Porous Cake Layer Research Articles

Membrane fouling characteristics and mechanisms in coagulation-ultrafiltration process for treating microplastic-containing water

Microplastics (MPs) are recognized as a significant challenge to water treatment processes due to their ability to adsorb or accumulate alginate foulants, impacting the coagulation-ultrafiltration (CUF) process. In this study, the mechanisms of membrane fouling caused by MPs under varying dosages of polymeric aluminum chloride (PAC) coagulant in the CUF process were investigated. It was revealed that MPs contribute to membrane fouling, which initially intensifies and then alleviates as coagulant concentration increases, with a turning point at 0.05 mM PAC dosage. The most significant alleviation of membrane fouling was observed at 0.2 mM PAC dosage. An in-depth analysis of interfacial interaction energy changes during filtration was conducted using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, demonstrating how MPs alter the interaction forces between foulants and the membrane surface, leading to either the exacerbation or mitigation of fouling. Additionally, it was shown that at optimal coagulant concentrations, the presence of MPs promotes the formation of a loose and porous cake layer, disrupting the original structure and creating a more open block structure, thereby alleviating membrane fouling. These findings provide valuable insights for optimizing the CUF process in microplastic-containing water treatment, presenting a novel approach to enhancing efficiency and reducing membrane fouling.

A membrane fouling control strategy based on a combination of pre-treatment mitigation and in-situ membrane surface regulation using a composite coagulant

Ultrafiltration technology (UF) is efficient in surface water treatment, but its development and widespread application are limited by membrane fouling. Herein, an efficient and stable polymerized ferric titanium coagulant (PFTC) was synthesized and used as a UF pretreatment agent in actual lake water treatment. The control mechanism of PFTC on membrane fouling was investigated from the perspective of organic removal efficiency and in-situ membrane surface regulation. PFTC demonstrated a remarkable affinity for soluble metabolic intermediates and hydrophilic proteins through complexation and hydrogen bonding force, achieving removal efficiencies of 66.4 % for UV254 and 81.3 % for DOC, respectively. The hydrophilic pollutants with high molecular weight and non-saturated structure could be preferentially removed by PFTC due to its diverse hydrolysates including positively charged Fe-based hydrolysates, amorphous Ti-based hydrolysates, and highly polymerized Fe-Ti copolymers. The flocs generated by PFTC exhibited strong hydrophilicity, allowing for the formation of a loose porous cake layer on the ultrafiltration membrane, which acted as a hydrophilic layer to enhance the anti-fouling performance of ultrafiltration membrane. With its dual function of contaminant removal and in-situ membrane surface regulation, PFTC alleviated 98.9 % of membrane fouling. This study provides new insights into membrane fouling control by coagulation pretreatment and efficient treatment of surface water.

Enhanced performance of aerobic granular sludge-membrane system through the utilization of different iron-based nano-metal oxides for mitigating membrane fouling

Fe3O4, γ-Fe2O3, and α-Fe2O3 nanoparticles play a crucial role in influencing the adsorption capacity and pretreatment efficacy as iron-based nano-metal oxides due to their distinct structural and physicochemical properties. However, the impact of these adsorbents on membrane filtration efficiency remains unexplored. This study aimed to investigate the influence of these three adsorbents on membrane fouling in an aerobic granular sludge–membrane system (AGSMS) used for municipal wastewater reuse treatment. The results demonstrated that under optimal conditions, γ-Fe2O3 exhibited superior effectiveness in removing low and medium molecular weight contaminants from wastewater, resulting in a higher normalized flux (0.59) and reduced total fouling resistance (2.66 × 1011 m−1). It also showed the highest removal rate for organic matter and suspended solids, making it particularly effective in mitigating AGSMS membrane fouling. However, excessive addition (2 g/L) of Fe3O4, γ-Fe2O3, and α-Fe2O3 could potentially hinder the proper operation of the AGSMS. Pre-adsorption facilitated the formation of a porous cake layer while inhibiting standard blocking behavior. Additionally, the extended Derjaguin–Landau–Verwey–Overbeek theory analysis revealed a substantial energy barrier between membrane-foulant interactions (125.65 kT) as well as foulant-foulant interactions (62.06 kT) within the γ-Fe2O3 system, confirming its exceptional antifouling characteristics. This study offers valuable insights into the selection of iron oxide adsorbents for membrane fouling mitigation and wastewater reuse.

