Nano-enabled water disinfection technology development that harnesses the power of microwaves




Plazas Tuttle, Jaime Guillermo

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Due to the position of microwave (MW) radiation in the electromagnetic spectrum, it has not yet been successfully utilized to inactivate waterborne microorganisms at a reasonable (energy) cost. Exceptional properties at the nano-scale, namely MW absorption-abilities of carbon nanotubes and excellent spectral conversion-capabilities of lanthanide series metal oxides in concert, hold promise to overcome the energetic barrier of this widely used and affordable MW technology. This dissertation reports the synthesis of a nano-heterostructure that combines carbon nanotubes’ and erbium oxides’ properties to generate reactive oxygen species (ROS) and inactivate Pseudomonas aeruginosa. Detailed characterization of the synthesized nanohybrid (NH) material with electron microscopy, X-ray techniques, and thermal gravimetric analysis confirms effective hybridization. At least one log unit of microbial inactivation was achieved via ROS generation with only 20 s of microwave irradiation at 110 W (0.0006 kW∙h energy use), using a conventional MW oven. Inactivation studies with ROS scavenger molecules prove that generated oxygen species played the dominant role in bacterial inactivation. The roles of wavelength, input power, and irradiation time on inactivation are explored, in an effort to unlock the mechanism of inactivation. To achieve such results with a high degree of control, a setup including a MW power generator and waveguide, capable of delivering precise frequency, while controlling input power and irradiation exposure time, has been designed and constructed. Results demonstrate inactivation of P. aeruginosa in presence of MW irradiation and aided by the nanohybrids. Finally, the inactivation efficacy of MW spectral conversion for a wide range of waterborne microorganism is determined. Inactivation of Legionella pneumophila, Flavobacterium columnare, Bacillus subtilis spores, and MS2 bacteriophages was also attempted using this system. A low degree of inactivation varying between (0.38 to 4.13 log removal) was achieved. These initial results are promising, but they do demonstrate a need for redesign of the NH and and reconsideration of the key irradiation parameters to achieve higher log removal, which will enable development of a technology that will be elevated from an agent of inactivation to an enabler of disinfection.


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