Fouling Layer Research Articles

Mechanistic insights into simultaneous reversible and irreversible membrane fouling control in a vibrating anaerobic membrane bioreactor for sustainable municipal wastewater treatment

Vibrating membrane (VM) technology has shown low energy demands for in-situ antifouling enhancement in aerobic membrane bioreactors, and is expected to have greater potential for sustainable wastewater treatment applied in anaerobic membrane bioreactors (AnMBRs). However, it remains unclear how VM improves antifouling performance in AnMBRs and how the membrane fouling orignates, develops and diminishes in comparison to the conventional in-situ biogas scouring. This study reported the successful adoption of VM as a effective antifouling strategy for the vibrating AnMBR (V-AnMBR) in long-term (514 days) municipal wastewater treatment. The V-AnMBR showed superior performance, achieving 61.8%–89.4% longer filtration time, 0.68%–1.04% more organics removal and 10.7%–30.6% higher methane yields compared to the conventional biogas-scouring AnMBR (C-AnMBR). Both AnMBRs showed that membrane foulant layer (FL) was dominated in the order of colloid(FL) > EPS(FL) > SMP(FL), which could be reduced by VM to lower 10.7%–11.5% of the reversible fouling and 21.4%–26.9% of the irreversible fouling compared to biogas scouring. Furthermore, VM minimized the breakdowns of biomass typically caused by biogas scouring and reduced the release of fouling contributors from the mixed liquor, including the half of reductions of biopolymers and aromatic proteins. This work offers in-depth explanations of how membrane fouling develops in AnMBRs treating municipal wastewater, and elucidates the mechanisms of how VM achieves dual benefits on preventing foulant self-development and reducing membrane fouling contributors. Such mechanistic insights into fouling development and membrane fouling contributors would advance the understandings of antifouling mechanisms and guide next-generation sustainable AnMBR technology for mainstream wastewater treatment.

Interaction Mechanisms and Predictions of the Biofouling of Polymer Films: A Combined Atomic Force Microscopy and Quartz Crystal Microbalance with Dissipation Monitoring Study.

Biofouling of polymeric membranes is a severe problem in water desalination and treatment applications. A fundamental understanding of biofouling mechanisms is necessary to control biofouling and develop more efficient mitigation strategies. To shed light on the type of forces that govern the interactions between biofoulants and membranes, biofoulant-coated colloidal AFM probes were employed to investigate the biofouling mechanisms of two model biofoulants, BSA and HA, toward an array of polymer films commonly used in membrane synthesis, which included CA, PVC, PVDF, and PS. These experiments were combined with quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The Derjaguin, Landau, Verwey, and Overbeek (DLVO) and the extended-DLVO (XDLVO) theoretical models were applied to decouple the overall adhesion interactions between the biofoulants and the polymer films into their component interactions, i.e., electrostatic (El), Lifshitz-van der Waals (LW), and Lewis acid-base (AB) interactions. The XDLVO model was found to predict better the AFM colloidal probe adhesion data and the QCM-D adsorption behavior of BSA onto the polymer films than the DLVO model. The ranking of the polymer films' adhesion strengths and adsorption quantities was inversely proportional to their γ- values. Higher normalized adhesion forces were quantified for the BSA-coated colloidal probes with the polymer films than the HA-coated colloidal probes. Similarly, in QCM-D measurements, BSA was found to cause larger adsorption mass shifts, faster adsorption rates, and more condensed fouling layers than HA. A linear correlation (R2 = 0.96) was obtained between the adsorption standard free energy changes (ΔGads°) estimated for BSA from the equilibrium QCM-D adsorption experiments and the AFM normalized adhesion energies (WAFM/R) estimated for BSA from the AFM colloidal probe measurements. Eventually, an indirect approach was presented to calculate the surface energy components of biofoulants characterized by high porosities from Hansen dissolution tests to perform the DLVO/XDLVO analyses.

