Inorganic Fouling Research Articles

Manuscript for: Journal of Environmental Chemical Engineering New insights into the influence of ultrafiltration pretreatment on reverse osmosis membrane fouling during urban sewage reclamation: Interaction between extracellular polymeric substances and inorganic foulants

Ultrafiltration (UF) has been frequently employed as pretreatment to mitigate reverse osmosis (RO) membrane fouling. The organic and inorganic substances outflowing from UF pretreatment collectively determine the subsequent RO membrane fouling behavior. However, most of the previous studies were focused on single organic compounds as well as CaSO4 scaling, yet complex organic matter such as extracellular polymeric substances (EPS) and various inorganic scaling (i.e. CaCO3, Ca3(PO4)2) coexisted during urban sewage reclamation. In this study, the impact of UF pretreatment on RO membrane fouling behavior, especially the interaction between EPS and CaCO3/Ca3(PO4)2 scaling, were systematically investigated. Results showed that the presence of UF significantly reduced the normalized flux decline (9.3% vs. 14.3%) and enhanced cleaning recovery efficiency (84.6% vs. 51.6%) of RO membrane, but increased scattered crystals (CaCO3 and Ca3(PO4)2) formation on RO membrane surface. Further investigation showed that the binding energy of the Ca2p1/2 and Ca2p3/2 peaks on fouled RO membrane exhibited a shift towards lower energy, which indicated a weak complexation between EPS and Ca2+, thereby increasing inorganic scaling and confirming the two-sides role of EPS retained by UF in RO membrane fouling. Moreover, static experiments indicated that EPS inhibited CaCO3 scaling rather than Ca3(PO4)2 scaling with the inhibition rates of 7.3% and 0.7%, respectively. To the best of our knowledge, it is the first to reveal the different effect of EPS on CaCO3 and Ca3(PO4)2 scaling. The results may provide a new insight into the effect of UF pretreatment on RO membrane fouling during urban sewage reclamation process.

Fouling and Chemical Cleaning Strategies for Submerged Ultrafiltration Membrane: Synchronized Bench-Scale, Full-Scale, and Engineering Tests

This study investigated membrane fouling issues associated with the operation of a submerged ultrafiltration membrane in a drinking water treatment plant (DWTP) and optimized the associated chemical cleaning strategies. By analyzing the surface components of the membrane foulant and the compositions of the membrane cleaning solution, the primary causes of membrane fouling were identified. Membrane fouling control strategies suitable for the DWTP were evaluated through chemical cleaning tests conducted for bench-scale, full-scale, and engineering cases. The results show that the membrane foulants were primarily composed of a mixture of inorganics and organics; the inorganics were mainly composed of Al and Si, while the organics were primarily humic acid (HA). Sodium citrate proved to be the most effective cleaning agent for inorganic fouling, which was mainly composed of Al, whereas sodium hypochlorite (NaClO) combined with sodium hydroxide (NaOH) showed the best removal efficiency for organic fouling, which predominantly consisted of HA and Si. However, sodium hypochlorite (NaClO) combined with sodium hydroxide (NaOH) showed the best removal efficiency for organic fouling and Si; organic fouling predominantly consisted of HA. Based on the bench-scale test results, flux recovery was verified in the full-scale system. Under a constant pressure of 30 kPa, the combined acid–alkali cleaning achieved the best flux recovery, restoring the flux from 22.8 L/(m2·h) to 66.75 L/(m2·h). In the engineering tests, combined acid–alkali cleaning yielded results consistent with those of the full-scale tests. In the practical engineering cleaning process, adopting a cleaning strategy of alkaline (NaClO + NaOH) cleaning followed by acidic (sodium citrate) cleaning can effectively solve the membrane fouling problem.

Phenomenological Interpretations of Membrane Properties Following Repeated Chemical Cleaning of an End-of-Life Potable Reuse Reverse Osmosis Element Dominated by Inorganic Fouling

Phenomenological Interpretations of Membrane Properties Following Repeated Chemical Cleaning of an End-of-Life Potable Reuse Reverse Osmosis Element Dominated by Inorganic Fouling

Hybrid membrane process for nutrient recovery and sodium reduction in aquaculture wastewater

