Membrane Photoreactor Research Articles

Integration of a 3D-printed electrochemical reactor with a tubular membrane photoreactor to promote sulfate-based advanced oxidation processes

This study investigates the integration of an in-house 3D printed electrochemical cell − SERPIC-UCLM® cell – for the in situ generation of peroxymonosulfuric acid (PMSA) witha lab-scale tubular membrane photoreactor (TMPr) to evaluate the effectiveness of sulfate-radical advanced oxidation processes (SR-AOPs) in eliminating contaminants of emerging concern (CECs) from reverse osmosis and nanofiltration concentrates (ROC and NFC, respectively). First, the SERPIC-UCLM® cell was evaluated in terms of mass transport features employing the limiting current technique, demonstrating favorable volumetric mass transport rates (kmA ∼ 10–3 s-1) and Sherwood values (Sh > 300) under the laminar regime (110 < Re < 790). Afterwards, the effect of the electrolyte (sulfuric acid, H2SO4) initial pH in the electrochemical generation of PMSA was studied, with an initial pH of 1 selected as optimal. PMSA is a highly reactive peroxyacid that undergoes self-decomposition at neutral pH mediums (e.g., ROC and NFC with a pH of 7.6 and 7.9, respectively), primarily existing in the form of peroxomonosulfate (PMS). Additionally, the phototreatment of the ROC and NFC was assessed using the electrogenerated PMS and commercial peroxydisulfate (PDS) under the same conditions. The results indicated comparable degradation patterns for CECs in both ROC and NFC. Furthermore, the application of 2.4 mM PMS resulted in removals higher than 60 % for 7 of the 11 CECs identified in the NFC, and ensured compliance with wastewater discharge regulations for pH, chemical oxygen demand (COD), and total suspended solids (TSS) levels. These findings emphasize the importance of this technology, showing its advantages in terms of versatility and logistics.

Continuous UV-C/H2O2 and UV-C/Chlorine applied to municipal secondary effluent and nanofiltration retentate: Removal of contaminants of emerging concern, ecotoxicity, and reuse potential

As global effects of water scarcity raise concerns and environmental regulations evolve, contemporary wastewater treatment plants (WWTPs) face the challenge of effectively removing a diverse range of contaminants of emerging concern (CECs) from municipal effluents. This study focuses on the assessment of advanced oxidation processes (AOPs), specifically UV-C/H2O2 and UV-C/Chlorine, for the removal of 14 target CECs in municipal secondary effluent (MSE, spiked with 10 μg L−1 of each CEC) or in the subsequent MSE nanofiltration retentate (NFR, no spiking). Phototreatments were carried out in continuous mode operation, with a hydraulic retention time of 3.4 min, using a tube-in-tube membrane photoreactor. For both wastewater matrices, UV-C photolysis (3.3 kJ L−1) exhibited high efficacy in removing CECs susceptible to photolysis, although lower treatment performance was observed for NFR. In MSE, adding 10 mg L−1 of H2O2 or Cl2 enhanced treatment efficiency, with UV-C/H2O2 outperforming UV-C/Chlorine. Both UV-C/AOPs eliminated the chronic toxicity of MSE toward Chlorella vulgaris. In the NFR, not only was the degradation of target CECs diminished, but chronic toxicity to C. vulgaris persisted after both UV-C/AOPs, with UV-C/Chlorine increasing toxicity due to potential toxic by-products. Nanofiltration permeate (NFP) exhibited low CECs and microbial content. A single chlorine addition effectively controlled Escherichia coli regrowth for 3 days, proving NFP potential for safe reuse in crop irrigation (<1 CFU/100 mL for E. coli; <1 mg L−1 for free chlorine). These findings provide valuable insights into the applications and limitations of UV-C/H2O2 and UV-C/Chlorine for distinct wastewater treatment scenarios.