Degradation of sulfamethazine in coastal aquaculture tailwater by Na2S2O4@iron-electrode electrooxidation combined with ceramic membrane process

Offshore aquaculture's explosive growth improves the public food chain while also unavoidably adding new pollutants to the environment. Consequently, the protection of coastal marine eco-systems depends on the efficient treatment of wastewater from marine aquaculture. For the sulfamethazine (SMZ) of representative sulfonamides and total organic pollutants removal utilizing in-situ high salinity, this work has established an inventive and systematic treatment process coupled with iron-electrode electrochemical and ultrafiltration. Additionally, the activated dithionite (DTN) was being used in the electrochemical and ultrafiltration processes with electricity/varivalent iron (FeII/FeIII) and ceramic membrane (CM), respectively, indicated by the notations DTN@iron-electrode/EO-CM. Quenching experiments and ESR detection have identified plenty of reactive species including SO4·-, ·OH, 1O2, and O2·-, for the advanced treatment. In addition, the mass spectrometry (MS) and the Gaussian simulation calculation for these primary reaction sites revealed the dominate SMZ degradation mechanisms, including cleavage of S–N bond, hydroxylation, and Smile-type rearrangement in DTN@iron-electrode/EO process. The DTN@iron-electrode/EO effluent also demonstrated superior membrane fouling mitigation in terms of the CM process, owing to its higher specific flux. XPS and SEM confirmed the reducing membrane fouling, which showed the formation of a loose and porous cake layer. This work clarified diverse reactive species formation and detoxification with DTN@iron-electrode/EO system and offers a sustainable and efficient process for treating tailwater from coastal aquaculture.

Enhanced performance and mechanism of adsorption pretreatment for alleviating membrane fouling in AGMBR: Impact of structural variations in carbon adsorbents

The structural variances of adsorbents play a crucial role in determining the number of effective adsorption sites and pretreatment performance. However, there is still a gap in comprehending the impact of different carbon structural adsorbents on membrane fouling. Therefore, this study aimed to compare the efficacy of granular activated carbon (GAC), powdered activated carbon (PAC), and activated carbon fiber (ACF) in mitigating membrane fouling during municipal sewage reclamation using an aerobic granular sludge membrane bioreactor (AGMBR). The results demonstrated that the utilization of PAC significantly enhanced the normalized flux and reduced fouling resistance in comparison to GAC and ACF systems. PAC effectively adsorbed low and medium-molecular-weight pollutants present in raw sewage, resulting in an increase in average particle size and a decrease in foulant content on the membrane surface. The Hermia model indicated that adsorption pretreatment minimized standard blocking while promoting the formation of a sparse and porous cake layer. Moreover, according to the extended Derjaguin–Landau–Verwey–Overbeek theory, PAC has been demonstrated as the optimal antifouling system owing to its enhanced repulsion between membrane-foulant and foulant-foulant interactions. Correlation analysis revealed that the exceptional antifouling performance of the PAC system was due to its high removal rates of chemical oxygen demand (~78 %) and suspended solids (~97 %). This research offers valuable insights into the mitigation of membrane fouling through the utilization of adsorbents featuring diverse carbon structures.

