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Ferrate (VI) is a unique and “green” chemical that can be utilized for oxidation, disinfection and coagulation simultaneously in a single unit without producing by-product. Herein, for the first time, we reported the integrated process of ferrate (VI) pretreatment coupled with ceramic membrane reactor for mitigating membrane fouling in natural reclaimed water treatment. Membrane fouling was effectively mitigated by ferrate pretreatment with the maximum trans-membrane pressure (TMP) reduction of 81.8% achieved at ferrate dosage of 0.15 mM. Moreover, the fouling mechanism changed from intermediate-standard blocking to cake-intermediate blocking with ferrate pretreatment and the contribution of cake layer fouling was significantly diminished with increase of ferrate dosage (≤ 0.15 mM). Statistical analysis including redundancy analysis and clustering correlation analysis showed that chemical oxygen demand (COD), dissolved organic carbon (DOC) and polysaccharide were the most important positive factors to R t with their correlation coefficients above 0.92 while SS and turbidity were the most important negative factors to R t with their correlation coefficients below − 0.87. Long-term filtration experiments also confirmed the membrane fouling control performance by ferrate with the significant extension of the onset of membrane fouling. [ABSTRACT FROM AUTHOR]

Four pathways for cleaning of iron oxide-fouled membranes, namely i) proton (acid)-assisted, ii) ligand-promoted (citric acid), iii) reductive (ascorbic acid), and iv) ligand-promoted reductive (ascorbic acid-citric acid-mediated) were examined and their effectiveness were compared in this study. The cleaning effectiveness under oxic conditions followed the order: proton-assisted < ligand-promoted < reductive < ligand-promoted reductive. Iron oxide dissolution rate initially increased with increase of citrate concentration in the ascorbic acid-citric acid solutions but declined at higher citrate concentrations indicating that an intermediate citrate concentration was required for optimal cleaning. The mechanism of ligand-promoted reductive dissolution mediated by ascorbate and citrate was investigated through studies of dissolution behaviour under both oxic and anoxic conditions with citrate shown to have a mitigating effect on the consumption of oxygen, apparently by reducing the iron catalyzed oxidation of ascorbate. Kinetic modelling showed that the dynamics of dissolution could be reasonably well simulated with the inclusion of a surface > Fe(III)-citrate-Fe(II) ternary complex which facilitates the detachment of surface Fe(II). Use of dual reagents (ascorbic acid and citric acid) under oxic conditions is recommended for the cleaning of iron-fouled membranes in view of the extreme cleaning effectiveness though it is critical that cleaning conditions be carefully optimised. [ABSTRACT FROM AUTHOR]

Pre-ozonation or in-situ ozonation coupled with membrane filtration has been actively utilized for membrane fouling control in water treatment, however, the comparative analysis of these two ozonation processes on membrane fouling control has not been reported so far. In this study, the comparative effect of pre-ozonation and in-situ ozonation on mitigation of ceramic UF (ultrafiltration) membrane fouling caused by alginate was systematically investigated through characterization of TMP, fouling resistance, MW distribution, dissolved ozone concentration, the formation of hydroxyl radical and modeling. Results showed that both pre-ozonation and in-situ ozonation were effective in alleviating the cake layer fouling. Ozonation efficiently broke down the high molecular weight (MW) fractions (>150 kDa and 80–150 kDa) of alginate into the low MW fractions (6–80 kDa; 0.4–6 kDa and 0.1–0.4 kDa), reducing the membrane interception of alginate. Pre-ozonation achieved better fouling mitigation performance compared with in-situ ozonation at low ozone dosages of 2 and 4 mg/L. However, in-situ ozonation had better fouling control performance at high ozone dosage of 10 mg/L with the normalized TMP (ΔTMP) maintaining below 0.2 kPa after 60 min filtration. Besides, in-situ ozonation was more effective in hydraulically irreversible fouling control than pre-ozonation regardless of ozone dosage. Integration of in-situ ozonation and ceramic membrane filtration catalyzed ozone decomposition with the increased generation of hydroxyl radical, which further strengthened the oxidation of the accumulated foulants on the membrane surface and within the membrane pores and thus effectively alleviated the reversible and irreversible fouling. [ABSTRACT FROM AUTHOR]

