Enhanced water treatment performance of ceramic-based forward osmosis membranes via MOF interlayer

Forward osmosis (FO) membrane processes could operate without hydraulic pressures, enabling the efficient treatment of wastewaters with mitigated membrane fouling and enhanced efficiency. Designing a high-performance polyamide (PA) layer on ceramic substrates remains a challenge for FO desalination applications. Herein, we report the enhanced water treatment performance of thin-film nanocomposite ceramic-based FO membranes via an in situ grown Zr-MOF (UiO-66-NH2) interlayer. With the Zr-MOF interlayer, the ceramic-based FO membranes exhibit lower thickness, higher cross-linking degree, and increased surface roughness, leading to higher water flux of 27.38 L m-2 h-1 and lower reverse salt flux of 3.45 g m-2 h-1. The ceramic-based FO membranes with Zr-MOF interlayer not only have an application potential in harsh environments such as acidic solution (pH 3) and alkaline solution (pH 11), but also exhibit promising water and reverse salt transport properties, which are better than most MOF-incorporated PA membranes. Furthermore, the membranes could reject major species (ions, oil and organics) with rejections ＞94 % and water flux of 22.62-14.35 L m-2 h-1 in the treatment of actual alkaline industrial wastewater (pH 8.6). This rational design proposed in this study is not only applicable for the development of a high-quality ceramic-based FO membrane with enhanced performance but also can be potentially extended to more challenging water treatment applications.

Highly efficient ceramic membrane synthesized from sugar scum and fly ash as sustainable precursors for dyes removal

Recycling solid industrial wastes into valuable materials is always the priority solution in waste management. In this perspective, sugar scum and fly ash were used to produce an effective low-cost porous ceramic membrane. The impacts of the sintering temperature, amount of sugar scum, and sintering time on the properties of the prepared ceramic membrane were investigated and optimized using experimental design. A simultaneous rise in both the sintering temperature and the amount of sugar scum leads to a notable increase in porosity. Moreover, the simultaneous increase or decrease in the time and the amount of sugar scum causes a significant decrease in the compressive strength. The optimal conditions have been determined as a sintering temperature of 1197 °C, a sugar scum amount of 12.06 %, and a sintering time of 253 min. Under these conditions, the density, porosity, and compressive strength were found to be 2.16 g/cm³, 34.66 %, and 28.24 MPa, respectively. In addition, the obtained ceramic membrane has a water permeability of 2356.68 L/h m2 bar, a pore size in the range 0-4.5 μm, and excellent chemical resistance in both acidic and basic media. Finally, the performance of the prepared ceramic membrane was evaluated by the filtration of methylene blue. The results indicate that sugar scum and fly ash are suitable precursors to manufacture an effective ceramic membrane for the treatment of 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.

Preparation and characterization of clay based ceramic porous membranes and their use for the removal of lead ions from synthetic wastewater with an insight into the removal mechanism

The present study explores the use of local clay from the United Arab Emirates (UAE) to prepare porous ceramic membranes (flat disk shape) for the purpose of removing toxic heavy metals from contaminated water. Four distinct ceramic membranes, crafted from locally sourced clay and incorporated with activated carbon and graphite, underwent careful and thorough preparation. The initial set of membranes was subjected to open-air sintering, resulting in the creation of mACA and mGrA membranes. Concurrently, a second set of meticulously prepared membranes underwent sintering under inert nitrogen conditions, yielding the formation of mACI and mGrI membranes, respectively. Prior to making the membranes, the clay material was characterized by thermogravimetric analysis (TGA), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). The clay presented the lowest weight loss compared to AC and Gr, implying that these two materials could be used as porogen agents. The X-ray fluorescence results indicated that the natural clay contained 65.5 wt% of silicon dioxide (SiO2), aluminium oxide (Al2O3), and iron (III) oxide (Fe2O3) falling within the class C category of clays according to ASTM. The FTIR analysis showed different clay regions allocated to various stretching and deformation vibrations of hydroxide, organic fraction, and (Si, Al, Fe)-O groups. The XRD analysis revealed the presence of kaolinite, illite, smectite and calcite phyllite phases in the clay mineral. The membranes were characterized using FESEM, with those containing AC (used as porogen) exhibiting large pores clearly visible on the surface, and were tested for the removal of lead (Pb2+) ions from synthetic wastewater. The removal efficiencies of the membranes were 33 %, 75.2 %, 100 % and 100 % for mACA, mACI, mGrA and mGrI respectively after 100 min operation. The wettability of the membranes was found to follow the order mACI < mACA < mGrI < mGrA, which corroborated well with water fluxes of 7, 8, 112 and 214 L h-1 m-2 recorded after 60 min duration and 1.0 bar applied pressure. The mechanisms of filtration of Pb2+ ions were adsorption for the AC-based membranes (mACA, mACI) and a combination of adsorption and size exclusion for the Gr-based membranes (mGrA, mGrI).

Application of coal fly ash based ceramic membranes in wastewater treatment: A sustainable alternative to commercial materials

The continued increase in the global population has resulted in increased water demand for domestic, agricultural, and industrial purposes. These activities have led to the generation of high volumes of wastewater, which has an impact on water quality. Consequently, more practical solutions are needed to improve the current wastewater treatment systems. The use of improved ceramic membranes for wastewater treatment holds significant prospects for advancement in water treatment and sanitation. Hence, different studies have employed ceramic membranes in wastewater treatment and the search for low-cost and environmentally friendly starting materials has continued to engender research interests. This review focuses on the application of coal fly ash in membrane technology for wastewater treatment. The processes of membrane fabrication and the various limitations of the material. Several factors that influence the properties and performance of coal fly ash ceramic membranes in wastewater treatment are also presented. Some possible solutions to the limitations are also proposed, while cost analysis of coal fly ash-based membranes is explored to evaluate its potential for large-scale applications.

Effective remediation of leachate concentrate by peroxymonosulfate in a catalytic ceramic membrane filtration process: Performance and mechanism

Membrane concentrated landfill leachate has been characterized by complex component and degradation resistant. In this work, a new catalytic ceramic membrane (CuCM) was developed by in-situ integrating copper oxide in the membrane and used in combination with peroxymonosulfate (PMS) for leachate concentrate treatment. The performance and key factors of the CuCM/PMS system were systematically studied. Results showed that the CuCM/PMS system experienced promising efficiency in the pH range of 3 ∼ 11. The highest COD, TOC, UV254 and Color removal efficiency achieved by the CuCM-3/PMS system under the conditions of pH = 7.0 and CPMS = 10 mM, which reached up to 63.4%, 50.5%, 75.1% and 90.2%, respectively. The possible mechanism of leachate remediation was proposed and non-free radicals (Cu(Ⅲ), 1O2) played an important role in the CuCM/PMS system for leachate remediation. The fluorescence spectrum and GC-MS analysis showed that the refractory organics with a high molecular weight in the leachate concentrate were mostly oxidized into small molecules, which also alleviated the membrane fouling. In addition, the slight decrease in COD (7.4%) and TOC (9.7%) after 6 cycles revealed the good catalytic stability and reusability of CuCM-3/PMS. This work provides a feasible strategy for leachate concentrate remediation via a nonradical oxidation process.

An indigenous tubular ceramic membrane integrated bioreactor system for biodegradation of phthalates mixture from contaminated wastewater

Endocrine-disrupting phthalates (EDPs) are widely used as plasticizers for the manufacture of different plastics and polyvinyl chloride by providing flexibility and mechanical strength. On the other hand, they are categorized under priority pollutants list due to their threat to human health and the environment. This study examined biodegradation of a mixture of dimethyl, diethyl, dibutyl, benzyl butyl, di-2-ethylhexyl, and di-n-octyl phthalates using a CSTB (continuous stirred tank bioreactor) operated under batch, fed-batch, continuous, and continuous with biomass recycle operation modes. For operating the CSTB under biomass recycle mode, microfiltration using an indigenous tubular ceramic membrane was employed. Ecotoxicity assessment of the treated water was carried out to evaluate the toxicity removal efficiency by the integrated bioreactor system. From the batch experiments, the EDPs cumulative degradation values were 90 and 75% at 1250 and 1500 mg/L total initial concentration of the mixture, respectively, whereas complete degradation was achieved at 750 mg/L. In the fed-batch study, 93% degradation was achieved at 1500 mg/L total initial concentration of the mixture. In continuous operation mode, 94 and 85% degradation efficiency values were achieved at 43.72 and 52.08 mg/L⋅h inlet loading rate of phthalate mixture. However, continuous feeding with 100% biomass recycle revealed complete degradation at 41.67 mg/L⋅h inlet loading rate within the 84 h operation period. High seed germination index and low mortality percentage of brine shrimps observed with phthalate degraded water from the integrated bioreactor system revealed its excellent potential in the treatment and toxicity removal of phthalates contaminated environment.

