Severe Fouling Research Articles

UV/Fe(II)/S(IV) Pretreatment for Ultrafiltration of Microcystis aeruginosa-Laden Water: Fe(II)/Fe(III) Triggered Synergistic Oxidation and Coagulation

Ultrafiltration (UF) has been proven effective in removing algae during seasonal algal blooms, but the algal cells and the metabolites can induce severe membrane fouling, which undermines the performance and stability of the UF. Ultraviolet-activated sulfite with iron (UV/Fe(II)/S(IV)) could enable an oxidation-reduction coupling circulation and exert synergistic effects of moderate oxidation and coagulation, which would be highly preferred in fouling control. For the first time, the UV/Fe(II)/S(IV) was systematically investigated as a pretreatment of UF for treating Microcystis aeruginosa-laden water. The results showed that the UV/Fe(II)/S(IV) pretreatment significantly improved the removal of organic matter and alleviated membrane fouling. Specifically, the organic matter removal increased by 32.1% and 66.6% with UV/Fe(II)/S(IV) pretreatment for UF of extracellular organic matter (EOM) solution and algae-laden water, respectively, while the final normalized flux increased by 12.0-29.0%, and reversible fouling was mitigated by 35.3-72.5%. The oxysulfur radicals generated in the UV/S(IV) degraded the organic matter and ruptured the algal cells, and the low-molecular-weight organic matter generated in the oxidation penetrated the UF and deteriorated the effluent. The over-oxidation did not happen in the UV/Fe(II)/S(IV) pretreatment, which may be attributed to the cyclic redox Fe(II)/Fe(III) coagulation triggered by the Fe(II). The UV-activated sulfate radicals in the UV/Fe(II)/S(IV) enabled satisfactory organic removal and fouling control without over-oxidation and effluent deterioration. The UV/Fe(II)/S(IV) promoted the aggregation of algal foulants and postponed the shift of the fouling mechanisms from standard pore blocking to cake filtration. The UV/Fe(II)/S(IV) pretreatment proved effective in enhancing the UF for algae-laden water treatment.

Recovery of magnesium from flue gas desulfurization wastewater using thermomorphic hydrophilicity amines

The concentrations of hardness ions in saline wastewater from flue gas desulfurization (FGD) are usually very high, which could result in severe membrane fouling in consequent membrane systems. Hence, we investigated the feasibility of recovering Mg2+ from saline wastewater collected from a coal-fired power plant through utilizing thermomorphic hydrophilicity amines. Triethylamine (TEA), diisopropylamine (DIPA) and N,N-dimethylisopropylamine (DMIPA) were chosen as thermomorphic hydrophilicity amines. The effects of temperature change on solubility of amines in aqueous phase were evaluated, and the influences of molar ratio of amine to Mg2+ were also investigated. Results show that the solubility of amines in aqueous phase decreased substantially when temperature was increased from 25 °C to 60 °C. Thermomorphic hydrophilicity amines could be regenerated by mild heating, and regenerated TEA could remove up to 95% of Mg2+ in the actual FGD wastewater. Meanwhile, three amines could effectively increase the pH value of the solutions, and the recovery of Mg2+ was more than 98% as Mg(OH)2 at an amine ratio molar ratio of 2.5. This study demonstrated the great potential of using thermoresponsive amines as alkali sources to recover Mg2+ and the synthesis of reactive MgO in FGD wastewater, providing a reference for the recovery of resources such as Mg2+.

Can Heat-Activated Peroxymonosulfate Be Used as a Pretreatment to Mitigate Fouling for Membrane Distillation: Performance of Individual Organics?

