Irreversible Fouling Resistance Research Articles

Enhanced electrooxidation/electrocoagulation-ultrafiltration membrane process with S2O42− for saline algae-containing surface water treatment: Purification and membrane performance

The surface water in coastal areas involving algae, is often affected by saline and emerging contaminants caused by saltwater intrusion, and expanding aquaculture industry. Therefore, it is necessary to conduct studies to address the issues that affect ecological safety and health of aquatic environments. This study presents the development of an enhanced electrooxidation/electrocoagulation-ultrafiltration (EO/EC-UF) membrane process using S2O42− (DTN@EO/EC-UF) for the treatment of saline water containing algae. Our results have shown that significant removal of NH3–N (95.1 %), UV254 (89.4 %) and algae (75.7 %) was achieved with the addition of S2O42− (DTN). Additionally, an optimal DTN dosage of 40 mg/L was used in the DTN@EO/EC process to enhance water purification, utilizing reactive species such as SO4·- and ·OH. After coupling with the ultrafiltration (UF) process, optimal operating conditions (DTN: 40 mg/L, current density: 4.65 mA/cm2, electrolysis: 60 s) were applied to treat the saline algae-containing surface water. The generated free chlorine, including NHCl2, accounted for approximately 22 % (0.14 mg/L). In addition, DTN significantly improved the ceramic membrane's permeability and anti-fouling characteristics, with a maximum increasing specific flux from 0.76 to 0.93, mainly attributing to the reduced the irreversible fouling resistance. Furthermore, we discovered that common membrane cleaning using acid or base enhanced the DTN@EO/EC-UF process. In conclusion, this study established an innovative DTN@EO/EC-UF process with excellent performance in terms of water purification and membrane self-cleaning. The results provided a promising alternative for treating saline algae-containing surface water.

Insights into coagulation, softening and ozonation pre-treatments for reverse osmosis membrane fouling control in reclamation of textile secondary effluent

Pre-treatment was an effective strategy to mitigate membrane fouling, while controversial fouling control performance and mechanism still restricted its application. Herein, coagulation, softening and ozonation pre-treatments were applied to mitigate reverse osmosis (RO) fouling in reclamation of textile secondary effluent. The results showed coagulation pre-treatment negligibly alleviated membrane fouling by dosing FeCl3 coagulant due to the low coagulation efficiency and dissolved organic carbon (DOC) removal (only 11 %) toward effluent organic matter (EfOM) with low molecular weight (2300–6145 Da). Unexpectedly, pre-ozonation caused more severe RO fouling with the increasing ozone doses owing to the enhanced bridging action of divalent cations between membrane and ozonated EfOM; however, the opposite phenomenon was observed when divalent cations were removed by softening due to the preferential removal of biopolymers, the decrease in molecular weight and hydrophobicity of EfOM. Especially, at ozone dose of 1.0 mg O3/mg DOC, flux loss and irreversible fouling resistance enhanced by 8.60 % and 25.4 %, but markedly reduced by 24.0 % and 41.2 % in the absence of divalent cations, respectively. Extended DLVO (XDLVO) theory further unveiled the different roles of pre-treatments in RO fouling control was mainly due to the variation of adhesion interfaces between RO membrane and foulants, especially for the Lewis acid-base (AB) interaction energy. We proposed that softening + ozonation pre-treatment was effective to control RO fouling. More importantly, the reclaimed water satisfy the national standard of China (GB/T 19923–2005) for industrial water reuse after softening + ozonation + RO membrane treatment, which is promising to reclaim textile wastewater.