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.

Clarification of citrus fruit juices using microfiltration technique equipped with indigenously developed novel ceramic membrane

Microfiltration of citrus fruit juices using membrane technology is a promising method for clarification without losing their inherent properties to extend their shelf life. The present work discusses the development of a tubular ceramic microfiltration membrane and its performance in clarifying two kinds of citrus fruit juices, mandarin and sweet orange. The membrane was prepared by the extrusion method from indigenous bentonite clay, exhibited a porosity of 37% with 0.11 μm pore size, and possessed adequate flexural strength of 18 MPa. The fabricated membrane's potential was evaluated by conducting the tangential filtration of both centrifuged and enzyme-treated centrifuged fruit juices. Also, the applied pressure (68.94-344.7 kPa) and crossflow rate (110-150 Lph) were varied to study the clarified juice properties. At low operating conditions, the highest clarity of the juices was identified despite low permeate flux. The desired properties of juices, including pH, citric acid content, and total soluble solids, were unaffected by pretreatment and tangential membrane filtration, whereas the pectin content, which reduces the juice quality, was eliminated entirely. Furthermore, fouling analysis was carried out using Hermia's models, and cake filtration was identified to be dominant for both juices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05734-y.

Hybrid system coupling ozonation and nanofiltration with functionalized catalytic ceramic membrane for ibuprofen removal

The investigations on the removal of ibuprofen (IBU) in a hybrid system coupling ozonation and nanofiltration with functionalized catalytic ceramic membrane are presented. The gaseous ozone into feed water in concentration of 11 g Nm^-3 was supplied. Positive influence of catalytic ozonation on ibuprofen decomposition was observed. The application of catalytic nanofiltration membrane led to the ibuprofen removal of 91% after the first 15 min from the beginning of the O₃/NF process, while at the same time, for the pristine membrane, it was equal to 76%. The investigations revealed incomplete degradation of drug under pH 3 after 2 h, i.e., 89%. On the other hand, the addition of inorganic salts did not affect the catalytic ibuprofen removal efficiency. Under acidic pH, the highest permeate flux decline (26%) was noted, whereas no differences between permeate flux measured under natural and alkaline conditions were observed. During the treatment process, three IBU by-products were detected, which significantly affected the permeate toxicity; however, after 2 h of catalytic nanofiltration, the product of treatment process was found as non-toxic.

Intelligent optimization for modelling superhydrophobic ceramic membrane oil flux and oil-water separation efficiency: Evidence from wastewater treatment and experimental laboratory

Due to the significant energy and economic losses brought on by the global oil spill, there has been an increased interest in oil-water separation. This study presents strong non-linear machine learning models (support vector regression (SVR) and Gaussian process regression (GPR)) with the Response surface method (RSM) to predict the oil flux and oil-water separation efficiency of wastewater using ceramic membrane technology. For the model development and prediction of oil flux (OF) and oil-water separation efficiency (OSE), oil concentration (mg/L), feed flow rate (mL/min), and pH were considered as input variables. The input variables are combined in three combinations to study the most contributing input features to the models' performance. Mean square error (MSE) and Nash-Sutcliffe coefficient efficiency (NSE) were used to assess the prediction performances of the developed models with the different number of input combinations considered in the study. For the two target variables (OF and OSE), GPR and SVR models were used to separately predict them. For OF, the SVR-2 [Combo-2] model (MSE = 0.9255 and NSE = 2.7976) performed better with higher prediction accuracy compared to GPR-2 [Combo-2] model (MSE = 0.763 and NSE = 6.437). In addition, for OSE, the GPR-3 [Combo-3] model (MSE = 0.995 and NSE = 0.5544) performed slightly better than SVR-3 [Combo-3] model (MSE = 0.992 and NSE = 0.8066). The results showed that the SVR model with the combo-2 and GPR-3 models for OF and OSE variables are the proposed models with the best performance and accuracy. This machine learning study will aid in better evaluating the function of materials such as ceramic in membrane performance features such as oil flux and rejection prediction, separation efficiency, water recovery, membrane fouling, and so on. As for academics and manufacturers, this machine learning (ML) strategy will boost performance and allow a better understanding of system governance.

Characterization and application of novel fly ash blended ceramic membrane in MFC for low-cost and sustainable wastewater treatment and power generation

Field-scale application of the microbial fuel cell (MFC) technology faces a major constraint due to the widely used high-cost proton exchange membrane Nafion, prompting lately, the development of ceramic membranes using different clay minerals. In the present study, the characteristics and applicability of a novel ceramic membrane fabricated using potter's clay (C) blended with varying proportions (0, 5, 10, and 20 wt%) of fly ash (FA), designated as CFA₀, CFA₅, CFA₁₀, and CFA₂₀, were assessed for cost-effective and sustainable use in MFC. On assessing the properties of the membrane, CFA₁₀ was found to exhibit superior quality with fine pore size distribution (average 0.49 μm) favoring higher water uptake and less oxygen diffusion. The CFA₁₀ membrane showed a maximum proton mass transfer coefficient (4.32 ± 0.04 × 10^-5 cm/s) that was about three times that of the control CFA₀. The oxygen mass transfer coefficient of CFA₁₀ was 5.13 ± 0.12 × 10^-5 cm/s, which was about 40% less than in the control. X-ray diffraction (XRD) analysis of CFA membrane revealed the richness of quartz, which facilitates proton conductance and water retention. The CFA₁₀ membrane fitted MFC demonstrated a peak power output of 4.57 W/m³ (twice that in CFA₀) with an average of 80.02 ± 0.86% COD removal and 68.03 ± 0.13% coulombic efficiency in a long-term study indicating its improved applicability and durability. Electrochemical kinetics involving cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) also affirmed the efficacy of CFA₁₀ membrane in MFC showing peak current output of 13.95 mA and low ohmic resistance (74.2 Ω). The novel (CFA₁₀) ceramic membrane amalgamated with the coal fly ash, a waste of concern, shows promise for high MFC performance at a much reduced (98% less) cost that can be used for sustainable scale-up of the technology.

Performance of Anaerobic Membrane Bioreactor (AnMBR) with Sugarcane Bagasse Ash-based Ceramic Membrane treating Simulated Low-strength Municipal Wastewater: Effect of Operation Conditions

This study assesses the performance of waste sugarcane bagasse ash (SBA)-based ceramic membrane in anaerobic membrane bioreactor (AnMBR) treating low-strength wastewater. The AnMBR was operated in sequential batch reactor (SBR) mode at hydraulic retention time (HRT) of 24 h, 18 h, and 10 h to understand the effect on organics removal and membrane performance. Feast-famine conditions were also examined to evaluate system performance under variable influent loadings. An average removal of >90% chemical oxygen demand (COD) was obtained at each HRT and starvation periods up to 96 days did not significantly affect removal efficiency. However, feast-famine conditions affected extracellular polymeric substances (EPS) production and consequently the membrane fouling. EPS production was high (135 mg/g MLVSS) when the system was restarted at 18 h HRT after shutdown (96 days) with corresponding high transmembrane pressure (TMP) build-up; however, the EPS content stabilized at ~60-80 mg/g MLVSS after a week of operation. Similar phenomenon of high EPS and high TMP was experienced after other shutdowns (94 and 48 days) as well. Permeate flux was 8.8±0.3, 11.2±0.1 and 18.4±3.4 L/m² h at 24 h, 18 h and 10 h HRT, respectively. Filtration-relaxation (4 min - 1 min) and backflush (up to 4 times operating flux) helped control fouling rate. Surface deposits (that significantly attributed to fouling) could be effectively removed by physical cleaning, resulting in nearly complete flux recovery. Overall, SBR-AnMBR system equipped with waste-based ceramic membrane appears promising for treatment of low-strength wastewater with disruptions in feeding.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-023-06173-3.

