Photocatalytic Membrane Reactor Research Articles

Fouling control in a submerged membrane reactor: Aeration vs membrane oscillations

• Aeration and membrane oscillation as fouling mitigation strategies were compared. • Membrane oscillation is effective for mitigating membrane fouling due to particle deposition. • Predicted and experimental results matched reasonably well. • Model can predict the operating conditions for particle deposition on submerged membrane. • Membrane oscillation enhanced diclofenac removal by ∼ two times in a SPMR. Membrane fouling potential due to particle deposition in a submerged membrane reactor (SMR) was investigated using aeration and membrane oscillations. A mathematical model describing the particle dynamics and the magnitude of the forces acting on a particle/agglomerate near a membrane surface was developed. The simulation results were verified by conducting experiments with inert glass bead sizes (2.5–33.0 μm) at various aeration rates (1.0–4.0 LPM), oscillation intensity (frequency 0–11.34 Hz; amplitude 2–6 mm). Additionally, photocatalytic degradation of diclofenac (DCF) (initial concentration = 4 mg/L) using UV 365 nm and TiO 2 photocatalyst was used to characterize the system performance. The results indicate that membrane oscillation was significantly superior as a fouling mitigation strategy due to higher shear rates (up to 10 times) than that of aeration. In the studied operating parameter range, the simulation results indicate that in case of aeration, particles below ∼ 10 µm will be deposited on the membrane. Whereas, in case of membrane oscillation, a much smaller size of 0.1 µm below which particles will be deposited on membrane surface. This was further confirmed by the photocatalytic degradation of DCF using oscillatory membrane in a submerged photocatalytic membrane reactor (SPMR) where close to two times higher DCF degradation occurred using membrane oscillation with a negligible transmembrane pressure drop (TMP) of (0.1–3 kPA). The presented approach will be useful in predicting the membrane fouling due to deposition of polydisperse particles in submerged oscillatory membrane reactors.

A new submerged photocatalytic membrane reactor based on membrane distillation for ketoprofen removal from various aqueous matrices

The removal of ketoprofen from simulated sea, brackish and surface water as well as secondary effluent of a municipal wastewater treatment plant in a submerged photocatalytic membrane reactor (SPMR) coupling photocatalysis and direct contact membrane distillation was investigated. TiO2 photocatalyst was suspended in a feed. The investigations revealed almost complete photooxidation of ketoprofen (initial concentration of 10 mg·L−1) after 5 h, regardless of the matrix, and mineralization ranging from 19 to 56%. For comparison, ketoprofen mineralization in deionized water reached about 86%. No ketoprofen was found in distillate, however, the type of the feed affected the amount of total organic carbon (TOC) and total inorganic carbon (TIC). The highest TOC content in distillate was observed for the secondary effluent. The type of the aqueous matrix affected the concentration of dissolved oxygen in feed, which decreased to the highest extent in the case of surface water (61% after 5 h). The analysis of toxicity towards Aliivibrio fischeri revealed that regardless of the feed type the distillate was non-toxic. A slight increase of permeate flux was observed during the process compared to pure water flux which was explained in terms of thermal conductivity of the TiO2 layer on a membrane surface.

Emerging investigator series: photocatalytic membrane reactors: fundamentals and advances in preparation and application in wastewater treatment

Photocatalytic membrane reactors (PMRs) can degrade organic compounds in wastewater and in water from different real matrices. The PMR surface can be modified for anti-fouling/self-cleaning properties, enabling reuse and extending lifespan.

Preparation of porous fused silica support with high UV transmittance for photocatalytic membrane reactors

A porous support with sufficient strength and high UV transmittance is of key importance for potential applications of the light conducting photocatalytic membrane reactors. In this work, we report a simple method for the preparation of amorphous fused silica support with boric acid as sintering aid. The effect of experimental conditions on sintering was investigated by orthogonal test. The effect of porosity and refractive index of pore medium on the UV transmittance of the supports was also studied. It is demonstrated that boric acid not only assists the sintering of the fused silica supports with short sintering time, but also inhibits the crystallization of cristobalite. Fused silica supports prepared at 1150 °C for 1 h show average porosity of 42.3%, bending strength of 14.9 MPa and UV transmittance as high as 64.2% in water. These properties make fused silica a good candidate as support for light conducting photocatalytic membrane reactors.