Chalcopyrite functionalized ceramic membrane for micropollutants removal and membrane fouling control via peroxymonosulfate activation: The synergy of nanoconfinement effect and interface interaction

This work developed a novel chalcopyrite (CuFeS2) incorporated catalytic ceramic membrane (CFSCM), and comprehensively evaluated the oxidation-filtration efficiency and mechanism of CFSCM/peroxymonosulfate (PMS) for organics removal and membrane fouling mitigation. Results showed that PMS activation was more efficient in the confined membrane pore structure. The CFSCM50/PMS filtration achieved almost complete removal of 4-Hydroxybenzoic acid (4-HBA) under the following conditions: pH = 6.0, CPMS = 0.5 mM, and C4-HBA = 10 mg/L. Meanwhile, the membrane showed good stability after multiple uses. During the reaction, SO4•− and •OH were generated in the CFSCM50/PMS system, and SO4•− was considered to be the dominant reactive species for pollutant removal. The roles of copper, iron, and sulfur species, as well as the possible catalytic mechanism were also clarified. Besides, the CFSCM50/PMS catalytic filtration exhibited excellent antifouling properties against NOM with reduced reversible and irreversible fouling resistances. The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis showed an increased in repulsive energy at the membrane-foulant interface in the CFSCM50/PMS system. Membrane fouling model analysis indicated that standard blocking was the dominant fouling pattern for CFSCM50/PMS filtration. Overall, this work demonstrates an efficient catalytic filtration process for foulants removal and outlines the synergy of catalytic oxidation and interface interaction.

Copper Nanoparticles Coupled with Fine-Powdered Active Carbon-Modified Ceramic Membranes for Improved Filtration Performance in a Membrane Bioreactor

Membrane fouling is a key factor limiting the application of a membrane bioreactor (MBR), and membrane-surface modification holds the potential to control membrane fouling and solves this problem. In the research, novel nanocomposite membranes were designed and fabricated using antimicrobial copper nanoparticles (CuNPs) coupled with powdered active carbon (PAC) to mitigate membrane fouling. The successful coating was confirmed by SEM, XRD, and FTIR analysis. Compared with a pristine membrane, the functionalization of CuNPs and PAC improved the hydrophilicity of the modified membrane but led to a lower permeate flux. The result of antimicrobial adhesion experiments showed that the modified M-CuOC displayed high antibacterial activity with the bacteria count decreased by 72%. In MBR operation, the modified M-CuOC leads to the removal efficiency of chemical oxygen demand (COD) increasing to 93%, with better filtration performance under a lower TMP rise. The fouling-resistance analysis demonstrated that, although the intrinsic membrane resistance of modified M-CuOC slightly increased, the reversible and irreversible fouling resistances obviously decreased by 45% and 90%. Moreover, the membrane flux recovery efficiency of the modified M-CuOC also increased by 35%. Overall, these results indicated that, in addition to an improvement in antifouling performance, the functionalization of CuNPs and PAC also enhanced the membrane flux recovery efficiency, revealing a good antifouling potential in a practical application.

Novel insight into secondary effluent quality improvement and ultrafiltration fouling mitigation by UV/peracetic acid pretreatment

Ultrafiltration (UF) technology is widely used in the treatment for deep purification of municipal secondary effluent, however, the membrane fouling and low removal of N, P, and organic matter during actual operation have been the main bottlenecks limiting its wide-spread application. To address the above problems, this study employed peracetic acid (PAA) and UV/PAA to evaluate the effects of PAA-based pre-oxidation on ultrafiltration membrane fouling and secondary effluent water quality. The results demonstrated that the activated PAA pre-oxidation could prominently enhance the hydrophilicity of effluent organic matter, effectively destroy the high molecular weight organic matter and mineralize the low molecular weight organic matter. PAA and its metabolites, as well as the by-products of EfOM, increased the C/P ratio in water samples from 118 to 563 and the C/N ratio from 0.86 to 8.53. After UV/20 mg/L PAA pretreatment, the reversible and irreversible membrane fouling resistance significantly decreased by 55.97 % and 65.67 %, respectively. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory showed lower adhere potential of the foulants to the membrane surface. In general, UV/PAA as ultrafiltration pretreatment has a huge potential for secondary effluent treatment for membrane fouling mitigation and water quality improvement.