An investigation of the filtration performance and mechanism of oil-solid mixed particles on filter materials with different wettability

In the process of air filtration, filter materials may encounter oil-solid mixed particles from various sources such as industry and household, and the influence of filter material with different wettability on the filtration performance of oil-solid mixed particles has not been fully reported. The objective of this study was to prepare filter materials with varying wettability properties and investigate their filtration performance for oil-solid mixed particles with diverse oil contents. In this study, four filter materials were prepared using the impregnation method, exhibiting 0° (superoleophilic), 46° (oleophilic), 90° and 122° (oleophobic) oil contact angles. The oil-solid mixed particles with varying oil contents were loaded on the four different filter materials. The loading behavior of the filter materials was characterized from two aspects: macroscopic loading behavior (changes in pressure drop and DHC) and microscopic particle deposition behavior. The results demonstrated that, under the conditions of 25% and 50% oil content, the enhanced liquid bridge force between the oil-solid mixed particles on the oleophobic filter material facilitated the formation of a loose and porous cake layer structure compared with other filter materials, resulting in a lower growth rate of pressure drop and a higher dust holding capacity (DHC). However, in 75% and 100% oil content environments, the superoleophilic filter material owned a remarkably high affinity for oil particles compared with other filter materials, leading to the gradual formation of an oil film structure on the filter material, yielding lower the growth rate of pressure drop and higher DHC. These findings shed light on the mechanism of particle deposition under diverse filtration conditions and are applicable to the filtration of various oil-solid mixed particles over a wide range of oil contents.

Membrane fouling control and contaminant removal during direct nanofiltration of surface water

Direct nanofiltration (NF) is an attractive separation process that produces high-quality drinking water without pretreatment. However, the propensity for membrane fouling is a considerable challenge. This study evaluated the potential of direct NF treatment of surface water using submerged flat-sheet (polyamide composite) NF membranes to achieve stable operation and high-quality water production. Direct NF treatment at a constant permeate flux of 5.0 L/m2h (NF270) and 2.5 L/m2h (NF90) was successfully continued for over 100 d with a monthly one-wipe sponge cleaning. Sponge cleaning eliminated the foulants on the NF270 membrane surface, thereby recovering the membrane permeability. Contrastingly, tight NF90 membranes did not exhibit significant changes in membrane permeability. The rejection of odorous compounds and other dissolved organic matter by the NF90 membrane was significant (>95 %), whereas those by the NF270 membrane considerably varied with the feed temperature. Further investigation suggested that the visible foulant on the membrane surface could be a porous cake layer mainly composed of constituents with a molecular weight of >300 Da, resulting in low hydraulic resistance. One-wipe sponge cleaning can readily detach fluffy cake layers. The results of this study suggest the viability of direct NF treatment as a low-energy advanced drinking water treatment system.

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

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

Effect of fouling and cleaning upon the surface charge and porosity of polyethersulphone membranes during coffee brew decaffeination

Filtration processes could offer a viable alternative to use of solvents for the production of reduced caffeine coffee beverages (so called ‘half-decaf’) which have recently gained increased commercial attention. However fouling phenomena and membrane deterioration could significantly alter the process performance; hence fouling and cleaning mitigation strategies must be explored by monitoring key membrane properties such as porosity and surface charge. In this study, multiple cycle filtration of coffee brews for the selective reduction of caffeine has been performed. A commercially available synthetic tight ultrafiltration polyethersulphone (PES) membrane (GP95PP – Alfa Laval) and a bespoke loose nanofiltration mixed matrix PES membrane fabricated, were used for three consecutive fouling and cleaning filtration cycles. The impact and mechanisms of fouling and the cleaning protocol effectiveness were investigated using surface charge, porosity, membrane surface and membrane morphology characterization techniques. Streaming potential studies revealed negative surface zeta potential for the membranes in a pH range of ca. 3.5–8.0. The fouled membrane classes exhibited elevated negative charges, which were partially restored to the pristine levels when chemically cleaned, suggesting the presence of residual negatively charged foulants. Porosity studies revealed the presence of a porous cake layer with an increase of average pore size and pore volume, and a decrease of 10–20 % on the BET surface area of the fouled membranes. Presence of key compounds on the membrane surface and structure was confirmed via EDX and FT-IR spectroscopy. Surface roughness along with SEM microscopy verified the uniform deposition of the foulants with absence of bulky particles. The presence of a cake layer was confirmed via SEM cross-sectional images due to selective thick layer thickness increase of the fouled membranes. Flux differences between the membrane classes can be related to the thickness of the top layer. Flux decreases and flux recovery ratios were also reported over multiple cycles and linked with porosity and other surface properties.

