Recent advances in heterogeneous micro-photoreactors for wastewater treatment application

Optimization and Parameter Investigation of the Planar Photocatalytic Microreactor

The microreactor could break the limitation of mass transfer and photon transmission in photocatalysis. Through a facile assembly method, a planar photocatalytic microreactor was constructed to fit most of the photocatalysts regardless of their strict preparation method. This microreactor exhibits a 2.41-fold efficiency compared to a bulk reactor. Parameters that affect the photocatalytic performance were discussed in detail by experiment and calculation. The diffusion rate is the main bottleneck in a planar microreactor under a laminar flow. The microreactor with lower height shows higher efficiency owing to faster mass transfer, while the length and width affect slightly. Elevating the light power density provides a diminishing benefit. Faster flow speed reduces the apparent degradation percent but increases the chemical reaction rate, in fact. The reaction rate increases to 9.31 times by reducing the height from 500 to 100 μm and grows another 1.76 times by adding the flow speed from 10 to 40 mL/h. This work illustrates the influence of parameters on planar photocatalytic microreactors and offers a promising prospect for large-volume photocatalytic water treatment.

Role of lamp type in conventional batch and micro-photoreactor for photocatalytic hydrogen production

The use of an irradiation source with a homogeneous distribution of irradiation in the volume of the reaction mixture belongs to the essential aspects of heterogeneous photocatalysis. First, the efficacy of six lamps with various radiation intensity and distribution characteristics is contrasted. The topic of discussion is the photocatalytic hydrogen production from a methanol-water solution in the presence of a NiO-TiO2 photocatalyst. The second section is focused on the potential of a micro-photoreactor system-the batch reactor with a micro-reactor with a circulating reaction mixture, in which the photocatalytic reaction takes place using TiO2 immobilized on borosilicate glass. Continuous photocatalytic hydrogen generation from a methanol-water solution is possible in a micro-photoreactor. This system produced 333.7 ± 21.1 µmol H2 (252.8 ± 16.0 mmol.m-2, the hydrogen formation per thin film area) in a reproducible manner during 168 h.

Advanced oxidation processes in microreactors for water and wastewater treatment: Development, challenges, and opportunities

The miniaturization of reaction processes by microreactors offers many significant advantages over the use of larger, conventional reactors. Microreactors' interior structures exhibit comparatively higher surface area-to-volume ratios, which reduce reactant diffusion distances, enable faster and more efficient heat and mass transfer, and better control over process conditions. These advantages can be exploited to significantly enhance the performance of advanced oxidation processes (AOPs) commonly used for the removal of water pollutants. This comprehensive review of the rapidly emerging area of environmental microfluidics describes recent advances in the development and application of microreactors to AOPs for water and wastewater treatment. Consideration is given to the hydrodynamic properties, construction materials, fabrication techniques, designs, process features, and upscaling of microreactors used for AOPs. The use of microreactors for various AOP types, including photocatalytic, electrochemical, Fenton, ozonation, and plasma-phase processes, showcases how microfluidic technology enhances mass transfer, improves treatment efficiency, and decreases the consumption of energy and chemicals. Despite significant advancements of microreactor technology, organic pollutant degradation mechanisms that operate during microscale AOPs remain poorly understood. Moreover, limited throughput capacity of microreactor systems significantly restrains their industrial-scale applicability. Since large microreactor-inspired AOP systems are needed to meet the high-throughput requirements of the water treatment sector, scale-up strategies and recommendations are suggested as priority research opportunities. While microstructured reactor technology remains in an early stage of development, this work offers valuable insight for future research and development of AOPs in microreactors for environmental purposes.