Heat-activated persulfate preoxidation was recently proposed as a potential approach to mitigate membrane fouling in membrane distillation (MD) for treating actual water. However, the possible mitigation mechanism involved has not yet been elucidated. In this study, we explored the relationship between membrane fouling and the pretreatment of natural organic matter (NOM) solutions with peroxymonosulfate (PMS). Individual humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA) contaminants were chosen as model NOM samples. The degradation efficiency of heat-activated PMS preoxidation was investigated. The removal rates of organic contaminants improved as the PMS dose and activation temperature of the feed increased. Specific flux (J/J0) measurements coupled with multiple characterizations were performed to assess the fouling behavior. The fouling data showed that when pretreatment was conducted without PMS, pure HA caused the most severe fouling, followed by pure BSA, whereas pure SA caused almost no membrane fouling. After PMS preoxidation, the oxidation products of the NOM unexpectedly caused more fouling, despite the reduction in the amount of the NOM. Further work is needed to evaluate fouling mitigation when working with complex streams.

Effect of Membrane Pore Size on Membrane Fouling of Corundum Ceramic Membrane in MBR.

Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the mean pore size of 0.50, 0.63, 0.80, and 1.02 μm were prepared, which were designated as C5, C7, C13, and C20, respectively. Long-term MBR experiments showed that the C7 membrane with medium pore size experienced the lowest trans-membrane pressure development rate. Both the decrease and increase of membrane pore size would lead to more severe membrane fouling in the MBR. It was also interesting that with the increase of membrane pore size, the relative proportion of cake layer resistance in total fouling resistance was gradually increased. The content of dissolved organic foulants (i.e., protein, polysaccharide and DOC) on the surface of C7 was quantified as the lowest among the different ceramic membranes. Microbial community analysis also revealed the C7 had a lower relative abundance of membrane fouling associated bacteria in its cake layer. The results clearly demonstrated that ceramic membrane fouling in MBR could be effectively alleviated through optimizing the membrane pore size, which was a key structural factor for preparation of ceramic membrane.

Efficient Recovery of Organic Matter from Municipal Wastewater by a High-Rate Membrane Bioreactor Equipped with Flat-Sheet Ceramic Membranes

High-rate processes have been investigated for the recovery of organic matter from municipal wastewater. High-rate membrane bioreactors (HR-MBRs) may simultaneously achieve the increased recovery of carbon and high effluent quality, although control of membrane fouling is extremely difficult. To address the severe fouling in HR-MBRs, the combination of granular scouring and frequent chemically enhanced backwashing was examined. The use of robust flat-sheet ceramic membranes enabled the application of those cleaning strategies. Experiments were carried out at an existing wastewater treatment plant. To operate as a high-rate system, the bioreactor solid residence time and hydraulic residence time were set at 0.5 days and 1.6 h, respectively. Although a relatively high flux of 20 L m-2 h-1 was applied, the proposed HR-MBR exhibited a very low fouling rate of 1.3 kPa/day. The system could recover >70% of the carbon from raw wastewater, whereas the concentration of chemical oxygen demand in the effluent was lowered to <20 mg/L. The performance of the proposed HR-MBR observed in this study was clearly superior to those reported in previous related studies.

Treatment of simulated saline brine water by membrane distillation process enhanced through alternating current electric field

Treatment of saline brine has been a tricky challenge in recent years, and membrane distillation (MD) is considered as a promising alternative technology. But it was found that the normalized flux significantly decreased to 0.6 within 15 h when treating simulated salinity brine, which was caused by the deposition of the humic acids (HA), CaSO4, and HA-Ca complex, suggesting the severe membrane fouling. In this study, a composite membrane was fabricated by coating carbon nanotubes (CNT) on the commercial PTFE membrane, and an alternating current (AC) electric field was subsequently applied that aimed to improve MD performance. Specially, the application of 50 Hz square wave dramatically retarded the inorganic fouling and the intensity of membrane organic matter was reduced by 60.6% due to its hydrophilic surface and instantaneous polarity conversion, thus its normalized flux even maintained around 0.9 after 15 h operation. Coupled with the modified XDLVO analysis, the coating CNT layer exhibited good resistance of HA due to their electrostatic repulsions, both of which carried a strong negative charge and high density hydrophilic functional groups. It was also found that except the movement distance of charged substances far greater than the thickness of the fixed electrostatic double layer, AC electric field with certain frequency significantly reduced the coexistence time for substances with opposite charge by keeping them in motion that could further alleviate the fouling. This study suggested that a hybrid system of AC electric field and MD would provide a potential alternative for treating the salinity brine water.

