Pulsed field electroflotation for harvesting microalgae

Abstract

Microalgae are used in a number of commercial applications including biofuel production, nutraceuticals, and as feedstock for aquaculture. Typical methods for harvesting microalgae like centrifugation, microfiltration, and foam fractionation are extremely energy intensive. Reducing the energy input for harvesting microalgae would improve the overall energy balance for algae based biofuels and benefit any industry where algae is required. One method for harvesting microalgae is electrolytic flotation (electroflotation). This is simply using electrolysis-generated bubbles to float particles out of suspension and to the surface. The primary objective of this research project is to examine the effects that electrical waveform characteristics have on bubble size, gas generation efficiency, biomass separation, and lipid separation of Chlorella sp. from a marine media. Sets of 23 factorial tests were performed on a coplanar interdigitated electrode array. The waveform variables reviewed included applied potential, duty cycle, and frequency. The smallest mean bubble diameter (30.1 μm) occurred at 3V, 20%, 25 Hz. The smallest median bubble diameter (25.0 μm) occurred at 3 V, 10%, 25 Hz. The highest observed gas generation efficiency (1.69x10-6 (mol J-1)) occurred at 3 V DC. The highest observed biomass recovery (6.8%) occurred at 6 V, 20%, 25 Hz. Lipid recovery analysis was attempted as well but high variability in results rendered it inconclusive.