1. Airlift loop bioreactors with fluidic oscillator drive microbubbles
Will Zimmerman
Professor of Biochemical Dynamical Systems
Chemical and Process Engineering, University of Sheffield
with Jaime Lozano-Parada and Hemaka Bandulasena, PD research associates
with Kezhen Ying and James Hanotu, doctoral students

2. Outline Why and how microbubbles? ALB concept Performance studies
Steel stack gas trials
Advantages for microbial and mammalian cell ALBs
Sterilization: Ozone plasma microreactor in the lab
Prototype designs

3. Why microbubbles?
Steep mass transfer
enhancement.
Faster mass transfer -- roughly proportional to the inverse of the diameter
Flotation separations small bubbles attach to particle / droplet and the whole floc rises

4. The Fluidic oscillator
What is it?
No moving part, Self-excited Fluidic Amplifier.
Outlets
Inlet
Mid Ports
Linked by a feedback Loop

5. Fluidic oscillator makes microbubbles!
Same Diffuser
20 micron sized bubbles from 20 micron sized pores
Rise / injection rates of 10-4 to 10-1 m/s without coalescence: uniform spacing/size
Watch the videos!

6. Production of Mono-dispersed Uniformly spaced, non-coalescent
Gas Inlet
Production of Mono-dispersed
Uniformly spaced, non-coalescent
Microbubbles
Relatively large coalescent and
fast rising bubbles
Gas Inlet
Oscillatory Flow
Conventional Continuous Flow

7. Air lift loop bioreactor design
Schematic diagram of an internal ALB with draught tube configured with a tailor made grooved nozzle bank fed from the two outlets of the fluidic oscillator. The microbubble generator is expected to achieve nearly monodisperse, uniformly spaced, non-coalescent small bubbles of the scale of the drilled apertures.
Journal article has won the 2009 IChemE Moulton Medal for best publication in all their journals.
Designed for biofuels production
First use: microalgae growth
Current TSB / Corus / Suprafilt grant on carbon sequestration feasibility study on steel stack gas feed to produce microalgae.

8. Construction Top with lid Inner view: Heat transfer coils separating
riser /downcomer.
Folded
perforated
Plate m-bubble
generator.
Replaced by
Suprafilt 9inch diffuser
Body / side view

9. Growing algae in the lab
Dunaliella salina
Internal of the ALB
The gas separator section links the riser to the downcomer at the top, permitting gas disengagement and recirculation of fluid. Consequently, this drives a flow from the top of the riser to the bottom.

10. Gas Dissolution
Day 3
Day 10

11. Biomass Concentration
Algal biomass / bioenergy production (~30% extra biomass from CO2 microbubble dosing for only 1 hour per day).

12. Current programme of field trials
Corus: steel plant algal culture
Aecom: separation/harvesting
Air lift loop bioreactor development for biofuels
Approximately
1 cubic metre
cube design with
0.8 m2 square
ceramic microporous
diffusers.

13. Features From the other experiments,
Microbubbles formed from fluidic oscillation draw 18% less electricity than the same flow rate of steady flow forming larger bubbles bar gauge pressure needed.
3-4 fold better aeration rates with ~ micron bubbles, up to 50 fold larger with 20 micron sized bubbles
Very low shear mixing is possible at low injection rates (rise rate 10-4 m/s )
From the air-lift loop bioreactor performance,
Microbubbles dissolve CO2 faster and therefore increase algal growth.
Microbubbles extract the inhibitor O2 produced by the algae from the liquid so that the growth curve is wholly exponential.
Algal culture with the fluidic oscillator generated bubbles had ~30% higher yield than conventionally produced bubbles with only dosing of one hour per day over a two week trial period.
Bioenergy could become a more attractive option in the recycling of the high concentration of CO2 emissions from stack gases (ongoing field trials).

14. Ozone Kills and mineralizes!
Ozone dissolves in
water to produce
hydroxyl radicals
One ozone molecule kills one bacterium in water!
Hydroxyl radical attacks bacterial cell wall, damages it by ionisation, lyses the cell (death) and finally mineralises the contents.

15. Microfluidic onchip ozone generation
Our new chip design and associated electronics produce ozone  from O2 with key features:
1. Low power.  Our estimates are a ten-fold reduction over conventional ozone generators.
2. High conversion.  The selectivity is double that of conventional reactors (30% rather than 15% single pass).
Recently discovered strong irradiation in UV “killing zone” of ~300 nm.
Operation at atmospheric pressure, at room temperature, and at low voltage (170V, can be mains powered).

16. Plasma discs
25 plasma reactors each with treble throughput over first microchip

17. Dosing lance assembly New lance = 70 microdisc reactors
Quartz for UV irradiation
Axial view of the old lance
With 8 or 16 microdisc reactors

18. Consequence
Our low power ozone plasma microreactor can be inserted into the microporous diffusers to arrange for ozone dosing on demand in an ALB, for sterilization or other uses.