On photocatalytic membrane reactors in water and wastewater treatment and organic synthesis

A brief overview of hybrid photocatalysis-membrane processes and their possible applications in water/wastewater treatment and organic synthesis is presented. Moreover, a short introduction to photocatalysis is shown. The paper summarizes the main advantages and disadvantages of photocatalytic membrane reactors (PMRs) with photocatalytic membranes or a photocatalyst in suspension. Furthermore, the influence of photocatalysis on membranes performance in terms of fouling and efficiency of removal of organic contaminants during treatment of water and wastewater is discussed. In the second part of the review the examples showing the possibilities of application of PMRs in recovery of valuable compounds (benzaldehyde, vanillin) or photocatalytic partial oxidation of benzene to phenol are presented. It was concluded that PMRs exhibit numerous advantages over the conventional photoreactors, however, further investigations are still needed in order to improve the hybrid processes performance

Performance of hybrid systems coupling advanced oxidation processes and ultrafiltration for oxytetracycline removal

In this study, the efficiency of three different hybrid systems coupling ultrafiltration (UF) with (i) UVC/H2O2, (ii) UVC/TiO2, and (iii) UVC was evaluated for the treatment of a secondary effluent (SE) from a municipal wastewater treatment plant and a surface water (SW) from Miedwie Lake, both spiked with 5 mg L-1 of oxytetracycline (OTC). A ceramic membrane made of TiO2 was tested. The effect of H2O2 concentration (30 to 120 mg L-1) on the UVC/H2O2-UF system and of P25-TiO2 loading (0.5 to 1.5 g L-1) in suspension on the photocatalytic UVC/TiO2-UF system were investigated. A photonic flux of 5.1 J s(-1) was provided in all systems. The maximum pure water flux (PWF) was 111 L m(-2) h(-1). Adsorption on the photocatalyst particles and/or on the membrane surface was found to be an important contribution for the removal of OTC and dissolved organic carbon (DOC). The UF membrane contributed significantly to photocatalyst and pollutants rejection in the photocatalytic membrane reactor (PMR) with the UVC/TiO2 system; whereas when using the UVC/H2O2 process, with the highest H2O2 dose, the membrane effect was negligible. Using SE as reaction matrix in the UVC/ TiO2-UF system with 1.0 g L-1 of TiO2, the complete OTC removal was achieved in 5 h with a mineralization of 49%. For the same reaction period, a DOC removal of 52% was achieved with the UVC/H2O2-UF system (120 mg H2O2 L-1). A similar permeate flux decrease (ca. 40%) was observed in both cases. Furthermore, the highest reduction of permeate flux (60%) was observed when using the UVC-UF system. Using SW as reaction matrix, higher OTC degradation rates and percentage of mineralization were reached for the same reaction period, when compared with SE, due to the lower COD and inorganic salts concentration present in the surface water

Synthesis of titanate nanofibers co-sensitized with ZnS and Bi2S3 nanocrystallites and their application on pollutants removal

The synthesis of nanocomposite materials combining titanate nanofibers (TNF) with nanocrystalline ZnS and Bi2S3 semiconductors is described in this work. The TNF were produced via hydrothermal synthesis and sensitized with the semiconductor nanoparticles, through a single-source precursor decomposition method. ZnS and Bi2S3 nanoparticles were successfully grown onto the TNF's surface and Bi2S3-ZnS/TNF nanocomposite materials with different layouts were obtained using either a layer-by-layer or a co-sensitization approach. The samples' photocatalytic performance was first evaluated through the production of the hydroxyl radical using terephthalic acid as probe molecule. All the tested samples show photocatalytic ability for the production of this oxidizing species. Afterwards, the samples were investigated for the removal of methylene blue. The nanocomposite materials with best adsorption ability for the organic dye were the ZnS/TNF and Bi2S3ZnS/TNF. The removal of the methylene blue was systematically studied, and the most promising results were obtained considering a sequential combination of an adsorption-photocatalytic degradation process using the Bi2S3ZnS/TNF powder as a highly adsorbent and photocatalyst material.Comment: 26 pages, 10 figure

Hybridization of Advanced Oxidation Processes with Membrane Separation for Treatment and Reuse of Industrial Laundry Wastewater

A new attempt to treat and reuse the industrial laundry wastewater using biological treatment followed by advanced oxidation processes (AOPs) and membrane separation is presented. Three various configurations of the hybrid systems were investigated: (1) biological treatment in a Moving Bed Biofilm Reactor (MBBR) – photocatalysis with suspended TiO2 P25, enhanced with in situ generated O3 – ultrafiltration (UF) – nanofiltration (NF); (2) biological treatment in MBBR– photocatalysis with immobilized TiO2 P25, enhanced with in situ generated O3 – UF - NF; (3) biological treatment in MBBR – photolysis/ozonation (with in situ generated O3) – UF – NF. For comparison purpose the wastewater was additionally treated in the MBBR – UF – NF mode (4). Application of AOPs contributed to the UF membrane fouling mitigation during treatment of the biologically pretreated laundry wastewater. The highest improvement of the UF permeate flux was found in case of the MBBR effluent treated with application of the immobilized TiO2 bed which was attributed to the highest efficiency of mineralization observed for that system. Since the applied wastewater contained significant amounts of inorganic ions, mainly Na+ and Cl-, the NF as the final polishing step was proposed. The quality of NF permeate was independent on the AOP mode applied and, moreover, significantly higher than the quality of water currently used in the laundry. It was concluded that the NF permeate could be recycled to any stage of the laundry system. Taking into consideration that application of TiO2 increases the overall treatment costs and that although the O3/UV pretreatment is less efficient than photocatalysis, it still allows to improve the UF permeate flux for ca. 35% compared to the direct UF of the MBBR effluent, the MBBR – UV/O3 – UF – NF system was proposed as the most beneficial configuration for the treatment and reuse of the industrial laundry wastewater