Enhancing wastewater treatment with a novel separated algae membrane oxygenated activated sludge reactor

In this investigation, a separated algae membrane oxygenated activated sludge wastewater treatment reactor was developed. During the phase of aeration pump absence, the system, featuring a separated algae biofilm oxygenation activated sludge mechanism with an internal reflux ratio of 5 and a C/N ratio of 10, demonstrated remarkable efficiency in pollutant removal. Specifically, it achieved COD, TN, NH4+-N, and TP removal rates of 96.6 %, 81.9 %, 98.6 %, and 95.5 %, respectively. Despite a decline in dissolved oxygen (DO) during the transition of wastewater from the algae membrane reactor to the aerobic tank, the internal circulation reflux ratio of 5 ensured that the oxygen-enriched effluent from the algae membrane photoreactor maintained a stable DO level in the aerobic tank, ranging from 1.5 to 2.0 mg/L, thus meeting the oxygen demand of the activated sludge. Alterations in the aeration method had a notable impact on the diversity of the microbial community. Notably, the community shifted from bacteria adapted to intermittent aeration to those acclimated to internal recirculation for oxygen supply. The dominant microbial position was reinforced, with the Patescibacteria phylum and the norank_f__norank_o __ Saccharimonadales genus emerging as the dominant entities within the community. Under internal circulation reflux aeration, filamentous green algae persisted, resulting in a significant increase in biomass and chlorophyll content by 3.07 and 2.93 times, respectively. Furthermore, microalgae exhibited elevated protein and polysaccharide content, which increased by 3.14 and 3.16 times, respectively, due to the influence of the internal circulation reflux process, promoting the maturation of the algae membrane.

Continuous-flow titration of low iron doses to promote photo-Fenton and photo-Fenton-like processes at neutral pH

Photo-Fenton (PF) is a promising process for degrading a wide range of contaminants of emerging concern (CECs) present in urban wastewater (UWW) after secondary treatment, mitigating their spread in aquatic systems. However, the near-neutral pH of UWW poses a challenge to PF performance. In this research, a tubular membrane photoreactor, designed for continuous “titration” of Fe2+, is explored to promote the PF process for the tertiary treatment of UWW. The application of persulfate (PF-like) as an alternative oxidant and the impact of phosphate (PO43−) content in UWW were also assessed. Process efficiency was evaluated in continuous mode, applying low residence times (RT: 6.1, 36.6, and 73.2 s) and low Fe2+ doses (1, 2, and 5 mg L−1), for the oxidation of 19 CECs (each spiked at 10 µg/L), in demineralized water (DW) and secondary-treated UWW. Despite the persistence of certain short-chain perfluoroalkyl substances (PFAS) and saccharine across all conditions tested, the PF-like process exhibited superior performance when compared with PF, attaining higher removals for most target CECs, especially for melamine. In UWW, for an RT = 73.2 s, [Fe2+] = 5 mg L−1, and [oxidant] = 1.2 mM, PF process removed 7 CECs > 60 % and PF-like 10 CECs > 60 %. Moreover, higher residual concentrations of Fe2+ and lower precipitation of PO43− were observed for PF-like treatments, evidencing its advantages for tertiary treatment. These results emphasize the importance of photoreactor design to achieve efficient PF/PF-like at neutral pH, avoiding the use of chelating agents while managing iron concentrations compatible with UWW discharge or reuse limits.

Reflector design for the optimization of photoactivated processes in tubular reactors for water treatment