Impact of pre-coagulation on the ceramic membrane process during oil-water emulsion separation: Fouling behavior and mechanism

Coagulation has been evaluated as an economical and effective pre-treatment method for controlling membrane fouling. We investigated the influence of the pre-coagulation of oil-water (O/W) emulsions on the formation of membrane fouling in the ceramic membrane process. The results confirmed that pre-coagulation effectively mitigated the fouling formation on the ceramic membrane surface during the O/W emulsion separation. The mechanism of mitigating membrane fouling by pre-coagulation was proposed, owing to the reduction in the zeta potential value of oil droplets by pre-coagulation, resulting in weak electrostatic attraction between oil droplets and ceramic membrane surfaces, and an increase in the size of the oil droplets by pre-coagulation, leading the formation of a cake layer fouling. In addition, the decrease in the hydrophobicity of oil droplets by pre-coagulation resulted in alleviating the hydrophobic interaction between oil droplets and membrane surface. The proposed fouling mechanism was supported by the characterization of the virgin and fouled membrane surfaces and the analysis of the fouling resistance ability of the membranes. Our study could be indicative of mitigation protocols that can be used to alleviate membrane fouling on ceramic membranes during oily wastewater treatment.

Peroxymonosulfate activated by composite ceramic membrane for the removal of pharmaceuticals and personal care products (PPCPs) mixture: Insights of catalytic and noncatalytic oxidation

A composite manganese-based catalytic ceramic membrane (Mn-CCM) was developed by a solid-state sintering method, and its effectiveness toward activation of peroxymonosulfate (PMS) for the degradation of 11 pharmaceutical and personal care products (PPCPs) mixture was tested. The optimized Mn-CCMs/PMS system showed remarkable degradation efficiencies for PPCPs mixture with total removal >90% in ultrapure water, river water and natural organic matter (NOM) solution. The Mn-CCMs/PMS system showed the contribution of different phenomena in PPCPs removal in the order of catalytic oxidation (54.7%, Mn-CCMs/PMS) > noncatalytic oxidation (42.3%, PMS oxidation) > adsorption (3.0%, by Mn-CCMs). The singlet oxygen (¹O₂) was the dominant reactive oxygen specie for the degradation of PPCPs in all water matrices proved by the quenching experiments and electro-paramagnetic resonance (EPR) spectroscopy. The extraordinary stability of Mn-CCMs for the activation of PMS has been noted in terms of repeatability experiments for PPCPs degradation with fewer leaching of Mn (1.9 to 3.6 µg/L). Mineralization was achieved in the range of 28-65% for different water matrices. The toxicity of the PPCPs mixture was reduced by 85.9%. The Mn-CCMs/PMS system showed a reduction (25-100%) in precursors of different carbon- and nitrogen-based disinfection by-products. This study found the Mn-CCMs/PMS system as a feasible purification unit for removing trace concentrations of PPCPs (ng/L) in real drinking water matrices.

Sustainable ceramic membrane for decontamination of water: A cost-effective approach

A sustainable ceramic membrane embedded with silver has been developed using quartz, kaolin and calcium carbonate. All the chemicals involved in this process were commonly available, non-toxic and cheap. The process was very simple, convenient and does not involve any wastage of water. Decoration of silver particles onto the porous ceramic membrane with the help of APTES as a connecting molecule leads to the formation of a durable material having strong antibacterial capacity. The fabricated membrane holds wide pore morphology with pore size of 4.4 μm and average porosity of 19.5% with an estimated cost of fabrication of about 60 dollar/m². The membrane was found capable in reducing the TDS, BOD and COD of water samples that confirms that it is efficient for water treatment applications.

Transport of emerging organic ultraviolet (UV) filters in ceramic membranes: Role of polyethylene (PE) microplastics

Microplastics can be considered potential carriers of emerging organic ultraviolet (UV) filters due to their considerable adsorption capacity in wastewater treatment. The adsorption behavior of organic UV filters, which are commonly contained in personal care products to preserve the skin against UV radiation, onto polyethylene (PE) microplastics were systematically studied to investigate their combined effects. Kinetics and isotherm analyses revealed that the adsorption of four organic UV filters onto PE microplastic surfaces followed a multi-rate and a heterogeneous multi-layer pattern. Several factors including salinity, microplastic size, and dosage also influenced the adsorption efficiency due to hydrophobic interactions. A bench-scale cross-flow ceramic membrane filtration experiment was investigated to evaluate the role of PE microplastics on the retention performance of organic UV filters. The retentions for organic UV filters were 34.2%-37.8% in the non-existence of PE microplastics. Conversely, organic UV filter retentions were significantly increased up to 82.2%-97.9% when they were adsorbed onto the PE microplastics, which were almost completely retained by the ceramic membrane. Therefore, organic UV filters can likely migrate and eventually be carried by PE microplastics, thus increasing the retention of both emerging organic UV filters and microplastics prior to discharge from wastewater treatment facilities.

Silicon carbide catalytic ceramic membranes with nano-wire structure for enhanced anti-fouling performance

Membrane fouling is a critical challenge for current ceramic membranes, which suffer from low flux and insufficient removal. Development of self-cleaning catalytic ceramic membranes is promising to address this challenge. Herein, we design heterogeneous silicon carbide ceramic membranes featuring a novel structure of g-C₃N₄-decorated β-SiC nano-wire catalytic functional layer, which enables enhanced anti-fouling self-cleaning performance. At chemical harsh (alkaline or especially acidic) conditions, the nano-wire membrane exhibits catalysis-enhanced removal performance for organic contaminants. Unlike conventional particle-packing membrane structure, such a nano-wire network membrane structure has not only high porosity (56.1%), but exceptional water permeance (110 L·m^-2·h^-1·bar^-1) and removal (100%) of organic substance under simulated sunlight, outperforming state-of-the-art organic membranes and ceramic membranes. Superoxide radical (∙O₂^-) was experimentally confirmed to be major reactive species responsible for self-cleaning function. We also propose a catalytic mechanism model with radical formation pathway, enabled by the as-formed g-C₃N₄@β-SiC heterojunction structure with reduced electron-hole recombination. This work would provide new insights into not only rational design of next-generation ceramic membranes with self-cleaning function but also more applications of efficient treatment of refractory wastewaters containing degradable organic substances by using such membranes.

Progress in alumina ceramic membranes for water purification: Status and prospects

Ceramic membranes have gained increasing attention in recent years for the removal of various contaminants from water. Alumina membrane is considered as one of the most important ceramic membranes, which plays important roles not only in separation processes such as microfiltration, ultrafiltration, and nanofiltration, but also in catalysis- and adsorption- enhanced separation applications in water purification and wastewater treatment. However, there is currently still lack of a comprehensive critical review about alumina membranes for water purification. In this review, we first discuss recent developments of alumina membranes, and then critically introduce the state-of-the-art strategies for lowering fabrication cost, improving membrane performances and mitigating membrane fouling. Especially, aiming to improve membrane performance, some emerging methods are summarized such as tailoring membrane structure, developing flexible membranes, designing nano-pores for precise separation, and enhancing multi-functionalities. In addition, engineering applications of alumina membranes for water purification are also briefly introduced. Finally, the prospects for future research on alumina membranes are proposed, such as economic preparation/application, challenging precise separation, enriching multi-functionalities, and clarifying separation mechanisms.

Molecular transformations of dissolved organic matter during UV/O3-assisted membrane filtration of UASB-treated real textile wastewater

A ceramic membrane reactor (CMR) integrated with in-situ UV/O₃ was assessed for post-treatment of the effluent out of an up-flow anaerobic sludge blanket (UASB) reactor treating real textile wastewater, focusing on the transformation of dissolved organic matter (DOM). Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) revealed the transformation of heteroatomic DOM containing S, N or both to simpler DOM containing mainly C, H, and O atoms. The decreased N contents in products (N/C = 0.0249) compared to precursors (N/C = 0.0311) and the higher O/C ratios in the N-containing products suggest the removal of R-NH₂ groups accompanying DOM oxidation. While, S-containing compounds in the products had lower O/C and H/C ratios, suggesting a reduced state and the transformation of R-SO₃ to R-S-R. H-abstraction and OH addition were identified as the primary oxidation mechanisms, thus enhancing the dominance of highly unsaturated and phenolic DOM in the effluent (70.3%) compared to the feed (56.6%). The double bond equivalent (DBE) was also increased by 26% in the effluent compared to the feed and by 33% in products compared to precursors. These findings help understand the DOM transformation in UV/O₃-assisted ceramic membrane reactors and call for comprehensive toxicity analyses of effluents from the advanced oxidation processes.

