on the stable filtration of dynamic membranes. In the present study, a large-pore stainless steel mesh (70 µm pore size) was used as the support material for dynamic membrane formation to explore the formation, filtration performance, and structural characteristics of two dynamic membranes, P-SFDM (filtration under constant transmembrane pressure) and J-SFDM (filtration under constant flux), with the same initial filtration flux. The results showed that the stable filtration period of J-SFDM went up to 22.5 h, which was significantly longer than that of P-SFDM (5.5 h) with a higher resistance growth speed. The blocking process of the P-SFDM membrane conformed to the complete blocking model, whereas that of the J-SFDM membrane conformed to the standard blocking model in the initial stage and follows the intermediate blocking model in the later stage. Besides, the P-SFDM cake layer had a higher extracellular polymer content and smaller particle size (106 ± 2 mg·g−1 VSS, 546 ± 63 µm) than that of the J-SFDM cake layer (89 ± 3 mg·g−1 VSS, 615 ± 51 µm). During a 39-day continuous long-term operation, the energy consumptions per ton of water for J-SFDM and P-SFDM were 0.14 kw·h·t−1 and 0.19 kw·h·t−1, respectively. The above results show that the J-SFDM has a longer stable filtration period with lower energy consumption per ton of water.

Comparison of the reverse osmosis membrane fouling behaviors of different types of water samples by modeling the flux change over time

Fouling of RO membranes has long been a complex but inevitable problem in wastewater reclamation. In this study, a modified intermediate blocking model with two parameters was applied to describe the flux change of RO membranes treating various water samples, including municipal secondary effluent, treated industrial wastewater, surface water, and groundwater. The model was validated by 55 sets of data reported by 13 articles, and the results were promising, with 90% of the determination coefficient (R2) exceeding 0.90. Relatively large flux and high operational pressure were found likely to aggravate membrane fouling. Treated industrial wastewater had the highest fouling potential (fouling constant k: 0.061–2.433) compared to municipal wastewater secondary effluent, surface water, and groundwater, even with similar dissolved organic carbon concentration. With industrial wastewater excluded, water samples exhibited lower fouling potential than organic matter solutions, with the majority (25%∼75%) of k distributing in 0.03–0.12, much lower compared to the major k range of the latter (0.05–0.28). This suggested a deviation in fouling behaviors between model organic matters and real water samples. Xanthan gum and guar gum were proposed to be model polysaccharides based on their model parameters, which were relatively close to real water samples.

Development of a novel model by combining the intermediate blocking and cake filtration models for assessment of the prevailing fouling mechanism in a microbial fuel cell-facilitated membrane bioreactor

This study was carried out on a membrane bioreactor (MBR) facilitated with an electric field provided by a microbial fuel cell (MFC), which effectively reduced membrane contamination and extended the operation time of the MBR from 18 to 24 days. To understand the theory of membrane fouling in the MFC-MBR, a novel model based on the operation of the MFC-MBR was proposed with the modification of the classical filtration models to assess the membrane fouling. With this model, a two-phase membrane fouling development was observed, which was initially dominated by the intermediate-blocking model and then gradually changed to cake filtration. In the combined model of two-phase development, fouling was significantly mitigated by the electric field in phase 1, but its function was barely observed in phase 2. The combined model fit well with the experimental data, which could predict membrane fouling in the application of the MFC-MBR.