Upgrade of a Slurry Photocatalytic Membrane Reactor Based on a Vertical Filter and an External Membrane and Testing in the Photodegradation of a Model Pollutant in Water

Upgrade of a Slurry Photocatalytic Membrane Reactor Based on a Vertical Filter and an External Membrane and Testing in the Photodegradation of a Model Pollutant in Water

Desalination and Detoxification of Textile Wastewater by Novel Photocatalytic Electrolysis Membrane Reactor for Ecosafe Hydroponic Farming.

In this study, a novel photoelectrocatalytic membrane (PECM) reactor was tested as an option for the desalination, disinfection, and detoxification of biologically treated textile wastewater (BTTWW), with the aim to reuse it in hydroponic farming. The anionic ion exchange (IEX) process was used before PECM treatment to remove toxic residual dyes. The toxicity evaluation for every effluent was carried out using the Vibrio fischeri, Microtox® test protocol. The disinfection effect of the PECM reactor was studied against E. coli. After PECM treatment, the 78.7% toxicity level of the BTTWW was reduced to 14.6%. However, photocatalytic desalination during treatment was found to be slow (2.5 mg L−1 min−1 at 1 V potential). The reactor demonstrated approximately 52% COD and 63% TOC removal efficiency. The effects of wastewater reuse on hydroponic production were comparatively investigated by following the growth of the lettuce plant. A detrimental effect was observed on the lettuce plant by the reuse of BTTWW, while no negative impact was reported using the PECM treated textile wastewater. In addition, all macro/micronutrient elements in the PECM treated textile wastewater were recovered by hydroponic farming, and the PECM treatment may be an eco-safe wastewater reuse method for crop irrigation.

Fabrication and performance of polysulfone/H2O2-g-C3N4 mixed matrix membrane in a photocatalytic membrane reactor under visible light irradiation for removal of natural organic matter

The coupling of photocatalysis with membrane technology, which is known as photocatalytic membrane reactors (PMRs), has received great consideration in recent years and become a promising approach with the high potential to improve the fouling of membranes. In this paper, the photocatalyst of g-C3N4 treated with H2O2 was incorporated with a polysulfone membrane to enhance the anti-fouling properties of the membrane. AFM, FE-SEM images, porosity, and contact angle analysis indicated that the membrane properties like hydrophilicity, porosity, and surface roughness were improved. Also, UV–visible DRS, PL spectra, EIS analysis confirmed that the treated g-C3N4 (H2O2-g-C3N4) had high light absorption and low electron-hole recombination rate. The polysulfone/H2O2-g-C3N4 membrane with photocatalytic influences improved the removal of humic acid and anti-fouling properties under light conditions. Also, this incorporating was enhanced the water permeability from 266.6 to 412.1 L m−2 h−1 bar−1 in the optimum condition. To a considerable extent, the modified membranes maintained the humic acid solution fluxes during long-time experiments under visible light irradiation, so that after a 10 h run, the flux decline of the modified membrane was 21.9% compared to the initial flux, while for the pristine membrane was 53% in the same condition. The unique properties of polysulfone/H2O2-g-C3N4 membrane, like photocatalytic activity, led to a reduction in fouling resistances, especially block resistance. These results demonstrated the high potential of the polysulfone/H2O2-g-C3N4 mixed matrix membrane exposed to light irradiation for treating humic acid solution.

Foulant layer degradation of dye in Photocatalytic Membrane Reactor (PMR) containing immobilized and suspended NH2-MIL125(Ti) MOF led to water flux recovery