Electrified ceramic membrane actuates non-radical mediated peroxymonosulfate activation for highly efficient water decontamination

Electrified ceramic membranes (ECMs) achieve high water decontamination efficiency mainly through implementing in situ radical-mediated oxidation in membrane filtration, whereas ECMs leveraging non-radical pathways are rarely explored. Herein, we demonstrated a Janus ECM realizing ultra-efficient micropollutant (MP) removal via electro-activating peroxymonosulfate (PMS) in a fast, flow-through single-pass electro-filtration. The Janus ECM features two separate palladium (Pd) functionalized electrocatalytic reaction zones engineered on its two sides. We confirmed that the PMS/electro-filtration system induced non-radical pathways for MP degradation, including singlet oxygenation and mediating direct electron transfer (DET) from MP to PMS. Under the design of the ECM featuring dual electrocatalytic reaction zones in the ceramic membrane intrapores, the Janus ECM showed over one-fold increase in micropollutant removal rate as 94.5% and lower electric energy consumption as 1.78 Wh g^-1 MP in the PMS electro-activation process, as compared with the conventional ECM assembly implementing only half-cell reaction. This finding manifested the Janus ECM configuration advantage for maximizing the PMS electro-activation efficiency via singlet oxygenation intensification and direct usage of cathode for DET mediation. The Janus ECM boosted the PMS electro-activation and water decontamination efficiency by enhancing the convective mass transfer and the spatial confinement effect. Our work demonstrated a high-efficiency PMS electro-activation method based on electro-filtration and maximized the non-radical mediated PMS oxidation for MP removal, expanding the ECM filtration strategies for water decontamination.

Effect of fine bubbles for washing of monolith type porous ceramic membranes treating oil-in-water emulsions

Produced water generated in the recovery of crude oil contains oil and high concentrations of salts, organic matter, and suspended solids and must therefore be treated appropriately prior to disposal. Monolithic ceramic membranes have high oil removal rates and have the advantage of being compact, having a long life, and withstanding chemicals, heat, and high cleaning pressures. Membrane fouling, however, is a significant drawback to membrane filtration. Scrubbing using air bubbles generated by a diffuser is generally used to physically clean membranes. However, monolithic ceramic membranes cannot be scrubbed using air bubbles because their fluid channels are only a few millimeters wide. Membrane washing efficiency was therefore evaluated using fine bubbles smaller than the diameter of the channels. In dead-end filtration, flushing the membrane surface with air-microbubble water or air-ultra-fine bubble (UFB) water after backwashing and air-blowing (conventional cleaning) of the channels was more efficient than conventional cleaning. Flushing with UFB water was not influenced by changes in pH that changed the zeta potential of the UFB. Membrane fouling was suppressed in crossflow filtration by mixing UFB water with feed water. There was no significant change in the diameter of the oil droplets in the feed water before and after UFB mixing. The ZP of the oil droplets peaked at around -20 mV before UFB mixing. However, the peak shifted to around -25 to -29 mV after UFB mixing.

Cost and efficiency perspectives of ceramic membranes for water treatment

More robust ceramic membranes with tailorable structures and functions are increasingly employed for water treatment, particularly in some harsh applications for their ultra-long service lifespan due to their high mechanical, structural, chemical and thermal stability and anti-fouling properties. Decreasing cost and enhancing efficiency are two key but quite challenging application-oriented issues for broader and larger-scale engineering application of current ceramic membranes, and are required to make ceramic membranes a highly efficient and economic water treatment technique. In this review, we critically discuss these two significant concerns of both cost and efficiency for water treatment ceramic membranes, focusing on an overview of various advanced strategies and mechanism insights. A brief up-to-date discussion is first introduced about recent developments of ceramic membranes covering the major advances of novel membranes and applications. Then some promising strategies for decreasing the cost of ceramic membranes are discussed, including membrane material cost and processing cost. To fully address the issue of moderate efficiency with single separation function, valuable and considerable insights are provided into recent major progress and mechanism understandings in application with other unit processes, such as advanced oxidation and electrochemistry techniques, to significantly enhance treatment efficiency. Subsequently, a review of recent ceramic membrane applications emphasizing harsh operating environments is presented, such as oil-water separation, saline water, refractory organic and emerging contaminant wastewater treatment. Finally, engineering application, conclusions, and future perspectives of ceramic membrane for water treatment applications are critically discussed offering new insight based on understanding the issues of cost and efficiency.

Electrocoagulation coupled with conductive ceramic membrane filtration for wastewater treatment: Toward membrane modification, characterization, and application

Membrane separation is an effective solution for pollutant removal, however, achieving high permeability and antifouling ability remains a pressing challenge for its widespread application. In this study, a novel method of coating flat ceramic membranes (CMs) with a conductive film (Sb-SnO₂) was developed to enhance the filtration and antifouling performance of CMs when the membrane filtration was coupled with electrocoagulation. After comparing the parameters, including the film sheet resistance and pure water flux, with those of other coating methods (i.e., gel coating and immersion hydrolysis), a well-fixed conductive coating with optimal permeability and stability was generated using spray pyrolysis with a substrate ceramic membrane surface temperature of 475 °C, precursor concentration of 0.5 M (calculate as SnO₂), and spraying amount of 50 mL (120 cm²), during membrane modification. Batch filtration experiments using wastewater from the mechanical industry demonstrated that the conductive ceramic membrane (CCM) cathode integrated with electrocoagulation at an electric field of 2.8 V/cm (3.0 mA/cm²) achieved permeate fluxes that were 0.34, 0.70, 0.75 and 1.41 times higher than those of sole CM separation after four cycles. Moreover, the membrane separation process was dominated by the standard pore-blocking model, and its correlation coefficient decreased with the exertion of the electric field, indicating that membrane filtration fouling changed from irreversible to reversible. This CCM combined with electrocoagulation exhibited significant potential for alleviating membrane fouling and widespread application, and could act as a promising technology for industrial wastewater treatment.

Efficient removal of micropollutants from low-conductance surface water using an electrochemical Janus ceramic membrane filtration system

Electrochemical membrane filtration (EMF) technology is effective to remove the micropollutant in the wastewater but its efficacy is drastically compromised in treating the surface water having a typically low conductivity. In this work, a Janus Fe-Pt electrochemical ceramic membrane (ECM) was fabricated by depositing a thin Fe layer on the side of a ceramic membrane facing feed (cathode) and Pt layer on the other side facing permeate (anode). The low Fe-Pt electrode distance (∼1 mm) ensured a decent conductance of the EMF system even in the low-salinity surface water and thereby maintained the removal efficiency of the micropollutant. It was identified that hydroxyl radicals (•OH) generated via anodic water oxidation and cathodic heterogenous Fenton process on bilateral sides of ECM were the dominant reactive oxygen species. The EMF system not only achieved 74% removal of atrazine (ATZ) from the low-conductance synthetic surface water with a low energy consumption (3.6 Wh per gATZ or 7.2 Wh m ^- 3), but also realized a stable removal of ATZ from real surface water over a continuous filtration experiment of 168 h. The theoretical computations and experimental analysis identified the degradation pathway, i.e., the dechlorination and dealkylation of ATZ in the EMF system. This study highlights the great potential of the Janus ECM in removing micropollutants from low-conductance surface water and wastewater.

3D spray-coated gradient profile ceramic membranes enables improved filtration performance in aerobic submerged membrane bioreactor

Rational design of cross-sectional microstructure in ceramic membranes has shown to improve membrane filtration efficacy without affecting rejection performance. In this work, we adopted 3D spray-coating technique to generate multi-layered membrane layers on macro-porous flat-sheet ceramic supports. The thickness of each layer was controlled by spray-coating cycles, and a gradient membrane layer was rationalized by successively coating three ceramic slurries containing alumina powders of gradually refined particle sizes, followed by co-sintering. Gradient membrane layers on both sides of the various sized flat-sheet ceramic supports were fabricated. Compared to the non-gradient counterpart, the gradient membranes showed both higher pure water flux (at the same TMP) and lower membrane resistance, which clearly evidenced the benefits of gradient profile in the membrane layer. Further, their performance in aerobic membrane bioreactors (AeMBR) was comparably studied for the first time. The treatment performance was not significantly affected by the types of membranes used, while the gradient membrane showed better filtration performance (i.e., a slower rise in TMP). Although the fouling mechanisms were revealed to be similar, the fouling layer in the gradient membrane was composed of a higher percentage of smaller foulants compared to that of the non-gradient counterpart. The observed differences were closely correlated to the larger internal pore structure in the gradient membrane. The present work provides a feasible 3D spray-coating technique for the fabrication of gradient flat-sheet ceramic membranes, and clarifies the benefits in AeMBR for domestic wastewater treatment.