Role of Titanium Dioxide-Immobilized PES Beads in a Combined Water Treatment System of Tubular Alumina Microfiltration and PES Beads.

The membrane process has a limit to the decay of various pollutants in water. To improve the problem, the roles of backwashing media and titanium dioxide (TiO2) photocatalyst-immobilized-polyethersulfone (PES) beads' concentration were investigated in a combined system of tubular alumina MF and the PES beads for advanced drinking water treatment. The space between the outside of the MF membrane and the module inside was filled with the PES beads. UV at a wavelength of 352 nm was irradiated from outside of the acryl module. A quantity of humic acid and kaolin was dissolved in distilled water for synthetic water. Water or air intermittent backwashing was performed outside to inside. The membrane fouling resistance after 3 h process (Rf,180) was minimum at 30 g/L of the PES beads for water backwashing, and at 40 g/L for air backwashing when increasing the PES beads from 0 to 50 g/L. The irreversible membrane fouling resistance after physical cleaning (Rif) was at the bottom at 5 g/L of the PES beads for water backwashing, which was 3.43 times higher than minimal at 40 g/L of the PES beads for air backwashing. The treatment effectiveness of turbidity increased when increasing the PES beads' concentration from 0 to 50 g/L; however, it reached a maximum at 98.1% at 40 g/L and 99.2% at 50 g/L for water and air backwashing, respectively. The treatment effectiveness of UV254 absorbance, which was dissolved organic matter (DOM), increased dramatically when increasing the PES beads; however, it reached a peak of 83.0% at 40 g/L and 86.0% at 50 g/L for water and air backwashing, respectively. Finally, the best PES beads' concentration was 20~30 g/L to minimize the membrane fouling; however, it was 50 g/L to remove pollutants effectively. The water backwashing was better than the air at treating DOM; however, the air backwashing was more effective than the water at removing turbid matter and reducing membrane fouling.

Salt tide affecting algae-laden micropolluted surface water treatment and membrane performance based on BDD electro-oxidation coupled with ceramic membrane process

Harmful algal blooms pose an emerging threat to freshwater ecological security and human health, necessitating further study in offshore areas. In this work, boron-doped diamond electro-oxidation (BDD/EO) coupled with a ceramic membrane filtration was employed aiming to assess the salt tide affecting algae-laden water treatment involving with various natural organic matters (e.g., HA, SA, and BSA). The results have demonstrated that BDD/EO remove chlorophyll from the algae-laden water effectively due to the inactivation of algal cells. Moreover, considering the influence of salt tide, NH3–N would be mainly oxidized through the in-situ generated active chlorine at the electrode-liquid interface. In addition, in three kinds of salt tide affecting algae-laden water, TOC content in BSA group was decreasing remarkably after BDD/EO with TOC removal efficiency above 80%; while those in HA and SA groups had no obvious reducing due to the more algae cells breakage synchronous with HA and SA removal. Based on the fluorescent characteristics and particle size distribution, the generated small molecular organics after electro-oxidation might raise the pore blockage probability and the hydrophobic organic and fluorescent substances were preferentially oxidized in BDD/EO process being beneficial to reducing membrane fouling. Besides, the membrane special flux in three groups were decreasing significantly and the irreversible fouling resistance in SA group accounted for a larger proportion of the total resistance than those of HA and BSA. At last, in BDD/EO-CM process, macromolecular substances degradation rate was greater than that of small molecules based on the molecular weight distribution in three groups of salt tide affected algae-laden water treatment. In a word, this work provides effective and innovative strategies for the harmful algal bloom control and contributes interesting insights of membrane fouling performance of electrochemical coupled ultrafiltration membrane process.

