BEEMS Module A3
Algae
BEEMS
Wei Liao1, Samir Khanal2, Stephen Y. Park3, Yebo Li3
1. Department of Biosystems and Agricultural Engineering, Michigan State
University
2. Deptartment of Molecular Biosciences and Bioengineering , University
of Hawaii
3. Department of Food, Agricultural, and Biological Engineering, The Ohio
State University
Contact: Yebo Li, [email protected]
Sponsored by: USDA Higher Education Challenger Program 2009-38411-19761
Outline
Introduction

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Algae as a Source of Biofuels and Bioproducts
Importance and Rationale of Algal Biofuels
What are Algae?

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Physiology and Characteristics
Classification
Growth Conditions
Steps in Algal Biodiesel Production
Culturing Technologies
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2
Open Systems
Closed Systems
Outline (Continued)
Harvesting Technologies
Water Removal Technologies
Lipid Extraction Technologies
Economics of Biodiesel Production
Direct Production of Biofuels from Algae
Algal Biorefinery Concept
Summary
Suggested readings
Evaluation (homework and questions)
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3
Algae as a Source of Biofuels and
Bioproducts

Algal culture
Sunlight

CO2

Nutrients
> 30,000 species
4
Soil conditioners and agrochemicals

Fertilizers

Proteins
Fine chemicals and bioactive
substances

Phycobiliproteins

ω-3 & ω-6 fatty acids

Polysaccharides

Antioxidants (carotenoids)

Bactericides, fungicides (polyketides,
amides, alkaloids, and peptides)

Proteins and enzymes
Energy Carriers

Biodiesel

Hydrocarbons (n-Alkane)

Ethanol

Methane
Current Commercial Applications of
Algae
Algin (Alginate) – a thickening agent for food processing (brown algae)
Carrageenan – foods, puddings, ice cream, toothpaste (red algae)
Iodine (brown algae)
Agar – growth media used in research (red algae)
As food – red (rhodophytes) and brown algae, especially in Asia
Plant fertilizers
Diatomaceous earth – used for filtering water, insulating, soundproofing
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5
Sources:
Current Commercial Applications of
Algae
Species
End Product
Origin
Main Culture Systems
Chlorella spp.
Health food
Germany
Indonesia
Japan
Tubular photobioreactors
Circular pivot ponds
Raceway ponds
Spriulina spp.
Health food
China
India
Japan
Thailand
USA
Raceway ponds
Dunaliella salina
β-carotene
Australia
India
Extensive open ponds
Raceway ponds
Haematococcus pluvialis
Astaxanthin
Israel
USA
Photobioreactors
Raceway ponds
Crypthecodinium cohnii
DHA
USA
Heterotrophic cultivation (glucose)
Chaetoceros spp.
Nannochloropsis spp.
Navicula spp.
Tetraselmis spp.
Pavlova spp.
Aquaculture feed
Throughout the world
Tanks
Bag reactors
Raceway ponds
6
Roles of Algae


Base of the aquatic food chain – photosynthetic organisms
Lichens: algae and fungi symbiosis

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Pigments
Reduce harmful amounts of sunlight
Kill bacteria (antibiotics)
Also serve as shelters: Kelp form underwater forests; red
alga form reefs
Base of food chain
7
Underwater forest
Source:
Negative Impacts via Eutrophication
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Clogging of waterways, streams, and filters
Decrease in water taste and quality
Potential toxicity
Red tide – caused by dinoflagellates
Red tide (sea)
Tai Lake, China
8
Source:
Why Algal Biofuels?
High lipid content (up to 70%)
Rapid growth rates
More lipids per area (10–100×) than other terrestrial
plants
Can use non-arable land and saline/brackish water
No competition with food or feed
CO2 sequestration
Nutrient (N, P) removal in agricultural and municipal
wastewater
Utilization of residual biomass
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9
Source:
Oil Yields at a Greater Level
Source
Annual oil yield
(m3/ha)
Corn
0.14
Soybeans
0.45
Sunflower
0.95
Canola (Rape)
1.20
Jatropha
1.90
Palm
5.90
Microalgae (30% lipids)
59.00
Microalgae (50% lipids)
98.00
Microalgae (70% lipids)
140.00
10
Source: Mata et al. (2010) Renew. Sust. Energy Rev. 14: 217–232.
What are Algae?
1. Eukaryotic organisms
2. Live in moist environments (mostly aquatic)
3. Contain chlorophyll
11
Sources:
What are NOT Algae?