Contrasting behaviors of pre-ozonation on ceramic membrane biofouling: Early stage vs late stage

Pre-ozonation coupled with ceramic membrane filtration has been widely used to alleviate membrane fouling. However, information on the efficiency and underlying mechanism of pre-ozonation in the evolution of ceramic membrane biofouling is limited. Herein, filtration experiments with a synthesis wastewater containing activated sludge were conducted in a cross-flow system to evaluate the effects of pre-ozonation on ceramic membrane biofouling. Results of flux tests show that pre-ozonation aggravated biofouling at the early stage, but alleviated the biofouling at the late stage. In situ FTIR spectra show that the aggravated biofouling with pre-ozonation was mainly caused by the enhanced complexation between phosphate group from DNA and Al₂O₃ surface and the increased rigid of proteins' structure. At the early stage, more severe pore blockage further substantiated the higher permeate resistance. By contrast, more dead cells were observed on membrane surface at the late stage, indicating the prevention of biofouling development after long-term pre-ozonation. Additionally, the structures and compositions of cake layers at the early and late stages exhibited considerable differences accompanied by the variation in microbial community with the evolution of biofouling. Therefore, this work demonstrates the effectiveness of pre-ozonation in biofouling in long-term operation and provides mechanistic insights into the evolution of biofouling on ceramic membrane.

Peracetic acid integrated catalytic ceramic membrane filtration for enhanced membrane fouling control: Performance evaluation and mechanism analysis

Endowing ceramic membrane (CM) catalytic reactivity can enhance membrane fouling control in the aid of in situ oxidation process. Peracetic acid (PAA) oxidant holds great prospect to integrate with CM for membrane fouling control, owing to the prominent advantages of high oxidation efficacy and easy activation. Herein, this study, for the first time, presented a PAA/CM catalytic filtration system achieving highly-efficient protein fouling alleviation. A FeOCl functionalized CM (FeOCl-CM) was synthesized, possessing high hydrophilicity, low surface roughness, and highly-efficient activation towards PAA oxidation. Using bovine serum albumin (BSA) as the model protein foulant, the PAA/FeOCl-CM catalytic filtration notably alleviated fouling occurring in both membrane pores and surface, and halved the flux reduction degree as compared with the conventional CM filtration. The PAA/FeOCl-CM catalytic oxidation allows quick and complete disintegration of BSA particles, via the breakage of the amide I and II bands and the ring opening of the aromatic amino acids (e.g., Tryptophan, Tyrosine). In-depth investigation revealed that the in situ generated ^•OH and ¹O₂ were the key reactive species towards BSA degradation during catalytic filtration, while the organic radical oxidation and the direct electron transfer pathway from BSA to PAA via FeOCl-CM played minor roles. Overall, our findings highlight a new PAA/CM catalytic filtration strategy for achieving highly-efficient membrane fouling control and provide an understanding of the integrated PAA catalytic oxidation - membrane filtration behaviors.

Silicon carbide microfiltration membranes for oil-water separation: Pore structure-dependent wettability matters

Both the pore size and surface properties of silicon carbide (SiC) membranes are demonstrated to significantly affect their separation efficiency when used for oily water treatment. However, the potential influences of open porosity together with the pore size of SiC membranes on their surface properties and oil-water separation performance have rarely been investigated. In this work, porous SiC ceramic membranes with tunable open porosity and pore size were purposely prepared and selected to systematically study the effect of pore structure-dependent wettability on the oil-water separation performance. The measured pure water flux of selected membranes as a function of open porosity (34-48%) and pore size (0.43-0.67 μm) was well-fitted by using a modified H-P equation. Interestingly, the hydrophilicity of SiC membranes was improved with the increase in open porosity and pore size, as evidenced by the gradually decreased dynamic water contact angle and underwater adhesion of oil droplets. Further, the open porosity of SiC membranes was found to contribute more to the improved surface wettability. As a result, the stable flux of SiC membranes in oil-in-water (O/W) emulsions was increased by 24% with the increased open porosity while the oil rejection rate remained above 90%. This work quantitatively reveals the contributions of the pore structure to the surface wettability of ceramic membranes, and thus provides an effective pathway to improve their performance in oil-water separation.

A novel ceramic-based thin-film composite nanofiltration membrane with enhanced performance and regeneration potential

The rational design of a ceramic-based nanofiltration membrane remains a significant challenge due to its performance and fabrication cost. Herein, we report a high-performance ceramic-based thin-film composite (TFC) membrane fabricated via a typical interfacial polymerization on an interwoven net substrate assembled by titanium dioxide (TiO₂) nanowires. The chemical properties and morphologies were systematically investigated for ceramic substrates and their corresponding TFC membranes. Due to the significantly improved hydrophilicity of the TiO₂ framework, more reactive amine monomers were uniformly adsorbed on the modified surface of the ceramic substrate, yielding an ultrathin polyamide layer with less resistance. In addition, the smooth surface and decreased pore size of the TiO₂ framework contributed to forming a defect-free polyamide layer. As a result, the obtained ceramic-based TFC membrane evinced high permeance of 26.4 L m^-2 h^-1 bar^-1 and excellent salt rejection efficiency, leading to simultaneous improvements compared with the control TFC membrane without the TiO₂ framework. Notably, the potential regeneration ability of the ceramic-based TFC membrane could be achieved via facile low-temperature calcination and re-polymerization process due to the varied thermostability between the polyamide layer and the robust ceramic substrate. The operation of regeneration helped to prolong the lifetime and decrease the cost for the ceramic-based TFC membrane. This research provides a feasible protocol to fabricate sustainable ceramic-based nanofiltration membranes with enhanced performance for water treatment.

Novel method for the facile control of molecular weight cut-off (MWCO) of ceramic membranes

This study demonstrates a simple and novel preparation method to prepare ceramic nanofiltration membranes with a precise and tunable molecular weight cut-off (MWCO) by packing variously sized nanoparticles into existing membrane pores. As a result, ceramic membranes with a MWCO from 1000 Da to 10,000 Da were successfully prepared with the narrow distribution of the pore size after the filtration-coating process. In addition, the effective porosity of the ceramic membranes was calculated from the results of the membrane properties by the Hagen-Poiseuille equation which fit within the range of the sphere packing theory from 17.3% to 41.8%. Furthermore, the results of nonlinear curve fitting between the MWCO and the nanoparticle size show a high accuracy, which implies that the MWCO of the ceramic membranes can be predicted using the curve fitting model with variously sized nanoparticles in the filtration-coating process. In conclusion, the novel filtration-coating method enables precise pore control and provides a tunable MWCO to ceramic membranes by preparing various sizes of nanoparticles.

Enriched autoinducer-2 (AI-2)-based quorum quenching consortium in a ceramic anaerobic membrane bioreactor (AnMBR) for biofouling retardation