Application of laminarin as a novel coagulant aid to improve coagulation-ultrafiltration efficiency

Polyacrylamide (PAM) is the most commonly used coagulant aid in coagulation-ultrafiltration (C-UF) systems; however, its hydrolyzed monomer is harmful to the human nervous system. In this study, laminarin (LA), was extracted from Laminaria japonica and used as a novel coagulant aid to improve coagulation efficiency and reduce membrane fouling during the C-UF process. Optimal LA usage conditions were systematically examined and compared with those of PAM to evaluate their potential for industrial applications. The results revealed that coagulation efficiency could be enhanced by 15–35% with moderate LA addition, which exhibited comparable aid effects to PAM. LA exhibited the highest coagulation aid effect at pH 8–9, and under this condition, turbidity and natural organic matter (NOM) removal achieved 82% and 54%, respectively. Compared with a one-time LA dosing strategy, the pollutant removal capacity of batch dosing was superior. Even in lower water temperatures (5–15 °C), coagulation efficiency was still satisfied, which exhibited a good practical application perspective. The coagulation aid role of LA should be attributed to its long-chain molecular structure, which enhances the bridging role between micro flocs and assists floc growth, thus facilitating the formation of large flocs. In addition, LA adsorption on floc surface was conducive to the direct electrostatic repulsion effect of electronegative membrane, which resulted in a more porous cake layer and higher membrane flux. Therefore, LA exhibits excellent application potential for eliminating NOM while simultaneously reducing membrane fouling through the C-UF process.

Polymer-flooding produced water treatment using an electro-hybrid ozonation-coagulation system with novel cathode membranes targeting alternating filtration and in situ self-cleaning

Polymer-flooding produced water is more difficult to treat for reinjection compared with normal produced water because of the presence of residual hydrolyzed polyacrylamide (HPAM). A novel cathode membrane integrated electro-hybrid ozonation-coagulation (CM-E-HOC) process was proposed for the treatment of polymer-flooding produced water. This process achieved in situ self-cleaning by generated microbubbles in the cathode membrane. The CM-E-HOC process achieved a higher suspended solid (SS), turbidity and PAM removal efficiency than the CM-EC process. The SS in the CM-E-HOC effluent was ≤ 20 mg/L SS, which met the reinjection requirements of Longdong, Changqing Oilfield, China (Q/SYCQ 08,011–2019) at different current densities (3, 5 and 10 mA/cm2). The CM-E-HOC process greatly mitigated both reversible and irreversible membrane fouling. Therefore, excellent flux recovery was obtained at different in situ self-cleaning intervals during the CM-E-HOC process. Furthermore, alternating filtration achieved continuous water production during the CM-E-HOC process. On one hand, the effective removal of aromatic protein-like substances and an increase in oxygen-containing functional groups were achieved due to the enhanced oxidation ability of the CM-E-HOC process, which decreased membrane fouling. On the other hand, the CM-E-HOC process showed improved coagulation performance because of the increased oxygen-containing functional groups and polymeric Fe species. Therefore, larger flocs with higher fractal dimensions were generated, and a looser and more porous cake layer was formed on the membrane surface during the CM-E-HOC process. Consequently, the CM-E-HOC process exhibited better in situ self-cleaning performance and lower filtration resistance than the CM-EC process.

Low-maintenance anti-fouling and phosphorus removal of an electro-MBR with Fe anode-cathodic membrane