Terrestrial plants
-

Presence of true roots, stems, leaves
Vascular (conducting) tissues – xylem and phloem
Lack of non-reproductive cells in the reproductive structures
Cyanobacteria
-
12
Prokaryotes
Lack of membrane-bound
organelles
Presence of a single circular
chromosome
Peptidoglycan in cell walls
Ribosomes different in size and content
Source:
Physiology
13
Source:
Composition

Approx. 50% carbon, 10% nitrogen, and 2% phosphorus
Species
Protein
Carbohydrates
Lipids
Nucleic acid
50-56
10-17
12-14
3-6
47
-
1.9
-
8-18
21-52
16-40
-
48
17
21
-
51-58
12-17
14-22
4-5
57
26
2
-
6-20
33-64
11-21
-
Dunaliella bioculata
49
4
8
-
Dunaliella salina
57
32
6
-
Euglena gracilis
39-61
14-18
14-20
-
Prymnesium parvum
28-45
25-33
22-38
1-2
Tetraselmis maculata
52
15
3
-
28-39
40-57
9-14
-
Scenedesmus obliquus (green alga)
Scenedesmus quadricauda
Scenedesmus dimorphus
Chlamydomonas rheinhardii (green alga)
Chlorella vulgaris (green alga)
Chlorella pyrenoidosa
Spirogyra sp.
Porphyridium cruentum (red alga)
14
Characteristics of Algae
1. Eukaryotic Organisms

Cells have organelles
Eukaryotes
Structure of a typical plant cell
15
Source: www.wikipedia.com
Prokaryotes
Cell structure of a bacterium, one of the two
groups of prokaryotic life
Prokaryotic and Eukaryotic Cells
Prokaryotic Cells
Very minute in size
Nuclear region (nucleoid) not
surrounded by a nuclear membrane
Single chromosome present
Membrane bound cell organelles are
absent
16
Eukaryotic Cells
Fairly large in size
Nuclear material surrounded by a
nuclear membrane
More than one chromosome present
Membrane bound cell organelles are
present
Source:
Characteristics of Algae
2. Live in Moist Environments

Lack of a waxy cuticle (prevents water loss in terrestrial
plants)
The structure of a leaf
17
Source: http://en.wikipedia.org/wiki/File:Leaf_anatomy.svg
A Wide Variety of Growth
Environments

A wide range of conditions
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More common in moist, tropical regions than dry places
Marine and fresh water
Where do freshwater algae grow?
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18
Animals
Aquatic plants
Farm dams: algae species that are tolerant to high ammonia
Sewage: tolerant to P, N
Lakes
Rivers
Lagoons
Snow: ‘red snow’, colored by Chlamydomonas sp.
Mud and sand
Soil
Characteristics of Algae
3. Contain Chlorophyll

Algae are mostly photosynthetic, like plants:


Have 5 kinds of photosynthetic pigments (chlorophyll a, b, c, d, f)
Many accessory pigments – blue, red, brown, gold
Haematococcus sp. (red algae)
Algae chloroplast
19
Chlamydomonas sp. (green algae)
Source: http://www.biologyreference.com/Ph-Po/Photosynthesis.html
Characteristics of Algae
3. Contain Chlorophyll (Continued)

