Conception and Development of a Pulsed Microwave Applicator for Exposure of Fresh Microalgae Biomass

This study presents the conception and development of a microwave (MW) applicator based on a TM010 cavity and a pulsed MW source, both custom-designed for evaluation of MW disruption of microalgae. The objective is the selective heating of microalgae immersed in their environment. The applicator enables exposing microalgae suspension to MW in continuous flow mode and monitoring the energy absorbed by the sample. The design was based on dielectric characteristics of microalgae in water, but other solvents might be considered. A tuning element ensures efficient MW coupling into the samples whose relative permittivity ranges from 10 to 80. The applicator includes a customized power supply operating a commercial magnetron source in pulse mode. The MW pulses are in the range of multiple kilowatts with adjustable duration in the microseconds range. The applicator enables to reach a power density in the microalgae sample beyond 1010 W/m3. Preliminary proof-of-principle experiments of MW disruption on fresh microalgae biomass Auxenochlorella protothecoides followed by lipid extraction enabled almost complete lipid recovery, while yields were negligible on untreated samples. Total energy consumption was below 4.2 MJ per kg of dry microalgae. Finally, the applicator characteristics are promising for future upscaling and deployment in the industry.