The effect of mixed liquor properties changed by ozonation especially with high dosages on membrane fouling is very complex and remains unclear. In this study, the effect of mixed liquor properties changed by ozonation especially with high dosages on ceramic ultrafiltration (UF) membrane fouling in wastewater treatment and the corresponding mechanism were systematically studied by characterization of the mixed liquor properties, hydraulic performance, the fouling layers and modeling at different ozone dosages (0, 2, 5, 10 mg/L). The membrane filterability of the mixed liquor after pre-ozonation (⩽5 mg/L) was enhanced and the corresponding membrane fouling was mitigated. After pre-ozonation, activated sludge had the better settleability and larger floc size. Meanwhile, there was a remarkable reduction of dissolved organic carbon (DOC), soluble microbial products (SMP) and extractable extra-cellular polymeric substances (EPS) after pre-ozonation and the removed organics were mainly belonged to the high molecular weight (MW) (1–10 kDa) and very high MW (10–200 kDa) substances. Intermediate blocking was the main membrane fouling during the mixed liquor filtration process and the best fouling mitigation performance was achieved for the sample with an intermediate ozone dosage of 5 mg/L (1.7 mg-ozone/g-mixed liquor suspended solids (MLSS)). Meanwhile, the water quality of permeate was even better after pre-ozonation (⩽5 mg/L) with the lower DOC and total nitrogen (TN) concentrations. Severe cell lysis occurred with the significant increase of the released organics in the mixed liquor and the activated sludge had smaller floc size and worse settleability when the pre-ozonation dosage was above 10 mg/L, which in turn resulted in the deteriorated membrane fouling control performance. [ABSTRACT FROM AUTHOR]

Cleaning strategies for iron-fouled membranes from submerged membrane bioreactors (MBRs) dosed with iron salts are investigated here. Severe membrane fouling resulting from iron dosing was observed with amorphous ferric oxyhydroxide particles and gelatinous assemblages containing Fe(III) bound to polysaccharide materials responsible particularly for irreversible membrane fouling. Sodium hypochlorite (NaOCl) and citric acid, the most commonly used chemical cleaning agents, were not particularly effective in removing iron species from the membrane surface while the Fe(III) reducing agents ascorbic acid and sodium dithionite were very effective in removing iron-containing deposits under the conditions used in this study. In the presence of oxygen, the Fe(III)-catalysed oxidation of ascorbic acid and direct oxygen-mediated oxidation of dithionite control the dissolution rate constant. Use of NaOCl followed by ascorbic acid at concentrations of 10–20 mM is recommended as a reasonable balance between cleaning effectiveness and cost though further investigation of cleaning of fouled membranes from full scale MBRs is required. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ceramic membrane (CM) market is growing with many full-scale applications. • CM is superior to polymeric membrane–high stability & flux, long life, low fouling. • Physicochemical processes (e.g., ozonation) are effective for fouling control. • Catalytic (nano) CMs can enhance antifouling, and pollutant removal capability. • Cost analysis of CMs, fouling control & cleaning should be evaluated at full-scale. Application of ceramic membrane technology in water and wastewater is rapidly growing. Inherent advantages of ceramic membrane including chemical/thermal stability, low fouling propensity and long lifespan make ceramic membrane technology attractive, and the ceramic membrane market is expected to achieve a compound annual growth rate of 12%. Ceramic membranes could be integrated with advanced oxidation processes such as in-situ ozonation that cannot be applied in the case of polymeric membrane due to their potential degradation during long-term exposure. In addition, the hybrid-ceramic membrane processes such as ceramic membrane bioreactor are superior to polymeric counterparts due to higher flux, higher pollutant removal, lower fouling rate and higher cleaning efficiency. Although ceramic membrane has high capital cost, life-cycle costs of ceramic and polymeric plants are comparable. Notably, full-scale ceramic membrane water/wastewater treatment plants have been installed in many countries such as Japan, USA, Singapore and United Kingdom. Given the attractiveness of this technology, performance of ceramic membrane is critically reviewed with a focus on their applications in water and wastewater treatment under mild conditions. In addition, fouling mechanisms and control strategies are elucidated and are compared with polymeric membranes. Importantly, for the first time, the status of full-scale applications and market prospects of ceramic membranes are critically analysed to show their future potential. Lastly, future research directions such as development of cost-effective ceramic membranes, understanding the biofouling evolution and economic evaluation of physicochemical processes for fouling control are proposed. [ABSTRACT FROM AUTHOR]