Chlorophyll

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A green pigment found in almost all plants algae, and cyanobacteria
Absorbs light and transfers light energy to ATP
5 kinds of chlorophyll (a, b, c, d, f)
Chlorophyll a
Chlorophyll b
Chlorophyll c1
Chlorophyll c2
Chlorophyll d
Chlorophyll f
Molecular formula
C55H72O5N4Mg
C55H70O6N4Mg
C35H30O5N4Mg
C35H28O5N4Mg
C54H70O6N4Mg
C55H70O6N4Mg
C2 group
-CH3
-CH3
-CH3
-CH3
-CH3
-CHO
C3 group
-CH=CH2
-CH=CH2
-CH=CH2
-CH=CH2
-CHO
-CH=CH2
C7 group
-CH3
-CHO
-CH3
-CH3
-CH3
-CH3
C8 group
-CH2CH3
-CH2CH3
-CH2CH3
-CH=CH2
-CH2CH3
-CH2CH3
C17 group
-CH2CH2COOPhytyl
-CH2CH2COOPhytyl
-CH=CHCOOH
-CH=CHCOOH
-CH2CH2COOPhytyl
-CH2CH2COOPhytyl
C17-C18 bond
Single
Single
Double
Double
Single
Single
Occurrence
Universal
Mostly plants
Various algae
Various algae
Cyanobacteria
Cyanobacteria
Chlorophyll a
20
Source:
Classification of Algae
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Algae belong to the kingdom Protista
There are millions of algal species
Phylogenetic tree
21
Sources: http://nicolkardos.googlepages.com/life, http://www.nbii.gov/
Classification based on Chlorophyll
Content

Chromista: contains chlorophylls a and c, such as brown
algae (golden brown algae) and diatoms

Red algae: contains chlorophyll a, such as marine algae
(seaweed)

Dinoflagellates: unicellular protists, associated with red
tide and bioluminescence

Green algae: contains chlorophylls a and b, such as
Chlamydomonas spp.
22
Sources: http://nicolkardos.googlepages.com/life, http://www.nbii.gov/
Chromista – Diatoms
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Division Bacillariophyta
Large group of algae (many unidentified). Relatively recently evolved
group
Habitat: cool freshwater and marine environments
Structure: mostly unicellular, have silica in their cell walls
Very important for aquatic food chains: they provide phytoplankton
Phytoplankton  Zooplankton  small fish (mollusks)  larger fish
Can reproduce asexually for many generations, then sexually
23
Sources: http://en.wikipedia.org/wiki/File:Diatomeas_w.jpg
Chromista – Brown Algae and Kelp
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Division Phaeophyta
Closely related to diatoms, but appearance is different
Habitat: rocky coasts in temperate zones or open seas (cold waters)
Structure: multicellular
Holdfast, blade, air bladder
Up to 50 m long
24
Sources: http://en.wikipedia.org/wiki/Kelp
Red Algae
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Division Rhodophyta (4000 species)
Are some of the oldest eukaryotic organisms on earth (2 billion year
old fossils)
Abundant in tropical, warm waters
Act as food and habitat for many marine species
Structure: from thin films to complex filamentous membranes
Accessory pigments! Phycobilins (red) mask the chlorophyll a.
Due to these accessory pigments, red algae can photosynthesize in
deeper waters (at different light wavelengths).
Rhodophyta
25
Polysiphonia
Sources:
Haematococcus
Green Algae
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Division Chlorophyta
Largest and most diverse group of algae
Found mostly in fresh waters and also on land (rocks, trees, soil)
Structures: single cells (Micrasterias), filamentous algae, colonies (Volvox),
Thalli (leaf-like shape)
26
Sources:
Green Algae and Terrestrial Plants
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Terrestrial plants arose from a green algal ancestor
Both have the same photosynthetic pigments (chlorophylls a
and b).
Some green algae have a cell wall made of cellulose
Cells divide similarly
Algae
27
Plant
Sources:
Life Cycle of Algae


Some green algae are unicellular and demonstrate the simplest
possible life cycles (such as Chlamydomonas sp.)
Most algae have two recognizable phases


Sporophyte
Gametophyte
Seaweed (macroalgae)
28
Chlamydomonas spp. (microalgae)
Sources:
Growth Curve
1.
Lag phase
2.
Exponential phase
3.
Linear phase
4.
Stationary phase
5.
Decline of death
phase
29
Source:
Growth Conditions:
Temperature

Culture temperatures vary with species

The optimal temperature range for phytoplankton cultures:
20–30ºC

Temperatures higher than 35ºC are lethal for a number of
species, especially green microalgae

Temperatures lower than 16ºC slow down growth
30
Sources:
Growth Conditions:
Photosynthetic Flux

Light must not be too strong nor too weak
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
31
In most algal
cultivation, algae
only need about
1/10 the amount of
light from direct
sunlight
Light only
penetrates the top
7-10 cm of the
water due to the
bulk algal biomass
that blocks light
from reaching
deeper into the
water
Sources:
Growth Conditions:
Mixing