Ultrahigh-flux two-dimensional metal organic frameworks membrane for fast antibiotics removal

Two-dimensional metal organic frameworks (2D-MOFs) membrane was constructed by in-situ deriving from CoFe-Layered double hydroxides (CoFe-LDH) on substrate membrane using hydrothermal strategy and LDH is fully converted to the 2D-MOFs based on X-ray diffraction (XRD) patterns. Compared to LDH membrane, 2D-MOFs formed a defect-free layer with higher hydrophilicity (water droplet quickly filtrated through membrane), interlayer space (1.03 nm), more negative charge (zeta potential = −18.4 mV at pH = 7.0) and lower molecular weight cut-off (436.1 Da). As a result, 2D-MOFs membrane presented superior water permeability (flux = 622.9 L m−2 h−1 bar−1) and tetracycline (TC) rejection (98.5%) at wide range of pH (5–9) and concentration (0.002–0.02 mM) of TC solution, superior to most state-of-the-art 2D membranes due to the synergy of fast water transport, molecular sieving and electrostatic repulsion. In addition, it also efficiently rejected other negatively charged antibiotics (e.g., norfloxacin and sulfamethoxazole) with high removal efficiency (>87%), which can break the trade-off between permeability and rejection. What's more, after filtration of simulated pharmaceutical wastewater for 2 days, flux loss and irreversible fouling resistance for 2D-MOFs membrane significantly reduced by 31.6% and 89.9% in comparison to the pristine membrane without the addition of MOFs, respectively; moreover, negligible leaching of 2D-MOFs demonstrated its good anti-fouling performance and stability, which was promising to remediate antibiotics contaminated water.

Leveraging coagulation mechanisms to reduce fouling and increase natural organic matter removal during coagulation/flocculation-ultrafiltration treatment

Despite widespread application of coagulation/flocculation prior to ultrafiltration (UF), a lack of knowledge remains regarding the appropriate selection of conditions to reduce fouling and/or improve the removal of natural organic matter (NOM). The present study investigates the impact of conditions (alum dosage, pH) associated with specific coagulation mechanisms along with two different coagulation/flocculation configurations, on UF performance in terms of fouling and NOM removal. In-line coagulation/flocculation configurations were provided at bench-scale under continuous-flow conditions, which enabled quantification of hydraulically reversible/irreversible fouling over multiple permeation cycles. When compared to raw water without the addition of coagulant, utilization of coagulation/flocculation generally increased hydraulically irreversible fouling resistance. Conditions that promote adsorption destabilization (2.5 mg/L alum, pH 5.5) substantially reduced or eliminated the hydraulically irreversible accumulation of NOM, likely by minimizing interactions between certain NOM components (e.g. biopolymers and humic substances) and the membrane surface. When considering conditions that promote combined (8 mg/L alum, pH 7.5) and sweep (15 mg/L alum, pH 7) mechanisms, inclusion of flocculation increased TOC removal while reducing total/hydraulically irreversible fouling resistance (when compared to coagulation alone), despite greater amounts of NOM being retained by the membrane. The reduced fouling resistance was likely due to the formation of larger floc which formed a more permeable foulant layer. Results from the present study suggest that if only fouling control is required, conditions that promote adsorption destabilization are optimal, whereas if NOM removal is required, conditions that promote sweep are optimal. Inclusion of flocculation provided an optimal trade-off between fouling reduction and NOM removal for both adsorption destabilization and sweep, which should be considered during the design of coagulation/flocculation-UF systems to reduce operating costs despite potentially higher construction costs when compared to coagulation alone.