Integrated ferrate and calcium sulfite to treat algae-laden water for controlling ultrafiltration membrane fouling: High-efficiency oxidation and simultaneous cell integrity maintaining

To alleviate severe algal-source membrane fouling in the ultrafiltration (UF) process, calcium sulfite (CaSO3) integrated with ferrate (Fe(VI)) was proposed. With the integrated pre-treatment, the maximum removal rate of algae cells was improved to 91.19 %, and numerous larger flocs with great settleability were generated. The fluorescent organic components were effectively eliminated, as well as the dissolved organic matter decreased by 38.20 %. During the Fe(VI)/CaSO3 process, oxidation played a fateful role in fouling alleviation and promoted the in-situ coagulation efficiency. Compared with single Fe(VI) treatment, the oxidation capacity was strengthened through the formation of a series of reactive intermediates (involving Fe(V), Fe(IV), SO3•−, SO5•−, SO4•− and •OH), which were easy to be quenched by the cell-coated extracellular organic matter. Moreover, the consumption of all the oxidants was also remarkably accelerated, thereby the cell integrity was well-kept, and the intercellular organic matter (IOM) was not released. The IOM which already existed in water could also be eliminated, as well as the effluent safety was well guaranteed. During UF, the terminal J/J0 was elevated to 0.87 at most from 0.10, and the fouling resistances were strikingly reduced. The algal foulants deposition was effectively decreased, and the contact angle of the fouled membrane was closer to the virgin membrane. The dominant fouling mechanism was also converted to intermediate and standard blocking without forming the cake layer.

Effect of bio-electrochemical systems on the removal of organic and inorganic membrane fouling from anaerobic membrane bioreactors

To alleviate the fouling of membrane bioreactors, a coupling system was constructed in which a conductive membrane served as the anode of a bio-electrochemical system, whereas ordinary carbon felt served as the cathode. The membrane module showed approximately 90 % performance for wastewater chemical oxygen demand removal. As the external resistance increased from 50 to 1500 Ω, the number of operating days increased from 25 to 62. The respective concentrations of polysaccharide and protein on R-1500 membrane surface were 6.81- and 2.05-fold greater than the concentrations on the R-50 membrane, and the concentration of Ca2+ on the surface of the R-50 membrane was 1.48-fold greater than the concentration on the R-1500 membrane. Therefore, inorganic fouling is the main type of membrane fouling in coupled systems with low external resistance. For coupled systems with higher external resistance, severe organic fouling eventually causes membrane blockage. Variance partitioning analysis showed that the micro-electric field contributed to 95.34 % of the effect on the control of membrane fouling, significantly greater than the 67.19 % contributed by the current. Therefore, in the system where organic and inorganic fouling coexists, appropriate enhanced field strength (increase in external resistance) is particularly important for membrane fouling control.

Fouling Control Strategies for High Concentrated Liquid Desiccants Concentrating Using Membrane Distillation

Air conditioning using a liquid desiccant (LD) is an energy-efficient air purification and cooling system. However, high energy is required to concentrate or regenerate the LD. This study aimed to investigate the characteristics of membrane fouling in more detail and determine control strategies for LD concentrating using membrane distillation (MD). Two different LDs-lithium chloride (LiCl) and potassium formate (HCOOK)-were used. Because LDs require high concentrations by nature (i.e., 40 wt% for LiCl and 70 wt% for HCOOK), the concentration was started from half of those concentrations. This resulted in a flux decline with severe membrane fouling during the concentration using MD. Different membrane fouling mechanisms were also observed, depending on the LD type. Three different physical membrane fouling control methods, including water flushing (WF), air backwashing (AB), and membrane spacer (SP), were introduced. Results showed that WF was the most effective. Both AB and SP showed a marginal change to no cleaning; however, an initial flux with SP was about 1.5 times higher than no cleaning. Therefore, WF combined with the SP could maintain a high flux and a low fouling propensity in the treatment of a high-concentration solution using MD.