Agitation or circulation needed to mix algal culture
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32
Agitator is used for deep photo reactor system
Paddle wheels are used for open pond system
Pump circulation is used for photo tube system
Sources:
Growth Conditions:
Nutrients and pH

Autotrophic growth requires carbon, hydrogen, oxygen,
nitrogen, phosphorus, sulfur, iron and many trace
elements

Compositional formula CO1.48H1.83N0.11P0.01 can be used
to calculate the minimum nutrient requirement

Under nutrient limiting conditions, growth is reduced
significantly and lipid accumulation is triggered

Algae prefer neutral to alkaline pH
33
Sources:
Typical Media for the Growth of
Microalgae
Glucose
NaNO3
Bacto peptone
KH2PO4
K2HPO4
MgSO4*7H2O
FeSO4*7H2O
Thiamine HCl
CaCl2
CaCl2*7H2O
NaCl
Aaron’s solution
Autotrophic
(g/L)
-0.125
0.5
0.0875
0.0375
0.0375
---0.0125
0.0125
--
Glucose-peptone
(g/L)
10.0
-0.5
0.7
0.3
0.3
0.003
1x10-6
0.015
-0.0125
2 ml
Glucose-NO3
(g/L)
10.0
0.125
0.7
0.3
0.3
0.003
1x10-6
0.015
-0.0125
2 ml
Aaron’s solution (per liter): H3BO3, 2.9 g; MnCl2*4H2O, 0.0125 g; ZnSO4*7H2O,
0.22 g; CuSO4*5H2O, 0.08 g; MoO3, 0.018 g.
34
Source: Cooney and Guay, 2009
Steps in Algal Biodiesel Production

Algal cultivation
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Site selection, algal culture
selection (high cell yield/lipid)
Process optimization (bioreactor
design, nutrients, light, mass
transfer)
Harvesting
Biomass processing
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35
Dewatering
Thickening
Drying
Oil extraction
Biodiesel production
Source: Mata et al. (2010) Renew. Sust. Energy Rev. 14: 217–232.
Site Selection

Areas with adequate sunlight year round: tropical and
sub-tropical climate (HI, CA, AZ, NM, TX, FL)

Moderate to high temperature year round
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Adequate land availability (for open-pond system)

Availability of CO2 in close proximity
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Availability of water and nutrients at lower costs

Availability of manpower at reasonable rates
36
Culturing Technologies

Open systems
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Tanks
Circular ponds
Raceway ponds
Closed systems
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Flat-plate
Tubular
Vertical-column
High density vertical bioreactor
Valcent Products, Inc.
37
Sources:
Open Systems
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Natural waters
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Lakes
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Lagoons
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Ponds
Engineered systems

Tanks
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Circular ponds

Raceway ponds
Algal tanks
Spirulina production raceways (Parry Nutraceuticals Ltd., India)
38
Sources:
Lagoons
Open Systems
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Advantages

Simple design

Low capital and operating costs

Easy to construct and operate
Disadvantages

Little control of culture conditions

Significant evaporative losses
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Poor light utilization
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Expensive harvesting

Occupy large land area
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Limited to few species of algae
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Prone to contamination

Low mass transfer rates
Open pond raceways (Seambiotic, Israel)
39
Sources:
Raceway Ponds
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Closed loop recirculation
channel for mass culture (1950’s)
Paddlewheel:
mixing/recirculation
Baffles guide flow at bends
Algal harvesting done behind the
paddlewheel
40
Sources:
Raceway Pond Example:


Located in Kona, Hawaii, USA
Reddish ponds


Haematococcus (Astaxantin)
Other ponds

41
Spirulina
Source: www.cyanotech.com
Algal Kinetics


Similar to other microbial kinetics, with an important
difference
Most algae are phototrophic
  f ( I , T , S , pH , species)
where
µ ≡ specific growth rate
I ≡ light intensity
T ≡ temperature;
S ≡ substrate concentration
42
Algal Kinetics

Specific growth rate of algae (μ, d-1)
dX
1 dX
 X

dt
X dt
where X ≡ biomass concentration (g/L); t ≡ time (d)

