Fouling Mechanisms Research Articles

Pilot scale application of a rotating hollow fibre membrane for direct membrane filtration of domestic wastewater

This study investigates the direct ultrafiltration process of municipal wastewater (MWW) at pilot scale. Short-term trials were conducted with two membrane modules to assess the fouling mechanisms using different physical cleaning methods: gas sparging (hydraulic cleaning) and rotation (mechanical cleaning). This work demonstrates that membrane rotation effectively erodes and re-disperses external fouling during the backwashing stages. Consequently, shear stress generated by the rotational movement enables the operation with permeate fluxes ranging between 24 and 30 L/hm2, above the threshold flux value (22–24 L/hm2), while maintaining fouling rates (rf) below 10 Pa/s. In contrast, rf values increases up to 12.4–17.8 Pa/s when gas sparging is employed. Furthermore, the feasibility of up-concentrating municipal wastewater up to 12 times while operating with a net permeate flux of 20 L/hm2 is demonstrated through a long-term trial. The increase in suspended solids concentration (TSS = 5750 mg/L and VSS = 4750 mg/L) favours the rapid formation of a reversible cake on the membrane surface during filtration, at moderate transmembrane pressures (26 cmHg). These operating conditions avoid cake layer compression and protect the inner surface of the membrane module from severe internal residual fouling with an energy consumption of 0.027 kWh/m3.

One-step fabrication of asymmetric alumina ceramic membranes with tunable pore parameters for oil-water separation

Porous ceramic membranes with low-cost and high performance are desirable in industrial filtration field. To improve the performance while reducing the production cost, various measures were developed, however, pre-sintering of supports, preparation of membrane-forming suspensions and adoption of extensive organic additives that involved were adverse to cost reduction. Herein, cost-effective one-step co-pressing and co-sintering technique was proposed to prepare asymmetric ceramic membranes. The results revealed that pore parameters and performance of the fabricated membranes could be adjusted by altering mole ratio of Al2O3 to SiO2 (Al2O3/SiO2) in the support and sintering temperature. The influence of supports on the permeation flux of membranes surpassed that of the parameters of membrane layer. Additionally, the oil rejection rate of the membranes exceeded 96 % within 2 min and even reached 100 % (~60 min), the water flux and steady-state feed flux were 1330–1730 L·m−2·h−1 and 470–620 L·m−2·h−1 at 1 bar, respectively. Moreover, cake filtration was the main fouling mechanism throughout the separation process. This research provides a feasible and simple method for preparing low-cost high-performance ceramic membrane for wastewater treatment.

A membrane-assisted green strategy for purifying bioactive compounds from extracted white wine lees

This work was aimed at investigating the recovery of wine-derived bioactive compounds from white wine lees through a combination of hydroalcoholic extraction and membrane-based operations, as a potential alternative for winery wastewater treatment and valorisation.Hydroalcoholic extracts obtained in selected conditions of solid–liquid ratio, extraction time and working temperature (1:10, 25 % and 32 ± 2 °C, respectively) were previously clarified by ultrafiltration (UF) in order to produce a clarified solution free of suspended solids and colloidal substances. The concentration of bioactive compounds from the clarified extract was investigated by using three different spiral-wound NF membranes with molecular weight cut-off (MWCO) in the range of 200–1000 Da (TS40, XN45 and NP010, all from Microdyn-Nadir); their performance was analysed in terms of productivity, fouling index and retention towards target compounds (polyphenols, flavonoids, sugars) and antioxidant activity.Low molecular weight polyphenols (i.e. gallic acid, catechin, vanillic acid, epicatechin and caffeic acid) were highly rejected by the selected membranes despite their difference in MWCO; on the other hand, the rejection index for total phenolic content (TPC), flavonoids and glucose was in agreement with the MWCO. The TS40 membrane, with a lowest cut-off (200–300 Da), showed the highest rejection for flavonoids (100 %) and rejections for total phenolic compounds of 85 % resulting in concentrated fractions containing 1.7 g of gallic acid equivalents per liter (GAE/L); most of the components analysed in the retentate samples showed a concentration factor of approximately 3.5 in agreement with the weight reduction factor of the NF process. The analysis of fouling mechanisms according to the Hermia’s model revealed that the cake filtration mechanism was the predominant one for all selected NF membranes.