Photoactivated advanced oxidation processes have excellent performance in removing recalcitrant pollutants from water. However, the high operating cost associated with the energy consumption of UV lamps is a big drawback. In this work, the design and optimization of the reflector in a tube-in-tube membrane photoreactor were carried out using a ray tracing methodology to maximize the light deployed to the reactor. Simulations were carried out using different lamps/reactor arrangements with 1, 2 and 3-sided flat reflectors and with circular and parabolic geometries. Results showed that direct radiation is maximized when the distance reactor-lamps is minimized, increasing optical efficiency. On the other hand, it was observed that for the flat reflectors, the closer the furthest point of the reflector to the center of the reactor, the higher optical efficiency is achieved due to the reduction in the number of bouncing rays in the reflector. In the case of parabolic geometries, some additional considerations are necessary, since not only the distance at which the reflector is placed matters, but also its geometrical focus. The best performance is achieved for those in which the distance from the furthest point of the reflector to the center of the reactor was lower and the lamps placed near the focus of the parabola. For the studied reflector geometries, the calculated optical efficiencies when using anodized aluminum were 46.1%, 56.5%, 60.0%, 41.8%, and 65.9% for reflectors of 1, 2, and 3 sides, cylinder, and parabola, respectively. Model predictions were successfully validated using experimental ferrioxalate actinometry data, confirming the huge potential of this simple simulation methodology for photoreactor design purposes.

Tubular membrane photoreactor for the tertiary treatment of urban wastewater towards antibiotics removal: application of different photocatalyst/oxidant combinations and ozonation

A tubular membrane photoreactor, operated in continuous mode and low residence times (τ from 3.9 to 12.2 s), was applied for the removal of 14 antibiotics (sulfonamides, fluoroquinolones, macrolides, cephalexin, and trimethoprim) in demineralized water (DW) and secondary-treated urban wastewater (UWW). In this setup, the oxidant (hydrogen peroxide (H2O2), persulfate (S2O82−) or ozone (O3)) is permeated through the membrane pores and delivered to the catalyst (titanium dioxide (TiO2) or silver molybdate (Ag2MoO4)), embedded in the membrane shell side, and to the annular reaction zone (ARZ) where the DW or UWW fortified with the target antibiotics (50 µg L−1 each) flows. The antibiotics removal in the tested processes - photolysis (UVC), photocatalysis (UVC/TiO2 or UVC/Ag2MoO4), photochemical oxidation (UVC/H2O2 or UVC/S2O82−), their combinations (UVC/TiO2/H2O2, UVC/TiO2/S2O82‾, UVC/Ag2MoO4/H2O2 and UVC/Ag2MoO4/S2O82‾) and O3 - were evaluated at steady-state conditions by ultra-high performance liquid chromatography followed by quadrupole time-of-flight high-resolution mass spectrometry (UHPLC-QTOF-HRMS). In the DW, the treatment efficiency followed the sequence: UVC < UVC/TiO2 ≈ UVC/Ag2MoO4 < UVC/H2O2 < UVC/TiO2/H2O2 ≈ UVC/Ag2MoO4/H2O2 < UVC/S2O82‾ < UVC/TiO2/S2O82‾ < UVC/Ag2MoO4/S2O82‾ < O3. In the UWW, the O3 process proved again to be the most efficient (12 antibiotics removed >90%), followed by UVC/Ag2MoO4/S2O82‾ (five antibiotics removed >60%). UHPLC-QTOF-HRMS tentatively identified seven by-products stemming from macrolides for O3 treatment. This is a pioneer study on the application of Ag2MoO4 combined with H2O2 or S2O82- for advanced treatment of UWW, laying the groundwork for future research. The membrane reactor proves to be an effective technological approach for the O3 process.

Submerged Membrane Photo Reactor (SMPR) with Simultaneous Photo Degradation and TiO2 Catalyst Recovery for Efficient Dyes Removal

In this study, a polyvinylidene difluoride (PVDF) hollow fiber membrane module incorporated with TiO2 was submerged into a photocatalytic reactor to create a hybrid photocatalysis with membrane separation process (a submerged membrane photoreactor, SMPR), for advanced dyes wastewater treatment. The SMPR performance was assessed by the degradation of single component Rhodamine B (RhB) and degradation of mixed dyes (RhB and Methyl orange (MO)) in a binary solution. Several operational parameters such as the amount of catalyst loading, permeate flux, and the effect of aeration were studied. Fouling tendency on the membrane was also investigated to determine the optimum operating conditions. The results show that the synergetic effect of the low catalyst loading and permeate flux creates the environment for optimum light penetration for high photocatalytic activity as the hybrid system with low catalyst loading (0.5 g/L) and 66 L/m2h of flux with aeration at 1.3 L/min has proven to increase the photocatalysis performance by 20% with additional catalyst recovery. In addition, applying the low catalyst loading and flux permeate with aeration brings minimal fouling problems.