Mass balance of algal biomass at steady state
dX
F
0  XV  FX
V
 XV  FX
 D
dt
V
where V ≡ reactor volume (L); F ≡ flow rate (L/d); D ≡ dilution rate (d-1)

Mass balance of limited substrate at steady state
dS


X  ( S 0  S )YXS
V
 FS  FS 0 
XV
0  FS  FS 0 
XV
dt
YXS
YXS
where S ≡ substrate concentration (g/L)
YXS ≡ biomass yield with respect to limited substrate (g/L)
43
Algal Kinetics

Algal productivity (P, g dry wt m-2 d-1)
PX
1 dX V
V
 X  Xd
X dt A
A
where V ≡ reactor volume (L); A ≡ surface area of reactor (m2);
d ≡ reactor depth (m)

Considering the specific growth rate is a function of light intensity,
temperature, and nutrient, the specific growth rate (d-1) can be
expressed as:
E
S
I

   max
T


ae
max
KS  S Ik  I
where S ≡ substrate concentration (g/L); a ≡ temperature constant;
I ≡ incident light energy (cal cm-2 d-1); T ≡ temperature (K);
X ≡ biomass concentration (g/L); E ≡ active energy (kJ)
44
Relationships Between Algal Growth
and Environmental Parameters
45
Source:
Example: Kinetics of an Open Algae
System

Calculate the algal productivity of Chlorella vulgaris in an
open pond system given the following parameters:


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
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
46
Active energy, E = 6842 kJ
Temperature constant, a = 1.8x 1010
Mean culture temperature, T = 298 K
Initial limited substrate (nitrogen) concentration, S0 = 200 mg/L
Limited substrate concentration in the reactor, S = 100 mg/L
Substrate constant, KS = 40 mg/L
Biomass yield with respect to substrate, YXS = 10
Incident light energy, I = 12.5 cal cm-2 d-1
Light intensity for which extended initial slope of light curve intersects with
maximum growth rate, IK = 6.24 cal cm-2 d-1
Depth of reactor, d = 20 cm
Example: Kinetics of an Open Algae
System

Solution:
max  ae
  max

E
T
 1.8 10  e
10

6842
298
 1.92 / day
S
I
100
12.5
 1.92 
 0.94 / day
KS  S Ik  I
40  100 6.24  12.5
X  (S0  S )YXS  (200  100) 10  1g / L
P  Xd  0.94 / day 1g / L  20cm  18.4 g / m2 / day
47
Open Pond Design
1. Pond size
2. Mixing depth relationships
3. Paddle wheel design
4. Carbonator
48
Source:
Open Pond Design
1. Pond Size

To determine the channel length (L) based on a given change in depth, a
given width, friction factor, hydraulic radius, and velocity
Manning equation:
s
V 2n2
R
4
3
s = ∆d/L and R = dw/(w + 2d),
4
dw
d (
)3
( w  2d )
L
V 2n2
LV 2 n 2
d 
4
dw 3
(
)
w  2d
The limiting pond area (A)
A  Lw
where V ≡ cross sectional average velocity (m/s); n ≡ friction factor constant;
R ≡ hydraulic radius (m); d ≡ pond depth (m); ∆d ≡ change in depth (m);
s ≡ slope of the water surface or the linear hydraulic head loss (m/m);
w ≡ width of the channel (m); A ≡ pond area (m2)
49
Example: Determination of Pond Size

Calculate the size of a raceway algal cultivation system with a high
density polyethylene (HDPE) liner, given the following parameters:






Channel width, w = 5 m
Manning’s coefficient (friction factor constant), n = 0.012
Pond depth, d = 30 cm
Change in pond depth, Δd = 15 cm
Cross sectional average velocity, V = 0.2 m/s
Solution:
R = dw/(w + 2d) = 0.3x5/(5+2x0.3) = 0.27
s
V 2n2
4
3

0.2 2  0.012 2
4
3
 0.000033
R
0.27
d
0.15
L

 4,545m
s
0.000033
50
A  Lw  4,545  5  22,727 m 2
Pond Area Relationship With Current
Velocity and Average Pond Depth