A novel catalytic membrane integrated with ozone process for secondary wastewater treatment: Micropollutant removal, membrane fouling control, and its mechanisms

The integration of membrane filtration and catalytic ozonation is increasingly investigated in micro-polluted wastewater treatment, whereas membrane fouling still inhibits its practical application. In the present study, a novel MnCe-catalytic membrane integrated with ozone process (O3/MnCe-CM) was established and applied to remove four micropollutants from the real secondary effluent in continuous operation. Efficient removal of four representative micropollutants with the removal rate ranging from 89.33 % to 99.49 % and superior performance on conventional pollutants, with the DOC, UV254, polysaccharide, and protein reduced by 30 %, 88 %, 32.5 %, and 24 %. The O3/MnCe-CM process had an improved TMP control effect, explicitly reducing the irreversible fouling resistance given a Rir/Rt of 10.17 % which is 42.9 % of that of the O3/CM process. After filtering for 70 days, the TMP only increased by 24.51 kPa. More importantly, the antifouling mechanism was proposed as the combined effects of the decrease of the membrane isoelectric point that elevated its repulsion towards pollutants and the catalytic ozonation that reduced the organic foulants accumulated on the membrane surface and inside the pores. In addition, ozonation in the membrane tank decreased the pollutant load passing through MnCe-CM. In all, the present study provides a novel O3/MnCe-CM process with a promising application perspective.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Enhanced membrane fouling control in a hybrid membrane bioreactor with coarse and fine pore sponge pre-filters

Membrane Bioreactors (MBR) have several advantages, but membrane fouling is a major disadvantage that prevents them from being widely used. Therefore, in the present study, the sponge was utilized as a pre-filter with coarse and fine pores in successive compartments before the membrane compartment and termed a “Hybrid-Membrane Bioreactor (H-MBR)”. In the present study, Conventional Membrane Bioreactor (C-MBR) and H-MBR were operated under similar operating conditions to evaluate the performance of H-MBR. The C-MBR experienced more frequent fouling within 60 days of operation, whereas in the H-MBR, the fouling was very low and gradual (i.e., 4.6 kPa at the end of 150 days of operation). Because of the low fouling, the need for cleaning was also eliminated for the stipulated operational period. The overall fouling rate of C-MBR and H-MBR was 5.83 kPa/d and 0.03 kPa/d, respectively. Both MBRs were good at organic pollutant removal. Because of the modification made in the present study, the H-MBR showed 14.66 times less cake layer resistance and 30 times less irreversible fouling resistance than the C-MBR. As a result, the H-MBR is effective in reducing both cake layer resistance and irreversible fouling resistance by retaining both cake-forming materials and irreversible foulants.

Cobalt oxide decorated activated carbon/peroxymonosulfate pretreatment for ultrafiltration membrane fouling control in secondary effluent treatment: Insights into interfacial interaction and fouling model transformation

To control the ultrafiltration (UF) membrane fouling caused by the secondary effluent, cobalt oxide loaded activated carbon (CoOx-PAC) activating peroxymonosulfate (PMS) was applied as a pretreatment. The degradation of natural organic matter (NOM) and membrane fouling mitigation performance for the CoOx-PAC/PMS pretreatment were comprehensively investigated. The dissolved organic carbon (DOC), fluorescent organics, and phenol in the secondary effluent system were utilized to evaluate the removal effect of the CoOx-PAC/PMS process on the organic matter. Results showed that 100 mg/L 0.5 %CoOx-PAC combined with 2 mM PMS (0.5 %CoOx-PAC/PMS) had an excellent degradation on NOM, removing 84.92 % of DOC, and above 97 % of fluorescent organics within 120 min. The catalytic activity of phenol in this process was even superior to that of homogeneous catalysis (Co2+/PMS). Moreover, the normalized specific flux and membrane fouling resistance were employed to verify the influences of the CoOx-PAC/PMS on membrane fouling. The 0.5 %CoOx-PAC/PMS system significantly improved the specific flux, with a 94.26 % decline in reversible membrane fouling resistance and a 53.05 % reduction in irreversible fouling resistance. O2•− and 1O2 were involved in the reaction as crucial reactive oxide species according to electron paramagnetic resonance and quenching tests. They changed the physicochemical properties of NOM, which decomposed the high molecular weight organics into low molecular weight hydrophilic fractions, thereby delaying the formation of cake layers and alleviating membrane fouling. The Extended Derjaguin-Landau-Verwey-Overbeek theory was used to assess the interaction between the foulants and the UF membranes. The transformation of fouling models was analyzed and found that the intricate membrane fouling filtration mechanisms were transformed into a single standard blocking mode after 0.5 %CoOx-PAC/PMS pretreatment.

