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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

• Motivation

• 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

• Motivation

• Results

• Conclusions

• Motivation

• 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

• Motivation

• Results

• Conclusions

• Motivation

• 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.

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

FACOUSTIC

FGRAVITY

• Motivation

• Results

• Conclusions

• Motivation

• Results

• Conclusions

New ApproachCombination of Inclined Plate Settler with Ultrasonic Field

Gravity

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

𝜂𝑣𝑓sin(𝛾)

𝜌𝑝 − 𝜌𝑚 𝑔

Critical radius rc

Piezoelectric

InfluentUltrasonic

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

• Motivation

• Results

• Conclusions

• Motivation

• 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

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)!

• Motivation

• Results

• Conclusions

• Motivation

• 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

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

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

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

• Motivation

• Results

• Conclusions

• Motivation

• 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

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