Based on



51
Channel width of 6 m
Manning’s n value of 0.015
∆d equal to (1/2) d
Open Pond Design
2. Mixing Depth Relationships


Due to the light requirement of algal growth, it is desirable to maintain
pond depths as shallow as possible. In reality, it is impossible to
significantly increase limiting pond area (constructional and operational
concerns)
Empirical depth-algae concentration equation for green algae:
6000
dp 
C
where dp ≡ light penetration depth (cm)
C ≡ light-limited concentration of algae (mg/L)

Continuously mixed culture, allows light to penetrate 2/3 of the actual
culture depth (d)
2
dp  d
3
52
9000
C
d
Open Pond Design
3. Paddle Wheel Design

Shaft and spokes of paddle wheel


Carbon steel pipe coated with epoxy paint
Paddle wheel blades (~2 mm thick)

Plastic

Metal

Fiberglass

Marine plywood
Fiberglass paddlewheel
53
Fiberglass paddlewheel
Plastic paddlewheel
Sources:
Plywood paddlewheel
Paddle Wheel Motor

Hydraulic power requirement can be calculated from the
head losses, channel dimensions, and speed
Power required:
QWd
P
102e
The quantity of flow:
Q = wdV
where P ≡ power (kW)
Q ≡ volumetric flowrate (m3/s)
W ≡ specific weight of water =1000 kg/m3
e ≡ paddle wheel efficiency
w ≡ channel width (m)
d ≡ pond depth (m)

102 is the conversion factor required to convert m kg/s to kW
54
Paddle Wheel Motor
55
Source:
Open Pond Design
4. Carbonator

Most large-scale algae
cultures are CO2 limited

Methods to supply CO2

Gas sparger

Spraying the liquid via the gas
phase

Floated plastic sheet
56

Diffusers on the pond bottom
release CO2 into the liquid

The gas inflates the plastic
dome

The spoilers across the
injector produce a high
turbulence for efficient gas
transfer into he liquid
Source: Green Star Products, Inc., MT, USA
Open Pond Design
4. Carbonator

Limiting factor for CO2 gas transfer: liquid file side of the gas-liquid
interface
Mass transfer: Q = kLA(Cs – Cl)
where Q ≡ mass transfer rate (mmol L-1 min-1)
kL ≡ mass transfer coefficient (min-1 m-2); A ≡ interface area (m2)
CS ≡ equilibrium concentration of dissolved gas at interface (mmol/L)
C1 ≡ equilibrium concentration of CO2 in the liquid (mmol/L)

If the CO2 flows into the injector and the partial pressure of the gas
mixture are known,
k
Qt
A2 (Cs1  Cl ) 1000
A2 
Qt
k (Cs1  Cl ) 1000
where Qt ≡ CO2 inflow (mmol L-1 min-1)
A2 ≡ area of the injector (m2)
Cs1 ≡ saturated concentration of dissolved CO2 in equilibrium with the
partial pressure at the injector (mmol/L)
C1 ≡ actual concentration of dissolved CO2 in algal suspension (mmol/L)
57
Closed Systems:
Photobioreactors (PBR)


Advantages

Compact design

Full control of
environmental
conditions

Minimal
contamination

High cell densities

Low evaporative
losses
Disadvantages

High production costs
(one order of
magnitude higher than
open ponds)

Overheating

Biofouling
58
Sources:
PBR Example: Algatechnologies


Located in Kibbuz Ketura, Israel
Haematococcus plant

59
Astaxanthin and other
nutriceuticals/cosmeceuticals
Source: www.algatech.com
Flat Plate PBR

Advantages




60

Large surface area
Good light path
Good biomass productivity
Low O2 build-up
Disadvantages



Source:
Difficult to scale-up
Difficult to control
temperature
Wall growth
Tubular PBR


Advantages

Good biomass productivity

Good mass transfer

Good mixing and low shear stress

Reduced photoinhibition and
photooxidation
Disadvantages

Gradients of pH, dissolved O2 and CO2
along the tubes

O2 build-up

Wall growth

Requires large land area

Decrease of illumination surface area
upon scale-up
61
Sources:
Vertical Column PBR