The swift growth of the aquaculture industry has exacerbated nutrient discharge, leading to eutrophication, while low nutrient but high sodium content impedes effective nutrient recovery and reuse. This study presents a novel hybrid membrane-based treatment sequence comprising ammonia stripping (AS), vacuum membrane distillation (VMD), and nanofiltration in diafiltration mode (NF), designed to efficiently recover ammonia and phosphate and reduce sodium from mixed aquaculture effluents. The process achieved ammonia and phosphate recovery efficiencies of 88.74 % and over 99 %, respectively, with a corresponding sodium reduction of 99.04 wt%. The AS stage concentrated ammonia from 20.37 mg/L to 2046.67 mg/L, whereas the subsequent VMD and NF stages produced phosphate-rich (rose from 10.33 mg/L to 50.50 mg/L) and sodium-reduced retentates (decreased from 510 mg/L to 44.50 mg/L). Long-term testing over eight consecutive batches showed robust performance with ammonia flux decline by only 2.81 %, permeate flux reduction by 4.30 %, and minimal inorganic fouling, maintaining consistent permeate quality that met environmental standards. These findings underline the proposed hybrid process's potential for sustainable aquaculture wastewater management, offering substantial enhancement in nutrient and water recycling.

Effects of pre-chlorination on ultrafiltration process in directly treating seasonal high-turbidity surface water: Membrane fouling control and shock load resisting

The seasonal high turbidity in the surface water is posing great challenges to the feasibility of direct ultrafiltration (UF) due to the severe membrane fouling. In this study, a direct UF process was employed to treat the high-turbidity surface water. With the conventional operational protocols, severe membrane fouling encountered. Model fitting indicated that membrane fouling, resulting from the UF of high turbidity water, was predominantly associated with the complete obstruction of pores on the surface of the membrane and the subsequent formation of a cake layer. A pre-disinfection process using sodium hypochlorite was developed in this study, and the membrane fouling was significantly mitigated during long-term (885 h) filtration. The optimized chlorine dosage was 1.5 mg/L in treating the 800 NTU surface water, and enabled the transmembrane pressure (TMP) stabilization of UF process at a low level (<10 kpa). Pre-disinfection can effectively inactivate microorganisms and diminish the presence of microbial extracellular polymeric substances (EPS). This results in a transition from complex and viscous fouling to inorganic fouling on the cake layer caused by high turbidity water. With pre-chlorination, the adhesion force of the cake layer attached on the membrane reduced significantly to make the fouling more easily detach and be removed from on the membrane surface by the shear stress caused by the hydraulic backwash. These findings are expected to develop new insights into the membrane fouling control of UF in directly treating the seasonal high-turbidity surface water.

Rejection of heavy metal ions in water by zeolite forward osmosis membrane

Water treatment of heavy metals using zeolite membranes in forward osmosis was demonstrated. A continuous Na-ZSM-5, aluminosilicate zeolite, crystal layer was synthesized on the outer surface of a porous tubular α-alumina support and used as the forward osmosis membrane. The rejection performances and fouling resistances of Na-ZSM-5 membrane were studied. Na-ZSM-5 membrane exhibited a high rejection performance of 99 % for various metal species (As(III), As(V), Se(IV), Se(VI), Cr(VI)). This superior rejection performance was achieved by combining the molecular sieving effect and electrostatic repulsion between the anions and the anionic framework of the zeolite. Na-ZSM-5 membrane exhibited a stable water flux in the presence of model foulants such as sodium alginate, humic acid, bovine serum albumin, and silica particles, suggesting that the membrane had excellent antifouling properties against both organic and inorganic foulants.

Selective electrodialysis for nutrient recovery and pharmaceutical removal from liquid digestate: Pilot-scale investigation and potential fertilizer production

The present research employs a pilot-scale selective electrodialysis system to treat liquid digestate, fractionating nutrient ions and exploring fertilizer creation via ammonia stripping and phosphorus precipitation, while studying pharmaceutical transport behavior and examining membrane fouling. The influence of diverse potentials was studied in simulated and real digestate, with 30 V application proven more efficient overall. Applying consecutive runs resulted in products that were 7.9, 7.4, 1.7, 5.3, and 6 times more concentrated compared to the feed solution for NH4+, K+, PO43-, Ca2+, and Mg2+, respectively. Pharmaceuticals analysis showed that ciprofloxacin was completely retained in the liquid digestate, while ibuprofen was detected in the anionic product. Diclofenac was initially present in the digestate but was undetectable in the final products, suggesting it adhered to the membrane. Membranes showed inorganic and organic fouling. The monovalent cation exchange membrane had severe salt scaling, showing calcium and magnesium deposits, and fewer functional groups.