Coupling of the electrochemical oxidation (EO-BDD)/photocatalysis (TiO2-Fe-N) processes for degradation of acid blue BR dye

We report on the successful preparation of Fe-N codoped Titania powders, using TiO2Degussa P25, salt of Fe (II), and Urea. Modified Titania-based materials were characterized by SEM, EDS, BET, Raman, XRD diffraction and diffuse reflectance UV–vis spectroscopy measurements. The doping of TiO2 induced a shift in the absorption threshold toward the spectral range, obtaining catalysts with a greater photoactivity than the one of pure Degussa P25. The degradation of 200 mL of a solution with 50 mg L− 1acid blue BR dye in sulfate medium at pH 3.0 has been comparatively studied by electrochemical oxidation using a boron doped diamond anode (EO-BDD), Photocatalysis TiO2-Fe-N, and coupled material of EO-BDD/Photocatalysis TiO2-Fe-N. The solution was slowly degraded by EO-BDD (25%) and single Photocatalysis TiO2-Fe-N because of the low rate of dye degradation and its colored by-products with hydroxyl radicals generated at the BDD anode and catalyst surface from water oxidation (29%), whereas the solution was more rapidly degraded using coupled material of EO-BDD/Photocatalysis TiO2-Fe-N (82%), owing to the additional generation of hydroxyl radicals from the photocatalysis of TiO2-Fe-N and BDD anode.The authors thank the PRODEP Program (PRODEP-UGTO-PTC-472 and PRODEP 2015 UGTO-PTC-457) of UGTO under the Project 007/ 2015 (Convocatoria Institucional para Fortalecer la Excelencia Académica 2015), and the Project 778/2016 (Convocatoria Institucional de Apoyo a la Investigación Científica 2016-2017) is acknowledged. Authors thank Guanajuato University-CONACYT National Laboratory for SEM-EDX analysis. Financial support from the Spanish Ministry of Economy and Competitiveness in projects CTM2015-69845- R and CTQ2015-66078-R (MINECO/FEDER, UE) is gratefully acknowledged. C. J. Escudero thanks CONACYT-CONCYTEG for the postgraduate research grant (230713/383108) from Mexico

Simulation of hybrid trickle bed reactor-reverse osmosis process for the removal of phenol from wastewater

YesPhenol and phenolic derivatives found in different industrial effluents are highly toxic and extremely harmful to human and the aquatic ecosystem. In the past, trickle bed reactor (TBR), reverse osmosis (RO) and other processes have been used to remove phenol from wastewater. However, each of these technologies has limitations in terms of the phenol concentration in the feed water and the efficiency of phenol rejection rate. In this work, an integrated hybrid TBR-RO process for removing high concentration phenol from wastewater is suggested and model-based simulation of the process is presented to evaluate the performance of the process. The models for both TBR and RO processes were independently validated against experimental data from the literature before coupling together to make the hybrid process. The results clearly show that the combined process significantly improves the rejection rate of phenol compared to that obtained via the individual processes

The relationship between local structure and photo-Fenton catalytic ability of glasses and glass-ceramics prepared from Japanese slag

Local structure and the photo-Fenton reactivity of iron-containing glasses and glass-ceramics prepared from Japanese domestic waste slag were investigated. The largest rate constant (k) of (2.8 ± 0.08) × 10−2 min−1 was recorded for the methylene blue degradation test by using H2O2 with a heat-treated ‘model slag’. The 57Fe Mössbauer spectrum was composed of a paramagnetic doublet with isomer shift of 0.18 ± 0.01 mm s−1 attributed to distorted FeIIIO4 tetrahedra. These results indicate that the paramagnetic Fe3+ provided strong photo-Fenton catalytic ability, and that waste slag can thus be recycled as an effective visible-light activated photocatalyst

Solar Hydrogen Generation from Lignocellulose

Photocatalytic reforming of lignocellulosic biomass is an emerging approach to produce renewable H2 . This process combines photo-oxidation of aqueous biomass with photocatalytic hydrogen evolution at ambient temperature and pressure. Biomass conversion is less energy demanding than water splitting and generates high-purity H2 without O2 production. Direct photoreforming of raw, unprocessed biomass has the potential to provide affordable and clean energy from locally sourced materials and waste