New insight into the irreversible membrane fouling in different pore-sized ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater treatment

Despite great achievements in ceramic membrane bioreactor applications, membrane fouling, which decreases the permeability and separation performance of bioreactors and is associated with increased operational costs and energy consumption, remains a problem. The aim of this study was to expand our understanding of the fouling behavior in the long-term performance of ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater reclamation. Using real textile wastewater effluent, the effects of ultrafiltration (UF) membrane pore sizes, cleaning strategies, and foulant distribution were systematically evaluated over more than three months of continuous operation. The results showed that UCMBR system achieved chemical oxygen demand and total nitrogen removal efficiencies as high as 91–95% and 39–43%, respectively. The high PN concentration can easily increase the viscosity of mixed liquor samples, contributing to a fouling layer on the membrane surface. In addition, the fouling layer formed on the surface of small-pore-sized ceramic UF membranes was not completely reversible but was difficult to eliminate by simple physical cleaning. Soluble extracellular polymeric substances, especially proteins and low molecular weight neutrals, remained, resulting in irreversible fouling on the UF membrane. However, saturated CO2 backwash showed great potential for enhancing the system through efficient fouling control without using environmentally unfriendly cleaning chemicals. The cake-intermediate and complete-standard models were suitable for explaining the fouling mechanism in the large- and small-pore-sized UF membranes, respectively.

Effect of soot particle deposition on porous fouling formation and thermal characteristics of an exhaust gas recirculation cooler

Exhaust gas recirculation (EGR) systems have been successfully employed to reduce the NOx emissions in diesel engines. However, the fouling problem in EGR coolers challenges their capability to comply with stringent environmental regulations. A few numerical simulations have considered the fouling growth in EGR coolers. Those studies modeled the evolving fouling layer to be a solid medium, therefore, fluid flow and convection heat transfer within the fouling layer, which is well-documented to be a porous medium permeable to gas flow, have not been considered yet. As such, the present study investigates the simultaneous effects of the formation of the evolving porous fouling layer (EPFL) at the walls of an EGR cooler and fluid flow and convection heat transfer simulation within this EPFL to determine its coupled effects on the thermal performance of the EGR cooler. This study also investigates the possibility of formation of a steady fouling layer (SFL) because of the opposing effects of the fouling layer growth and deposition rate. The effects of two pertinent dimensionless parameters, namely Darcy number (10-4≤Da≤5×10-3) and Reynolds number (100≤Re≤400) on the time history of the fouling layer growth, deterioration of the thermal performance of the duct, and average Nusselt number ratio (Nuav/Nuavt=0) are studied. The results show that the thermal performance of the duct decreases as the EPFL grows, which agrees well with the available experimental data. It is shown that the steady fouling layer is obtained due to a decrease in thermophoretic force and deposition rate, as a result of the EPFL formation. Finally, a correlation is proposed in terms of Reynolds and Darcy numbers for the time at which the SFL occurs.

Anaerobic membrane bioreactor for real antibiotic pharmaceutical wastewater treatment: Positive effect of fouling layer on antibiotics and antibiotic resistance genes removals

Anaerobic membrane bioreactor (AnMBR) is a potential candidate for high-strength pharmaceutical wastewater treatment. However, its contribution to reduce the antibiotic and antibiotic resistance genes (ARGs) is still largely unclear. Herein, this study investigated the antibiotics and ARGs removal in AnMBR for real high-strength antibiotic (levofloxacin (LEV)) pharmaceutical wastewater treatment, focusing on the positive effect of membrane fouling layers (biofilms). Results indicated that membrane biofilm has a positive effect on AnMBR treatment with improved COD and LEV removal efficiency by 12% and 10%, respectively. This might be ascribed to the enhanced biodegradation ability of the organic matter by the biofilm due to the enrichment of fermentation bacteria (Anaerobium), hydrogen-producing bacteria (Clostridium_sensu_stricto_1) and hydrogenotrophic methanogenic archaea (Methanobacterium and Methanobrevibacter). Importantly, the membrane biofilm can also effectively mitigate the ARGs (qnrS, qnrA) and class 1 integrator (intI1) dissemination and the absolute abundance of ARGs in the medium fouling (MF) biofilm effluent was 0.27 orders of magnitude lower than that of low fouling (LF) biofilm effluent. This can be explained by the variation of membrane surface becoming more hydrophobic in MF than LF biofilm with increased contact angle and more negative surface zeta potential, suggesting higher adsorption and adhesion properties. The strong correlation between extracellular polymer substance (EPS) and soluble microbial product (SMP) contents and qnrA, qnrS and intI1 further indicated the important role of EPS and SMP in membrane biofilm on ARGs reduction. Furthermore, the entrapment of ARGs potential hosts bacteria of Comamonas and Enterococcus with high biofilm formation potential also attributed to the improved ARGs removal with the increase of membrane fouling degree. Our findings suggest that AnMBR is effective for antibiotic pharmaceutical wastewater treatment and membrane biofilm has a positive effect on antibiotic and ARGs removal, which promotes the AnMBR application in the pharmaceutical industry.