Optimized removal of silica during manure treatment by electrocoagulation-flotation (EC-F) in view of fouling prevention of reverse osmosis membranes

Reverse osmosis (RO) membrane fouling threatens the performance of manure treatment. In this regard, silica is considered one of the most challenging inorganic foulants. Removing silica fouling from RO membranes is difficult, ultimately leading to performance deterioration, including reduced permeability and premature membrane failure. This study examines the removal of silica during manure treatment using a novel tubular electrocoagulation-flotation (EC-F) reactor with an Al electrode. The EC-F was positioned between an ultrafiltration and a RO membrane filtration system. The operational parameters—current density, electrolysis residence time, and initial pH—were optimized for maximum silica removal efficiency and minimum operational cost. At the optimum conditions (pH of 8.2, current density of 160 A/m2 and electrolysis residence time of 23 s), 88 % of silica (initial concentration of 104 mg/L) was removed. Subsequent membrane fouling assessment revealed that EC-F pretreatment decreased the fouling potential by 28 % (from 7.11 × 1016 to 5.10 × 1016 Pa·s/m2·t), indicating efficient foulant removal. SEM-EDX analysis of the membrane confirmed the lack of scale formation when using EC-F pretreated manure as a feed stream. This study demonstrates that the use of innovative EC-F pretreatment significantly reduces the operational expenditure (1.75 €/m3) compared to prior EC-F research for silica removal from manure, thereby reducing the fouling of RO membranes.

Optimizing fouling mitigation in membrane distillation by controlled microbubble size and concentration

Fouling control strategies play a crucial role in membrane distillation (MD) process, primarily due to the significant limitation of fouling during the scaling-up process. The utilization of microbubbles (MBs) aeration has exhibited promising potential in mitigating membrane fouling when treating high salinity wastewater. Aeration can introduce gas-liquid two-phase flow on the membrane surface, thereby increasing the membrane surface shear force. The mechanism of aeration technology for controlling fouling includes the following points: introduction of gas-liquid two-phase flow; physical substitution of concentration polarization layer; pressure pulses caused by bubbles flowing through the membrane surface and increasement of the cross flow velocity. This research aims to optimizing the effect of air MBs with different concentrations and sizes introduced in the feed side on membrane fouling control, we creatively used the method of releasing pressure gradiently to achieve size regulation of MBs within a certain range for the first time, firstly regulated the generation of MBs by manipulating gas flow rate and release pressure. Under the optimal condition of 40 mL/min and 0.6 MPa, it will yield concentration of 1.58 × 104/mL and D50 Sauter size of 64.69 μm MBs with pure water permeance flux of 12.32 kg/(m2·h). It was observed that higher gas flow rates primarily increased MBs concentration, while lower pressures predominantly reduced MBs size through the method of inline imaging. Experimental results indicated that introduction of MBs can slightly improve the temperature polarization coefficient and mass transfer coefficient under different operating modes. Consequently, further investigations focused on the influence of MBs characteristics on different fouling control. All conditions reach 99 % rejection for inorganic salt and HA. This study provided empirical evidence that higher concentration and larger size of MBs intensify the gas-liquid two-phase flow disruption and exhibit a better shear effect on scaling phenomena, which yield advantageous outcomes in terms of augmenting permeance flux and water vapor production, with permeance flux increased from 40.12 % to 55.42 % for inorganic fouling and increased from 68.35 % to 80.15 % for inorganic and HA fouling. These results were confirmed via membrane surface using scanning electron microscopy and energy dispersive spectroscopy. In summary, this research aided in identifying appropriate operating conditions for mitigating inorganic and composite scaling by implementing air-infused MBs in direct contact membrane distillation (DCMD), which provides scientific and technical guidance for controlling fouling in MD in practical applications.

