Chemical &Process Engineering. Bioculture Growth Enhancement Mediated by CO 2 Enriched Microbubbles 2009 Prof. W.B.J. Zimmerman Dr D. J. Gilmour Introduction Algae are a rich source of biofuel and by-products such as: protein, glycerol and beta carotene. Although readily available, the main challenge however has been best practice in their cultivation. Microbubbles on the other hand (Fig. 1), have been proven due to their high surface area to volume ratio to have a high mass transfer coefficient, but their production has not been simple. With the recent invention of the fluidic oscillator, bubbles nearly same size as their exit apertures can be obtained (Zimmerman et al., 2008). Results Algal growth is dependent on the pH of the culture medium (Richmond, 1986). Also, pH of algal medium is inversely proportional to gas (CO 2 ) dissolution. In course of the experiment, gas dissolution was investigated by comparing the changes in pH of culture medium (Galloway and Krauss, 1961) when sparged with CO 2 enriched bubbles generated with and without the fluidic oscillator. Conclusions Microbubbles dissolve CO 2 faster and therefore increase algal growth. Algal culture with the fluidic oscillator generated bubbles had ~30% higher yield than conventionally produced bubbles. Bioenergy could become a more attractive option in the recycling of the high concentration of CO 2 emissions from stack gases. References 1.Galloway and Krauss (1961) Plant & Cell Physiol., 2, 331—337 2.Richmond (1986) Handbook of Microalgal Mass Culture, Zhang (2007) Novel aerator studies on yeast growth, MSc EEE University of Sheffield. 4.Zimmerman W.B., Tesař V., Butler S.L., Bandulasena H.C.H.(2008) Recent Patents in Engineering, 2:1-8. JAMES HANOTU Figure 4: Graph of pH drop vs. time Methods Algea (D.salina) was grown in a 250L bioreactor (Figure 3) with nutrient (CO 2 ) sporadically supplied in the form of bubbles. The experiments conducted are with: The fluidic oscillator generated CO 2 microbubbles Conventionally produced bubbles. Figure 5: Plot of Chlorophyll content versus time for both main and control experiment. (a) (b) Fig 1: (a) Additional surface area with microbubbles. (b) Graph of Transfer rate vs. bubble size. (b)(c) Aim 1.Gas Dissolution 2.Biomass Concentration The Fluidic Oscillator Algae in growth medium sparged with CO 2 enriched bubbles CO2 Microbubbles Experimental Set-Up Figure 3 : ( a)Photograph of experimental set-up. (b) Artistic model of the Airlift loop bioreactor (ALB) showing the internal culture process. ALB CO 2 Light Fluidic Oscillator Water bath for temperature control Flowmeter Algal cell D. salina cultured with the fluidic oscillator generated bubbles yielded highest chlorophyll content of 3.43 µg/ml, while results without the equipment showed highest algal growth yield to be 3.04 µg/ml after 12 days. Bubble Production Fluidic Oscillator + With the Fluidic Oscillator Without the Fluidic Oscillator Formation of nearly mono-dispersed, uniformly spaced cloud of microbubbles. Formation of coalescent large bubbles from the same diffuser. Diffuser Highest chlorophyll concentration assayed from both experimental runs was found in cells inoculated under the influence of bubbles generated with the fluidic oscillator. Algal growth with the novel equipment was ~30% more than the conventional sparging method. This result agrees with result from Zhang (2007) who found that microbubbles have a significant effect on yeast growth. Determine the effect of CO 2 enriched microbubbles on algal (Dunaliella salina) growth. Compare algal growth rate under fluidic oscillator generated bubbles and conventionally-generated bubbles. (a) (b) Fig:2