This study is the first to enrich a facultative QQ consortium for AI-2-based quorum sensing (QS) disruption (FQQ2) and discover its quorum quenching (QQ) performance in an anaerobic membrane bioreactor (AnMBR) for membrane fouling retardation. Herein, FQQ2 was enriched by the enrichment culture using 4,5-dihydroxy-2,3-pentanedione (DPD) followed by anaerobic screening. FQQ2 was composed of various facultative AI-2-based QQ microorganisms including Acinetobacter, Comamonas, Stenotrophomonas, and FQQ2 was capable to degrade 96.96% of DPD in 9 h. More importantly, FQQ2 prolonged membrane filtration operation by an average of 3.72 times via reduction of DPD in the AnMBR treating domestic wastewater (p ≤ 0.05). QQ was implicated to reduce the content of proteins and carbohydrates of the extracellular polymeric substances (EPS) of suspended biomass by 24.16% and 10.39%, respectively, and concentration of proteins of the soluble microbial products (SMP) by 18.77%. Parallel factor (PARAFAC) modelling of excitation-emission matrix (EEM) demonstrated that QQ could reduce the content of fulvic acid-like and humic acid-like substances, aromatic proteins and soluble-microbial-by-product-like proteins of the EPS (p ≤ 0.05) and abate the content of soluble-microbial-by-product-like proteins in the SMP (p ≤ 0.05). The lower EPS content of suspended biomass could be rendered with the reduced relative abundance of AI-2-regulated Christensenellaceae;g-, Hyphomicrobium, Leucobacter and Microbacterium by 48.48%, 76.56%, 64.78% and 59.26%, respectively, and QQ led to the reduction of the relative abundance of Christensenellaceae;g- and Leucobacter in the cake layer by 31.07% and 51.43%, respectively. Moreover, quantity of organics as well as planktonic microorganisms in the supernatant decreased in presence of FQQ2 (p ≤ 0.05). Of note, markedly lower relative abundance of AI-2-regulated Sulfurovum in supernatant by 97.74% resulted in its lower abundance of cake layer. Intriguingly, in the presence of QQ, methane production was statistically enhanced by 62.5% (p ≤ 0.05). It was closely linked to the decrease of sulfate reduction (p ≤ 0.05), which resulted from 37.93% lower abundance of sulfate-reduction Desulfomonile in the suspended biomass (p ≤ 0.05). Collectively, this study sheds lights on the development of AI-2-based QQ for biofouling control in AnMBRs.

Treatment of oily wastewaters by highly porous whisker-constructed ceramic membranes: Separation performance and fouling models

Efficient treatment of challenging oily emulsion wastewater can alleviate water pollution to provide more chances for water reuse and resource recovery. Despite their promising application potential, conventional porous ceramic membranes have challenging bottleneck issues such as high cost and insufficient permeance. This study presents a new strategy for highly efficient treatment of not only synthetic but real oily emulsions via unexpensive whisker-constructed ceramic membranes, exhibiting exceptional permeance and less energy input. Compared with common ceramic membranes, such lower-cost mullite membranes with a novel whisker-constructed structure show higher porosity and water permeance, and better surface oleophobicity in water. Treatment performance such as permeate flux and oil rejection was explored for the oily emulsions with different properties under key operating parameters. Furthermore, classical Hermia models were used to reveal membrane fouling mechanism to well understand the microscopic interactions between emulsion droplets and membrane interface. Even for real acidic oily wastewater, such membranes also exhibit high permeance and less energy consumption, outperforming most state-of-the-art ceramic membranes. This work provides a new structure concept of highly permeably whisker-constructed porous ceramic membranes that can efficiently enable more water separation applications.

Bioelectricity production and shortcut nitrogen removal by microalgal-bacterial consortia using membrane photosynthetic microbial fuel cell

Membrane photosynthetic microbial fuel cell (MPMFC) utilizes O₂, NO₃^- and NO₂^- as cathodic electron acceptors, enabling simultaneous treatment of nitrogen, CO₂ and organic carbon in the cathode compartment. In this work, development of a novel cathodic process with in situ nitritation via microalgal photosynthesis during the light period is reported for achieving shortcut nitrogen removal (SNR) from ammonium-rich wastewater. Moreover, a tubular low-cost ceramic membrane was used to separate and recycle the microalgal-bacterial biomass to the cathode compartment during the continuous operation. The influence of NH₄⁺ concentration and ratio of chemical oxygen demand to total nitrogen on the MPMFC performance was examined. Denitritation under dark and anoxic conditions occurred due to denitrifying bacteria (DNB) subsequent to nitritation under light and aerobic conditions by ammonia-oxidizing bacteria (AOB) in the consortia. Final concentrations of NH₄⁺ and NO₂^- in the effluent of 0.10 mg NH₄⁺-L^-1 and 0.02 mg NO₂^--L^-1, respectively, were obtained using MPMFC which resulted in a nitrogen removal efficiency of 99 ± 0.5%. The maximum electricity production achieved using the MPMFC was 56 ± 0.1 mA. This study demonstrated that combining microalgal photosynthesis, nitritation and denitritation in the cathode compartment of MPMFC is advantageous for avoiding the cost due to external aeration and organic carbon source necessary for ammonium removal as well as utilization of NO₂^- or NO₃^- as an electron acceptor.

Robust zirconia ceramic membrane with exceptional performance for purifying nano-emulsion oily wastewater

While membrane-based oil-water separation has been widely explored, using conventional membranes to treat oily wastewaters remains practically challenging especially when such wastewaters contain more stable nano-sized oil droplets and are of high oil content, and harsh chemical conditions. Herein, we report a novel protocol of efficiently separating both synthetic and real oil nano-emulsions via specially designed robust zirconia membranes. The best-performing zirconia membrane, fabricated at low sintering temperature, has relatively uniform sub-100 nm pores and is underwater superoleophobic. Such zirconia membranes possess not only outstanding separation performance under long-term operation but robust structural stability at harsh conditions. At different cross-flow velocities, a combined model of intermediate pore blocking and cake filtration dominated membrane fouling behavior. Specifically, at high pH value (especially > pH_(IEP)), membrane fouling was effectively mitigated due to a dominant role of electrostatic repulsion interaction at membrane-oil interface. Compared with conventional and commercial ceramic membranes, our zirconia membrane is the first reported in literature that can effectively reject nano-sized oil droplets (∼18 nm) with over 99% rejection. Moreover, the zirconia membrane has also been challenged with real degreasing wastewater with very high oil content (∼4284 mg L^-1) and pH (∼12.4) and delivered consistently high separation performance over many operation cycles.

Degradation of antibiotics, organic matters and ammonia during secondary wastewater treatment using boron-doped diamond electro-oxidation combined with ceramic ultrafiltration

In this study, a BDD electrolytic oxidation-ceramic membrane ultrafiltration (EO-CM) system for the removals of antibiotics, organic matters and ammonia in wastewater was evaluated. Sulfamethazine (SMZ) was degraded following a pseudo first-order kinetics. The removal rate of SMZ improved with the increase of electro-oxidation time (0-60 min) and current density (5-30 mA/cm²). During the BDD electro-oxidation process, H₂O₂ and hydroxyl radicals (•OH) were generated which were detected by N, N-diethyl-p-phenylenediamine (DPD) method and electron paramagnetic resonance spectroscopy (EPR), respectively. Chemical oxygen demand (COD) was able to be removed by EO and CM processes, in which proteins and humic acids were regarded as the main removed components measured using excitation-emission matrix (EEM) technique. Moreover, BDD electro-oxidation pretreatment could make the CM process maintain a high water flux and significantly control the membrane fouling and relieve transmembrane pollution. In addition, the removal of ammonia was enhanced with the increase of chloride ions (Cl^-) in wastewater during EO process due to the generation of active chlorine (i.e., ClO^-, HClO, or Cl₂) from the oxidation of Cl^-. Chloramine and nitrogen were produced in the oxidation of ammonia by active chlorine. Overall, the results of this study suggest that BDD EO-CM system is a promising process for removing antibiotics, organic matters and ammonia.

Ex-situ biogas upgrading in thermophilic up-flow reactors: The effect of different gas diffusers and gas retention times

Four different types of ceramic gas distributors (Al₂O₃ of 1.2 μm and SiC of 0.5, 7 and 14 μm) were evaluated to increase biomethane formation during ex-situ biogas upgrading process. Each type of gas diffuser was tested independently at three different gas retention times of 10, 5 and 2.5 h, at thermophilic conditions. CH₄ production rate increased by increasing input gas flow rate for all type of distributors, whereas CH₄ concentration declined. Reactors equipped with SiC gas distributors effectively improved biomethane content fulfilling natural gas standards. Microbial analysis showed high abundance of hydrogenotrophic methanogens and proliferated syntrophic bacteria, i.e. syntrophic acetate oxidizers and homoacetogens, confirming the effect of H₂ to alternate anaerobic digestion microbiome and enhance hydrogenotrophic methanogenesis. A detailed anaerobic bioconversion model was adapted to simulate the operation of the R₁-R₄ reactors. The model was shown to be effective for the simulation of biogas upgrading process in up-flow reactors.