Advantages

High mass transfer

Good mixing and low shear stress

Low energy consumption

High potential for scalability

Easy sterilization

Reduced photoinhibition and
photooxidation
Disadvantages

Small illumination surface area

Construction requires sophisticated
materials

Decrease of illumination surface area
upon scale-up
62
Source:
Comparison of Open and Closed
Systems
63
Parameters
Open systems
Closed systems
Contamination
High
Low
Process control
Difficult
Possible
Species control
Not possible
Possible
Mixing
Not uniform
Uniform
Foot-print
Extremely high
Very low
Area/volume ratio
Low (5 to 10 m-1)
High (20-200 m-1)
Capital cost
Low
High
Operation cost
Low
High
Water losses
Very high
Low
Light utilization
Low
High
Productivity
Low
High (3-5 times)
Biomass conc.
Low
High (3 to 5 times)
Mass transfer
Low
High
Harvesting Technologies


Biomass recovery from dilute medium accounts
for 20–30% of total production cost
Algae can be harvested using:

Sedimentation (based on gravity)

Membrane separation (micro/ultrafiltration)

Flocculation

Flotation

Centrifugation
64
Sources:
Membrane Separation

Advantages


Disadvantages


Collection of microalgae with
very low density
Membrane fouling
Modified methods



65
Reverse-flow vacuum
Direct vacuum with stirring
blade above filter
Belt compressor
Sources:
Flocculation




Alum and ferric chloride are chemical flocculants
Chitosan is a biological flocculant (high costs)
Flocculant cause algae colloids in liquids to aggregate and
form a floc
Autoflocculation


Introduction of CO2 to an algal system to cause algae to flocculate
on its own
Flocculation is used in combination with filter
compressor
66
Flotation

Froth flotation

Dissolved air flotation

Adjusts pH and bubbles air


Froth of algae that accumulates above
liquid level
Features of both froth flotation and
flocculation

Provide fine bubbles to float algae
Too expensive for commercial use

Alum (AlK(SO4)2) to flocculate an
algae/air mixture

Often used in combination with filter
compressor

67
Source:
Centrifugation

Continuous-flow centrifugation




68
Widely used method
Efficient
Collects both algae and other particles
Used for the production of value-added products (not fuels)
Source:
Water Removal Technologies






Moisture reduction for subsequent processing and to
improve shelf-life
Algae concentration in pond: 0.10-0.15% (v/v)
Algae concentration after flocculation and settling: 0.7%
(v/v)
Algae concentration after belt filter press: 2% v/v
Energy content of algae cells: 5 Wh/g
Drying algae from 2% to 50% v/v requires ~60% of the
energy content of algae
69
Dewatering vs. Drying
Approximate energy curve for harvesting, dewatering, and drying
considering a process of flocculation, sedimentation, belt filter processing,
and drum oven drying
70
Lipid Extraction Technologies


Algal cells subject to cell disruption for release of desired
products
Physical






Mechanical disruption (i.e. bead mills)
Electric fields
Sonication
Osmotic shock
Expeller press
Chemical and Biological



71
Solvent extraction (Single solvent, co-solvent, direct transesterification)
Supercritical fluids
Enzymatic extraction
Single Solvent Extraction




Hexane or petroleum ether
Commercial process
Extraction under elevated temperature and pressure
Advantages
 Increased rate of mass transfer and degree of solvent
accessibility
 Reduced dielectric constant of immiscible solvent
72
Co-solvent Extraction

Two criteria to select a co-solvent system
1. The ability of a more polar co-solvent to disrupt the
cell membrane
2. The ability of a second less polar co-solvent to better
match the polarity of the lipids being extracted
73
Source:
Examples of Co-solvent Extraction

Bligh and Dyer method (1959)




Alcohol and chloroform
Majority of lipid in chloroform phase
Interaction of water/methanol > methanol/chloroform >
lipid/chloroform
Other combinations of co-solvents



74
Hexane/isopropanol
Dimethyl sulfoxide (DMSO)/petroleum ether
Hexane/ethanol
Direct Transesterification of Lipids
into Fatty Acid Methyl Esters (FAMEs)



Alcohol (methanol) and acid catalyst (acetyl chloride)
Reaction conditions: 100˚C and 1 h in a sealed vessel
Advantages
 High recovery of volatile medium chain triglycerides
 No need to use antioxidants to protect unsaturated
lipids
75
Economics of Algal Biodiesel
Production
76
Source: Chisti (2007) Biotechnol. Adv. 25: 294–306.
Economics of Algal Biodiesel
Production