Alleviating Ultrafiltration Membrane Fouling Caused by Effluent Organic Matter Using Pre-Ozonation: A Perspective of EEM and Molecular Weight Distribution.

Wastewater reclamation has gradually become an important way to cope with the global water crisis. Ultrafiltration plays an imperative part as a safeguard for the aim but is often limited by membrane fouling. Effluent organic matter (EfOM) has been known to be a major foulant during ultrafiltration. Hence, the primary aim of this study was to investigate the effects of pre-ozonation on the membrane fouling caused by EfOM in secondary wastewater effluents. In addition, the physicochemical property changes of EfOM during pre-ozonation and the subsequent influence on membrane fouling were systemically investigated. The combined fouling model and the morphology of fouled membrane were adopted to scrutinize the fouling alleviation mechanism by pre-ozonation. It was found that membrane fouling by EfOM was dominated by hydraulically reversible fouling. In addition, an obvious fouling reduction was achieved by pre-ozonation with 1.0 mg O3/mg DOC. The resistance results showed that the normalized hydraulically reversible resistance was reduced by ~60%. The water quality analysis indicated that ozone degraded high molecular weight organics such as microbial metabolites and aromatic protein and medium molecular weight organics (humic acid-like) into smaller fractions and formed a looser fouling layer on the membrane surface. Furthermore, pre-ozonation made the cake layer foul towards pore blocking, thereby reducing fouling. In addition, there was a little degradation in the pollutant removal performance with pre-ozonation. The DOC removal rate decreased by more than 18%, while UV254 decreased by more than 20%.

Relative importance of drag force and adhesion forces in the fouling of ultrafiltration membranes by secondary effluent organic matter after pre-ozonation

Pre-ozonation prior to ultrafiltration is widely used, but its influencing mechanism on membrane fouling is still debated. Herein, the root influencing factors of pre-ozonation on membrane fouling by secondary effluent organic matter (EfOM) were analyzed from the perspectives of drag force, adhesion forces and the properties of EfOM and membranes. The results showed that EfOM fouling could be either exacerbated or mitigated by pre-ozonation, which depended on the relative magnitudes of the drag force and the adhesion forces. For membranes with a relatively low molecular weight cutoff (MWCO), fouling was exacerbated by pre-ozonation. This was attributed to the fact that pre-ozonation weakened electrostatic repulsion and enhanced hydrogen bonding, causing the adhesion forces of EfOM at the membrane surface to increase, which eventually promoted the deposition of foulants and resulted in a denser fouling layer. Nevertheless, when the MWCO reached a certain degree, the drag force increased substantially, which could push greater amounts of smaller ozone-treated EfOM into or through the membrane pores, thus reducing the deposition of foulants and increasing the probability of pore blocking. Therefore, after pre-ozonation, the fouling rate decreased, but irreversible fouling increased. However, membrane structure-related steric effects could weaken the influence of the drag force on membrane fouling.

In situ surface modification of forward osmosis membrane by polydopamine/polyethyleneimine-silver nanoparticle for anti-fouling improvement in municipal wastewater treatment.