Protein-folding-inspired approach for UF fouling mitigation using elevated membrane cleaning temperature and residual hydrophobic-modified flocculant after flocculation-sedimentation pre-treatment

Hydrophobic-modified flocculants have demonstrated considerable promise in the removal of emerging contaminants by flocculation. However, there is a lack of information about the impacts of dosing such flocculants on the performance of subsequent treatment unit(s) in the overall water treatment process. In this work, inspired by the ubiquitous protein folding phenomenon, an innovative approach using an elevated membrane cleaning temperature as the means to induce residual hydrophobic-modified chitosan flocculant (TRC), after flocculation-sedimentation, to reduce membrane fouling in a subsequent ultrafiltration was proposed; this was evaluated in a continuous flocculation-sedimentation-ultrafiltration (FSUF) process treating samples of the Yangtze River. The hydrophobic chains of TRC had similar temperature-dependent hydrophobicity to those of natural proteins. In the 40-day operation of the FSUF system with combined dosing of alum and TRC, a moderately elevated cleaning water temperature (45 °C) of both backwash with air-bubbling and soaking with sponge-scrubbing cleaning, significantly reduced reversible and irreversible fouling resistance by 49.8%∼61.3% and 73.9%∼83.3%, respectively, compared to the system using cleaning water at 25 °C. Material flow analysis, statistical analysis, instrumental characterizations, and computational simulations, showed that the enhanced fouling mitigation originated from three factors: the reduced contaminant accumulation onto membranes, the strengthened membrane-surface-modification role of TRC, and the weakened structure of the fouling material containing TRC, at the elevated cleaning temperature. Other measures of the performance, these being water purification, membrane stability and economic aspects, also confirmed the potential and feasibility of the proposed approach. This work has provided new insights into the role of hydrophobic-modified flocculants in membrane fouling control, in addition to emerging contaminant removal, in a FSUF surface water treatment process.

Enhanced membrane fouling control through Self Forming Dynamic Membrane and sponge-wrapped membrane: A Novel membrane bioreactor.

Membrane technology offers a wide variety of advantages in wastewater treatment, but fouling impedes its widespread applications. Hence, in this study, a novel method was tried to control membrane fouling by combining the self-forming dynamic membrane (SFDM) with a sponge-wrapped membrane bioreactor. The configuration is termed a "Novel-membrane bioreactor" (Novel-MBR). To compare the performance of Novel-MBR, a Conventional membrane bioreactor (CMBR) was operated under similar operating conditions. CMBR and Novel-MBR were run consequently for 60 days and 150 days, respectively. The Novel-MBR was comprised of self-forming dynamic membranes (SFDMs) in two compartments before a sponge-wrapped membrane in the membrane compartment. In Novel-MBR, the formation times for SFDMs on coarse (125μm) and fine (37μm) pore cloth filers were 43 minutes and 13 minutes, respectively. The CMBR experienced more frequent fouling; the maximum fouling rate was 5.83 kPa/d. In CMBR, the membrane fouling due to cake layer resistance (6.92×1012 m-1 ) was high, and that alone contributed to 84% of fouling. In Novel-MBR, the fouling rate was 0.0266 kPa/d and the cake layer resistance was 0.329×1012 m-1 . Also, the Novel-MBR experienced 21 times less reversible fouling and 36 times less irreversible fouling resistance than the CMBR. In Novel-MBR, the formed SFDM and the sponge wrapped on the membrane helped to reduce both reversible and irreversible fouling. With the modification tried in the present study, the Novel-MBR experienced less fouling, and the maximum transmembrane pressure at the end of 150 days of operation was 4 kPa.

