Investigation of zinc oxide photocatalytic reactor membrane system for waste water treatment

Photocatalysis is a highly promising technology which utilized photon energy for the mineralization of organic pollutants through chemical oxidation reaction processes. Post-treatment is needed to recover the photocatalyst from the solution after the reaction. Membrane filtration is integrated to the photocatalysis process due to their ability to reject the suspended photocatalyst and further improving the permeate quality by rejecting un-treated or remained organic matter in the feed. However, the major drawback of the integration is membrane fouling. Severe membrane fouling occurred due to the filtration of feed containing mixture of organic matter and photocatalyst. Continuous decline of photocatalyst in the bulk feed solution could happen due to the filtration process / precipitation on the membrane and thus decrease the degradation efficiency. The main purpose of this work was to develop an integrated photocatalytic reactor / membrane system in water treatment using solar and ultraviolet irradiation. Zinc oxide (ZnO) was selected as photocatalyst due to its excellent electrical, mechanical, and optical properties which are quite similar but cheaper compared to TiO2 . A simple sol-gel method at low temperature was used to prepare ZnO nanoparticles. Performance of ZnO was improved by using different solvents, doped with Fe 3+ and coupled with graphene oxide (GO). ZnO has the particle size range from 10-50 nm. Photocatalytic activities of ZnO and Fe-doped ZnO samples were evaluated based on the removal of Congo red (CR) using solar irradiation. 1.5 wt.% Of Fe 3+ doped ZnO (FZ-3) was able to attain ~ 70% CR degradation. It was the highest among different Fe 3+wt.%. The best FZ-3 was then used to fabricate nanoparticles with graphene oxide (FZG-3) for performance enhancement. 24% of degradation improvement was achieved by layering FZ-3 onto graphene oxide. In the recovery step of the photocatalyst, serious membrane flux decline and fouling layer on membrane was found. To study the most suitable options to reduce membrane fouling, mitigation of organic fouling of ceramic membranes in submerged photocatalytic membrane reactor (SPMR) was also investigated in this work using custom-made membrane reactor, where UV irradiation source and the membrane modules are integrated in the same reactor. In parallel, the performance of the combined photocatalytic process and membrane filtration with respect to the removal of natural organic matter (NOM) was also studied in terms of time-dependent and overall removals. ZnO was employed as a photocatalyst and potting soil extract (B2000) as NOM surrogate. Experiments were conducted in batch and continuous modes. Photocatalysis process was able to reduce the membrane fouling by ~ 80% and ~ 47% in batch and continuous mode, respectively, compared to without photocatalysis. SPMR was able to retain up to ~ 90% of ZnO in the system. These findings indicate that properties of photocatalyst is vital in determining efficiency of photocatalysis. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future. Experiments were conducted in batch and continuous modes. Photocatalysis process was able to reduce the membrane fouling by ~ 80% and ~ 47% in batch and continuous mode, respectively, compared to without photocatalysis. SPMR was able to retain up to ~ 90% of ZnO in the system. These findings indicate that properties of photocatalyst is vital in determining efficiency of photocatalysis. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future. Experiments were conducted in batch and continuous modes. Photocatalysis process was able to reduce the membrane fouling by ~ 80% and ~ 47% in batch and continuous mode, respectively, compared to without photocatalysis. SPMR was able to retain up to ~ 90% of ZnO in the system. These findings indicate that properties of photocatalyst is vital in determining efficiency of photocatalysis. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future. respectively, compared to without photocatalysis. SPMR was able to retain up to ~ 90% of ZnO in the system. These findings indicate that properties of photocatalyst is vital in determining efficiency of photocatalysis. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future. respectively, compared to without photocatalysis. SPMR was able to retain up to ~ 90% of ZnO in the system. These findings indicate that properties of photocatalyst is vital in determining efficiency of photocatalysis. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future. The findings also highlight that it is possible to mitigate and control the membrane fouling in the PMR using photocatalysis process by manipulating the operating conditions. All these findings and challenges are important for the implementation of the photocatalysis process in water treatment in future.