Exploring the potential of photocatalytic dual layered hollow fiber membranes incorporated with hybrid titania nanotube-boron for agricultural wastewater reclamation

The emergence of hybrid photocatalytic membranes has provided a new direction in search of efficient technologies to separate and degrade pollutants present in wastewaters. Colour pigments originated from different sources including agricultural waste pose serious threats towards water bodies as their presence will lead to multiple environmental problems. This study investigated the potential of a photocatalytic dual layered hollow fiber membrane (DLHFM) incorporated with boron doped titania nanotubes (TNT-B) photocatalyst for the photodegradation and removal of colour pigment molecules present in aerobically treated palm oil mill effluent (AT-POME). The colour removal efficiencies and separation performance of the DLHFM were evaluated through a submerged membrane photo reactor (SMPR) system driven by visible light. Polyvinylidene fluoride-based DLHFM loaded with 2% of photocatalyst (PVDF-L2%) exhibited the best membrane performance with a flux of 39.62 L/m2h and colour removal efficiency of 79.42%. The controlled distribution of photocatalysts as well as the synergistic combination of membrane filtration and photodegradation concertedly contributed to the improvement in membrane’s performance. 95% of flux and colour removal efficiency were sustained after four filtration cycles. The membrane exhibited efficient performance in terms of consistent flux and colour removal efficiency after 20 days of continuous photocatalytic filtration, implying their high long-term stability. This study highlights the efficiency and potential of visible light photocatalytic membranes in treating colour laden wastewaters.

A novel PEBAX-1657/PES-(BiFeO3@ZnS) photocatalytic membrane for integrated hybrid systems coupling CO2 separation and photoreduction

Suspended photocatalyst systems face the problems of poor light distribution, photocatalyst separation, and inappropriate transfer of reducing agent and CO2 gas to the active photocatalyst sites. To overcome these issues, Poly(ether-block-amide)−1657/Polyethersulfone (PEBAX-1657/PES) -(BiFeO3 @ZnS) photocatalytic membrane was synthesized and applied for simultaneous separation and photoreduction of CO2 to methanol as the valuable product. The two-phase membrane photoreactor was tested under both ultraviolet (UV) and visible light irradiation in the presence of water. Based on UV–visible and photoluminescence spectroscopy (PL) analyses, PEBAX-1657/PES-(BiFeO3@ZnS) exhibited wider light absorption range and lower recombination rate of photogenerated species compared with pristine PEBAX-1657/PES, respectively. Meanwhile, the separation features of the photocatalytic membrane remained almost constant even after 6 h reaction time. In addition, the schematic representation of proposed mechanism was clarified in detail based on the p-n junction photogenerated charge carrier transfer process of BiFeO3@ZnS. Finally, photocatalytic performance of the prepared photocatalytic membrane with different water flow rates and light powers were examined. The photocatalytic activity tests revealed the maximum methanol concentrations of 0.85 mmol/L and 0.56 mmol/L and the maximum methanol production yields of 5100 and 3360 µmol/gcat.h under UV and visible irradiation, respectively at the optimized operating conditions (water flow rate of 3 mL/min and light power of 250 W). Therefore, the present study provides a new insight into the effective visible-light-driven photocatalytic membranes for simultaneous separation and photocatalytic conversion of CO2 to solar fuels.