Effect of membrane blocking on attached cultivation of microalgae

Membrane blocking is of great importance to nutrients transfer and illumination in attached cultivation of algae, which subsequently affects the biomass and nutrients production of algal biofilm. Accordingly, a vertical-algal-biofilm (VAB) with cellulose acetate (CA) membranes with pore size of 0.45, 1.2, 2.0, and 3.0 μm is settled to study the effect of membrane blocking on attached cultivation of microalgae. According to the results, the algae production is independent of the roughness, hydrophilicity, and surface free energy of membranes because the VAB is inoculated via filtration-on method in this work. Nevertheless, the algae productivity of first-cultivation on VABs increases to 5.02 g/m2. day when the pore size of CA membrane increases to1.2 μm, while it decreases to 4.5 g/m2. day on VABs with CA-3.0 due to the complete blocking of CA membranes by algae cells. The growth rates of first-cultivation and re-cultivation are well fitted by a logistic model and a linear model, respectively. The total lipids contents of microalgae on different CA membranes are affected by pore size due to the variations of nutrients transfer resistance and light intensity under different membrane blocking models. A maximum total lipids content of algae biomass cultivated on VABs with CA-1.2 is about 23.74% due to the nitrogen starvation and high illumination intensity under intermediate blocking model. Therefore, the attached cultivation of algae on VABs under intermediate blocking model is much favorable for algal biomass and lipid production.

Membrane fouling in a powdered activated carbon – membrane bioreactor (PAC-MBR) for micro-polluted water purification: Fouling characteristics and the roles of PAC

To identify the characteristics of fouling in the powdered activated carbon – membrane bioreactor (PAC-MBR) for micro-polluted water treatment, a pilot-scale PAC-MBR was continuously operated for 4 months without chemical cleaning. The membrane autopsy suggested that physically recoverable and irrecoverable fouling accounted for 56.6 and 43.4% of the total fouling, respectively, and intermediate blocking model showed the best fitting for fouling evolution. Colloidal matter, which had a large proportion of protein and polysaccharide, was the major contributor to the physically recoverable fouling resistance, while polysaccharide and humic substances were the major contributors to the physically irrecoverable fouling resistance. By comparing the MBRs with and without PAC, it was found that PAC increased fouling rate because it exerted a marginal effect on foulants reduction and membrane scouring, but a synergistic effect on cake layer formation. These fouling characteristics in PAC-MBR were different from those in the MBRs for municipal wastewater treatment, which could be ascribed to the poor-nutrient of the micro-polluted water.

Simulating and predicting the flux change of reverse osmosis membranes over time during wastewater reclamation caused by organic fouling

During the operation of the RO system, it’s significant to predict the flux change over time. Previous research conducted detailed exploration on the dynamics of RO membrane fouling, and provided a solid database for modelling. In this study, a modified intermediate blocking model with two parameters was proposed to describe the flux change of RO membranes under a huge variety of conditions. Raw data reported by over 20 research groups from 11 different countries was used to validate the feasibility of this model. It proved applicable to describe the flux change of RO membranes fouled by pure organic matter or mixture and tertiary treated wastewater. In order to reveal the relationship between model parameters and foulant concentrations, RO membrane fouling behaviors of typical foulants (sodium alginate (SA), bovine serum albumin (BSA) and mixture) were further investigated. We found that the change of model parameters with SA concentrations was in accordance with Langmuir adsorption isotherm model. Therefore, the model parameters could be calculated by SA concentrations under certain optional conditions, and then the flux change could be predicted by this model. In this way, a novel time-course model was established, which could predict the flux change of RO membranes over time only with SA concentrations. Besides, the synergic effect between SA and BSA on RO membrane fouling was directly quantified.

Fouling resistance of 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid zwitterion modified poly (vinylidene fluoride) membranes

Zwitterion polymer modified membranes have demonstrated fouling resistance in wide applications. The ubiquitous success in scientific progress, however, has not yet brought significant breakthrough in the application of such membranes in wastewater treatment. Limitation of zwitterion materials in membrane is seldomly discussed. In this paper, we aimed to bring an engineering view on the pros-and-cons of zwitterion modified microfiltration membrane in treating solutions containing humic acid (HA) and bovine serum albumin (BSA). A 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid (TMAPS) grafted zwitterionic PVDF membrane was selected as a model membrane. The membranes were prepared via a two-step “hydroxylation-grafting” method; surface modified PVDF membrane was transformed from hydrophobic to hydrophilic with significant improvement in pure water flux. An 87% increase was obtained in the stable flux for the grafted membrane when treating HA, but very similar flux pattern to the pristine one was found when treating BSA. The membrane resistance model showed that cake layer was the main fouling factor for both foulants. For HA, the cake layer blocking model predicted the membrane flux well; but for BSA, the intermediate blocking model fits best the experimental results. Zwitterion grafted surface failed to show improvement in the fouling resistance even at very low BSA feed concentration. Adsorption experiment indicated that the interaction of BSA to membrane is significantly stronger than HA and membranes independent from the surface characteristics. Present work clarified the limitation of zwitterion modified membranes in treating solutions containing HA-like and protein matters.