In this work, we demonstrate the surface functionalization of cellulose triacetate membrane with co-deposition of polydopamine (PDA)/polyethyleneimine (PEI) and silver nanoparticles (AgNPs) for antifouling property in municipal wastewater treatment. PDA/PEI was first coated on the membrane surface by single-step co-deposition, while AgNPs were formed in situ through catechol groups of PDA immobilizing silver ions and subsequently reducing. The successful surface modification was verified by different membrane characterization techniques. The modified PDA/PEI-nAg CTA membrane exhibits enhanced hydrophilicity and improved antiadhesion and antimicrobial activity. Furthermore, the functional layer had an indistinctive effect on the membrane transport parameters. In addition, dynamic forward osmosis (FO) fouling experiment with raw municipal wastewater as feed solution indicated that the PDA/PEI-nAg CTA membrane exhibited notably lower water flux decrease compared to the nascent CTA membrane. The results of confocal laser scanning microscopy (CLSM) showed that PDA/PEI-nAg CTA membranes effectively reduced the adsorption of organic foulants (proteins and polysaccharides) and inhibited the formation and development of the fouling layer. The membrane surface modification of the CTA membrane with PDA/PEI and AgNPs efficiently mitigated membrane fouling in municipal wastewater treatment.

Preparation of a spherical biochar colloidal probe and its application in deciphering the mechanism of biochar mitigating membrane fouling

To better unravel biochar’s interface behavior and mitigation mechanism on membrane fouling, spherical biochar colloidal probes were prepared by adhering microspheres to the free end of the probe cantilever. The prepared colloidal probes were used to measure the interaction forces between the membrane and foulant/biochar and between the foulant and foulant/biochar by atomic force microscopy (AFM). The study investigated the differences in physicochemical properties of biochars and their mitigating effects on membrane fouling caused by bovine serum albumin (BSA). Results indicated that dosing biochar strengthened the electrostatic repulsion between BSA and membranes, thereby, mitigating the adhesion or deposition of BSA on the membrane surface. Additionally, spherical biochar (SBC) and hydrochar (HC) exhibited better membrane fouling mitigation than conventional biochar (CBC) due to better physicochemical properties, adsorption capacity, and a more porous fouling layer structure composed of microparticles. Importantly, the stronger adhesion force of SBC-PVDF (0.90 mN/m) than BSA-PVDF (0.50 mN/m) alleviated membrane fouling in the initial stage of the filtration, and the adhesion force of SBC-BSA (0.049 mN/m) alleviated membrane fouling in the later stage, resulting in higher water flux. The interaction force between mature SBC and BSA was comparable to that between BSA and BSA (0.14 mN/m) and stronger than that between original SBC and BSA (0.049 mN/m), implying further membrane fouling mitigation.

Evaluation of the Anti-Fouling Effects of Micro-Nano Bubbles on the Performance of Reverse Osmosis Membrane

Colloidal fouling on a brackish water reverse osmosis (BWRO) membrane was simulated by a lab-scale plate-and-frame module in the presence and absence of air micro-nano bubbles (AMNBs). Synthetic feed water samples with the same physical and chemical properties, but various concentrations of colloidal silica (50, 100, 200, and 300 mg/L), were used for experiments. The results illustrate that colloidal fouling caused a severe decrease in permeate flux (24%–56%) and salt rejection (1.25% to 4.18%) in the absence of AMNBs. This reduction in membrane performance was attributed to the high hydraulic resistance and the cake-enhanced osmotic pressure (CEOP) of a fouled gel layer that were intensified with increase in the colloidal concentration. On the other hand, presence of AMNBs decreased the deposition rate of colloidal particles significantly and increased the porosity of fouling layer. Thus, an improvement in the membrane permeate flux (21%–40%) and salt rejection (1.2%–2.6%) were seen in the different concentrations of colloidal particles. The SEM images also confirmed the formation of loose fouling layers which were easily removed from the membrane surface by a clean-in-place (CIP) process. This research introduces AMNBs technology as an effective in-line method to control the adverse effects of colloidal fouling in reverse osmosis (RO) systems.