Silver doped titania nanotubes incorporated photocatalytic dual layer antibiofouling hollow fiber membrane for palm oil wastewater treatment

Photocatalytic dual layer hollow fiber membrane (DLHFM) is advantageous over its single layer counterpart due to a better photocatalyst dispersion on the outer layer to maximize the potential of the photocatalyst in improving the overall membrane performance. In this study, a polyvinylidene fluoride (PVDF) dual-layer hollow fiber membrane with antibiofouling properties was successfully synthesized via dry-wet spinning phase inversion method, where the Ag-TNT was incorporated onto the outer layer membrane for photocatalytic degradation of AT-POME pigments in a submerged membrane photoreactor (SMPR). The results revealed that the incorporation of Ag-TNT into the PVDF matrix increased pure water flux from 16.20 L/m2 h for pristine PVDF membrane to 37.12 L/m2 h. The synergistic advantages of photocatalysis and membrane filtration was exhibited by the photocatalytic Ag-TNT membrane which showed the highest AT-POME color removal efficiency of 84.0% compared to the other membranes prepared in this work. With the presence of silver nanoparticles, the modified membrane exhibited antibacterial efficiency of 95.8% with a 1.73 mm inhibition zone around the membrane against P. aeruginosa. Based on the results obtained, the photocatalytic PVDF Ag-TNT membrane showed immense potential as an innovative technology for water reclamation in the palm oil industry.

Tube-in-tube membrane photoreactor as a new technology to boost sulfate radical advanced oxidation processes

This work proposes a tube-in-tube membrane photoreactor, operated in a continuous-mode, to boost the efficiency of peroxydisulfate (PDS), through the photolytic (UV-C radiation) and photocatalytic (TiO2-P25) processes. This new technology can efficiently facilitate the transportation of PDS to the catalyst surface and water to be treated. The ultrafiltration tubular ceramic membrane was used as support for the TiO2-P25 and oxidant-catalyst/water contactor. Tests were performed using a synthetic solution and a municipal secondary effluent, both spiked with a pharmaceutical mix solution (paracetamol (PCT), furosemide (FRS), nimesulide (NMD), and diazepam (DZP); 200 μg L−1 of each). At steady-state regime, the UVC/S2O82−/TiO2 system, with radial PDS addition, showed the highest removal of pharmaceuticals in both matrices. Furthermore, twenty-two transformation products (TPs) were identified by applying LC-QTOF MS technique. Hence, the transformation pathways including hydroxylation in aromatic moiety by an electrophilic attack, electron transfer reactions, cleavage of C−O, C−N bond, H−abstraction and ring opening were proposed. TPs chemical structures were evaluated by in silico (Q)SAR approach using TOXTREE and EPI Suite™ software.

Bacterial Nanocellulose/MoS2 Hybrid Aerogels as Bifunctional Adsorbent/Photocatalyst Membranes for in-Flow Water Decontamination.

To address the problems associated with the use of unsupported nanomaterials, in general, and molybdenum disulfide (MoS2), in particular, we report the preparation of self-supported hybrid aerogel membranes that combine the mechanical stability and excellent textural properties of bacterial nanocellulose (BC)-based organic macro/mesoporous scaffolds with the excellent adsorption-cum-photocatalytic properties and high contaminant removal performance of MoS2 nanostructures. A controlled hydrothermal growth and precise tuning of the synthetic parameters allowed us to obtain BC/MoS2-based porous, self-supported, and stable hybrid aerogels with a unique morphology resulting from a molecular precision in the coating of quantum-confined photocatalytic MoS2 nanostructures (2-4 nm crystallite size) on BC nanofibrils. These BC/MoS2 samples exhibit high surface area (97-137 m2·g-1) and pore volume (0.28-0.36 cm3·g-1) and controlled interlayer distances (0.62-1.05 nm) in the MoS2 nanostructures. Modification of BC with nanostructured MoS2 led to an enhanced pollutants removal efficiency of the hybrid aerogels both by adsorptive and photocatalytic mechanisms, as indicated by a detailed study using a specifically designed membrane photoreactor containing the developed photoactive/adsorptive BC/MoS2 hybrid membranes. Most importantly, the prepared BC/MoS2 aerogel membranes showed high performance in the photoassisted in-flow removal of both organic dye (methylene blue (MB)) molecules (96% removal within 120 min, Kobs = 0.0267 min-1) and heavy metal ions (88% Cr(VI) removal within 120 min, Kobs = 0.0012 min-1), separately and/or simultaneously, under UV-visible light illumination as well as excellent recyclability and photostability. Samples with interlayer expanded MoS2 nanostructures were particularly more efficient in the removal of smaller species (CrO42-) as compared to larger (MB) dye molecules. The prepared hybrid aerogel membranes show promising behavior for application in in-flow water purification, representing a significant advancement in the use of self-supported aerogel membranes for photocatalytic applications in liquid media.

