Chemical &
Process
Engineering
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
‘Engineering from Molecules’
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
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
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
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
The Fluidic oscillator
What is it?
No moving part, Self-excited Fluidic Amplifier.
Outlets
Inlet
Mid Ports
Linked by a feedback Loop
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
Fluidic oscillator makes microbubbles!
Same Diffuser
Chemical &
Process
Engineering
• 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
‘Engineering from Molecules’
• Watch the videos! ‘Engineering from Molecules’
Gas Inlet
Relatively large coalescent and
fast rising bubbles
Production of Mono-dispersed
Uniformly spaced, non-coalescent
Microbubbles
Gas Inlet
Oscillatory Flow
Conventional Continuous Flow
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
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.
Chemical &
Process
Engineering
• 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
‘Engineering from Molecules’
‘Engineeringmicroalgae.
from Molecules’
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
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
Growing algae in the lab
Dunaliella salina
Internal of the ALB
Chemical &
Process
Engineering
The gas separator section links the riser to the
downcomer at the top, permitting gas disengagement
and recirculation of fluid. Consequently, this drives a
‘Engineering
from Molecules’
flow from the top of the riser to
the bottom.
‘Engineering from Molecules’
Gas Dissolution
7.4
7.3
7.2
7.1
7
6.9
6.8
6.7
6.6
6.5
6.4
6.3
Day 3
Fluidic Oscillator
Fluidic Oscillator
Day 7
Without Fluidic
Oscillator
pH
Without F.O.
8.4
8.2
8
7.8
7.6
7.4
7.2
7
6.8
6.6
6.4
6.2
0
15
30
45
7.8
Day 10
7.6
Fluidic Oscillator
Without F.O.
7.4
7.2
7
6.8
6.6
6.4
0
Chemical &
Process
Engineering
15
30
45
0
60
60
7.4
7.3
7.2
7.1
7
6.9
6.8
6.7
6.6
6.5
6.4
6.3
15
30
45
Time (minutes)
Day 11
60
Fluidic Oscillator
Without F.O.
0
‘Engineering from Molecules’
15
30
45
60
‘Engineering from Molecules’
Biomass Concentration
Algal biomass / bioenergy production (~30% extra biomass from
CO2 microbubble dosing for only 1 hour per day).
Chlorophyll Content
(μg/ml)
4.00
3.50
With Fluidic Oscillator
3.00
2.50
Without Fluidic Oscillator
2.00
1.50
1.00
0.50
0.00
1
2
3
4
5
7
8
9
10
11
Time (days)
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
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.
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
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. 1.5-2 bar gauge pressure needed.
 3-4 fold better aeration rates with ~300-500 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
Chemical &
concentration
of CO2 emissions from stack gases (ongoing field trials).‘Engineering from Molecules’
Process
Engineering
‘Engineering from Molecules’
Ozone Kills and
mineralizes!
Ozone dissolves in
water to produce
hydroxyl radicals
One
ozone
molecule
kills one
bacterium
in water!
Chemical &
Process
Engineering
Hydroxyl radical attacks bacterial cell
wall, damages it by ionisation, lyses the
cell (death) and finally mineralises the
contents.
‘Engineering from Molecules’
‘Engineering from Molecules’
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).
3. Recently discovered strong irradiation in UV “killing zone” of ~300 nm.
4. Operation at atmospheric pressure, at room temperature, and at low voltage
(170V, can be mains powered).
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
Plasma discs
• 25 plasma reactors each with treble throughput over
first microchip
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
Dosing lance assembly
New lance = 70 microdisc reactors
Quartz for UV irradiation
Axial view of the old lance
With 8 or 16 microdisc reactors
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’
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.
Chemical &
Process
Engineering
‘Engineering from Molecules’
‘Engineering from Molecules’