CaO2-based tablet for effective and green membrane cleaning without additional catalysts

Natural organic matter humic acid (HA) coupled with the inorganic metal oxides FeOx + MnOx will cause severe irreversible membrane fouling. Chemical cleaning is indispensable for the removal of irreversible membrane foulants and sustainable membrane filtration, while conventional cleaning methods have limitations with low cleaning efficiency, high reagents consumption and potential membrane damage. For the first time, calcium peroxide (CaO2), a solid alternative for liquid hydrogen peroxide (H2O2), is proposed for the membrane cleaning. For membranes fouled by HA, it is noteworthy that 40 mg/32.15 cm2 CaO2 tablet without any other catalyst can restore the terminal membrane flux dramatically from 51% to 82% in only 5 min, which is far more than 3 wt% H2O2 alone (only from 51% to 59%). Moreover, Fenton-like reaction induced by in-situ membrane foulants FeOx + MnOx further enhances the membrane flux from 53% to 97%. Based on HA oxidation tests and reactive species identification in CaO2 tablets cleaning process for the case of HA-fouled membranes and HA + FeOx + MnOx-fouled membranes, singlet oxygen (O21) in CaO2 system dominated the strong oxidation of electron-rich compounds HA, which plays a key role in membrane flux recovery. With involvement of FeOx + MnOx, signal intensities of free radicals such as hydroxyl radicals (OH•) are enhanced greatly, which further achieves more outstanding membrane cleaning performance. These results underline that the novel CaO2 system provides a promising candidate for more portable and cost-effective membrane cleaning method in a nonradical pathway.

Improved procedure for square-wave voltammetric sensing of fenhexamid residues on blueberries peel surface at the anodically pretreated boron-doped diamond electrode

BackgroundFungicide fenhexamid (FH) has a high residual concentration on fruits and vegetables, thus, it is of high importance to monitor the level of FH residues on foodstuff samples. So far, the assay of FH residues in selected foodstuff samples has been conducted by electroanalytical methods on sp2 carbon-based electrodes that are well-known to be susceptible to severe fouling of the electrodes surfaces during electrochemical measurements. As an alternative, sp3 carbon-based electrode such as boron-doped diamond (BDD) can be used in the analysis of FH residues retained on the peel surface of foodstuff (blueberries) sample. ResultsIn situ anodic pretreatment of the BDDE surface was found to be the most successful strategy to remediate the passivated BDDE surface by FH oxidation (by)products, and the best validation parameters, i.e., the widest linear range (3.0–100.0 μmol L−1), the highest sensitivity (0.0265 μA L μmol−1) and the lowest limit of detection (0.821 μmol L−1), were achieved on the anodically pretreated BDDE (APT–BDDE) in a Britton-Robinson buffer, pH 2.0, using square-wave voltammetry (SWV). The assay of FH residues retained on blueberries peel surface was performed on the APT–BDDE using SWV, and the obtained concentration of FH residues of 6.152 μmol L−1 (1.859 mg kg−1) was found to be below the maximum residue value fixed for blueberries by the European Union regulations (20 mg kg−1). Significance and noveltyIn this work, a protocol based on a very easy and fast foodstuff sample preparation procedure combined with the straightforward pretreatment approach of the BDDE surface was elaborated for the first time for the monitoring of the level of FH residues retained on the peel surface of blueberries samples. The presented reliable, cost-effective, and easy-to-use protocol could find its application as a rapid screening method for the control of food safety.

Does Surface Roughness Necessarily Increase the Fouling Propensity of Polyamide Reverse Osmosis Membranes by Humic Acid?