Degradation of acetaminophen in a photocatalytic (batch and continuous system) and photoelectrocatalytic process by application of faceted-TiO2

In this study, anatase TiO2 rich in {0 0 1} (T-{0 0 1}), {1 0 1} (T-{1 0 1}) and {0 1 0} (T-{0 1 0}) facets were hydrothermally synthesized by a two-step reaction; the samples was utilized for the acetaminophen (ACE) degradation in an aqueous solution in the photocatalysis (batch and continuous system) and photoelectrocatalysis process. The characterization of the samples was performed by FE-SEM, XPS, UV–Vis and XRD. The photocatalytic performance of T-{0 0 1}, T-{1 0 1}, and T-{0 1 0} (for ACE phototdegradation) were evaluated and the results showed that T-{0 0 1} and T-{1 0 1} are more effective for ACE photocatalytic degradation. Photoluminescence (PL) spectra showed that separation efficiency order of photo-generated e−-h+ are {0 1 0} ~ {0 0 1} > {1 0 1}. Continuous flow membrane photoreactor (MPR) was used for photocatalytic degradation of ACE; the performance of MPR were studied at various hydraulic residence times (HRTs). The best performance of the MPR was observed at an HRT of 6.47 h. It was found that the transmembrane pressure (TMP) build-up was negligible at low flux, but a considerable increment was observed at the flux greater than 40 L/m2 h. However, it was also observed that periodic backwashing could be used for complete removal of the fouling. The photoelectrocatalytic degradation of ACE under UVC illumination was also investigated by synthesized samples; the results showed that T-{0 1 0} and T-{0 0 1} are more effective for photoelectrocatalytic degradation of ACE. The photo-generated current of the synthesized samples was also measured and the results showed that the T-{0 1 0} has the highest photocurrent.

Hybrid UV-C/microfiltration process in membrane photoreactor for wastewater disinfection.

A novel hybrid UV-C/microfiltration process for water disinfection is presented, and its application in continuous mode operation to the removal of different pathogen germs (Escherichia coli, Enterococcus faecalis, and Candida albicans) present in urban wastewater. The membrane photoreactor is based on porous stainless steel membranes coated with a TiO2 layer and illuminated by a UV-C lamp (254nm). A valve actuator in the outlet of the UV-C stream allows operation of the system under conditions of constant transmembrane pressure (TMP) keeping the UV-C contact time in few seconds, significantly lower than the typical irradiation time employed in TiO2 photocatalytic processes. An E. coli removal of up to 4-log in the permeate stream and up to 2-log in the UV-C outlet was achieved with a 0.2μm membrane operating with a TMP of 0.5bar and a UV-C contact time as low as 8s. The microbial balance data from the cells recovered from the membrane confirmed that 96-98% of the removed microorganisms died due to the UV-C action over the membrane surface. Modification of the membrane with a TiO2 layer has been also shown to be a suitable way to improve both the UV-C inactivation and the filtration efficiency. The results reported in this work constitute a proof of concept of the synergy between UV-C and filtration that can be achieved in a hybrid UV-C/microfiltration system, being a good example of process intensification where two products of different quality can be simultaneously obtained.