Secondary effluent from municipal wastewater treatment plants can be used to produce reclaimed water through membrane distillation (MD), providing a potential solution to the current global water crisis. However, membrane fouling over extended periods of operation reduces the separation performance of MD systems and significantly shortens the operational life-span of the membrane. Herein, in order to overcome these limitations, a novel surface-modified PTFE membrane was fabricated by depositing polydopamine and grafting dextro (d)-tyrosine (Tyr/PDA@PTFE). This synergistic coating was designed to reduce surface hydrophobicity of the PTFE membrane and provide anti-adhesive properties for bacteria, while enhancing flux and anti-fouling performance during MD. The Tyr/PDA@PTFE membranes demonstrated enhanced MD performance and the Tyr-300/PDA@PTFE membrane (with d -tyrosine coating solution concentration of 300 μM) exhibited the best MD performance during direct contact membrane distillation (DCMD) of the secondary effluent, with the highest flux (49.1 LMH) compared with the pristine PTFE membrane (34.7 LMH), achieving a flux increase of 41.5%. Long-term DCMD operation showed that the Tyr-300/PDA@PTFE membrane exhibited improved anti-fouling performance compared with the pristine PTFE membrane, with 43.8% flux decay observed after three cycles of use, while the pristine PTFE membrane was unable to complete three cycles of use with an 87.2% decrease in flux observed by middle of the third round. The quality of permeate formed by the Tyr/PDA@PTFE membranes during MD, indicated that they could be operated stably for three cycles of use over a 40 h period, intercepting organic matter in the feed solution. The Tyr-300/PDA@PTFE membrane was especially effective for the removal of low molecular weight and humus-like substances, achieving rejection rates of 89.5% and 86.7%, respectively. Additionally, the Tyr/PDA@PTFE membrane carried the more negative charge and exhibited a high level of resistance to bio-adhesion. This study demonstrates the feasibility of use of this novel Tyr/PDA@PTFE membrane in MD, for the effective treatment of secondary effluent from wastewater treatment plants and the production of reclaimed water. [Display omitted] • Dopamine and d -tyrosine-functionalized PTFE membranes (Tyr/PDA@PTFE) were prepared. • Membrane distillation (MD) performance of Tyr/PDA@PTFE membranes was investigated. • Secondary effluent from a WWTP was selected for MD to produce reclaimed water. • The Tyr-300/PDA@PTFE membrane demonstrated the best MD performance. • Tyr/PDA@PTFE membranes showed enhanced flux and anti-fouling performance during MD. [ABSTRACT FROM AUTHOR]

Inorganic salts (e.g., FeCl 3 and FeSO 4) are typically added to membrane bioreactor (MBR) for achieving improved total phosphorus (TP) removal and hydraulic performance. However, at the iron dose (e.g., Fe to P molar ratio of 1–4) required for effective TP removal, severe irreversible membrane fouling could become a significant concern. In this context, intermittent in-situ ozonation was provided for the first time directly in the membrane tank of Fe(II)-dosed membrane bioreactor, and its effect on membrane fouling mitigation was assessed and elucidated. The basic effluent quality remained unaffected, indicating that in-situ ozonation had no detrimental effects. In addition, concentration of foulants and the relative abundance of biofilm-forming microbes were comparable in both the Fe-MBR and Fe/O 3 -MBR. Importantly, as compared to the Fe-MBR, a 33% reduction in membrane fouling was achieved in the Fe/O 3 -MBR. The enhanced filterability of mixed liquor and the scrubbing of the membrane surface by ozone with the direct/indirect oxidation of the deposited foulants contributed to membrane fouling mitigation in the Fe/O 3 -MBR. Meanwhile, trans -membrane pressure profiles of MBRs followed cake-intermediate fouling mechanism. This study demonstrates that provision of intermittent in-situ ozonation is a simple and attractive approach to extend the operation of iron-dosed MBR. [Display omitted] • Performance of in-situ ozonation combined with Fe-MBR (Fe/O 3 -MBR) was elucidated. • Abundance of biofilm-forming bacteria was comparable in both Fe- and Fe/O 3 -MBR. • Ozonation improved mixed liquor properties and delayed the onset of severe fouling. • Increased floc size and membrane scrubbing by ozone contributed to fouling control. • Cake-intermediate fouling was the fouling mechanism in both Fe- and Fe/O 3 -MBR. [ABSTRACT FROM AUTHOR]

