Mn oxide coated catalytic membranes for hybrid ozonation-membrane filtration: Membrane microstructural characterization

Mitigation Mechanism of Membrane Fouling in MnFeOx Functionalized Ceramic Membrane Catalyzed Ozonation Process for Treating Natural Surface Water

In order to efficiently remove NOMs in natural surface water and alleviate membrane pollution at the same time, a flat microfiltration ceramic membrane (CM) was modified with MnFeOX (Mn-Fe-CM), and a coagulation–precipitation–sand filtration pretreatment coupled with an in situ ozonation-ceramic membrane filtration system (Pretreatment/O3/Mn-Fe-CM) was constructed for this study. The results show that the removal rates of dissolved organic carbon (DOC), specific ultraviolet absorption (SUVA) and NH4+-N by the Pretreatment/O3/Mn-Fe-CM system were 51.1%, 67.9% and 65.71%, respectively. Macromolecular organic compounds such as aromatic proteins and soluble microbial products (SMPs) were also effectively removed. The working time of the membrane was about twice that in the Pretreatment/CM system without the in situ ozone oxidation, which was measured by the change in transmembrane pressure, proving that membrane fouling was significantly reduced. Finally, based on the SEM, AFM and other characterization results, it was concluded that the main mitigation mechanisms of membrane fouling in the Pretreatment/O3/Mn-Fe-CM system was as follows: (1) pretreatment could remove part of DOC and SUVA to reduce their subsequent entrapment on a membrane surface; (2) a certain amount of shear force generated by O3 aeration can reduce the adhesion of pollutants; (3) the loaded MnFeOX with a higher catalytic ability produced a smoother active layer on the surface of the ceramic membrane, which was conducive in reducing the contact among Mn-Fe-CM, O3 and pollutants, thus increasing the proportion of reversible pollution and further reducing the adhesion of pollutants; (4) Mn-Fe-CM catalyzed O3 to produce ·OH to degrade the pollutants adsorbed on the membrane surface into smaller molecular organic matter, which enabled them pass through the membrane pores, reducing their accumulation on the membrane surface.

In-Situ H2O2 Cleaning for Fouling Control of Manganese-Doped Ceramic Membrane through Confined Catalytic Oxidation Inside Membrane

This work presents an effective approach for manganese-doped Al₂O₃ ceramic membrane (Mn-doped membrane) fouling control by in-situ confined H₂O₂ cleaning in wastewater treatment. An Mn-doped membrane with 0.7 atomic percent Mn doping in the membrane layer was used in a membrane bioreactor with the aim to improve the catalytic activity toward oxidation of foulants by H₂O₂. Backwashing with 1 mM H₂O₂ solution at a flux of 120 L/m²/h (LMH) for 1 min was determined to be the optimal mode for in-situ H₂O₂ cleaning, with confined H₂O₂ decomposition inside the membrane. The Mn-doped membrane with in-situ H₂O₂ cleaning demonstrated much better fouling mitigation efficiency than a pristine Al₂O₃ ceramic membrane (pristine membrane). With in-situ H₂O₂ cleaning, the transmembrane pressure increase (ΔTMP) of the Mn-doped membrane was 22.2 kPa after 24-h filtration, which was 40.5% lower than that of the pristine membrane (37.3 kPa). The enhanced fouling mitigation was attributed to Mn doping, in the Mn-doped membrane layer, that improved the membrane surface properties and confined the catalytic oxidation of foulants by H₂O₂ inside the membrane. Mn³⁺/Mn⁴⁺ redox couples in the Mn-doped membrane catalyzed H₂O₂ decomposition continuously to generate reactive oxygen species (ROS) (i.e., HO• and O₂¹), which were likely to be confined in membrane pores and efficiently degraded organic foulants.

Catalytic Ozonation and Membrane Contactors—A Review Concerning Fouling Occurrence and Pollutant Removal

