The deployment of photocatalysis for remediation of water has not yet been realized, although laboratory-scale studies have demonstrated promise. Accomplishing this requires the development of photocatalysis as a process, including studying its efficiencies in remedying water when high volumes of water are processed, and addressing the recovery, possible regeneration and reuse of the photocatalysts. To that end, this work is aimed at demonstrating the use of a custom-built mobile platform for disinfecting large quantities of water. The benchtop platform built is capable of processing 15.14 L (4 gallons) per minute of water, with possibility for further scale-up. Preliminary studies on the catalyst recovery, regeneration and reuse via gravity-assisted settling, centrifugation and air plasma treatment indicated that 77% of Aeroxide® P25 titania (TiO2) nanoparticle and 57% of porous TiO2 nanowire photocatalysts could be recovered and regenerated for further use. Overall, this study indicated that process improvements, including increasing the kinetics of the photocatalysis, and optimization of the efficacies of the catalyst recovery and regeneration processes will make it useful for water remediation on any scale. More importantly, the portable and flexible nature of the benchtop photocatalysis system makes it amenable for use in conjunction with existing technologies for remedying large quantities of water.
The water demand is projected to grow by 20% to 30% by the year 2050 as compared to 2018 to sustain the 2050 projected population of 9.4 to 10.2 billion [1]. As the demand for treated water useful for domestic, agricultural and industrial purposes increases, the current water supply and treatment infrastructure will be strained and will prove to be insufficient to meet this increased demand. The removal of emerging contaminants, such as pharmaceuticals, drug-resistant pathogens, and ‘forever chemicals’ make water treatment all the more challenging. Photocatalysis may serve as a great compliment to the existing train of treatment technologies in meeting this challenge. Photocatalysis could be employed to remove a wide variety of contaminants from water, ranging from organic and inorganic contaminants to pathogens, Moreover, if implemented in an effective manner, the photocatalysts employed to treat water could be recovered and reused. This, coupled with the use of renewable sources of energy, makes photocatalysis a sustainable process for water treatment on a large scale.While various materials have been investigated as photocatalysts for water remediation, Titanium dioxide (TiO2) is one of the most widely studied materials for this purpose. Various forms of TiO2, such as commercially available Aeroxide® P25, phase pure nanoparticles in Anatase as well as Rutile phases, and also alternative forms of TiO2 such as nanowires, have been explored for removal of dyes, pathogens etc. from water. Here, the capability of TiO2 in generating reactive oxygen species (ROS) when exposed to ultraviolet (UV) light is enhanced by the high specific surface areas of nanostructured TiO2. While the small size of the nanocrystalline photocatalyst is advantageous for enhancing kinetics, it may also be one of the major hurdles in the widespread use of photocatalysis for water treatment purposes. Enhanced scattering of light by nanostructured photocatalyst may make the process inefficient in certain cases. Also, the recovery and reuse of the nanostructured catalyst may be tedious.In this context, developing a roadmap towards scaling up the photocatalysis process, initially to a pilot plant scale and eventually to commercial scale is important for real-world applications of photocatalysis for water remediation. In this presentation, we will present a few strategies useful for accomplishing this goal. Changes to the catalyst morphology and their chemical composition, and the reactor geometry that have been implemented to make the photocatalysis process useful for treating large quantities of water, along with strategies developed for easy recovery and reuse of the photocatalyst will be discussed in detail in this talk.REFERENCES Boretti, A., Rosa, L. Reassessing the projections of the World Water Development Report. npj Clean Water 2, 15 (2019). https://doi.org/10.1038/s41545-019-0039-9
The current methods used to study photocatalysisassisted water disinfection at a laboratory scale may not lead to process scale-up for large-scale implementation. These methods do not capture the process complexity and address all the factors underlying disinfection kinetics, including the physical characteristics (e.g., shape and size) of the photocatalyst, the light intensity, the form of the catalyst (e.g., free-floating and immobilized), and the photocatalyst−microorganism interaction mode (e.g., collision mode and constant contact mode). This drawback can be overcome using in situ methods to track the interaction between the photocatalysts and the microorganisms (e.g., Escherichia coli) and thereby engineering the resulting disinfection kinetics. Contextually, this study employed microscopy and particle-tracking algorithms to quantify in situ cell motility of E. coli undergoing titanium dioxide (TiO 2 ) nanowire-assisted photocatalysis, which was observed to correlate with cell viability closely. This experimentation also informed that the E. coli bacterium interacted with the photocatalysts through collisions (without sustained contact), which allowed for phenomenological modeling of the observed firstorder kinetics of E. coli inactivation. Addition of fluorescent-tagging assays to microscopy revealed that cell membrane integrity loss is the primary mode of bacterial inactivation. This methodology is independent of the microorganism or the photocatalyst type and hence is expected to be beneficial for engineering disinfection kinetics.
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