Preparation, characterization, and fouling analysis of PVC/ND-PEG ultrafiltration membranes for whey separation

In this work, polyvinyl chloride (PVC) membranes were embedded with nanodiamond-Polyethylene glycol (ND-PEG) nanoparticles. Fabricated membranes were characterized by FTIR, FESEM, AFM, pore size distribution, contact angle, porosity, pure water flux (PWF), and tensile strength. Successful functionalization of ND nanoparticles by PEG was proved by the FTIR test. According to the FESEM and pore size distribution results, there was an increase in the quantity of surface pores, a shift toward smaller pores, and larger macro-voids in the porous substructure of the nanocomposite membranes as the ND-PEG content in the dope solution increased. The decrease water contact angle from 79.8° for neat PVC membrane to 59.5° for 2.00 wt% ND-PEG containing membrane along with the increase of porosity from 53.89 % to 80.80 % respectively showed that the hydrophilicity of the nanocomposite membranes was improved by increasing nanoparticles content, and this phenome along with surface roughness increment caused PWF improvement from 206.8 LMH to 266.4 LMH. In addition, due to the uniform dispersion of ND-PEG nanoparticles and the high mechanical strength of NDs, the tensile strength of nanocomposite membranes reached a maximum value of 2.91 Mpa for 1.5 wt% ND-PEG membrane. The performance results showed that PVC/ND-PEG nanocomposite membranes had acceptable whey rejection along with a significant increment in flux recovery ratio. Moreover, PVC/ND-PEG membranes with 2.00 wt% ND-PEG had lower flux reduction in long-term filtration, improved antifouling properties and more turbidity removal efficiency in comparison with neat PVC membranes. The analysis of the fouling mechanism based on Hermia's model revealed that the cake formation is the prevailing mechanism for all fabricated membranes.

Understanding the different effects of fouling mechanisms on working and reference electrodes in fast-scan cyclic voltammetry for neurotransmitter detection.

Fast-scan cyclic voltammetry (FSCV) is a widely used technique for detecting neurotransmitters. However, electrode fouling can negatively impact its accuracy and sensitivity. Fouling refers to the accumulation of unwanted materials on the electrode surface, which can alter its electrochemical properties and reduce its sensitivity and selectivity. Fouling mechanisms can be broad and may include biofouling, the accumulation of biomolecules on the electrode surface, and chemical fouling, the deposition of unwanted chemical species. Despite individual studies discussing fouling effects on either the working electrode or the reference electrode, no comprehensive study has been conducted to compare the overall fouling effects on both electrodes in the context of FSCV. Here, we examined the effects of biofouling and chemical fouling on the carbon fiber micro-electrode (CFME) as the working electrode and the Ag/AgCl reference electrode with FSCV. Both fouling mechanisms significantly decreased the sensitivity and caused peak voltage shifts in the FSCV signal with the CFME, but not with the Ag/AgCl reference electrode. Interestingly, previous studies have reported peak voltage shifts in FSCV signals due to the fouling of Ag/AgCl electrodes after implantation in the brain. We noticed in a previous study that energy-dispersive spectroscopy (EDS) spectra showed increased sulfide ion concentration after implantation. We hypothesized that sulfide ions may be responsible for the peak voltage shift. To test this hypothesis, we added sulfide ions to the buffer solution, which decreased the open circuit potential of the Ag/AgCl electrode and caused a peak voltage shift in the FSCV voltammograms. Also, EDS analysis showed that sulfide ion concentration increased on the surface of the Ag/AgCl electrodes after 3 weeks of chronic implantation, necessitating consideration of sulfide ions as the fouling agent for the reference electrodes. Overall, our study provides important insights into the mechanisms of electrode fouling and its impact on FSCV measurements. These findings could inform the design of FSCV experiments, with the development of new strategies for improving the accuracy and reliability of FSCV measurements in vivo.

Treatment of highly saline effluents laden with organic pollutants using ceramic ultrafiltration membranes and application to leachate treatment

The aim of this study is to assess the efficacy of three ultrafiltration ceramic membranes with distinct porosities (20, 50, and 100 nm) in treating highly charged effluents and their potential application in leachate treatment. In the initial phase, Response Surface Methodology (RSM) was employed using a solution containing NaCl (TDS = 20 g/L) and glucose (mass concentration (Cm) = 10 g/L). The investigation focused on operational parameters, specifically Circulation velocity (CV) and volumetric concentration factor (VCF). The responses considered encompass permeate flux (PF) and retention (R). In the subsequent phase, as part of a practical application, leachate was subjected to treatment, and the fouling mechanisms specific to each membrane were identified. The Hermia model was employed, distinguishing between four fouling modes: cake formation, intermediate blocking, pore constriction, and complete blocking. The results demonstrate that, during the treatment of the synthetic solution, VCF has a more significant influence on both responses compared to CV. Furthermore, CV impacts the critical flux of the three membranes, without affecting the retention of suspended matter (SS). When treating the leachate, removal efficiencies of 55%, 51%, and 47% for COD and 36%, 33%, and 29% for SS were achieved for membranes with porosities of 20 nm, 50 nm, and 100 nm, respectively. Modeling the flux over time showed that fouling of these three UF membranes is superficial, and the main fouling mechanism is cake formation.