Investigation of the fouling effect on a commercial semi-permeable membrane in the pressure retarded osmosis (PRO) process

Abstract One of the main challenges for generating osmotic power by using PRO technology is the membrane fouling which reduces the permeate flux and consequently increases the cost and decreases the osmotic power generation. In this research, different feed waters with various qualities were used to investigate the effect of fouling on a commercial membrane in PRO mode in continuous conditions. Also, the fouling mechanisms were investigated in order to study the cleaning of the membrane in PRO mode in the future research. In addition, four classic fouling models such as complete blocking model (CBM), intermediate blocking model (IBM), standard blocking model (SBM) and cake filtration model (CFM) were used. Cake enhanced osmotic pressure as a new mechanism for osmotically driven membranes was studied as well. According to the results, the fouling rate when the draw solution was synthetic salt water followed the order of: untreated river water > multimedia sand filter > microfiltration > ultrafiltration effluents. The fouling rate in ultrafiltration and microfiltration effluents using sea water occurred faster compared to the results for untreated synthetic salt water. Complete fouling (permeate flux was negligible) occurred after 580 h using feed water from ultrafiltration unit. It was observed that cake filtration and cake enhanced osmotic pressure were the main fouling mechanisms that governed the membrane fouling. These models could describe the membrane fouling in PRO processes.

Purification of Purple Sweet Potato Extract by Dead-End Filtration and Investigation of Membrane Fouling Mechanism

Pulsed ultrasound-assisted extraction with water was carried out to extract valuable compounds from purple sweet potato (PSP). Quality properties and dead-end filtration of PSP extract were investigated. Solutes concentration in PSP extract were 118.60 ± 2.83, 599.8 ± 8.28, and 0.72 ± 0.03 μg mL−1 for total protein, total polyphenol, and total anthocyanin, respectively. Filtration with PES 50 kDa membrane-augmented polyphenol purity from 83.4 % in extract to 99.6 %. A protein removal coefficient of 99 % was achieved. Resistance in series model and Hermia’s model was applied to quantify filtration resistance and investigate fouling mechanism during filtration. Gel layer resistance was the most important for all three used membranes (PES 0.1 μm, PES 100 kDa, and PES 50 kDa). Fitting of experimental data by Hermia’s model revealed that the most suitable fouling mechanism varied, cake layer model for PES 0.1 μm and PES 100 kDa membrane and intermediate blocking model for PES 50 kDa membrane. For the purpose of more efficient polyphenol production, advanced filtration modules, such as cross-flow and rotating disk filtration module, are expected.

Experimental investigation and modeling of industrial oily wastewater treatment using modified polyethersulfone ultrafiltration hollow fiber membranes

Hollow fiber membranes were prepared from polyethersulfone/additives/NMP&DMSO system via phase inversion induced by precipitation in non-solvent coagulation bath. The interaction effects of polyethylene-glycol (PEG), propionic-acid (PA), Tween-20, PEG molecular weight and polyvinyl-pyrrolidone (PVP) on morphology and performance of synthesized membranes were investigated. Taguchi method (L16 orthogonal array) was used initially to plan a minimum number of experiments. 32 membranes were synthesized (with two replications) and their permeation flux and TOC rejection properties to oily wastewater treatment were studied. The obtained results indicated that addition of PA to spinning dope decreases flux while it increases TOC rejection of prepared membranes. Also, the result shows that addition of PVP, Tween-20 and PEG content in spinning dope enhances permeation flux while reducing TOC rejection. The obtained results indicated that the synthesized membranes was effective and suitable for treatment of the oily wastewater to achieve up to 92.6, 98.2, and 98.5% removal of TOC, TSS, and OGC, respectively with a flux of 247.19 L/(m2h). Moreover, Hermia’s models were used for permeation flux decline prediction. Experimental data and models predictions were compared. The results showed that there is reasonable agreement between experimental data and the cake layer model followed by the intermediate blocking model.