Surface roughness has crucial influence on the fouling propensity of thin film composite (TFC) polyamide reverse osmosis (RO) membranes. A common wisdom is that rougher membranes tend to experience more severe fouling. In this study, we compared the fouling behaviors of a smooth polyamide membrane (RO-s) and a nanovoid-containing rough polyamide membrane (RO-r). Contrary to the traditional belief, we observed more severe fouling for RO-s, which can be ascribed to its uneven flux distribution caused by the "funnel effect". Additional tracer filtration tests using gold nanoparticles revealed a more patchlike particle deposition pattern, confirming the adverse impact of "funnel effect" on membrane water transport. In contrast, the experimentally observed lower fouling propensity of the nanovoid-containing rough membrane can be explained by: (1) the weakened "funnel effect" thanks to the presence of nanovoids, which can regulate the water transport pathway through the membrane and (2) the decreased average localized flux over the membrane surface due to the increased effective filtration area for the nanovoid-induced roughness features. The current study provides fundamental insights into the critical role of surface roughness in membrane fouling, which may have important implications for the future development of high-performance antifouling membranes.

Unveiling the residual membrane foulants in full-scale MBR plant after chemically enhanced backwash: Insights into microbe-associated compounds

Membrane fouling is a main bottleneck that limits the stable operation of membrane bioreactors (MBRs). However, the nature of residual foulants over frequent chemical cleaning remain elusive. Herein, we collected fouled membranes from a large-scale MBR with the treatment capacity of 200, 000 m3/d and explored the culprit for the key components resistant to chemically enhanced backwash. During 155 days of operation, transmembrane pressure increasing highly linked to the characteristics of membranes and bio-cakes. Fourier-transform infrared microscopy deciphered that a part of polyvinylpyrrolidone in the structure of polyvinylidene fluoride hollow fiber membrane was removed by NaOCl after chemical backwash. The stubborn uronic acids were mostly responsible for irreversible fouling due to pore constriction and the resistance to NaOCl. The fouling-related genera f_Rhodocyclaceae and f_Anaerolineaceae prevailed in the bio-cakes. According to the network analysis, the negative and competitive interactions on the bio-cake contributed more to severe membrane fouling than the positive and cooperative interactions. The keystone taxa c_WS6 (Dojkabacteria) and c_Deltaproteobacteria, which involved in secreting polysaccharides and hydrolyzing refractory matters, accelerated the accumulation of organic foulants. Our findings help to elucidate the key contributors to membrane fouling and anti-cleaning in full-scale MBR, which provide new insights for future fouling control.

Infrared thermography observations of crystallization fouling in a plate heat exchanger

Heat exchanger performance is significantly reduced in the presence of impurities in one or both fluid streams, frequently by deposits of inversely soluble salts. Accordingly, immense efforts were and still are spent to combat, predict, and investigate such fouling problems to mitigate the reduction of heat transfer performance. In this study, calcium carbonate crystallization fouling in a corrugated plate heat exchanger was investigated. Fouling was monitored using temperature and flow measurements, and, for the first time, coupled with infrared thermography observations. We show a clear and measurable local difference between clean and fouled conditions, regardless of operating conditions. Infrared measurements of temperature permit conclusions about flow distribution and the spatial location of areas with severe fouling. Compared to the clean state, completely skewed isotherms after fouling point out channel blockage and flow obstructions, resulting in large scale flow re-distribution within the channel. The presented results exhibit a clear benefit of this approach for heat exchanger fouling studies and serve as a foundation for future research of dynamic operation, transient response, and computational models.