Membrane fouling and control in algae-rich water treatment

Microfiltration and ultrafiltration membrane technology has now become one of the important methods for algae-rich water treatment due to its better solid-liquid separation effect and microbial retention capacity, while the existence of membrane fouling has been restricting the full-scale promotion and application of low-pressure membrane technology. The main foulants causing membrane fouling in algal-rich water include algal cells, algal debris and algal organic matter AOM (EOM and IOM). In this paper, the mechanism of membrane fouling caused by algal foulants in MF/UF for high algal water treatment is analysed in terms of both individual and composite fouling. Both individual and composite effects of algal foulants can lead to severe membrane fouling, in which algal cells and algal debris mainly dominate the accumulation of filter cake, while AOM mainly leads to membrane pore blockage membrane fouling is exacerbated by compounding effects, with severe reversible and irreversible fouling caused by filter cake formation and membrane pore shrinkage. This paper also discusses several common membrane fouling control methods, including pretreatment (oxidation, coagulation, combined oxidation-coagulation and adsorption) and membrane modification, and it is found that these several membrane fouling control methods can achieve good results.

Coupling pretreatment of ultraviolet/ferrate (UV/Fe(vi)) for improving the ultrafiltration of natural surface water.

Ultrafiltration (UF) is a high-potential technology for purifying natural surface water; however, the problem of membrane fouling has limited its widespread application. Herein, ultraviolet (UV)-activated ferrate (Fe(vi)) was used to purify natural surface water and improve the performance of the UF membrane. The combination of UV and Fe(vi) could generate active species (Fe(v), Fe(iv), ˙OH and O2˙-) to degrade pollutants, while the in situ produced Fe(iii) had the effect of coagulation. With the above action, pollutants were removed, and the pollution load of natural surface water was reduced. After treatment with the UV/Fe(vi) system, dissolved organic carbon was reduced by 49.38%, while UV254 was reduced by 45.00%. The removal rate was further increased to 54.88% and 51.67% after UF treatment. In addition, the fluorescent organics were reduced by 44.22%, and the molecular weight of the organics became smaller. In the stage of UF, the terminal J/J0 was increased from 0.61 to 0.92, and the membrane fouling resistance was decreased by 85.94%. The analysis of the membrane fouling mechanism indicates that the role of cake filtration was weakened among all the mechanisms. Fourier transform infrared spectroscopy showed that less pollutants were accumulated on the membrane surface, and scanning electron microscopy revealed that the membrane pore blockage was relieved. In summary, the UV/Fe(vi) co-treatment process proposed in this study can significantly improve the purification efficiency of the UF systems in natural surface water treatment.

A comprehensive study on combined organic fouling and gypsum scaling in reverse osmosis: Decoupling surface and bulk phenomena

Reverse osmosis (RO), as an energy efficient desalination technology that is critical to mitigate water scarcity, encounters feedwater containing both organic foulants and inorganic scalants. However, comparing with extensive studies on individual fouling or scaling, our knowledge of the behavior and mechanisms associated with combined organic fouling and mineral scaling is still lacking. Due to the potential occurrence of mineral formation in both bulk solution and on the membrane surface, a complete, mechanistic understanding of combined fouling and scaling requires decoupling of surface and bulk phenomena. Herein, our study employed a comprehensive investigation to delve into the intricate interplay of gypsum scaling and organic fouling in RO process. Our systematic approach is accomplished through three sets of experiments that include static experiments and two types of dynamic experiments (i.e., (1) combined fouling and scaling, and (2) gypsum scaling on foulant-conditioned membranes). A variety of model foulants including humic acid, alginate, bovine serum albumin (BSA), and lysozyme were used to investigate the effects of foulant type. Our results demonstrate that the behavior of combined organic fouling and gypsum scaling aligns more with that of gypsum scaling on foulant-conditioned membranes rather than static experiments where bulk nucleation occurs, indicating the predominance of surface nucleation in RO. BSA exhibited a remarkable hindering effect on gypsum scaling, whereas other foulants displayed an additive effect. The lack of scaling mitigation by lysozyme suggests that molecular properties of protein must play a role in regulating the behavior of combined fouling and scaling. Results from multiple characterization techniques reveal the foulant-scalant interactions by delineating the morphological and chemical features of the fouling/scaling layers. Our study not only elucidates the mechanisms of combined organic fouling and gypsum scaling but also sheds light on potential strategies for membrane scaling control in RO desalination.