Frequent membrane cleaning and chemical phosphorus removal increase the maintenance burden of membrane bioreactors (MBRs), greatly limiting their application in decentralized wastewater treatment. Herein, an electrochemical MBR (electro-MBR) integrating a Fe anode and a membrane cathode was constructed to simultaneously alleviate membrane fouling and enhance phosphorus removal using a low-maintenance method. Compared with conventional MBR, coagulation by Fe ions released from the sacrificial anode coupled with electrostatic repulsion from the cathodic membrane significantly mitigated membrane fouling in the electro-MBR. The coagulation significantly increased the sludge floc size, favoring the generation of a porous cake layer, and enhanced phosphorus removal by 69.0% without the addition of chemicals. The electrostatic repulsion impeded the adhesion of foulants, particularly extracellular polymeric substances (EPS), onto the conductive membrane. The EPS deposited onto the membrane surface declined by 31.5% under the synergistic effect of coagulation and electrostatic repulsion. Additionally, the applied electric fields increased microbial species diversity and enhanced the adaptability of biochemical systems to water quality variations. The service life of the membrane module in the electro-MBR was extended by 3 times, and the dosing coagulant was replaced by a sacrificial Fe anode with a working life of 600 d, resulting in 66.7% decrease in maintenance costs. This study suggests a low-maintenance method to achieve anti-fouling and phosphorus removal and promotes the development and application of MBRs.

Coagulation and membrane fouling mechanism of Al species in removing humic acid: Effect of pH and a dynamics process analysis

The pH conditions affected the binding sites and complexation ability of Al species and humic acid (HA), resulting in the difference of coagulation and membrane fouling mechanism. It is important to explore the dynamic process of coagulation for the mechanisms of Al species and HA. In this study, three Al species (Ala/Alb/Alc) were used in coagulation process to compare the pollution degree of ultrafiltration (UF). Then, the removal efficiency of Ala for DOC was better than that of Alb and Alc, that is, the removal performance of suspended and dissolved organic matter was better for Ala. Through the analysis of coagulation dynamic process and membrane resistances, the flocs formed were smaller size and grow slowly to the equilibrium stage at pH 4, which was easy to cause membrane fouling by concentration polarization. With the pH increasing to a neutral condition, the flocs had a large size and loose structure, and then the porous cake layer was easy to be removed by physical cleaning, leading to the membrane fouling mainly due to pore plugging. Under alkaline conditions, flocs with small size and dense structure were mainly formed by sweeping, which resulted in the cake layer as the main cause of membrane fouling. This study is helpful to optimize the process of HA removal by coagulation-UF, and provides technical support for the coagulation and membrane mechanism of Al species and HA under different pH conditions.

The role of heat/powdered activated carbon/persulfate in membrane fouling control in a coupled aerobic granular sludge–membrane system for municipal wastewater reclamation

This study proposed and applied an innovative heat/powdered activated carbon (PAC)/persulfate (PS) pre-treatment system for the first time in an aerobic granular sludge–membrane system (AGSMS). We examined the effects of the heat/PAC/PS system on membrane fouling mitigation and contaminant removal and qualitatively evaluated the contribution of adsorption and oxidation to membrane fouling control. Compared to other pre-treatment systems, the heat/PAC/PS system could enhance the removal of pollutants, reduce fouling resistance, and delay the decline of permeation flux, resulting in low foulant content on the membrane surface and formation of a loose and porous cake layer. According to radical scavenging experiments, the excellent heat/PAC/PS system pre-treatment performance was attributed to the PAC adsorption capacity and non-radical oxidation pathway. Thermal synergy played a significant role in promoting adsorption and oxidation abilities. The extended Derjaguin–Landau–Verwey–Overbeek theory indicated that the high-energy barrier in the heat/PAC/PS system was an important factor in inhibiting the adhesion of foulants to the membrane surface. Furthermore, the correlation analysis suggested that membrane fouling control should focus on the removal of chemical oxygen demand and suspended solids. This study provides a new approach for membrane fouling mitigation through AGSMS in municipal wastewater treatment.

Effect of adsorption and coagulation pretreatment sequence on ultrafiltration membrane fouling: Process study and targeted prediction