Investigation of membrane fouling behaviors triggered by different characteristics of anaerobic digestion effluent in membrane distillation

This study investigated the membrane fouling behaviors triggered by different characteristics of anaerobic digestion (AD) effluents in the operation of 851-h membrane distillation (MD). The AD effluents with different concentration factors (CF) were used as the feed separately. Results illustrated a stable normalized water flux in the treatment of raw AD effluent (CF = 1) over the 851-h MD experiment, showing negligible membrane fouling. While the sharp decreases in normalized water flux occurred when treating the concentrated AD effluents. The membrane fouling mechanism tended to change from inorganic scaling to organic fouling when the CF value increased from 1 to 3, while the combination of organic and inorganic fouling dominated the membrane fouling when CF was 5. Inorganic fouling was further intensified when the CF value increased to 10. The regression analysis demonstrated that the complete blocking model was the dominant development mechanism for CF = 3 treatment. The membrane fouling mechanism of CF = 5 treatment switched from the cake filtration model in the intermediate phase to the standard blocking model in the final phase. Additionally, there was a transition from the complete blocking model to the standard blocking model for CF = 10 treatment. The study may provide an in-depth knowledge of membrane fouling control during the actual AD effluent concentrating process.

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

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

Off-line chemical cleaning reduces the spatial heterogeneity of membrane fouling in full-scale membrane bioreactors: A case study

Full-scale membrane bioreactors (MBRs) are widely employed for wastewater treatment. Nevertheless, the spatial heterogeneity of membrane fouling within full-scale MBR modules has received limited attention, especially regarding the impact of off-line chemical cleaning on this spatial heterogeneity. This study, based on 192 hollow fiber samples collected from two full-scale MBRs, investigated the spatial fouling heterogeneity before and after off-line chemical cleaning. The membrane samples were categorized into different groups based on sampling locations, and statistical tools were employed to analyze spatial fouling heterogeneity. The results of foulant mass and filtration resistance of samples confirmed the presence of spatial fouling heterogeneity within the MBR modules after 5 months of operation. The off-line chemical cleaning removed organic foulants more effectively than inorganic foulants, and interestingly, it effectively reduced the spatial fouling heterogeneity. Computational fluid dynamics analysis in the cleaning tank and the chlorine concentration distribution indicated that chemical cleaning occurred without mass transfer or reaction limitations. We further offer insights into the reduction of spatial fouling heterogeneity by clarifying the fouling layer structure and the role of off-line chemical cleaning. Our findings suggest that with an appropriate cleaning strategy, the hollow fiber filtration performance can be rebalanced before a new operation cycle.

In situ disinfection and green hydrogen production using carbon-based cathodes in seawater electrolysis

Electrolysis is an advanced oxidation process used to treat aquaculture effluents, commonly by employing precious-metal-based electrodes. However, such electrodes increase operation costs, prompting the need for novel electrodes. Low-cost carbon-based electrodes have been suggested as large-surface-area electrodes; however, their stability under long-term electrochemical operation, particularly in natural seawater, should be improved. Herein, carbon-based cathodes were applied in seawater electrolysis for in situ disinfection and green hydrogen production to recycle aquaculture effluents. Functionalized carbon black (CB) generated the highest hydrogen production of 46.6 ± 4 mL (purity ≥99.9 ± 0.05 %), which was 1.4 times higher than that for bare carbon cloth (CC). The production of sodium hypochlorous acid at >600 ± 50 mg/L was higher over functionalized CB/CC than that over bare CC. Within 1 min, the aquaculture effluent was disinfected with a high removal efficiency of 99.5 ± 0.05 %, which was similar to that for a platinum/titanium cathode. The cathodes exhibited higher potential stability (3.7 ± 0.5 V) than platinum/CB/CC under a constant current for 20 h owing to the control of inorganic fouling. Thus, these electrodes are efficient alternatives that can promote commercialization by reducing the costs and facilitate electrochemical and green production of hydrogen and oxidants.

Study on the mechanism of mitigating membrane fouling in MFC-AnMBR coupling system treating sodium and magnesium ion-containing wastewater

ABSTRACT Anaerobic Membrane Bioreactors (AnMBR) offer numerous advantages in wastewater treatment, yet they are prone to membrane fouling after extended operation, impeding their long-term efficiency and stability. In this study, a coupled system was developed using modified conductive membranes as the filtration membrane for the AnMBR and as the anodic conductive membrane in the microbial electrochemical system, with a total volume of approximately 2.57 L. The research focused on understanding the membrane fouling characteristics of the AnMBR when treating wastewater containing sodium ion (Na+) and magnesium ion (Mg2+). When the system was treating wastewater containing Na+, organic pollutants such as proteins and polysaccharides were identified as the primary causes of membrane fouling. Three experimental groups generating different electric currents exhibited extended operational times compared to the open-circuit control group, with extensions of 30, 24, and 15 days, respectively. Conversely, when treating wastewater with Mg2+, organic–inorganic composite fouling, primarily driven by Mg2+ bridging, emerged as the key challenge, with the experimental groups showing operational extensions of 5, 8, and 23 days, respectively, in comparison to the control group. Analysis of proteins and polysaccharides indicated that electric current played a crucial role in reducing organic fouling in the sludge cake layer. When treating wastewater containing Na+, the effectiveness of membrane fouling control was directly proportional to the electric current, while when treating wastewater containing Mg2+, it was directly proportional to the voltage.