New insights into membrane fouling during direct membrane filtration of municipal wastewater and fouling control with mechanical strategies

Direct membrane filtration (DMF) technology achieves energy self-sufficiency through carbon recovery and utilization from municipal wastewater. To control its severe membrane fouling and improve DMF technology, targeted research on fouling behaviour and mechanisms is essential. In this study, a DMF reactor equipped with a flat-sheet ceramic membrane was conducted under three scenarios: without control, with intermittent aeration, and with periodic backwash. This system achieved efficient carbon concentration with chemical oxygen demand below 50 mg/L in permeate. Membrane fouling was dominated by intermediate blocking and cake filtration. And reversible external resistance accounted for over 85 % of total resistance. Predominant membrane foulants were free proteins, whose deposition underlies the attachment of cells and biopolymers. Backwash decreased the fouling rate and increased fouling layer porosity by indiscriminately detaching foulants from the membrane surface. While aeration enhanced the back transport of large particles and microbial activity, causing a relatively thin and dense fouling layer containing more microorganisms and β-d-glucopyranose polysaccharides, which implies a higher biofouling potential during long-term operation. In addition, aeration combined with backwash enhanced fouling control fivefold over either one alone. Therefore, simultaneous operation of backwash and other mechanical methods that can provide shear without stimulating aerobic microbial activity is a preferred strategy for minimizing membrane fouling during DMF of municipal wastewater.

Direct Membrane Filtration of Municipal Wastewater: Studying the Most Suitable Conditions for Minimizing Fouling Rate in Commercial Porous Membranes at Demonstration Scale.

This study aimed to evaluate the feasibility of applying a commercial porous membrane to direct filtration of municipal wastewater. The effects of membrane pore size (MF and UF), treated influent (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) and operating solids concentration (about 1 and 2.6 g L-1) were evaluated on a demonstration plant. Filtration periods of 2-8 h were achieved when using the MF membrane, while these increased to 34-69 days with the UF membrane. This wide difference was due to severe fouling when operating the MF membrane, which was dramatically reduced by the UF membrane. Use of raw wastewater and higher solids concentration showed a significant benefit in the filtration performance when using the UF module. The physical fouling control strategies tested (air sparging and backwashing) proved to be ineffective in controlling UF membrane fouling, although these strategies had a significant impact on MF membrane fouling, extending the operating period from some hours to 5-6 days. The fouling evaluation showed that a cake layer seemed to be the predominant reversible fouling mechanism during each independent filtration cycle. However, as continuous filtration advanced, a large accumulation of irreversible fouling appeared, which could have been related to intermediate/complete pore blocking in the case of the MF membrane, while it could have been produced by standard pore blocking in the case of the UF membrane. Organic matter represented more than 70% of this irreversible fouling in all the experimental conditions evaluated.

Hemin-Modified Multi-Walled Carbon Nanotube-Incorporated PVDF Membranes: Computational and Experimental Studies on Oil-Water Emulsion Separations.

The separation of oil/water emulsions has attracted considerable attention for decades due to the negative environmental impacts brought by wastewater. Among the various membranes investigated for separation, polyvinylidene fluoride (PVDF) membranes have shown significant advantages of ease of fabrication, high selectivity, and fair pore distribution. However, PVDF membranes are hydrophobic and suffer from severe fouling resulting in substantial flux decline. Meanwhile, the incorporation of wettable substrates during fabrication has significantly impacted the membrane performance by lowering the fouling propensity. Herein, we report the fabrication of an iron-containing porphyrin (hemin)-modified multi-walled carbon nanotube incorporated PVDF membrane (HA-MWCNT) to enhance fouling resistance and the effective separation of oil-in-water emulsions. The fabricated membrane was thoroughly investigated using the FTIR, SEM, EDX, AFM, and contact angle (CA) analysis. The HA-MWCNT membrane exhibited a water CA of 62° ± 0.5 and excellent pure water permeance of 300.5 L/m2h at 3.0 bar (400% increment), in contrast to the pristine PVDF, which recorded a CA of 82° ± 0.8 and water permeance of 59.9 L/m2h. The hydrophilic HA-MWCNT membrane further showed an excellent oil rejection of >99% in the transmembrane pressure range of 0.5−2.5 bar and a superb flux recovery ratio (FRR) of 82%. Meanwhile, the classical molecular dynamics (MD) simulations revealed that the HA-MWCNT membrane had greater solvent-accessible pores, which enhanced water permeance while blocking the hydrocarbons. The incorporation of the hemin-modified MWCNT is thus an excellent strategy and could be adopted in the design of advanced membranes for oil/water separation.