Membrane filtration has been widely used in water and wastewater treatment. However, this process is not very effective for the removal of refractory organic compounds (e.g., of pharmaceutical origin). Coupling membrane filtration with ozonation (or other Advanced Oxidation Methods) can enhance the degradation of these compounds and, subsequently, the incidence of membrane fouling (i.e., the major problem of membrane uses) would be also limited. Ozonation is an efficient oxidative process, although ozone is considered to be a rather selective oxidant agent and sometimes it presents quite low mineralization rates. An improvement of this advanced oxidation process is catalytic ozonation, which can decrease the by-product formation via the acceleration of hydroxyl radicals production. The hydroxyl radicals are unselective oxidative species, presenting high reaction constants with organic compounds. An efficient way to couple membrane filtration with catalytic ozonation is the deposition of an appropriate solid catalyst onto the membrane surface. However, it must be noted that only metal oxides have been used as catalysts in this process, while the membrane material can be of either polymeric or ceramic origin. The relevant studies regarding the application of polymeric membranes are rather scarce, because only a few polymeric materials can be ozone-resistant and the deposition of metal oxides on their surface presents several difficulties (e.g., affinity etc.). The respective literature about catalytic membrane ozonation is quite limited; however, some studies have been performed concerning membrane fouling and the degradation of micropollutants, which will be presented in this review. From the relevant results it seems that this hybrid process can be an efficient technology both for the reduction of fouling occurrence as well as of enhancement of micropollutant removal, when compared to the application of single filtration or ozonation.

1,4-Dioxane removal from water and membrane fouling elimination using CuO-coated ceramic membrane coupled with ozone

1,4-Dioxane is a synthetic cyclic ether traditionally used as a chlorinated solvent stabilizer. It is a small molecule and recalcitrant compound that is difficult to remove by conventional processes and in this regard, there is a need for the development of new technologies. In this study, an innovative CuO-coated ceramic membrane (CM) reactor system that can be used to oxidize 1,4-dioxane dissolved in surface water by catalytic ozonation was developed. The effect of the thickness of the CuO deposited on the ceramic membrane surface on the permeability, fouling resistance, 1,4-dioxane removal, and toxicity was evaluated. The efficiency of the hybrid ozonation coupled to the use of a CuO-coated CM in 1,4-dioxane removal and the antifouling properties were assessed from TOC and 1,4-dioxane removal kinetics data. Reusability in four cycles was also tested. The performance of the CuO-coated CM remained stable during the four cycles of the reusability test. The ceramic membrane coated with CuO particles coupled with ozonation is appropriate for 1,4-dioxane degradation in the aqueous phase (45% efficiency, rate constant increased by a factor of 2.98 compared with the uncoated-hybrid process) and fouling removal (60 min to recovery the permeate flux).

Ceramic nanocomposite membranes and membrane fouling: A review

Membrane technologies have broad applications in the removal of contaminants from drinking water and wastewater. In recent decades, ceramic membrane has made rapid progress in industrial/municipal wastewater treatment and drinking water treatment owing to their advantageous properties over conventional polymeric membrane. The beneficial characteristics of ceramic membranes include fouling resistance, high permeability, good recoverability, chemical stability, and long life time, which have found applications with the recent innovations in both fabrication methods and nanotechnology. Therefore, ceramic membranes hold great promise for potential applications in water treatment. This paper mainly reviews the progress in the research and development of ceramic membranes, with key focus on porous ceramic membranes and nanomaterial-functionalized ceramic membranes for nanofiltration or catalysis. The current state of the available ceramic membranes in industry and academia, and their potential advantages, limitations and applications are reviewed. The last section of the review focuses on ceramic membrane fouling and the efforts towards ceramic membrane fouling mitigation. The advances in ceramic membrane technologies have rarely been widely reviewed before, therefore, this review could be served as a guide for the new entrants to the field, as well to the established researchers.

The characteristics of organic matter influence its interfacial interactions with MnO2 and catalytic oxidation processes

The influence of dissolved organic matter (DOM) properties on its interfacial interactions with MnO₂ and on catalytic oxidation processes was studied by Time-Resolved Dynamic Light Scattering (TR-DLS) and Atomic Force Microscopy (AFM) under varied solution conditions. Four DOM fractions of different characteristics (e.g., SUVA, hydrophobic character, structural properties) were selected. Bared-MnO₂ nanoparticles readily aggregated in NaCl and CaCl₂ solutions. Classic DLVO Theory successfully described critical coagulation concentrations and aggregation behaviors. In NaCl solution, DOM adsorbed on MnO₂ nanoparticles and provided electrosteric stabilization. The two DOM fractions of higher hydrophobic (HPO) character were more efficient in decreasing the aggregation rates. Enhanced MnO₂ aggregation was observed at high Ca²⁺ concentrations due to charge screening and cation bridging between carboxyl groups in DOM structures. The addition of oxidant (H₂O₂) induced a high aggregation of bared-MnO₂ nanoparticles, possibly due to the release of Mn²⁺ (i.e., complexation mechanisms) and generation of reactive species (O₂^-, HO₂^-, and H). Contrasted with their hydrophilic (HPI) counterparts, HPO isolates adsorbed on MnO₂ significantly decreased the catalytic oxidation processes between H₂O₂/MnO₂; suggesting a more efficient and stronger DOM coating. Interfacial forces measured by AFM, showed weaker interactions between HPI isolates and MnO₂; suggesting unfavorable polar interactions. Conversely, the high adhesion forces between MnO₂/HPO isolate would indicate stronger bonds and hydrophobic interactions. This study provided a nanoscale understanding of the impact of DOM characteristics on: a) performance of the MnO₂ coated ceramic membranes in water treatment, and b) biogeochemical cycle of Mn-oxides in the environmental.