Application of Optical Coherence Tomography (OCT) to Analyze Membrane Fouling under Intermittent Operation

There is increasing interest in membrane systems powered by renewable energy sources, including solar and wind, that are suitable for decentralized water supply in islands and remote regions. These membrane systems are often operated intermittently with extended shutdown periods to minimize the capacity of the energy storage devices. However, relatively little information is available on the effect of intermittent operation on membrane fouling. In this work, the fouling of pressurized membranes under intermittent operation was investigated using an approach based on optical coherence tomography (OCT), which allows non-destructive and non-invasive examination of membrane fouling. In reverse osmosis (RO), intermittently operated membranes were investigated by OCT-based characterization. Several model foulants such as NaCl and humic acids were used, as well as real seawater. The cross-sectional OCT images of the fouling were visualized as a three-dimensional volume using Image J. The OCT images were used to quantitatively measure the thickness of foulants on the membrane surfaces under different operating conditions. The results showed that intermittent operation retarded the flux decrease due to fouling compared to continuous operation. The OCT analysis showed that the foulant thickness was significantly reduced by the intermittent operation. The decrease in foulant layer thickness was found to occur when the RO process was restarted in intermittent operation.

Performance of resin adsorption and ozonation pretreatment in mitigating organic fouling of reverse osmosis membrane

Effective pretreatment of reverse osmosis (RO) influent is of great importance for reducing membrane fouling risks during coking wastewater desalination. In this study, the combined resin adsorption and ozonation pretreatment was investigated on alleviating RO membrane organic fouling. The performance of combined process was compared with only resin adsorption or ozonation, which was evaluated in terms of changes in chemical oxygen demand (COD), ultraviolet-visible index, and three-dimensional excitation-emission matrix fluorescence spectra. RO membrane fouling tests were conducted to examine the effects of pretreatment on flux decline and filtration resistance. The surface morphology and functional groups of membrane before and after fouling was characterized by scanning electron microscopy and infrared spectroscopy. The correlation between major organic matter in the wastewater and normalized RO membrane flux was established via multiple linear regression equations. The results showed that ozonation was more effective in removing COD and fluorescent organics than resin adsorption. Moreover, the combined bifunctional resin adsorption/ozonation unit showed the best performance, with COD and UV254 removal rates of 49.4 % and 88.0 %, respectively. The fluorescence intensity of each component decreased significantly. Meanwhile, the polysaccharide and protein components of the RO membrane fouling layer were effectively reduced by 67.2 % and 80.8 %, respectively. Most importantly, the combined pretreatment substantially reduced the decline in membrane flux and filtration resistance. Meanwhile, the fulvic acid-like organics in the wastewater showed high correlations with normalized membrane flux. The regression equation was beneficial for RO membrane fouling evaluation.

Identification and Quantification of the Organic Matter in the Fouling Industrial of Wet Phosphoric Acid Process

The organic matter of rock phosphate has been the subject of numerous studies. The valuation and resolu-tion of some problems, such as fouling, encountered in the industrial production of phosphoric acid are of great interest, and enable better production yields of phosphoric acid. The solid deposits formed in the production of wet process phosphoric acid were characterized and revealed the malladrite, gypsum, trace metals, and the presence of organic matter. The identification of the organic matter was carried out in the fouling samples using FT-IR and Raman spectroscopies. The quantitative determination of the total organic matter content of the fouling samples was performed using the Walkley-Black and calcination methods. The knowledge of the organic matter in the fouling layers allows a better understanding of phenomena in processes.

Assessment of natural tannin-based coagulant for effective ultrafiltration (UF) of UASB effluent: Fouling mechanisms, pollutant removal and water reclamation feasibility