A novel combined pretreatment strategy, where the hydrophobicity of feedwater is reduced and the morphology of flocs is optimized by varying the sequence of powdered activated carbon (PAC) adsorption and coagulation, is applied to alleviate membrane fouling. To explore the effects of pretreatment sequence and the role of PAC on the membrane fouling, the combined pretreatments of adsorption followed by coagulation (A-C) and coagulation followed by adsorption (C-A) are investigated with various PAC dosages (10, 20, and 50 mg/L). The results reveal that since PAC directly participates in the growth of flocs as the core during A-C pretreatment, the A-C pretreatment is more conducive than the C-A pretreatment to form flocs with a larger size, higher strength, and smaller fractal dimension. Thus, the flocs can accumulate into a porous cake layer to improve the membrane permeability and fouling reversibility. Moreover, the irreversible fouling is highly linearly correlated SUVA values in the early ultrafiltration cycles (R2SUVA = 0.9536) and with the floc strength in the late cycles (R2Strength = 0.9348–0.9763). This finding can be used to make a targeted diagnosis of irreversible fouling in different cycles, providing valuable guidance for prolonging the service life of ultrafiltration membranes.

Mitigating membrane fouling by coupling coagulation and the electrokinetic effect in a novel electrocoagulation membrane cathode reactor

Membrane reactors with efficient antifouling and low maintenance are desirable for distributed membrane water treatment. In this study, a novel membrane separation reactor with an Al anode and a conductive membrane as the cathode was built to develop a chemical-free method for mitigating membrane fouling via electrocoagulation coupled with the electrokinetic effect. The electrostatic repulsion between humic acid (HA) and the membrane cathode reduced the adhesion of HA foulants on the membrane, thereby contributing to antifouling in the initial stage. Electrocoagulation and polarization induced by the electric field enlarged the HA-Al flocs, which prevented membrane pore blocking and facilitated the formation of a porous cake layer, thereby leading to a high water flux of the electrocoagulation membrane cathode reactor (ECMCR) in the stable stage. The bubbles from hydrogen evolution on the membrane cathode scoured the HA foulants and washed out the dense cake layer, thereby playing an important role in membrane fouling mitigation. Compared with membrane filtration, the membrane cathode reactor, membrane anode reactor, and HA removal of the ECMCR increased by 9.6, 8.3, and 2.8 times, respectively, whereas the transmembrane pressure decreased by 84.6%, 21.5%, and 63.0%, respectively. The synergy of electrocoagulation and the electrokinetic effect provides the ECMCR with a feasible method of antifouling and improved effluent quality with low maintenance.

Effect of modified microbial flocculant on membrane fouling alleviation in a hybrid aerobic granular sludge membrane system for wastewater reuse

Pre-coagulation is an excellent method for alleviating membrane fouling in aerobic granular sludge (AGS) membrane systems (AGSMSs) for wastewater reuse. However, little attention has been paid to modified microbial flocculants (MMFs) for membrane fouling mitigation. Herein, an MMF was prepared, and the effect of its dosage (5–30 mg/L) on membrane fouling mitigation was investigated. MMF pre-coagulation could effectively alleviate membrane fouling by utilizing electrical neutralization and adsorption bridging. When the MMF dosage was 10 mg/L, the membrane flux was increased by 79.4% and the total fouling resistance was reduced by 90.3%. The MMF dosage of 10 mg/L greatly inhibited the adhesion and accumulation of foulants, thereby forming a loose and porous cake layer on the membrane surface. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek theory further clarified that the greatest energy barriers existed throughout the filtration process with an MMF dosage of 10 mg/L. Correlation analysis showed that the occurrence of membrane fouling was mainly related to total phosphorus, chemical oxygen demand, and polysaccharides in the raw wastewater. This study reveals the effects of different MMF dosages on membrane fouling and provides a novel approach for MMF pre-coagulation to mitigate membrane fouling.

Pre-coagulation for membrane fouling mitigation in an aerobic granular sludge membrane bioreactor: A comparative study of modified microbial and organic flocculants