PES and PES/PAN Blend Ultrafiltration Hollow Fiber Membranes for Oily Wastewater Treatment: Preparation, Experimental Investigation, Fouling, and Modeling

ABSTRACTIn this research, polyethersulfone (PES)/polyacrylonitrile (PAN) blend ultrafiltration hollow fiber membranes were prepared via phase inversion induced by a dry‐jet wet spinning process. The membranes were characterized by water contact measurements, scanning electron microscopy analysis and permeability measurements, and fouling‐resistance measurements. The results show that water contacts of the membranes are enhanced by increasing the PAN content in the spinning dope. The results of an experimental study on separation of oil from oily wastewaters are presented. The results demonstrated that the prepared PES membranes are effective in removing chemical oxygen demand (80.6%), total organic carbon (89.3%), turbidity (99.3%), total suspended solid (100%), and oil and grease content (99.7%), and final permeation flux of about 73.5 L/m2h. Also, it was found that 75/25 wt% of PES/PAN have higher mechanical strength and good separation performance. Hermia's models were used for prediction of the decline in permeation flux. Experimental data and models predictions were compared. The results showed that there is reasonable agreement between experimental data and the cake layer model followed by the intermediate blocking model.

Fouling mechanisms of Pseudomonas putida on PES microfiltration membranes

The mechanisms by which Pseudomonas putida causes fouling on a microfiltration membrane have been studied. For an initial P. putida concentration of 0.77g/L (5.1×108cfu/mL) stirred dead-end tests indicated that approximately 70% of the permeability was lost during the first minute of filtration and only 15% more was lost during the following 24min. SEM observations showed the presence of aggregates within the most external part of the membrane pores, partially blocking these pores and leading to more or less regular surface deposits and consequently, an intermediate blocking model was proposed and successfully fitted. The analysis of fouling resistance-in-series indicated that the selection of a high TMP during the microfiltration of P. putida had no effect on the final permeate flux but provoked an increase in external in comparison to internal fouling. On the other hand, the selection of a lower TMP led to a low rate of accumulation of P. putida on the membrane, reducing the total membrane resistance and allowing a deeper penetration of the bacteria into the pore. Studies on the cleanability of the membrane using sonication showed how this technique was more effective when membrane was fouled at higher TMP, achieving permeability recoveries of around 80% in the best cases.

Application of filtration blocking models to describe fouling and transmission of large plasmids DNA in sterile filtration

Sterile filtration is considered as a final step in processing pharmaceutical grade plasmid DNA. During the development of the filtration process, fundamental understanding on the mechanism of fouling is critical to improve filtration operations. The mechanism of fouling of pQR150 (20kb) and pGEc47 (56kb) plasmids DNA during constant pressure filtration inside 0.22μm PVDF membrane is experimentally investigated. The decline of filtrate flux as a function of time is analysed using the framework of classical and combined blocking models. The results for both plasmids indicate a transition between fouling mechanisms. Initially, during the early part of the filtration, the intermediate blocking model provided the best fit of the experimental results suggesting that fouling of the membrane was mainly caused by deposition of particles onto its surface. Afterwards, the result trends were best captured by the standard blocking model indicating that internal fouling of the membrane was the dominant fouling mechanism. A study of the transmission of both plasmids shows a significant reduction of plasmid transmission which coincides with the transition of the fouling mechanism from intermediate to standard blocking. The study highlights how the fouling behaviour of large plasmid DNA during sterile filtration is determined by the complex interplay between the flexibility of the molecules and the internal structure of the membrane.