Several researches have been carried out to find a sustainable solution for overcoming the challenge of dyes released by industries in the environment. In this research, a photocatalytic membrane reactor (PMR) based on polysulfone (PSU) with an immobilized and suspended metal-organic framework (MOF: NH2-MIL125(Ti)) was applied for the decomposition of methylene blue (MB) as the model dye of textile wastewater. The MOF and the membranes were characterized through FESEM, XRD, FTIR, Raman, BET, AFM, and contact angle. The MOF incorporation with the concentration up to 0.2 wt% improved the porosity, hydrophilicity and water flux of the membrane, but in higher concentration, the system performance deteriorated due to the agglomeration of the MOF particles. Under UV illumination, MB photodegradation efficiency up to 60% was achieved with immobilized MOF. The combination of immobilized and suspended MOF as a novel strategy in the cross-flow PMR resulted in a significant MB removal efficiency boost up to 97%. Interestingly, using hybrid immobilized and suspended MOF nanoparticles resulted in a flux recovery ratio of 88% due to the self-cleaning properties of MOF nanoparticles and photo-degradation of the foulant layer. Therefore, the novel PMR has a promising potential for developing efficient membrane systems with significant flux recovery to remove dyes and other organic foulants.

Fabrication of visible-light assisted TiO2-WO3-PANI membrane for effective reduction of chromium (VI) in photocatalytic membrane reactor

In this work, TiO 2-WO3(40:1) nanoparticles were hydrothermally prepared and, embedded in Polyaniline (PANI) membrane with varying concentrations (3–7 wt%) and, used in photocatalytic membrane reactor for the removal of Cr(VI) from the aqueous solutions. 4-methyl piperidine (4-MP) was used as a gel inhibiting agent in N-methyl-2-pyrrolidone (NMP) solvent to prepare PANI-based flat-sheet membranes by phase inversion method. Through different characterization technique, it has been found that TiO 2-WO3 incorporated PANI membranes showed enhanced membrane properties like better hydrophilicity, better antifouling properties, higher water uptake, lower contact angle, higher porosity, and better heavy metal removal efficiency compared to bare PANI membranes. PANI membrane with 5 wt% TiO 2-WO3 exhibited a percentage rejection of 98.50% within 60 min at 0.5 MPa transmembrane pressure. Cr(VI) reduction under light and dark conditions was performed in a dead-end filtration cell with a quartz window at the top and the 5 wt% TiO 2-WO3– PANI membrane showed 67.32% reduction under visible light. TiO 2-WO3 incorporated PANI nanofiltration membranes can act as an integrated system consists of a short-circuited photo-anode and cathode under visible light irradiation. Overall, TiO 2-PANI membranes promote Cr(VI) reduction to Cr(III) in the photocatalytic membrane reactor and exhibits a better self-cleaning property.

Reduction of nitrates in a photocatalytic membrane reactor in the presence of organic acids

The present study explores the capability of the Photocatalytic Membrane Reactor (PMR) technology to remove nitrates from drinking water sources in the presence of organic electron donors. A systematic investigation was performed in a laboratory-pilot PMR, employing a hybrid TiO2/UV-A catalysis–ultrafiltration process, using formic acid as the most favorable hole scavenger for nitrate reduction. The naturally occurring humic acid as well as the cheaper and harmless acetic acid were also tested as sacrificial electron donors. The performance of the PMR system was evaluated in respect of nitrate and Total Organic Carbon (TOC) percentage removal. The results demonstrate the superiority of formic acid regarding nitrate reduction, followed by acetic acid and humic acid, as well as the negligible effect of nitrates on organic mineralization. Formic acid was further used to assess the effects of molar organic/nitrate ratio, catalyst dosage and power of irradiation per unit volume (PR) on nitrate reduction. With the present laboratory-pilot, the near optimum nitrate removal was ~60 % and the TOC reduction ~85 %; selectivity to dinitrogen was in the range 65–90 %. Key issues for improving this synergistic process and related R&D directions are discussed.

Comparative analysis of aeration and oscillation in a suspended catalyst photocatalytic membrane reactor

Comparative analysis of membrane oscillation and aeration in a photocatalytic membrane reactor is conducted. The investigation involved degradation of methylene blue dye as model pollutant using suspended ZnO photocatalyst and UV illumination. The effect of reactor hydrodynamics and design parameters on the system performance and its relation to the membrane-catalyst retention characteristics is evaluated using flat surface membranes roughed with transverse turbulence promoters (TP). The investigation showed that membrane oscillation is more energy efficient than aeration and can provide higher shear rates and better mixing which decreases both the catalyst agglomeration and deposition on the membrane surface. These, in turn, increase both the suspended catalyst concentration in solution and enhance the membrane flux. Compared to oscillation, achieving high shear rates through aeration is limited due to the adverse effects of high gas flow on photocatalytic reactions. Considering the above together with the small effect of aeration on ZnO photocatalytic kinetics, the need for aeration may be relaxed when using membrane oscillation in a ZnO photocatalytic reactor.