Copper ferrite modified catalytic ceramic membrane for effective pollutant degradation and membrane fouling alleviation: The coupling of peroxymonosulfate activation and membrane filtration

In this study, a copper ferrite decorated ceramic membrane (CFCM) for peroxymonosulfate (PMS) activation was synthesized, and the dual function of catalytic oxidation and membrane filtration on organics removal and fouling mitigation was systematically investigated. Characterization results demonstrated that the catalyst particles were uniformly anchored throughout the whole membrane. The catalytic membrane exhibited significantly improved bisphenol A (BPA) degradation and humic acid (HA) retention compared to the conventional CM filtration. SO4− and 1O2 were considered to be the main reactive species for BPA removal in the CFCM/PMS system by quenching experiments and EPR tests, and two possible degradation pathways were proposed. CFCM/PMS filtration showed superior antifouling property with reduced reversible and irreversible fouling resistances. Membrane performance evaluation in BPA-HA removal showed that the competition of HA for reactive radicals and the coverage of catalytic active sites by HA could lead to the decrease of BPA removal while the cake layer formed on membrane surface would increase HA retention. In addition, stable catalytic activity after 8 cycles, high removal efficiency for various organic pollutants and low metals leaching revealed the excellent applicability of CFCM in wastewater treatments.

New insights into interfacial interaction and nanoconfinement effect in synergistic oxidation-filtration via CoFe2O4-ceramic membrane activated peroxymonosulfate

Ceramic membranes incorporating CoFe2O4 (CoFeCM) were synthesized to activate peroxymonosulfate (PMS), and the performance and mechanisms of its oxidation-filtration were comprehensively investigated. The catalytic filtration performance of CoFeCM/PMS was evaluated by degradation of organic pollutants and the mitigation of membrane fouling. Results indicated that CoFeCM/PMS effectively removed toxic micropollutants, including phenol (82.56%), atrazine (93.42%), and carbamazepine (87.40%), ensuring the permeate quality and safety. Also, this synergistic process notably improved the degradation of natural organic matter (NOM) in the secondary effluent and Songhua River water. CoFeCM/PMS filtration effectively mitigated membrane fouling caused by three typical model organics, reducing their irreversible membrane fouling resistance by 70.85–83.62%, and increasing the normalized flux to 48.74–82.61%. The membrane fouling derived from two actual water systems was also greatly alleviated by CoFeCM/PMS. Based on the Extended Derjaguin-Landau-Verwey-Overbeek theory analysis, NOM was oxidized by reactive oxide species into hydrophilic small molecular fractions, resulting in remarkably increased repulsive interaction between NOM and CoFeCM surface. Density functional theory calculation results confirmed the nanoconfinement effect in CoFeCM pores, which can slow down the growth of foulants in pores and effectively alleviate irreversible membrane fouling. Consequently, standard blocking transformed into the dominant membrane fouling pattern due to the synergistic effects of nanoconfinement catalysis (in membrane pores) and repulsive interactions (on membrane surface) during oxidation-filtration.

Improvements of ferrate(VI) pretreatment on membrane flux and membrane rejection using cheap NaClO reagent