Electronic faucet powered by low cost ceramic microbial fuel cells treating urine

Hygienic measures are extremely important to avoid the transmission of contagious viruses and diseases. The use of an electronic faucet increases the hygiene, encourages hand washing, avoids touching the faucet for opening and closing, and it saves water, since the faucet is automatically closed. The microbial fuel cell (MFC) technology has the capability to convert environmental waste into energy. The implementation of low cost ceramic MFCs into electronic interfaces integrated in toilets, would offer a compact powering system as well as an environmentally friendly small-scale treatment plant. In this work, the use of low cost ceramic MFCs to power an L20-E electronic faucet is presented for the first time. A single MFC was capable of powering an electronic faucet with an open/close cycle of 8.5 min, with 200 ml of urine. With a footprint of 360 cm³, the MFC could easily be integrated in a toilet. The possibility to power e-toilet components with MFCs offers a sustainable energy generation system. Other electronic components including an automatic flush, could potentially be powered by MFCs and contribute to the maintenance efficiency and hygiene of the public toilets, leading to a new generation of self-sustained energy recovering e-toilets.

Gravity-driven ceramic membrane (GDCM) filtration treating manganese-contaminated surface water: Effects of ozone(O3)-aided pre-coating and membrane pore size

Achieving adequate manganese removal during water treatment is a challenging process. This study aimed to assess the effectiveness of gravity driven ceramic membrane (GDCM) filtration in the elimination of manganese from surface water. The impact of membrane pre-modification with birnessite and molecular weight cut-off on long-term water treatment efficiency was investigated by assessing filtration units with 300 kDa virgin membrane (300 kDa-blank), 300 kDa membrane pre-coated with manganese oxides (300 kDa-MnOx), and 15 kDa virgin membrane (15 kDa-blank). The results of 300 kDa-blank and 300 kDa-MnOx indicated that depositing manganese oxides (produced via ozone (O₃) oxidation) prior to water treatment was conducive to ripening of cake layer which played a major role in Mn removal. Reducing membrane molecular cut-off from 300 to 15 kDa also significantly reduced permeate Mn concentration, achieving a removal efficiency of 75% at the end of the trial (highest of all the units). Relative to 300 kDa-blank, the greater manganese removals in the other two systems can be attributed to 1) the long hydraulic retention times resulting from the higher membrane resistance, and 2) the higher abundance of biologically produced Birnessite materials in the cake layers for manganese oxidation. Raman analysis and X-ray diffraction analysis showed that 15 kDa-blank achieved the highest level of Birnessite production and most cake materials featured a flower-like structure and relatively small size (as shown under a scanning electron microscope and Energy Dispersive X-Ray Spectroscopy element mapping analysis), suggesting a higher surface area for Mn oxidation.

Comparison between permanganate pre-oxidation and persulfate/iron(II) enhanced coagulation as pretreatment for ceramic membrane ultrafiltration of surface water contaminated with manganese and algae

Concurrent presence of algae and manganese (Mn) in water poses a significant challenge for water treatment. This study compared the treatment efficiency of Mn-containing and algae-laden water using either permanganate pre-oxidation (KMnO₄) or persulfate/iron(II) (PMS/Fe²⁺) enhanced coagulation as pretreatment for ceramic membrane ultrafiltration. The results showed that KMnO₄ pre-oxidation achieved a slightly more effective Mn removal, and was almost unaffected by the initial dissolved organic carbon (DOC) concentrations. PMS/Fe²⁺ removed UV₂₅₄ more efficiently (above 90% at a dose of 0.25 mmol/L), compared with KMnO₄ (less than 60% UV₂₅₄ removal). According to X-ray photoelectron spectroscopy (XPS) analysis of aggregates, both KMnO₄ and Fe²⁺/PMS oxidation resulted in the formation of MnO₂ precipitate. Electron paramagnetic resonance(EPR) analysis demonstrated that only the reactors dosed with PMS/Fe²⁺ were able to generate the highly reactive hydroxyl radical(·OH). The production of ·OH caused significant rupture of algal cells and thus higher algal removal compared to the treatment with KMnO₄ (whereby insignificant cell breakage was observed). The cell rupture resulted in higher amounts of organic matter released in the systems containing PMS/Fe²⁺, as demonstrated by excitation-emission matrix (EEM) and protein analysis. Despite the elevated level of organic matter, adding PMS/Fe²⁺ was found to notably mitigate membrane fouling due to the formation of large flocs (311-533 μm) as well as the elimination of major ceramic membrane foulants, i.e. humic substances.

Emerging organic contaminants and odorous compounds in secondary effluent wastewater: Identification and advanced treatment

This study aims to address organic micropollutants in secondary effluents from municipal wastewater treatment plants (WWTPs) by first identification of micropollutants in different treatment units, and second by evaluating an advanced treatment process for removals of micropollutants. In secondary effluents, 28 types of pharmaceutical and personal care products (PPCPs), 5 types of endocrine disrupting chemicals (EDCs) and 3 types of odorous compounds are detected with total concentrations of 513 ± 57.8 ng/L, 991 ± 36.5 ng/L, 553 ± 48.3 ng/L, respectively. An integrated process consisting of in-situ ozonation, ceramic membrane filtration (CMF) and biological active carbon (BAC) filtration is investigated in a pilot scale (1000 m³/d) for removal of micropollutants in secondary effluents. The total removal efficiencies of PPCPs, EDCs and odorous compounds are 98.5%, 95.4%, and 91.1%, respectively. Removal mechanisms of emerging organic contaminants (EOCs) and odorous compounds are discussed based on their physicochemical properties. The remarkable removal efficiencies of micropollutants by the pilot system is attributed to synergistic effects of combining ozonation, ceramic membrane filtration and BAC filtration. This study provides a cost-effective and robust technology with the capability of treating secondary effluents for reuse applications.

Fouling mitigation in produced water treatment by conjugation of advanced oxidation process and microfiltration

This work explored the use of ozonation and photoperoxidation before the microfiltration process to reduce fouling. Produced water was synthesized with salt, viscosifier, and surfactant. The additives influence on membrane fouling was evaluated. Photoperoxidation process led to an overall better performance than ozonation in terms of oil removal and fouling reduction. The maximum oil removal efficiency was 86%, obtained for emulsions with salt after 2 h of treatment (COD: H₂O₂ ratio 1:1, UV dose of 965 J/m²). The inclusion of chemical additives impaired the oxidative power of hydroxyl radicals leading to a moderate oil removal; however, they were still able to reduce membrane fouling, mainly in oil/water emulsions with viscosifier. Higher salt concentration promoted fouling resistance and also benefited the permeate quality. Cross-flow microfiltration process integrated with photoperoxidation was able to improve the permeate flux from 84 to 182 L/m².h after 3 h of exposure to UV radiation, resulting in a permeate with less than 10 mg/L of oil content. Graphical abstract.

Effect of microbial fuel cell operation time on the disinfection efficacy of electrochemically synthesised catholyte from urine

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The MFC with the thickest ceramic membrane produced the best quality catholyte.

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MFC operation time contributes to the catholyte quality and killing properties.

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Catholyte from ceramic MFC (10 mm) reached pH 11 at day 42 and eradicated E. coli.

Microbial fuel cells (MFCs) offer an excellent solution to tackle some of the major challenges currently faced by humankind: sustainable energy sources, waste management and water stress. Besides treating wastewater and producing useful electricity from urine, ceramic MFCs can also generate biocidal catholyte in-situ. It has been proved that the electricity generation from the MFCs has a high impact in the catholyte composition. Therefore, the catholyte composition constantly changes while electricity is generated. However, these changes in catholyte composition with time has not yet been studied and that could highly contribute to the disinfection efficacy. In this work, the evolution of the catholyte generation and composition with the MFC operation time has been chemically and microbiologically evaluated, during 42 days. The results show an increase in pH and conductivity with the operation time, reaching pH 11.5. Flow cytometry and luminometer analyses of bioluminescent pathogenic E. coli exposed to the synthesised catholyte revealed killing properties against bacterial cells. A bio-electrochemical system, capable of electricity generation and simultaneous production of bactericidal catholyte from human urine is presented. The possibility to electrochemically generate in-situ a bacterial killing agent from urine, offers a great opportunity for water reuse and resource recovery for practical implementations.