The Evolution of Photocatalytic Membrane Reactors over the Last 20 Years: A State of the Art Perspective

The research on photocatalytic membrane reactors (PMRs) started around the year 2000 with the study of wastewater treatment by degradation reactions of recalcitrant organic pollutants, and since then the evolution of our scientific knowledge has increased significantly, broadening interest in reactions such as the synthesis of organic chemicals. In this paper, we focus on some initial problems and how they have been solved/reduced over time to improve the performance of processes in PMRs. Some know-how gained during these last two decades of research concerns decreasing/avoiding the degradation of the polymeric membranes, improving photocatalyst reuse, decreasing membrane fouling, enhancing visible light photocatalysts, and improving selectivity towards the reaction product(s) in synthesis reactions (partial oxidation and reduction). All these aspects are discussed in detail in this review. This technology seems quite mature in the case of water and wastewater treatment using submerged photocatalytic membrane reactors (SPMRs), while for applications concerning synthesis reactions, additional knowledge is required.

Degradation kinetics and removal efficiencies of pharmaceuticals by photocatalytic ceramic membranes using ultraviolet light-emitting diodes

The development of ultraviolet light-emitting diode (UV-LED) technology provides more potential for the application of photocatalytic membranes. In this study, graphene oxide-titanium dioxide (GO-TiO2) photocatalytic ceramic membranes were prepared and activated by UV-LED. We systematically evaluated the removal of naproxen (NAP), carbamazepine (CBZ) and diclofenac (DCF) under 365 nm, 300 nm and 275 nm UV-LED irradiation in photocatalytic ceramic membrane reactors (PCMRs). Our results showed that this GO-TiO2 modified ceramic membrane achieved simultaneous separation and photocatalytic degradation for tested pharmaceuticals. Through fluence-based and energy-based efficiencies analysis, the 300 nm UV-LED is a good option for achieving a high removal efficiency with low energy consumption. Membrane filtration enhanced the degradation efficiency by four times through enhancing the mass transfer effect in membrane pores, and reduced the electrical energy per order (EEO) by a factor of ten. In addition, high membrane flux, high degradation rate and strong catalytic stability could be simultaneously achieved in closed-loop dead-end filtration. The addition of H2O2 could further increased the removal efficiency. PCMRs equipped with UV-LEDs are promising for pharmaceuticals removal as well as solving the issue of membrane concentrated water.

A novel submerged photocatalytic oscillatory membrane reactor for water polishing

A submerged photocatalytic oscillatory membrane reactor was tested for micropollutants removal from water as a tertiary treatment method for water polishing. A detailed study of the system performance at various operating conditions of membrane reactor and background water matrices including humic acid (HA) and secondary wastewater effluent (SWE) was conducted. Initially, the system was evaluated using suspended nanosized TiO2 under UV illumination and antipyrine as a model pollutant. Experiments using central composite design (CCD) and response surface analysis (RSM) were used to analyze the effects of the oscillation amplitude and frequency, and airflow rate on the antipyrine removal and the membrane flux. Optimum conditions for the reactor operation were determined using a composite desirability function. These conditions were then applied for the removal of other micropollutants with varying physiochemical properties namely, diclofenac, sulfamethoxazole, and hydrochlorothiazide. Up to 90% micropollutants removal can be achieved in Milli-Q water, although, the performance was noticeably affected in presence of background organics in SWE and HA due to either catalyst blocking and/or competition of organics, as well as catalyst agglomeration. A significant process intensification can be achieved using the proposed photocatalytic oscillatory membrane reactor configuration, which could offer a promising potential as a final polishing step for water recycling.