Polyethersulfone membrane fouling mitigation during ultrafiltration of wastewaters from car washes

The car wash wastewater was separated by ultrafiltration. The commercial ultrafiltration (UF) polyethersulfone (PES) membranes (10 and 100 kDa) were applied. The FTIR analysis indicated that membrane matrix beside PES also contained poly(vinyl pyrrolidone) (PVP). These membranes were used for the wastewater separation, achieving over 50 % rejection of most contaminants and the permeate with a turbidity of <0.2 NTU. It has been shown that a severe membrane fouling was caused not only by the pollutants removed from the cars but also by the detergents used for car washing. As a result, the permeate flux disappeared after 5–10 h of filtration. The Hermia's models analysis indicated that raw wastewater (841 NTU) caused both complete blocking and intermediate fouling mechanism. Wastewater turbidity was reduced by sedimentation (29 NTU), and consequently, cake formation was dominant fouling mechanism in this case. Fouling was reduced by washing the membranes with alkaline agents (pH = 11–12), commonly used in car washes, to clean wheels and remove insects. By washing the membranes every 5–7 h for 30 min with solutions (0.3–0.5 %) of these agents a stable permeate flux at a level of 80 % of the initial flux was obtained during 100 h wastewater filtration tests.

Waste cellulose acetate-based dynamic membrane for NOM-containing river water filtration

Excessive leaching of natural organic matter (NOM) from swamp forests into water resources poses significant challenges for water treatment plants, primarily due to its high variability. In this study, a waste-based cellulose acetate (W-CA) membrane was explored as a dynamic membrane for the filtration of real river water containing NOM and compared to a commercial-based CA (C-CA) membrane. The membranes were fabricated and thoroughly characterized. The results revealed that the W-CA membrane exhibited greater hydrophilicity, as indicated by a static contact angle of 84°, compared to the hydrophobic nature of the C-CA membrane (104°). The mean pore diameters of the C-CA and W-CA membranes were 4.4 µm and 5.3 µm, respectively, suitable as the base for a dynamic filter. The formation of a dynamic cake filtration layer (identified mainly as humic and fulvic acids) was confirmed from visual observation, SEM image and the decrease in the pore sizes. It was further validated from the cake layer as the dominant fouling mechanism obtained from a curve fitting analysis. Despite the W-CA and C-CA membranes respectively showed a high steady-state river water permeabilities of 348 and 226 L/(m2 h bar) respectively, they were still unable to fully remove NOM (27% removal for W-CA and 39% removal for C-CA membrane), suggesting the necessity for further developments. This study underscores the potential of W-CA membranes for water treatment while promoting a circular economy by converting waste into valuable resources and sustainable products.

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.

Two birds, one stone: Simultaneous removal of saccharides and metal ions from ionic liquid solution by selective electrodialysis

The efficient and cost-effective elimination of saccharides and metal ions solving in the ionic liquid spinning solution produced in the regenerated cellulose fibers (RCFs) manufacture is highly desirable in view of the RCF quality and IL recycling. Herein, the ‘two birds and one stone’ strategy was proposed for simultaneous removal of saccharides and metal ions solving in [Emim]Dep spinning solution by selective electrodialysis (SED). Benefiting from the electric neutrality of saccharides, the differences of IL and metal ions (Mg2+ and Ca2+) in electrostatic interaction and hydration radius, the permeation ratio of IL (PIL), removal ratios of saccharides (Rs), Mg2+ (RMg2+) and Ca2+ (RCa2+) could reach up to 96.0 %, 94.8 %, 95.0 % and 95.0 %, respectively in the practical ionic liquid spinning solution. The structure of [Emim]Dep after SED process was similar to that of pristine, indicating the stability during the SED process. Interestingly, the presence of saccharides was beneficial to the removal of metal ions because of the complexation. Moreover, the membrane fouling process and mechanism were also investigated by the determination of ion exchange capacity and the characterization of morphology and structure. Along this line, the corresponding cleaning strategy was raised and the performance of the membrane did not change notably within 5-times recycle. Thus, this work put forward a facile and cost-effective method for one-step removal of saccharides and metal ions and the purification of ionic liquids, which could be popularized in the fields of biomass pretreatment and dissolution using ILs.