In this work, tannin coagulant (TANm) was applied at different dosages and compared with a PACl for UASB effluent filterability enhancement during membrane ultrafiltration. The results showed that TANm exhibited the greatest potential to improve UASB effluent filterability. Flux decay, total fouling resistance, and specific cake layer resistance were all reduced by both coagulants. However, the highest flux (55%) and fouling resistance reduction (70%) were obtained with 40 mg.L−1 of TANm, which was caused by an increase in particles larger than 200 μm, facilitating its removal by cross-flow filtration. Protein and carbohydrate reduction in the membrane was only observed at 25 mg.L−1 for both coagulants, with a higher influence of proteins in strongly/very strongly bound for all samples. In addition, fouling irreversibility increases, with a strong correlation between TANm dosage and Rirr and complete and intermediate pore blocking pointed as the main mechanisms responsible for irreversibility for both coagulants. Based on these and other findings, the mechanisms of the fouling layer adhered to the membrane with coagulants included the formation of complexes with proteins that were more strongly adhered (related to UASB effluent zeta potential increase), the density of the cake layer due to the presence of compact aggregates, and action of the coagulants themselves as foulants. Lastly, the economic evaluation revealed that the system without coagulant would have a lower total cost, but payback showed that the application of TANm has a lower investment time of return due to a lesser CAPEX.

Structural and Distribution of Impurities in the Fouling in Wet-Process Phosphoric Acid at T = 80°C

In this investigation, the mineral deposits formed in the digestion step in wet phosphoric acid production were studied. The mineralogical characterization of the fouling precipitates obtained at the temperature 80°C from the digestion step in 16-monthly production cycle was carried out. Observing successive layers, based on their colors, allowed us to distinguish fouling layers. Detailed structural aspects, and subsequently, chemical and physical properties of the fouling were determined using complementary analytical and characterization techniques. Particle size fractionation was then used to gain each fouling layer sample homogenized on the micro-scale (63μm). The major elements in the fouling were determined to be silica (Si₂O) and sodium (Na). Some chemical elements of major impurities, as well as traces, K, Al, Mg, Fe, Cu, and Zn, were detected using XRF which cannot appear in their proper solid phases. The obtained solid phases in different fouling layers are principally composed of the malladrite and gypsum minerals. The distribution of impurities into the present structures was investigated. Indeed, the mesh parameters of malladrite in the fouling layers were calculated and compared with those of the pure phase, and a good concordance is obtained. The FT-IR spectra confirm the presence of mallardite and gypsum phases and reveal a supplementary band that has been assigned to C-O vibrations in acids, esters, or ethers. The appearance of this band indicates the possible presence of organic matter within the fouling layer.

The improvement of heavy metals removal by wood membrane in drinking water treatment: Comparison with polymer membrane and associated mechanism

The application of commercial membranes is limited by the secondary pollution such as the usage of toxic chemicals for the membrane preparation and the disposal of aged membranes. Therefore, the green and environmentally friendly membranes are extremely promising for the sustainable development of membrane filtration in water treatment. In this study, the comparison of wood membrane with the pore size of tens microns (μm) and polymer membrane with the pore size of 0.45 μm was made to study the heavy metals removal in drinking water treatment by gravity-driven membrane (GDM) filtration system, and there was an improvement in the removal of Fe, Cu and Mn by wood membrane. The sponge-like structure of fouling layer for wood membrane made the retention time of heavy metals prolonged in contrast to the cobweb-like structure of polymer membrane. The carboxylic group (-COOH) content of fouling layer for wood membrane was greater than that for polymer membrane. Additionally, the population abundance of heavy metal-capturing microbes on the surface of wood membrane was higher compared with polymer membrane. The wood membrane provides a promising route to producing facile, biodegradable and sustainable membrane as a green alternative to polymer membranes in heavy metal removal from drinking water.

Effect of hydraulic retention time on performances of gravity-driven membrane (GDM) reactor for seawater pretreatment

This study aims to illustrate the effect of hydraulic retention time (HRT) on reactor performance and biofilm characteristics in the gravity-driven membrane (GDM) reactor pretreating seawater. Three GDM reactors were operated in parallel for ~62 days under HRTs of 22 h, 54 h, and 102 h, respectively. The results indicated that the GDM reactors at HRTs of 22 h and 102 h had relatively higher permeate flux and superior permeate quality (especially assimilable organic carbon, AOC) compared to that at HRT of 54 h. Extending HRT benefited to reduce irreversible fouling, but cake layer fouling was maximized at HRT of 54 h. As different HRTs led to significantly dissimilar microbial community structure and cake layer composition, such higher cake layer resistance at HRT of 54 h was attributed to homogenous nature of the biofilm, which contained greater amount of organics and less abundance of Nematoda (dominant predator). Lastly, as increasing ~5-time of HRT (from 22 h to 102 h) improved ~1.5 of permeate flux, a shorter HRT of 22 h was preferable for the GDM reactor in pretreating seawater with regard to treatment productivity and footprint.