Oscillating membrane photoreactor combined with salt-tolerated Chlorella pyrenoidosa for landfill leachates treatment

In this study, a novel oscillating membrane (OM) photoreactor combined with salt-tolerated Chlorella was developed for old landfill leachates treatment, in which harvesting of highly-active algae was easily performed on large scale. Compared with control membrane photo-bioreactor (CMPBR), OM-MPBR exhibited excellent NH3-N removal efficiency as high as 94.0%. With light time prolonged, an increase in biomass production and NH3 removal rates was observed due to more energy provided for Chlorella cells. By comparison, it was found the highest membrane flux (99.6 L/m2 h bar) was obtained in OM-MPBR, which was attributed to strong shear stress on interface of liquid/membrane effectively reducing bio-foulants. It was clear that energy consumptions of OM-MPBR on biomass productivity (0.68 kWh/kg cell) and NH3 removal (0.0151 kWh/kg NH3-N) were lower than CMPBR. The new coupling system opens a door to scalable development of promising and economical MBR for environmental pollution control and biomass energy production.

Environmental impact of nanomaterials in composite membranes: Life cycle assessment of algal membrane photoreactor using polyvinylidene fluoride – composite membrane

This study assessed the environmental impacts of a composite polyvinylidene fluoride (PVDF) membrane (incorporating nanomaterials) and compared with neat PVDF membrane on algal membrane photoreactor (A-MPR) system's overall sustainability. The life cycle assessment (LCA) was carried out using Simapro 8.4.0 with cradle-to-gate approach, including raw materials, equipment, transportation and electricity consumption using ReCiPe 1.13 (H) and IPCC 2013 GWP 100a methodology. From the LCA analysis, silver/graphene oxide - polyvinylidene fluoride (Ag/GO-PVDF) membrane fabrication showed higher environmental impact than the neat PVDF membrane fabrication due to the addition of Ag/GO nanohybrids into the polymer. However, the A-MPR system using the Ag/GO-PVDF membrane exhibited better environmental footprint due to the improved performance of the modified membrane in producing higher volume of permeate as the output. Therefore, the A-MPR system using Ag/GO-PVDF membrane had outweighed the additional environmental impact of the Ag/GO-PVDF membrane fabrication process. Energy demand was identified as the main environmental hotspot in the LCA analysis. Subsequently, sensitivity analysis was performed to find out the effect of various energy mix for electricity generation towards the environment. The analysis revealed that the energy source for electricity generation had significant influence on the overall sustainability of the A-MPR system. The use of grid with 100% renewable energy (hydropower and geothermal) and solar photovoltaic might be able to mitigate 94.8% and 97.5% of CO2 emission, respectively.

Improved visible photocatalytic activity of TiO2 nanoparticles to use in submerged membrane photoreactor for organic pollutant degradation

In this study, photocatalytic activity of TiO2 nanoparticles under visible light was improved and the modified photocatalysts were used in a pilot-scale continuous submerged photocatalytic membrane reactor (SPMR) for decolorization of Reactive Orange 29 (RO29) under visible light irradiation. The Taguchi method was used to optimize the activation of TiO2 nanoparticles. Effect of the activation precursors (urea, thiourea, ammonium thiocyanate and sulfanilic acid), TiO2: precursors w/w ratio (1:1–1:6), activation time (1–7 h) and activation temperature (350–500 °C) on the visible photocatalytic efficiency of the nanoparticles was investigated to achieve maximum decolorization efficiency. X-ray diffraction, scanning electron microscopy, Fourier transform infrared and diffuse reflection spectroscopy analysis were used to characterize the photocatalysts. The results presented that the doping source and the doping source:TiO2 ratio had the most and the lowest effect on the TiO2 activation process, respectively. When urea was applied as an activation precursor with mass ratio of 6:1 to TiO2 at 450 °C for 5 h, the decolorization efficiency of 84.2% was obtained in a continuous SPMR system. The RO29 degradation intermediates were analyzed by gas chromatography coupled with mass spectroscopy technique.