Beneficial utilization of Al/Si/O-rich solid wastes for environment-oriented ceramic membranes

Wide application of traditional multilayer ceramic membrane has been severely restricted by high costs associated with rare membrane materials and high sintering temperature. In this study, typical solid wastes (coal fly ash, river sediment and sewage sludge) were adopted as raw materials to provide an Al-Si-O matrix for single-layer ceramic membranes. Phase identification shows anorthite as major crystalline phase, while bulk density and pore characteristics of the membranes varied with different raw material compositions, with flexural strengths of 40.82-71.46 MPa, and average pore size of 0.23 μm, 0.28 μm, 0.32 μm and 0.84 μm. When the membranes were applied in an oily water treatment, the oil rejection reached >98 % when using any of the four membranes with oil/water emulsion permeate flux remaining at ∼1200 L/m²·h. Furthermore, the stability of ceramic membranes in harsh environmental conditions was confirmed, with negligible weight loss ratios after being corroded in acidic/alkalic media. In addition, more than 95 % of original flux can be achieved even after six cycles, which confirmed the excellent recyclability of the membranes. The successful fabrication and application of the environment-oriented single layer ceramic membranes from the Al-Si-O solid waste matrix provided a promising "waste-to-resource" strategy for beneficial utilization of typical solid wastes as ceramic raw materials.

An integrated process for the advanced treatment of hypersaline petrochemical wastewater: A pilot study

An integrated process combining ozonation, ceramic membrane filtration with biological activated carbon filtration (O₃+CMF + BAC process) was designed and evaluated using a pilot scale (10 m³/d) test for the advanced treatment of hypersaline petrochemical wastewater in a coastal wastewater plant. The membrane flux and ozone dosage were optimized for the optimal treatment performance of this integrated process. The results showed that this integrated process performed well in pollutant removal. The concentrations of COD_Cr, phosphate and color in the effluents were 17.9 mg/L, 0.25 mg/L, and 5 dilution times in average, respectively. The effluent quality met the local discharge standard even under a high influent COD concentration (195 mg/L in average). The synergistic effect of the ozonation and ceramic membrane filtration was investigated through the fluorescence characteristics and hydrophobic/hydrophilic properties of organic compounds. It revealed that ozonation mitigated the membrane fouling and the nanopores in the ceramic membranes enhanced the ozonation efficiency. Meanwhile, the Fenton process had a slightly better effluent quality than the integrated process, but Fenton process consumed much more chemicals and required the sludge disposal, resulting in higher cost. The estimated unit cost for this integrated process was only 34% of that for the Fenton process. Overall, the integrated process demonstrated high stability, reliable effluents and low cost, providing a promising and cost-efficient technology for the treatment of hypersaline petrochemical wastewater.

A new method for urine electrofiltration and long term power enhancement using surface modified anodes with activated carbon in ceramic microbial fuel cells

This work is presenting for the first time the use of inexpensive and efficient anode material for boosting power production, as well as improving electrofiltration of human urine in tubular microbial fuel cells (MFCs). The MFCs were constructed using unglazed ceramic clay functioning as the membrane and chassis. The study is looking into effective anodic surface modification by applying activated carbon micro-nanostructure onto carbon fibres that allows electrode packing without excessive enlargement of the electrode. The surface treatment of the carbon veil matrix resulted in 3.7 mW (52.9 W m-3 and 1626 mW m-2) of power generated and almost a 10-fold increase in the anodic current due to the doping as well as long-term stability in one year of continuous operation. The higher power output resulted in the synthesis of clear catholyte, thereby i) avoiding cathode fouling and contributing to the active splitting of both pH and ions and ii) transforming urine into a purified catholyte - 30% salt reduction - by electroosmotic drag, whilst generating - rather than consuming - electricity, and in a way demonstrating electrofiltration. For the purpose of future technology implementation , the importance of simultaneous increase in power generation, long-term stability over 1 year and efficient urine cleaning by using low-cost materials, is very promising and helps the technology enter the wider market.

Behavior of CO-water mass transfer coefficient in membrane sparger-integrated bubble column for synthesis gas fermentation

The gas-liquid mass transfer coefficient (k_La) of O₂ was investigated in a bubble column reactor (BCR) using a sintered gas filter (SF), ceramic membrane module (CMM), and hollow fiber membrane module (HFM), which have different ranges of gas supply areas. k_La was enhanced by increasing flow rate in all of the spargers. Different responses when changing the gas supply area were obtained depending on the sparger type. Average values of k_La that were 52 and 258% higher were obtained using a CMM-integrated BCR compared to SFs and HFMs. CO-water k_La was investigated using CMMs for application to gas fermentation. The CO-water k_La ranged from 28.3 to 113.7/h under the experimental conditions. Based on the experimental data from CO and O₂, a model to predict k_La was constructed for CMM-integrated BCRs. A dimensionless number indicating a gas supply area of the sparger was newly defined and included in the developed model.

Anaerobic hybrid membrane bioreactor for treatment of synthetic leachate: Impact of organic loading rate and sludge fractions on membrane fouling

In the present study, the treatment of synthetic landfill leachate was carried out using a lab-scale anaerobic hybrid membrane bioreactor (An-HMBR). The reactor was operated for 250 days at two days of hydraulic retention time (HRT). Average chemical oxygen demand (COD) removal efficiency was ≥ 88% at steady-state conditions at 100% raw leachate. As organic loading rate (OLR) increased from 1.6 to 13.9 Kg COD m^-3 d^-1, flux gradually declined from 70 to 52 L/m² h (LMH) within 250 days. Chemical membrane cleaning enhanced the flux up to 75% of the initial flux at the final stage of the reactor. Reversible fouling (>90%) dominated over irreversible fouling (<8%). Membrane fouling was mainly caused by extracellular polymeric substances (EPS) fraction, which resulted in cake layer formation on the ceramic membrane used in the An-HMBR system. Membrane resistance increased with variables in the following order OLR > MLSS (mixed liquor suspended solids) > EPS > SMP (soluble microbial products). A nonlinear regression model developed for prediction of membrane resistance at different OLR can predict with an error of ±7%.

A hybrid fluidized-bed reactor (HFBR) based on arrayed ceramic membranes (ACMs) coupled with powdered activated carbon (PAC) for efficient catalytic ozonation: A comprehensive study on a pilot scale

Taking advantage of the high mass transfer in the bulk solution of fluidized-bed reactor (FBR), and the benefits of simultaneous particle separation and ozone catalysis on ceramic membranes, we proposed a hybrid fluidized-bed reactor (HFBR) based on arrayed ceramic membranes (ACMs) coupled with powdered activated carbon (PAC) for efficient catalytic ozonation. The optimum HFBR performance on a pilot scale was found at PAC addition of 3 g/L, ozone dosage of 25 mg/L, hydraulic retention time of 60 min and auxiliary aeration strength of 5 m³/h. During the 30-day treatment of coal-gasification secondary effluent (200 L/h), the HFBR system revealed not only a 117% increase in ozone utilization efficiency (ΔCOD/ΔO₃) upon pure ozonation but also a highly purified effluent with better sterilization and low residual bromate (∼11 μg/L). Low-molecular-weight organic fragments and acids, as well as phthalate esters were identified as the main products in this process. By density functional theory (DFT) calculations, it was found the main functional groups (carbonyls, -C=O) on the PAC could be protected from direct ozonation in the presence of ozone-degradable organics (e.g. phenolic and aliphatic compounds) in the wastewater through an ozone-competing reaction, which prevented the rapid inactivation of the PAC in catalytic ozonation. A longer service life and cheaper materials for ceramic membranes would benefit low operation costs for the HFBR. Moreover, the addition of PAC could greatly reduce ozone demand by ∼60% in the HFBR, and therefore decrease energy consumption by ∼30%. Hence, the HFBR was proved to be a highly competitive technology for wide application in the near future.

Alginate to simulate biofouling in submerged fluidized ceramic membrane reactor: Effect of solution pH and ionic strength

Membrane fouling was investigated experimentally by fluidizing non-adsorbed plastic scouring media on flat-tubular ceramic membrane treating a sodium alginate solution as a representative of polysaccharides in wastewater. Fouling rate increased with set-point permeate flux, but it was remarkably reduced by fluidizing the scouring agent regardless of the flux applied. Higher solution pH resulted in more reduction in membrane fouling due to electrostatic repulsion enhanced between alginate foulant and membrane surface which are both negatively charged. The addition of divalent cations such as Ca²⁺ and Cu²⁺ mitigated alginate fouling significantly due to the back transport associated with formation of larger particles away from membrane. However, the addition of monovalent cations accelerated the membrane fouling with less effectiveness of the media fluidization in fluidized bed membrane reactor. Adding monovalent ions was thought to transform rigid, compact and spherocolloidal macromolecular structure of alginate into the intramolecular charge shielding to neutralize functional groups.