Effect of the chemical composition of fluid foods on the rate of fouling processing during sterilization

Background: This research was motivated by the determination of the sanitation schedule in the heat exchanger area for some products (milk, avocado juice, and orange juice), as well as the inconsistency of the results of previous studies related to the chemical composition of the fouling layer. Objectives: a) to test the effect of raw material composition on the chemical composition of the fouling layer. b) to test microbial growth's effect on fouling's chemical composition (protein). Methods: mathematical derivation of the formation process of Resistant Dirt Factor (Rd) in the form of an Equation; ANOVA was used to test the effect of the dependent variable (protein) and predictor (microbial). Results: a) The composition of the raw material strongly influences the chemical composition of the fouling layer; b) There is a strong effect between microbial growth and protein content as a fouling composition (p<0.05). Conclusion: A strong influence between microbial growth and the composition of the fouling layer (protein) can close the research gap related to the inconsistency of previous research results (fouling layer composition), so there is no prolonged debate.

Generalization and Expansion of the Hermia Model for a Better Understanding of Membrane Fouling

One of the most broadly used models for membrane fouling is the Hermia model (HM), which separates this phenomenon into four blocking mechanisms, each with an associated parameter n. The original model is given by an Ordinary Differential Equation (ODE) dependent on n. This ODE is solved only for these four values of n, which limits the effectiveness of the model when adjusted to experimental data. This paper aims extend the original Hermia model to new values of n by slightly increasing the complexity of the HM while keeping it as simple as possible. The extended Hermia model (EHM) is given by a power law for any n ≠ 2 and by an exponential function at n = 2. Analytical expressions for the fouling layer thickness and the accumulated volume are also obtained. To better test the model, we perform model fitting of the EHM and compare its performance to the original four pore-blocking mechanisms in six micro- and ultrafiltration examples. In all examples, the EHM performs consistently better than the four original pore-blocking mechanisms. Changes in the blocking mechanisms concerning transmembrane pressure (TMP), crossflow rate (CFR), crossflow velocity (CFV), membrane composition, and pretreatments are also discussed.

Evaluation of long-term operational and treatment performance of a high-biomass submerged anaerobic membrane bioreactor treating abattoir wastewater

Although anaerobic membrane bioreactors (AnMBR) are widely used in high-strength wastewater treatment and resource recovery, membrane operational performance and membrane fouling control remain critical issues. In this study, the operational and treatment performance of a high-biomass (18 ≤ MLSS (g/L) ≤ 35) submerged anaerobic membrane bioreactor (HBSAnMBR) was assessed at organic loading rates (OLR) of 1.05–5 kg-COD/m3/d to treat abattoir wastewater (AWW). The correlation between kinetic parameters representing biomass yield and extracellular polymeric substances (EPS) was thoroughly investigated using mathematical models. It was found that the yield of biomass and EPS correlated positively with applied OLR and were found in the range of 0.13–0.31 g-MLSS/g-COD and 0.00001–0.000013 g-EPS/g-MLSS, respectively. This study also systematically examined the cake layer fouling mechanisms of HBSAnMBR due to EPS and the influence of soluble microbial products (SMP) on membrane pore blocking. OLR above 4 kg-COD/m3/d negatively affected the performance in terms of TMP, filtration resistance, EPS/SMP production, and COD removal suggesting that HBSAnMBR can be operated sustainably at OLR 4 kg-COD/m3/d. The membrane autopsy analyses and foulant characterization found that cake layer foulants were primarily composed of polysaccharides and proteins, while the membrane did not experience pore-blocking. At the same time, sodium, phosphorous, and calcium triggered inorganic fouling. The efficient treatment of abattoir wastewater showed that the HBSAnMBR system could be applied to treat trade wastewater containing high-organic content.