Enhancement of struvite generation and anti-fouling in an electro-AnMBR with Mg anode-MF membrane module

Severe membrane fouling and the inability to remove/recover nitrogen and phosphorus are bottlenecks of anaerobic membrane bioreactors (AnMBRs) for large-scale application in wastewater treatment. Herein, an electrochemical AnMBR with a Mg anode-membrane module (electro-AnMBR) was built and showed good performance in terms of membrane fouling mitigation and nutrient recovery during sewage treatment. Compared with the traditional AnMBR, membrane fouling in the electro-AnMBR was reduced by up to 30%. The application of an electric field decreased the zeta potential, viscosity, and EPS concentration of the sludge-water liquor in the electro-AnMBR, which could improve the cake layer structure and thus enhance water permeability. Meanwhile, 26% of NH4+ and 48% of PO43- co-precipitated with Mg2+ generating from the sacrificial Mg anode and were recovered as struvite deposited onto cathode in the electro-AnMBR. Hydrogen evolution provided a relatively alkaline pH environment, resulting in struvite electrodeposition on the graphic cathode, which partly separated the formed struvite from the sludge with a purity of 77%. In the electro-AnMBR, the electrochemical reactions provided alkalinity and effectively inhibited anaerobic acidification. The applied voltage of 0.6 V reduced the relative abundance of methanosaeta, but increased that of methanosarcina, which is also beneficial for the membrane anti-fouling.

Ternary hetero-structured BiOBr/Bi2MoO6@MXene composite membrane: Construction and enhanced removal of antibiotics and dyes from water

Membrane separation technology is an effective treatment for complex wastewater. However, severe membrane fouling restricts its practical application. Photocatalytic composite membranes with self-cleaning properties can efficaciously ease the membrane fouling. Herein, we constructed an advanced ternary heterojunction photocatalytic composite membrane by coupling MXene, Bi2MoO6 and BiOBr nanomaterials. The prepared BiOBr/Bi2MoO6@MXene composite membrane had a high permeability (1296.91 L⋅m−2⋅h−1⋅bar−1) and exhibited excellent comprehensive removal ratios for antibiotics and dyes (Tetracycline hydrochloride and Ciprofloxacin: ≥90%, Congo red: >98%). During the self-cleaning performance test, the composite membrane maintained high permeability and selectivity after 5 cycles. Density functional theory calculation (DFT) analysis revealed that the enhanced photocatalytic activity was attributed to the efficient separation of electron-hole pairs between the ternary heterojunctions. This integrated membrane with both membrane separation and photocatalysis has good application prospects in the removal of various pollutants in the wastewater field.

Effect of semi-continuous water washing on the combustion behaviors of agricultural organic solid waste

Combustion of agricultural organic solid waste (AOSW) was an ideal solution for their resource utilization in view of their massive annual production and great potential for reduction of fossil fuel utilization. However, high alkali and alkaline earth metals (AAEMs) content in the feedstock can arose severe fouling and slagging issues and thus prohibiting its vast utilization. In this study, a semi-continuous water washing method was proposed to preliminarily remove AAEMs from agricultural organic solid waste and its effects on the combustion behaviors of washed solid product were investigated. Results showed that the combustion index S were improved to 2.63 × 10-6, over 68 % of the total ashes were removed from the cotton stalk, and 96.3 %, 89.0 % and 74.7 % of K, Na and Mg were effectively removed, respectively. Moreover, the softening temperature of low temperature ash from the washed sample was as high as 1450 °C, 538 °C higher than the low temperature ash from the original sample; the base acid ratio and fouling index were improved from high slagging and fouling risk (1.7 and 90.8) of the original organic solid waste to low and medium risk (0.4 and 3.5), respectively. All these results signified the contributing effect of proposed semi-continuous water washing method on the combustion of agricultural organic solid waste. In a word, this study provided a promising method for fouling and slagging inhibition during the agricultural organic solid waste combustion.