Chemical-free vacuum ultraviolet irradiation as ultrafiltration membrane pretreatment technique: Performance, mechanisms and DBPs formation

Membrane fouling induced by natural organic matter (NOM) has seriously affected the further extensive application of ultrafiltration (UF). Herein, a simple, green and robust vacuum ultraviolet (VUV) technology was adopted as pretreatment before UF and ultraviolet (UV) technology was used for comparison. The results showed that control effect of VUV pretreatment on membrane fouling was better than that of UV pretreatment, as evidenced by the increase of normalized flux from 0.27 to 0.38 and 0.73 after 30 min UV or VUV pretreatment, respectively. This is related to the fact that VUV pretreatment exhibited stronger NOM degradation ability than UV pretreatment owing to the formation of HO•. The steady-state concentration of HO• was calculated as 3.04 × 10−13 M and the cumulative exposure of HO• reached 5.52 × 10−10 M s after 30 min of VUV irradiation. And the second-order rate constant between NOM and HO• was determined as 1.36 × 104 L mg−1 s−1. Furthermore, fluorescence EEM could be applied to predict membrane fouling induced by humic-enriched water. Standard blocking and cake filtration were major fouling mechanisms. Moreover, extension of UV pretreatment time increased the disinfection by-products (DBPs) formation, the DBPs concentration was enhanced from 322.36 to 1187.80 μg/L after 210 min pretreatment. However, VUV pretreatment for 150 min reduced DBPs content to 282.57 μg/L, and DBPs content continued to decrease with the extension of pretreatment time, revealing that VUV pretreatment achieved effective control of DBPs. The variation trend of cytotoxicity and health risk of DBPs was similar to that of DBPs concentration. In summary, VUV pretreatment exhibited excellent effect on membrane fouling alleviation, NOM degradation and DBPs control under a certain pretreatment time.

Investigating the role of aliphatic olefins in fouling of thermally cracked bitumen by testing fouling tendency of model aliphatic olefin compounds in light fractions

Olefins are considered non-desirable compounds that are formed in the thermal cracking step of crude oil. Due to their high reactivity, they are linked to the fouling tendency of thermally cracked petroleum products. In this work, the role of aliphatic olefins in the fouling of thermally cracked petroleum products is studied by investigating the fouling tendency of model aliphatic olefin compounds blended with Western Canadian Select (WCS) crude, a low-fouling material, in an Alcor hot liquid process simulator (HLPS) fouling testing apparatus. The tested model olefin compounds were selected to have different types (mono-olefin, conjugated diolefins, non-conjugated diolefins), structures, and boiling points. The model olefin compounds were tested individually and in mixtures to determine the fouling tendency. Moreover, a light fraction of thermally cracked bitumen, which contains a significant concentration of olefinic species, was blended with the heavy fraction of WCS to simulate a thermal cracking derived olefin sample with a reasonable olefin content. Olefin and olefin mixture blends were tested in the Alcor HLPS unit to determine the temperature drop (ΔT) due to fouling on the heated rod of the Alcor HLPS unit that leads to a reduction in the heat transfer coefficient. All tested samples resulted in low or low-medium fouling when compared to a thermally cracked bitumen. The results indicated that aliphatic olefins, in the low boiling range, were not the sole contributor to fouling and other constituents, such as asphaltenes or high molecular weight olefins in the heavy fractions, and other properties, such as product stability (measured by P-value), might have a synergetic effect with olefins in the fouling mechanism. Therefore, the role of aliphatic olefins in fouling in petroleum products is reduced in the absence of the aforementioned constituents and properties.

Fe3S4/persulfate-based pre-oxidation for mitigating membrane fouling and enhancing synergistic perfluorooctanoic acid removal: Influence of pH and persulfate types