Owing to the lack of comprehensive studies on the impacts of a high concentration of powdered activated carbon (PAC) in a ceramic membrane bioreactor (MBR), its performance (at 20 g/L) in terms of mixed liquor properties, hydraulic performance and fouling mechanism was elucidated in this study. In addition to the increase in floc size by 29%, zeta potential of the mixed liquor in PAC-MBR increased (from −19 ± 2 mV to −11 ± 2 mV), which was due to the sorption of soluble microbial products on PAC. Importantly, even at a high dose of 20 g/L, membrane fouling was reduced by 33% in PAC-MBR and was attributed to the membrane scouring by PAC and reduced SMP and EPS concentration in the mixed liquor. The viability of the four single and five combined fouling models was assessed to explain the membrane fouling mechanisms in ceramic MBRs for the first time. The intermediate-standard and cake-intermediate models well explained the fouling mechanism in the 'control' and PAC-MBR, respectively, and the intermediate fouling was the major component of the combined models. This study clarifies that MBR could be operated at a high PAC concentration without compromising the effluent quality, mixed liquor properties and membrane hydraulic performance. Image 1 • PAC addition (20 g/L) in MBR improved mixed liquor properties and mitigated fouling. • Average fouling rate reduced from 1.67 kPa/d (in Control) to 1.17 kPa/d in PAC-MBR. • Fouling retardation was due to membrane scouring and EPS/SMP adsorption on PAC. • Cake-intermediate fouling was the main fouling mechanism in PAC-MBR. [ABSTRACT FROM AUTHOR]

The combined pretreatment of coagulation and ozonation is extensively adopted for water quality enhancement and membrane fouling reduction in wastewater reclamation. Herein, the integrated treatment of ferrate pretreatment and in-situ ozonation/ceramic membrane filtration on water quality improvement and fouling reduction of ceramic membrane in secondary wastewater effluent treatment was reported for the first time. The results showed that the hybrid treatment of ferrate pretreatment and in-situ ozonation greatly inhibited the generation of N-dimethyl nitrosamine (NDMA) and did not generate bromate. Meanwhile, the best removal efficiencies of low molecular weight (MW) organics (32.3%), humic-like substances (17.8%) and biopolymers (87.5%) in effluent were achieved by the combination of ferrate (0.15 mM) pretreatment and in-situ ozonation (10 mg/L). Moreover, the control sample (without any treatment) had a fouling transmembrane pressure (TMP) of 30.5 kPa after 7.0 h filtration under a constant flux of 90 L/(m2·h) while that was only 1.0 kPa by the hybrid treatment of ferrate (0.15 mM) pretreatment and in-situ ozonation (10 mg/L). Soluble microbial products (SMP)-like substances with high molecular weight (MW) of 20–2000 kDa were the main foulants and intermediate-standard fouling mechanism played a principal role during the membrane filtration process. Statistical analysis showed that dissolved organic carbon (DOC), UV 254 and protein had the greatest positive correlation (above 0.92) to the total fouling resistance, whilst turbidity displayed the greatest negative correlation (around −0.61) to the total fouling resistance. The remarkable fouling alleviation was due to the improved water quality and in-situ cleaning, which were contributed to the coagulation and oxidation by ferrate and in-situ ozonation. Image 1 • Ferrate pretreatment- in-situ ozonation greatly reduces ceramic membrane fouling. • NDMA and bromate are remarkably reduced by ferrate pretreatment- in-situ ozonation. • Intermediate-standard fouling is the main fouling mechanism. • DOC, UV 254 and protein are the most important positive factors to R t. • Fouling alleviation is due to the improved water quality and in-situ cleaning. [ABSTRACT FROM AUTHOR]