Die Photokatalyse ist eine vielversprechende Technologie, die Photonenenergie für die Mineralisierung von schwer abbaubaren Schadstoffen durch chemische Oxidationsreaktionsprozesse nutzt. Eine Nachbehandlung ist erforderlich, um den Photokatalysator nach der Reaktion aus der Lösung zurückzugewinnen. Die Membranfiltration ist in den Photokatalyseprozess integriert, da sie den suspendierten Photokatalysator zurückweisen und die Permeatqualität weiter verbessern kann, indem unbehandelte oder verbliebene organische Stoffe im Einsatzmaterial zurückgewiesen werden. Der Hauptnachteil der Integration ist jedoch das Membranfouling. Aufgrund der Filtration von Beschickung, die eine Mischung aus organischem Material und Photokatalysator enthielt, trat eine starke Membranverschmutzung auf. Ein kontinuierlicher Rückgang des Photokatalysators in der Bulk-Beschickungslösung könnte aufgrund des Filtrationsprozesses/Fällung auf der Membran auftreten und somit die Abbaueffizienz verringern. Das Hauptziel dieser Arbeit war die Entwicklung eines integrierten photokatalytischen Reaktor-/Membransystems zur Wasseraufbereitung mit Hilfe solarer und ultravioletter Bestrahlung. Zinkoxid (ZnO) wurde aufgrund seiner hervorragenden elektrischen, mechanischen und optischen Eigenschaften als Photokatalysator ausgewählt, da es kostengünstiger ist als das von seinen Eigenschaften her vergleichbare TiO2. Eine einfache Sol-Gel-Methode bei niedriger Temperatur wurde zur Herstellung von ZnO-Nanopartikeln verwendet. Die Leistung von ZnO wurde durch die Verwendung verschiedener Lösungsmittel, Dotierung mit Fe3+ und Kopplung mit Graphenoxid (GO) verbessert. ZnO hat den Partikelgrößenbereich von 10-50 nm. Die photokatalytischen Aktivitäten von ZnO und Fe-dotierten ZnO-Proben wurden anhand der Entfernung von Kongorot (CR) unter Sonneneinstrahlung bewertet. Eine Dotierung mit 1,5 Gew.-% Fe3+ (FZ-3) war in der Lage, ~70% CR-Abbau zu erreichen. Da dies der höchste Abbauwert für die verschiedenen untersuchten Fe3+-Gewichtsanteile war, wurde FZ-3 daraufhin zur Herstellung von Nanopartikeln mit Graphenoxid zur Leistungsverbesserung verwendet. Durch die Schichtung von FZ-3 auf Graphenoxid konnte 24 % Degradationsverbesserung erreicht werden. In der zur Rückgewinnung des Photokatalysators verwendeten Membran kam es zu einem starken Rückgang des Membranflusses und einer Fouling-Schicht auf der Membran. Um Möglichkeiten zur Verringerung des Membranfoulings zu untersuchen, wurde ein photokatalytischer Membranreaktor (SPMR) angefertigt, bei dem die getauchten keramischen Membranen und die UV-Bestrahlungsquelle in den gleichen Raum integriert wurden. Mit diesem wurde die Leistungsfähigkeit des kombinierten photokatalytischen Membranprozesses zur Elimination von natürlichen organischen Wasserinhaltsstoffen (NOM) in Bezug auf die zeitabhängige und die Gesamtentfernung untersucht. ZnO wurde als Photokatalysator und ein Blumenerdeextrakt (B2000) als NOM-Surrogat eingesetzt. Die Experimente wurden im Batch- und im kontinuierlichen Betrieb durchgeführt. Der Photokatalyseprozess konnte das Membranfouling im Batch- bzw. im kontinuierlichen Modus um ~80 % bzw. ~47 % im Vergleich zu ohne Photokatalyse reduzieren. SPMR konnte bis zu ~ 90 % ZnO im System zurückhalten. Diese Ergebnisse weisen darauf hin, dass die Eigenschaften des Photokatalysators entscheidend für die Effizienz der Photokatalyse sind. Die Ergebnisse zeigen auch, dass es möglich ist, das Membranfouling in der PMR mithilfe des Photokatalyseverfahrens durch Manipulation der Betriebsbedingungen abzuschwächen und zu kontrollieren. All diese Erkenntnisse und Herausforderungen sind wichtig für die zukünftige Implementierung von Photokatalyseprozessen in der Wasseraufbereitung.

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