Ferrate(VI) pretreatment can effectively alleviate membrane fouling during the ultrafiltration (UF) process, while instability and high expenditure limit its application. This study discovered that the cheap NaClO reagent would improve the performance of ferrate(VI) pretreatment, i.e., establishing Fe(VI)/NaClO (FC) process. 20 μM of Fe(VI) group can increase J/J0 from 0.323 to 0.391, while the optimization process of 20 μM Fe(VI)/4 μM NaClO [FC (5:1)] increased it to 0.491 at the end of cycle 1 filtration. Meanwhile, the reversible and irreversible membrane fouling resistance decreased by 50% and 56% in FC (5:1). This was attributed to the suppression of ferrate(VI) decomposing and in-situ formation of more dispersed ferric nanoparticles in FC process [730.33 nm in Fe(VI) and 606.80 nm in FC (5:1)] by applied NaClO. The rejection ratio of dissolved organic carbon (DOC) increased from 27.18% of Fe(VI) group to 40.34% of FC (5:1) due to the repulsive interaction amplification of acid-base (AB) interaction energy. That was derived from the hydrophilia promotion of the treated sample and the electrical property evolution of in-situ formed ferric nanoparticles by NaClO. It suggested that AB interaction energy, presenting repulsive interaction in membrane-foulants and foulants-foulants, was a major role in Fe(VI) group and FC process. There was no more side effect induced by FC pretreatment, which was confirmed by the result that FC caused no increase in the disinfection by-products (DBPs) formation potential. The present study provided insight into improving the effect of ferrate(VI) pretreatment without inducing side effect, and reduced the costs of ferrate(VI) pretreatment during the process of UF.

Mitigation of ultrafiltration membrane fouling by a simulated sunlight-peroxymonosulfate system with the assistance of irradiated NOM

Oxidation pretreatments prior to ultrafiltration are hindered by the need for energy input and sludge disposal. Herein, a simulated sunlight-induced natural organic matter (NOM) for peroxymonosulfate (PMS) activation was used as pretreatment to alleviate ultrafiltration membrane fouling caused by NOM itself in the Songhua River water. When light intensity was over 100 mW/cm2, the pretreatment removed NOM effectively, characterized with UV254, dissolved organic carbon (DOC) and maximum fluorescent intensity (Fmax), and improved filtration flux. At 200 mW/cm2 light intensity and 0.5 mM PMS, 57.5% of UV254 and 18.5% of DOC were removed, and humic-like fluorescent component was degraded by 84%-94% while ∼60% for protein-like substance. Membrane flux was increased by 94%, and reversible and irreversible fouling resistances were reduced by 62.4% and 51.9%, respectively. Both total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) were moderately correlated with the DOC, whereas they prominently correlated with the UV254 and the Fmaxs of all fluorescence components, which could be served as key indicators to predict and control membrane fouling. Mathematical modeling showed that the pretreatment alleviated the fouling in the membrane pores and cake layer. The simulated sunlight-induced NOM (3NOM* and eaq¯) could activate PMS to form active species, which enabled to oxidize high molecular weight (MW) substances and mineralize low MW compounds in NOM as well as hinder their linking with inorganic cations, thereby reducing organic and inorganic membrane fouling simultaneously. This study may provide a new strategy for decentralized potable water treatment, especially in a single household or community.

Synthesis and Characterization of g-C3N4/Ag3PO4/TiO2/PVDF Membrane with Remarkable Self-Cleaning Properties for Rhodamine B Removal

g-C3N4/Ag3PO4/TiO2 nanocomposite materials were loaded onto a polyvinylidene fluoride (PVDF) membrane using a phase inversion method to obtain a photocatalytic flat membrane for dye removal. The morphology, structure, and photocatalytic activity of the g-C3N4/Ag3PO4/TiO2 nanoparticles and composite membrane were evaluated. The g-C3N4/Ag3PO4/TiO2/PVDF membrane exhibited superior morphology, hydrophilic properties, and antifouling performance compared with the raw PVDF membrane. Four-stage filtration was performed to evaluate the self-cleaning and antifouling capacity of the g-C3N4/Ag3PO4/TiO2/PVDF membrane. Upon irradiating the composite membrane with visible light for 30 min, its irreversible fouling resistance (Rir) was low (9%), and its flux recovery rate (FRR) was high (71.0%) after five filtration cycles. The removal rate of rhodamine B (RhB) from the composite membrane under visible light irradiation reached 98.1% owing to the high photocatalytic activity of the membrane, which was superior to that of raw PVDF membrane (42.5%). A mechanism of photocatalytic composite membranes for RhB degradation was proposed. Therefore, this study is expected to broaden prospects in the field of membrane filtration technology.