Coagulation has become a hotspot for membrane fouling control; however, there is a gap in research regarding the application of modified microbial flocculants (MMFs) to mitigate membrane fouling. Herein, we prepared an MMF and compared it with conventional organic flocculants for their effects on mitigating membrane fouling in an aerobic granular sludge membrane bioreactor (AGMBR). The results showed that electrical neutralization played a dominant role in the flocculation process of polymeric aluminum chloride (PAC)/MMF, which exhibited the optimal performance for the removal of pollutants and membrane fouling control. Moreover, the characteristics of the fouled membrane and the fitting of membrane fouling models indicated that the cake layer formation was the main fouling mechanism underlying membrane fouling, and MMF could mitigate the accumulation of foulants on the membrane surface, forming a loose and porous cake layer. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the largest energy barriers of the membrane-foulant and foulant-foulant interactions were observed in the PAC/MMF-AGMBR hybrid system. Furthermore, correlation analysis revealed that total phosphorus, polysaccharide, zeta potential, and particle size had the greatest correlation with the fouling resistance. Thus, this study shows that MMF pre-coagulation is feasible and provides a new method for membrane fouling mitigation in an AGMBR. • The MMF was used for the first time to mitigate membrane fouling. • The cake layer was the major mechanism of membrane fouling in the MMF-AGMBR system. • The MMF promoted the formation of a loose, porous, and thin cake layer. • The MMF reduced the foulants deposited on the virgin/fouled membranes. • TP, PS, zeta potential, and particle size remarkably affect the fouling resistances.

A moderate activated sulfite pre-oxidation on ultrafiltration treatment of algae-laden water: Fouling mitigation, organic rejection, cell integrity and cake layer property

In this study, a moderate oxidation strategy, in-situ pretreatment with ferrous activated sulfite (Fe(II)/S(IV)), was employed to mitigate membrane fouling during the filtration of algae-laden water and to improve the rejection of organic matter. It was worth noting that the moderate oxidant can avoid serious cells breakage and control the release of intracellular organic matter. Besides, sulfite-based pretreatment had an excellent removal effect DBPs, including chloroform (TCM), dichloroacetonirile (DCAN) and trichloronitromethane (TCNM). Fe(II)/S(IV) pretreatment also improved the removal of DOC and UV254 and the proportion of hydrophilic substances was increased to 91.4% which was conductive to membrane fouling alleviation. With the increase in Fe(II) dosage, both the Rr and Rir were declined since the macromolecular organic transforming to micromolecular organic and the coagulation effect by the in-situ generation of Fe(III). Meanwhile, permeable channels formed on the loose and porous cake layer due to the in-situ Fe(III) could enhance the specific flux. When the ratio of Fe(II)/S(IV) was 2:1, the fouling mechanism was inferred to cake filtration which showed a great discrepancy with other condition.

Iron amended gravity-driven membrane (IGDM) system for heavy-metal-containing groundwater treatment

Gravity-driven membrane (GDM) system is a low-maintenance ultrafiltration system for decentralized drinking water treatment. GDM shows a high removal of pathogens, but a low removal of soluble heavy metal ions. In this study, to overcome this limitation, iron nails were introduced into a GDM system (IGDM) for the purification of heavy-metal-containing groundwater. The corrosion of iron nails continuously occurred in the influent, and rust particles were produced to remove heavy metal ions. The results suggested that the removal of As(V), Pb(Ⅱ), and Cd(Ⅱ) were all higher than 90% in the IGDM system; these removal efficiencies could be maintained because of the abundance of iron nails and the continuous formation of fresh rust. During the filtration, rust particles were partly deposited on the membrane surface, and the thickness of the cake layer in the IGDM correspondingly increased by 143% compared with that in the control GDM. The deposited rust had an inhibitory effect on the microorganisms in the cake layer, and the content of adenosine triphosphate (ATP) was reduced by 75% accordingly. However, the rust particles could adsorb organic membrane foulants, thereby alleviating organic fouling. Moreover, the bird’s-nest-like structure of the rust particles facilitated the formation of a porous cake layer, and no synergistic fouling effect of rust particles and organic foulants was observed. These positive effects offset the inhibitory effect of rusts on microorganisms and the thickness increase of the cake layer. Consequently, a stable flux of 3.5 L m-2 h-1 could still be achieved during the 105-day operation in IGDM system, although the value was 30% lower than that in the control GDM. All these results indicated that IGDM could be an economical and low-maintenance method for heavy metal removal in undeveloped areas. In addition, a house-hold scale (∼50 L d-1) IGDM was successfully operated, demonstrating the practical potential of this technology.