Aerobic granular sludge membrane system (AGSMS) represents a new wastewater reuse treatment technology. However, the challenges of membrane fouling and limited micropollutant removal efficiency significantly impact its potential for further application. Consequently, this study aimed to address these concerns by employing Fe3S4/persulfate pretreatment to mitigate membrane fouling and enhance perfluorooctanoic acid (PFOA) removal in AGSMS. The effects of pH and persulfate types were investigated by assessing membrane flux, fouling resistance, membrane characterization, and effluent properties. Results showed that optimal mitigation of membrane fouling and removal of PFOA were achieved using Fe3S4-activated PMS at a pH of 6. The primary mechanism for Fe3S4-activated PMS involved the generation of SO4•− and 1O2. Moreover, the fouling mechanism transitioned from cake layer fouling and intermediate blocking fouling to complete blocking fouling in the presence of Fe3S4/PMS. The application of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that at pH 6.0, there was a significant increase in the energy barrier for both foulant-membrane and foulant-foulant interactions, leading to an effective mitigation of membrane fouling. Correlation analysis demonstrated a significant influence of polysaccharides and total phosphorus concentration on mitigating membrane fouling. Furthermore, pH played a crucial role in mitigating membrane fouling as well as pollutant removal by influencing both coexisting ion states in solution and catalyst properties. This study offers valuable insights for future research and provides essential theoretical guidance for large-scale applications of AGSMS technology in wastewater treatment.

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.

MECHANISM OF MEMBRANE FOULING IN HYBRID MEMBRANE PHOTOCATALYTIC REACTOR FOR PALM OIL MILL SECONDARY EFFLUENT TREATMENT

Palm oil mill secondary effluent (POMSE) is a byproduct of the biological treatment of palm oil mill effluent. This research aims to investigate the mechanism of membrane fouling in the treatment of POMSE using a hybrid membrane photocatalytic reactor (MPR). The effectiveness of MPR in POMSE treatment is currently limited due to membrane fouling on the membrane surface. This study focuses on understanding the various mechanisms of membrane fouling, including complete blocking, intermediate blocking, standard blocking, and cake filtration. The determination of each fouling mechanism is achieved through an analysis of normalized flux data employing the Wiesner and Aptel equation. The results demonstrate a high degree of model fitness (R2 = 0.9576) for MPR Run 3, confirming its effectiveness. Based on the (R2) values and the fitted parameter (Ks^(-1)), it is evident that, under varying pH levels, catalyst types, catalyst loading, and initial POMSE concentrations, the cake formation fouling mechanism prevails in MPR Run. In conclusion, this research holds promising potential for implementation in the wastewater treatment industry while ensuring compliance with environmental regulations.

Membrane fouling and influencing factors of a submerged commercial ceramic flat membrane bioreactor in treatment of coal chemical wastewater

An anoxic/oxic (A/O) treatment unit was upgraded using a submerged commercial ceramic flat-membrane bioreactor. The upgraded bioreactor effectively treated coal chemical wastewater. However, the factors influencing membrane fouling remain unclear. Thus, this study explored the mechanisms of membrane fouling of a commercial ceramic flat membrane bioreactor. With increasing duration of backwash, the rate of growth of transmembrane pressure (TMP) gradually increased. The proportions of concentration polarization resistance Rp and cake layer resistance Rf were 48.87% and 50.08%, respectively. Under the action of static electricity, negatively charged particles in the mixed liquid do not easily adhere to the membrane. Under conditions of high mixed liquid suspended solids (＞12 000 mg/L), an increase in the suspended solid content in the mixture caused membrane fouling and pore blockage. When the flux exceeded 58 L·m−2·h−1, the TMP increased sharply. When the aeration rate exceeded 200 mL/min, the impact of membrane erosion on fouling was no longer significant. The optimal suction/cessation ratio was 7:3. After cleaning with NaOH and NaClO, surface fouling of the membrane was significantly reduced.

Treatment of food processing industries wastewater using a novel Fuller's earth clay-based tubular ceramic membrane.

This study investigates the feasibility of a robust, low-cost tubular microfiltration ceramic membrane fabricated using a mixture of locally available Fuller's earth clay (FEC) and solid waste material, rice husk ash (RHA), to treat effluents generated by a local dairy and palm oil industries. Fabrication of the membrane was carried out by employing the extrusion method followed by sintering at a temperature of 850 °C. Raw materials were characterized using XRD, XRF, FTIR, TGA, and differential thermal analysis (DTA). The membrane that underwent sintering exhibits a 61% porosity level, 43.29 L/m2 h bar water permeability, 0.115 μm average pore size, and relatively good corrosion resistance. Further, the effect of different operating conditions, including pressure (1.03-2.41 bar) and cross-flow rate (30-150 Lph), on the microfiltration of both the wastewaters is studied. The membrane lowered the COD levels below the discharge limit (<200 mg/L) of the Central Pollution Control of India for both wastewaters. Finally, Hermia's fouling models were used to identify the fouling mechanism concerned.