Membrane fouling in engineering nanofiltration process for drinking water treatment: The spatial and chemical aspects

Nanofiltration (NF) has become an established process for advanced treatment of drinking water, while membrane fouling remains as the main issue slowing the widespread application of the process. In this study, the key foulants were identified, and their spatial distribution and potential interactions were investigated based on a two-stage NF engineering project for municipal drinking water treatment. Over half a year of operation showed that the membrane fouling was mostly chemically reversible. Characterizations of the cleaning waste revealed that inorganic fouling dominated at both stages, which was mainly caused by the deposition of Al, Ca, and Si. While the overall fouling was much more severe at Stage 2, the organic fouling was the reverse. Autopsy of one full-size membrane element from each stage indicated that in addition to Al, P and humic acid-like compounds were abundant in the fouling layer for both stages despite the spatial differences. The spatial distribution of foulants was influenced by both concentration effects and presence of feed channel spacers. For the free membrane area, inorganic foulants and humic acid-like compounds had higher contents at Stage 2 than Stage 1. While for the membrane area contacting with spacers, Al and P at Stage 1 were 0.74 and 1.51 times higher than those at Stage 2, respectively. Moreover, statistical analysis, complexation experiments and engineering operation strongly supported that the residual Al and natural organic matter (NOM) were key foulants for the NF process, mainly by forming Al-NOM complexes. Besides the Al-NOM complexes, condensed phosphate, primarily sourced from the dosed phosphate-containing antiscalants, might also co-precipitate with Al or Al-NOM complexes.

Combined impacts of aluminum and silica ions on RO membrane fouling in full-scale ultrapure water production facilities

In this study, a fouled reverse osmosis (RO) membrane from a full-scale ultrapure water (UPW) facility was autopsied and investigated to propose the fouling mechanism and mitigation strategies. Although the influent was introduced to the coagulation and ultrafiltration as the pre-treatment processes, thick fouling layers were found over the entire RO surface. The foulant was mainly composed of aluminum silicates due to the elevated Al concentration (up to 100 μg/L) originated from the coagulation process utilizing polyaluminum chloride, and high recovery (up to than 90%) of RO process. Lab-scale fouling tests also confirmed that the elevated Al concentration in the RO influent contributed to significant flux decline due to a bridging effect with negatively charged organic matter and the formation of aluminum silicates. The application of polydiallyldimethylammonium chloride as an alternative coagulant successfully mitigated the organic and silicate fouling. Therefore, control of the residual aluminum ions originated from the coagulation process is critical to mitigate both organic and inorganic fouling on RO membrane surfaces during the production of UPW.

Electrochemical silica removal from carbon nanotube surfaces: Energy consumption and removal mechanisms

Inorganic fouling, or scaling, is a major challenge for engineered systems exposed to aqueous environments, particularly in water treatment, desalination, or thermal systems where the high salinity and temperature conditions favor surface scaling. Silica, in particular, is hard to remove once a scaling layer forms on the surface. Current scaling mitigation strategies include the addition of antiscalants, physical cleaning by flushing or backwashing, and pretreatment of the feed water. These mitigation strategies increase operation costs due to increased chemical use and system downtime, as well increase the complexity of the process. In this work, we investigated the ability of carbon nanotube (CNT) coatings to disperse silica from the surface via electrochemical reactions, providing a chemical-free approach to scaling control. Silica scaling was induced and then dispersed from CNT coupons upon the application of a potential difference across the experimental set up, with the CNT coupon acting as a cathode or anode. Scale removal was measured using optical coherence tomography at different applied current densities. In this study, a cathodic current of 2.5 A/m2 was found to achieve the highest silica removal: > 75% after 30 min. Control experiments conducted using pH-buffered solutions and pH-insensitive gypsum as the scaling mineral suggest that silica dispersion from the CNT surface was due to a combination of gas evolution and interfacial pH change. These results provide a better understanding of the potential of using electrochemical coatings for the removal of inorganic fouling from surfaces.