AT-POME colour removal through photocatalytic submerged filtration using antifouling PVDF-TNT nanocomposite membrane

Abstract This study explores the potential of novel hybrid polyvinylidene fluoride/titanate nanotube (PVDF-TNT) photocatalytic membranes for the colour removal of aerobically treated palm oil mill effluent (AT-POME) in a submerged membrane photo reactor (SMPR). Different loadings (0–1.0 wt%) of TNT photocatalysts were physically mixed into PVDF dope solution prior to the membrane fabrication through dry/wet phase inversion process. The membranes modules were subsequently fitted into a 15 L SMPR tank, with a UV light source placed at the center of the SMPR. The performance analysis indicated that PVDF-TNT0.5 showed the best colour removal of 67.3%. The synergistic effects rendered by both membrane filtration and photocatalysis have remarkably improved the colour removal efficiency compared to filtration alone that barely exhibited colour removal of 34.2%. The operating conditions of the SMPR, such as initial concentration and pH of the feed AT-POME were also investigated. The photocatalytic activity has greatly reduced the fouling susceptibility of PVDF-TNT membranes, where flux loss of only 5.7% was observed after 5 cycles of usage. With its promising performance in terms of colour removal, flux and low membrane fouling susceptibility, this hybrid SMPR holds great potential to be directly applied in the current POME treatment system to improve the effluent quality and reduce freshwater consumption for palm oil extraction process.

Performance of submerged oscillatory membrane photoreactor for water treatment

Enhancement of a slurry hybrid membrane photoreactor (MPR) is investigated using an oscillatory microfiltration membrane and ZnO photocatalyst. The investigation involved the photocatalytic decolourization of methylene blue (MB) dye as a model pollutant compound. The effect of the operating parameters on the dye decolourization and its relation to the membrane-catalyst retention characteristics is studied. The results showed that application of oscillatory motion resulted in minimizing catalyst particles deposition on the membrane which increased its concentration in suspension and led to higher decolourization rates. Such effect was further augmented by the increase in membrane permeate flux due to the lower hydraulic resistance caused by catalyst deposition on the membrane surface. Furthermore, use of ZnO as photocatalyst has the potential of providing several advantages in terms of high UV absorbance as well as alleviating the need for using oxygen scavenging for charge separation. The latter when combined with the relatively low transmembrane pressure drop requirements by microfiltration (MF) membranes, can result in reducing the overall process energy demand. Such effects suggest that the proposed configuration may be considered as an effective approach for augmenting the productivity of membrane photoreactor for water and wastewater treatment applications.

Central composite design optimization of Rhodamine B degradation using TiO2 nanoparticles/UV/PVDF process in continuous submerged membrane photoreactor

In this paper, efficiency of a hybrid system combining UV/TiO2 nanoparticles and polyvinylidene fluoride (PVDF) membrane in a continuous pilot-scale submerged membrane photocatalysis reactor (SMPR) was investigated to degradation of Rhodamine B (RhB). The PVDF microfiltration membrane has potential to separate TiO2 nanoparticles from the treated wastewater. Effects of different operational parameters such as TiO2 dosages, UV light intensity, solution pH and polluted water flux in treatment reactor, which affect the performance of the photoreactor were evaluated. For the setup of the experimental design, a central composite design (CCD) matrix of the statistical response surface methodology (RSM) was used. The results indicated that the TiO2 photocatalyst at 0.1g/L, 3 UV-C lamps, polluted water flux of 100L/hm2 and pH of 8 were the optimum conditions for the removal of the RhB. Under the optimum conditions, 95.0% degradation was experimentally obtained.