Photocatalytic quorum quenching: A new antifouling and in-situ membrane cleaning strategy for an external membrane bioreactor coupled to UASB

Microbial quorum sensing (QS) induces biofilm formation on the membrane surfaces leading to severe biofouling, which remains a major bottleneck for membrane-based systems. Here, we report an effective UV photocatalytic quorum quenching (QQ) strategy in an integrated upflow anaerobic sludge blanket – photocatalytic membrane reactor (UASB-PMR) system, where TiO2 nanoparticles immobilized in porous polymeric beads were kept in suspension as the photocatalysts. The UASB unit reached a methane yield of 0.30 ± 0.05 L CH4/g COD removal while treating the synthetic wastewater, slightly higher than a typical internal anaerobic membrane bioreactor (AnMBR). This novel system showed 7-fold higher efficacy in membrane fouling control than the UV photolytic QQ system (19.1 ± 2.4 d vs. 2.7 ± 1.0 d) under intermittent UV irradiation (17% of total operation time). Continuous UV irradiation, both in photolytic and photocatalytic QQ, significantly alleviated membrane biofouling, while long-term UV exposure exerted some changes in the surface properties of the membranes, which were not observed under intermittent UV irradiation. The reactive oxygen species (ROS) generated by the UV-excited TiO2 not only oxidized the foulants on the membrane surface, but also quenched acyl-homoserine lactones (AHLs), the QS signal molecules, thus retarding membrane fouling to the maximum extent. Additionally, in-situ membrane cleaning, enhanced COD removal, and almost complete disinfection of the effluent were realized in the photocatalytic QQ system. Equipped with these advantages, this innovative photocatalytic QQ can be a readily implementable strategy to prevent fouling in external membrane bioreactors (MBRs) for the pilot- and/or full-scale applications.

MIL-88B(Fe)-coated photocatalytic membrane reactor with highly stable flux and phenol removal efficiency

• MIL-88B(Fe)@Al 2 O 3 was used for photocatalytic membrane reactors. • High flux and phenol removal efficiency were obtained using the photocatalytic membrane reactors. • The Fe-clusters of MIL-88B(Fe) acted as reactive sites for the photocatalytic reaction. In this study, MIL-88B(Fe) was successfully prepared and coated onto an Al 2 O 3 substrate. Two photocatalytic membrane reactors (PMRs) for phenol degradation were fabricated using the MIL-88B(Fe)-coated substrates. A coated substrate was either placed into a flat-sheet membrane module to give a photocatalytic flat-sheet membrane reactor (PFMR) or integrated with an Al 2 O 3 hollow fiber membrane module to produce a photocatalytic hollow fiber membrane reactor (PHMR). In the PHMR system, the phenol removal efficiency was significantly enhanced, and the permeate flux remained stable at over 4000 L m –2 h −1 bar −1 . The flux of the PFMR was approximately 80–100 L m –2 h −1 bar −1 ; this lower flux was attributed to the coating and full coverage of MIL-88B(Fe) on the Al 2 O 3 surface. These two systems exhibited recyclability, reusability, and stability over at least three cycles of photocatalytic phenol removal. Characterization of the samples after the reaction illustrated that the iron clusters, which act as the reactive sites, remained stable even though the terephthalate organic linkers were partially destroyed during the photocatalytic reaction. The PMRs developed in this study show promise as effective, feasible, and sustainable systems for wastewater treatment.

Photodegradation of steroid-hormone micropollutants in a flow-through membrane reactor coated with Pd(II)-porphyrin

The efficient degradation of steroid-hormone micropollutants is demonstrated in a single-pass, continuous operation of the photocatalytic membrane reactor (PMR) holding a visible-light excited Pd(II)-porphyrin-coated poly(vinylidene fluoride) microfiltration membrane. The PMR operated at a water flux of 600 L m−2 h−1 exhibited a residence time of 0.6 s and significant removal of 17ß-estradiol and estrone at environmentally relevant (ng L−1) concentrations, when treated either individually (R = 85 ± 5 %) or as a mixture of estrone, 17ß-estradiol, testosterone and progesterone. The highest 17ß-estradiol removal achieved at a water flux 60 L m−2 h−1ensured the concentration in the permeate of 2 ng L−1. At alkaline pH, the photodegradation process was inhibited by the repulsion between the ionized 17ß-estradiol molecules and the membrane surface. An increase in a water flux through the PMR decreased the removal, but favoured the rate of disappearance. The rate constant for reactions of singlet oxygen with 17ß-estradiol (7·108 M−1 s−1) at ng L−1 concentrations was close to the diffusion limit. This study provides the new insights into solar-driven photocatalytic water treatment technologies for effective removal of micropollutants.