A novel catalytic ceramic membrane fabricated with CuMn2O4 particles for emerging UV absorbers degradation from aqueous and membrane fouling elimination

A novel catalytic ceramic membrane (CM) for improving ozonation and filtration performance was fabricated by surface coating CuMn₂O₄ particles on a tubular CM. The degradation of ultraviolet (UV) absorbers, reduction of toxicity, elimination of membrane fouling and catalytic mechanism were investigated. The characterization results suggested the particles were well-fixed on membrane surface. The modified membrane showed improved benzophenone-3 removal performance (from 28% to 34%), detoxification (EC₅₀ as 12.77%) and the stability of catalytic activity. In the degradation performance of model UV absorbers, the developed membrane significantly decreased the UV254 and DOC values in effluent. Compared with a virgin CM, this CM ozonation increased water flux as 29.9% by in-situ degrade effluent organic matters. The CuMn₂O₄ modified membrane enhanced the ozone self-decompose to generate O₂^- and initiated the chain reaction of ozone decomposition, and subsequently reacted with molecule ozone to produce OH. Additionally, CM was able to promote the interaction between ozone and catalyst/organic chemicals to form H₂O₂ that promoted the formation of OH. This catalytic ceramic membrane combining with ozonation showed potential applications in emerging pollutant degradation and membrane fouling elimination, and acted as a novel ternary technology for wastewater treatment and water reuse.

Prevention of PVDF ultrafiltration membrane fouling by coating MnO2 nanoparticles with ozonation

Pre-treatment is normally required to reduce or control the fouling of ultrafiltration (UF) membranes in drinking water treatment process. Current pre-treatment methods, such as coagulation, are only partially effective to prevent long-term fouling. Since biological activities are a major contributor to accumulated fouling, the application of an oxidation/disinfection step can be an effective complement to coagulation. In this study, a novel pre-treatment method has been evaluated at laboratory scale consisting of the addition of low dose ozone into the UF membrane tank after coagulation and the use of a hollow-fibre membrane coated with/without MnO₂ nanoparticles over a test period of 70 days. The results showed that there was minimal fouling of the MnO₂ coated membrane (0.5 kPa for 70 days), while the uncoated membrane experienced both reversible and irreversible fouling. The difference was attributed to the greatly reduced presence of bacteria and organic matter because of the catalytic decomposition of ozone to hydroxyl radicals and increase of the hydrophilicity of the membrane surface. In particular, the MnO₂ coated membrane had a much thinner cake layer, with significantly less polysaccharides and proteins, and much less accumulated organic matter within the membrane pores.

Study on an integrated process combining ozonation with ceramic ultra-filtration for decentralized supply of drinking water

An integrated process was specifically developed for the decentralized supply of drinking water from micro-polluted surface water in the rural areas of China. The treatment process combined ozonation with ceramic ultra-filtration (UF), coagulation for pre-treatment and granular activated carbon filtration. A flat-sheet ceramic membrane was used with a cut-off of 60 nm and the measurement of 254 mm (length) × 240 mm (width) × 6 mm (thickness). Ozonation and ceramic UF was set up whthin one reactor. The experimental results showed that the removal efficiencies of the dissolved organic carbon (DOC) and the formation potential of trihalomethanes (THMs), haloacetic acids (HAAs) and ammonia were 80%, 76%, 70% and 90%, respectively; that the turbidity of the product water was below 0.2 NTU and the particle count number (particles larger than 2 μm) was less than 50 counts per mL. The result also showed that all the pathogenic microorganisms were retained by the ceramic and that UF. Ozonation played a critical role in the control of membrane fouling and the removal of contaminants. Exactly, the membrane fouling can be controlled in situ with 3 mg L(-1) ozone at the permeate flux of 80 L m(-2) h(-1), yet the required dosage of ozone was dependent on the quality of the raw water. Therefore, this study is able to provide a highly compacted system for decentralized supply of high-quality drinking water in terms of both chemical and microbiological safety for the rural areas in China.