Fouling of reverse osmosis membrane in sugar mill condensate purification under sub- and super-boundary flux conditions

The sugar production process, inherently water-intensive, is characterized by pronounced condensate formation during the evaporation and boiling phases. Given the environmental and resource implications, there is a scholarly emphasis on the potable reuse of such condensate by reverse osmosis (RO) in sugar mills. However, membrane fouling presents a significant challenge to the consistent operation of the RO process. This research examines the influence of operating parameters, namely transmembrane pressure and crossflow velocity, on the performance and fouling tendencies of an RO membrane during the purification of sugar mill condensate. The boundary flux theory was employed to model the permeate flux throughout this process. A boundary flux (5.92 L h−1m−2) and its corresponding operating pressure (10 bar) were determined. Moreover, a comparative analysis of the fouling mechanisms and the composition of the foulant layer under both sub-boundary and super-boundary conditions was undertaken. Under sub-boundary conditions, the fouling mechanism was identified as cake-intermediate blocking, while the super-boundary condition exhibited intermediate blocking. Under both conditions, organic fouling emerged as the primary fouling type. The TOC of surface contaminants ranged from 1.07 to 1.86 g/m2. Within this, proteins (484.0 to 850.3 mg m−2) and polysaccharides (201.5 to 379.2 mg m−2) were the dominant components. However, when operating conditions surpassed the boundary, there was a noticeable rise in inorganic fouling such as Ca (from 44.95 to 149.43 mg m−2) and Fe (from 4.40 to 112.09 mg m−2), which is likely due to the co-deposition of organic materials with inorganic ions. This research contributes to a more nuanced understanding of how operating conditions influence fouling mechanisms and provides foundational insights for addressing fouling challenges in sugar mill condensate purification.

Effect of preoxidation on fouling mitigation in a low-pressure membrane system with clean-in-place (CIP) treatment

The study investigates the impact of biological (soluble microbial products), organic (humic acid), and inorganic foulants (Al, Mn, and Fe) on the structure of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes during filtration processes. While different forms of Al, including mononuclear (Ala), colloidal (Alc), and polymeric (Alb) species, were also analyzed and a chlorination dose of 1.5 mg.L−1 was used as pretreatment for the feed water. The results revealed that the PES membranes exposed to the untreated feed solution were more vulnerable to severe structural deterioration as compared to PVDF membranes, in the presence of organic/biological foulants and complex mixtures of organic and inorganic foulants. Presence of carbonate (O-C=O) and carboxylic groups on PES membranes and the reduction of hydrophilic additives on PVDF membranes after exposure to the feed streams was observed. Moreover, the pore size of the PES and PVDF membranes increased to 1308.1 nm and 287.8 nm, respectively, at the end of study. The PVDF membranes exhibited severe fouling than PES membranes due to strong adsorption potential for the foulants. Moreover, Alb had stronger fouling effect that Ala and Alc, while pre-chlorination increased charge neutralization and reduced fouling due to weaker binding with the organic foulants. Results from Hermia's fouling model confirmed the occurrence of complete blocking, followed by the formation of a cake layer and intermediate fouling.

Enhancing stormwater treatment through ultrafiltration: Impact of cleaning chemicals and backwash duration on membrane efficiency

Abstract The effect of chemical cleaning and regular backwashing on the efficiency of an ultrafiltration membrane fouled during stormwater treatment was studied. Increasing backwash time from 30 to 60 s resulted in an increase in productivity by 20%. However, the productivity was highest when a backwash time of 45 s was used (3% higher than using 60 s). Chemical cleaning was carried out using an alkaline solution (NaOH with or without NaOCl) followed by acid washing with HCl. The addition of NaOCl to the cleaning chemical did not significantly increase the efficiency of chemical cleaning, and the average pure water permeability increase was 97 ± 13 LMH bar−1 after chemical cleaning with NaOH followed by HCl and 117 ± 15 LMH bar−1 after chemical cleaning with NaOH + NaOCl followed by HCl, on average. In addition, reversibility after chemical cleaning was 96 ± 67%, on average. The result from scanning electron microscopy showed that at the end of the experiments, inorganic foulants existed in both the inner layer (feed side) and the outer layer (permeate side) of the membrane.