Photocatalytic membrane reactor based on Mexican Natural Zeolite: RB5 dye removal by photo-Fenton process

A Mexican natural zeolite (MNZ) of heulandite type was used to develop mesoporous cylindrical membranes based on the extrusion method, the mineral was previously mixed with additives to form a paste with 67.8% of solids. The membranes were calcined at 550 °C, the extruded parts suffered erosion upon water contact at lower calcination temperatures, while the structural properties such as surface area, pore volume and hardness were decreasing at higher temperatures. The MNZ had oxidation states Fe2+ and Fe3+ from the Fe3O4, and the bandgap was 2.42 eV. This cylindrical membrane was arranged as a photocatalytic membrane reactor (PCMR) to evaluate the RB5-dye removal by the Photo-Fenton process using a 2.2 W lamp as radiation source. The Fe effect in the solution and the permeation flow was analyzed at pH = 3, [H2O2] = 3 g/L, [RB5]0 = 100 mg/L, λmax = 405 nm (3.06 eV). The highest RB5-dye discoloration (D30% = 92.3) in the retained was obtained using Fe in solution and a permeation flow which did not show color signals from the reaction beginning (Dt% = 100). A pseudo-first order (n = 1) kinetics was assumed with an apparent kinetic constant of 0.0904 min−1 at the best reaction conditions. Finally, a total organic carbon removal TOC90% = 60.0 and TOC180% = 66.7 in the retentate flow was attained as well as TOC180% = 89.5 in the permeated flow.

Removal of volatile organic compounds from air using supported ionic liquid membrane containing ultraviolet-visible light-driven Nd-TiO2 nanoparticles

Volatile organic compounds (VOCs) with toxicity properties discharged from industrial emissions and combustion engines threaten human health and cause environmental problems. Therefore, it is important to develop technologies to remove VOCs from air. In this study, the performance of Nd (neodymium) -TiO2 nanoparticles embedded in a supported ionic liquid membrane (SILM) for removal of VOCs from air was investigated. Aiming at functionalizing the ionic liquid membrane with photocatalytic capability, we developed a facile and effective approach for the removal of VOCs by coupling highly efficient photocatalysts with the SILM. Nd-TiO2 nanoparticles, which are ultraviolet-visible (UV–Vis) light-driven photocatalysts, were prepared by sol-gel and immersed in the SILM for use as a photocatalytic membrane-based reactor. The gaseous VOCs tested were toluene, acetone, chloroform, benzene, and xylene. We confirmed that at a loading of 50 wt% Nd-TiO2 nanoparticles (1 wt% Nd content) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIm]PF6) as SILM ([HMIm]PF6/Nd-TiO2 SILM), the as-prepared photocatalytic membrane-based reactor exhibited higher removal efficiency of VOCs from air (60~80% removal after 10 h) under UV–Vis light illumination than individual SILM or photocatalytic systems. Effluent gas analysis revealed that 25–55% of VOCs was decomposed and mineralized in the photocatalytic membrane reactor, which exhibited higher VOCs removal efficiency than membrane separation. These results indicate that the photocatalytic membrane-based reactor containing Nd-TiO2 nanoparticles and SILM designed in this study is highly active and stable. This study on [HMIm]PF6/Nd-TiO2 SILM was initiated to couple membrane separation with photocatalytic degradation of gaseous VOCs and can serve as a promising way for eliminating harmful VOCs with low concentration from air.

Performance of a Slurry Photocatalytic Membrane Reactor for the Treatment of Real Secondary Wastewater Effluent Polluted by Anticancer Drugs

The emergence of non-biodegradable and persistent compounds in European surface waters calls for the development of innovative advanced water treatments. Therefore, this work aimed to assess the pe...