Esteban Hincapié Gómez1
Anthony J. Marchese2
2014 Algae Biomass Summit
September 29 to October 2, 2014, San Diego, CA
AN ULTRASONICALLY ENHANCED INCLINED
SETTLER FOR MICROALGAE HARVESTING
1Ph.D. Candidate, 2Director
Engines and Energy Conversion Laboratory
Department of Mechanical Engineering
Colorado State University, Fort Collins, CO
http://www.engr.colostate.edu/~marchese
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
The Algae Biofuels Value ChainConversion of Whole Wet Biomass to Liquid Fuels
Biology Cultivation Harvesting
Whole Wet
Algal Biomass
Conversion to
Biocrude
Upgrading to
Drop-In Fuels
Nutrient
Recycle
Microalgae Harvesting TechniquesEnergy Requirements and Operating Costs
Capital Operating
Algae dewatering represents the most substantial cost in the entire
microalgae to biofuels value chain (Davis et al., 2011).
Davis R, Aden A, Pienkos PT. Techno-economic analysis of autotrophic
microalgae for fuel production. Applied Energy. 2011;88(10):3524-3531
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
Ultrasonic Harvesting of MicroalgaeA Low-Energy, Scalable Solution
Acoustophoretic Force, Fac, acting on particles of radius, R, in a liquid media subjected to an ultrasonic standing wave:
Fac is proportional to R3 and Acoustic Contrast Factor, F:
F is a function of density ratio and speed of sound ratio between particle and medium:
s = ap/amL = rp/rm
Measurement of Acoustic Contrast Factor(Hincapie, 2014)
L/C/P %15/60/2562/23/15
Acoustic contrast factor is generally very small for microalgae.As microalgae accumulates lipids, its acoustic contrast factor approaches zero!
Measurement of Acoustic Contrast Factor, FAcoustophoretic Force is Proportional to R3F
Acoustic Contrast Factor x Volume (x 10-18 m3)
Acoustic C
ontr
ast F
acto
r x V
olu
me (
x 1
0-1
8m
3)
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
Ultrasonic Harvesting of MicroalgaeDevelopment of a Continuous Flow System
Previous Work:
• Vertical orientation
• Ultrasonic field traps
and agglomerates
algae cells
• Agglomerated cells
settle due to gravity and
exit device in
concentrated stream.
Inlet
Concentrated
Outlet
Dilute Outlet
Challenges Development of a Continuous Flow System
• Spacing Between Nodes: ~ 250 μm
• Acoustophoretic Force: 10-14 N
• Drag Force: 10-12 – 10-15 N
• Standing Wave: Fac ~ R3
• Progressive Wave: Fac ~ R6 (Small!)
• # Resonance Modes ~ Thickness
• Resonance Modes are dependent
on the temperature
FDRAG
FACOUSTIC
FGRAVITY
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
New ApproachCombination of Inclined Plate Settler with Ultrasonic Field
Gravity
Drag
1. Inclined Settling
2. Ultrasonic Field and ATL’s
Acoustic Transparent Layers (ATL’s) are
used as settling planes. Ultrasonic field
produces agglomeration.
Acoustic Transparent Layers (ATL)
𝑟𝑐 = 9
2
𝜂𝑣𝑓sin(𝛾)
𝜌𝑝 − 𝜌𝑚 𝑔
0.5
Critical radius rc
Piezoelectric
InfluentUltrasonic
Field
Ultrasonically Enhanced Inclined Settler (UEIS)
Exploded View
Chamber size: 1” x 1.5” x 3”
System has no moving parts and no
direct contact with the biomass
Schematic Diagram
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
Experimental Set Up
Filtration efficiency, concentration factor were
measured as a function of power input,
system throughput, inlet cell concentration and
inclination angle.
CulturesSystem Characterized with Yeast, Microalgae and Polyamide
NameDiameter
(μm)
Contrast
Factor (F)
R3 x F
(10-19 m3)Media
Nannochloropsis
oculata3.7 0.03 2 f/2
Saccharomyces
cerevisiae7.8 0.12 71 YPD
Spherical
polyamide particles5 0.05 8 -
The acoustic force is proportional to R3 and the
Acoustic Contrast Factor (F)!
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
Filtration Efficiency vs. Input Power
hf = 𝑥𝑖 − 𝑥𝑑𝑥𝑖
Filtration efficiency
increased proportionally
with the power input
until 100 W·L-1
3.6 kWh · m-3
Filtration efficiency
Filtration efficiency
decreased with the flow
rate squared
S. cerevisiae had a better
filtration efficiency for a
given flow rate due to the
size and the acoustic
contrast factor
Filtration Efficiency vs. Throughput
Filtration efficiency
decreased logarithmically
with the cell concentration
N. oculata culture had a
better performance for cell
concentrations found in
photobioreactors
Filtration Efficiency vs. Inlet Cell Concentration
e = 𝑥𝑐
𝑥𝑖
The critical radius
necessary for settling is
proportional to sin (γ)
Self cleaning effect
increase the biomass
recover from the chamber
Concentration Factor vs. Inclination Angle
Concentration Factor
Brief Description Filtration EfficiencyConcentration
Factor
Settling
AreaDesign Tested
a) Vertical UES
harvesting chamber
without internal ATL
30% ± 7% 3.0 ± 0.2 7.7 cm2
b) “U” shape UES
harvesting with an ATL
division
43% ± 7% 3.6 ± 0.2 9.6 cm2
c) Inclined UES
harvesting chamber
without an intermediate
ATL
48% ± 6% 2.0 ± 0.5 20.5 cm2
d) Inclined cell settler
without UES10% ± 1% 1.2 ± 0.1 34.2 cm2
e) Final design 70% ± 5% 11.6 ± 2.2 34.2 cm2
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
OverviewUltrasonically Enhanced Inclined Settler for Algae Harvesting
• Motivation
• Ultrasonic Harvesting of Microalgae
• Continuous Flow System Challenges
• Ultrasonically Enhanced Inclined Settler
• Experimental Setup
• Results
• Conclusions
Conclusions
1. Ultrasonically Enhanced Settling offers an alternative to harvest microalgae cells with no moving parts
2. Novel design by a combination of UES and Inclined settling (UEIS)
3. Performance efficiency decreased with the flow rate
4. The filtration efficiency increased with the input power but plateaued at a power threshold of 100 W ∙ L-1
5. Optimal inclination angle was found at 50°
6. Higher inlet cell concentrations increased the performance of the unit
7. The UEIS design had a filtration efficiency of 1.5 to 7 fold better than similar devices reported in the literature.
ACKNOWLEDGEMENTSSolix BioSystems National Science Foundation (IGERT 0801707)Los Alamos National LaboratoryCSU Mechanical Engineering Senior Design Students