Estimated cost of algal biomass production



For annual capacity of 10,000 ton–scale of economy



$2.96/kg (PBR)
$3.80/kg (Raceway pond)
$0.47/kg (PBR)
$0.60/kg (Raceway pond)
Cost for oil production (for 30% oil content by wt)


77
$5.30/gal (PBR)
$6.85/gal (Raceway pond)
Source: Chisti (2007) Biotechnol. Adv. 25: 294–306.
Economics of Algal Biodiesel
Production

Algal oil cost for lower cost biomass


$10.60/gal (assuming that recovery process contributes to 50% of
final recovered oil)
Processing cost (oil to biodiesel)



78
Palm oil: $0.53/gal
Soybean oil: $3.48/gal (as of Nov. 2009)
Algal oil: $11.13/gal
Source: Chisti (2007) Biotechnol. Adv. 25: 294–306.
Direct Production of Biofuels from
Algae



Alcohols
 Ethanol
 Butanol
Hydrogen
Alkanes
 Methane
Green algae grown in photobioreactors for the production
of hydrogen
79
Source:
Alcohol Production from Algae



Heterotrophic fermentation of starch to alcohols (ethanol
and butanol)
Chlorella vulgaris and Chlamydomonas perigramulata (marine
algae)
Procedures
 Starch accumulation via photosynthesis
 Subsequent anaerobic fermentation under dark
conditions to produce alcohol
 Alcohol extracted directly from the algal culture media
80
Hydrogen Production from Algae


Hydrogen can be produced by algae through photofermentation and dark-fermentation
Challenges
 Restriction of the photosynthetic hydrogen production
by proton gradient
 Competitive inhibition of photosynthetic hydrogen
production by CO2
 Competitive drainage of electrons by oxygen in algal
hydrogen production
81
Anaerobic Digestion of Algae



Methane can be produced through the anaerobic
conversion of algae biomass
Can be coupled with other processes (e.g. residuals after
primary process can be digested)
Challenges


82
High protein content of biomass can result in NH3 inhibition
Can be overcome by co-digestion with high-carbon co-substrates
Utilization of Whole Algae
83
Algal Extract Conversion
84
Algal Biorefinery Concept
Algae
Cultivation
Nutrients
(N. P, etc.)
From agricultural
& industrial effluents
Harvest
Industrial
grade water
CO2
Fine chemicals
Product
extraction
~80%
Biofuels
~20%
Fine
chemicals
Food supplements
Bioenergy
conversion
Cosmetic products
Electricity
85
Summary


Biodiesel production from algae has carries commercial
potential
Further research is required to decrease capital and
processing costs





Species selection
Growth
Harvesting
Post-processing
Biofuel production of algae is not restricted to a single
pathway, and a variety of techniques can be combined into a
biorefinery concept
86
Suggested Readings
1)
Barsanti and Gualtieri, 2006. Algae: Anatomy, Biochemistry, and Biotechnology.
CRC Press, Boca Raton.
2)
Brennan and Owende, 2010. Biofuels from microalgae – A review of technologies
for production, processing, and extractions of biofuels and co-products. Renew.
Sust. Energy Rev. 14: 557–577.
3)
Brune et al., 2009. Microalgal biomass for greenhouse gas reductions: Potential for
replacement of fossil fuels and animal feeds. J. Environ. Eng. 135(11): 1136–1144.
4)
Chen et al. 2010. System integration for producing microalgae as biofuel feedstock.
Future Sci. 1(6): 889–910.
5)
Chisti, 2007. Biodiesel from microalgae. Biotechnol. Adv, 25: 294–306.
6)
Hu et al., 2008. Microalgal triacylclycerols as feedstocks for biofuel production:
perspectives and advances. Plant J. 54(4): 621–639.
7)
Mata et al., 2010. Microalgae for biodiesel production and other applications: A
review. Renew. Sust. Energy Rev. 14: 217–232.
8)
Richmond, 2004. Handbook of Microalgal Culture: Biotechnology and Applied
Phycology. Blackwell Science, Oxford.
87
Questions
88