INCREASED MICROALGAE PRODUCTION METHODS TO MEET BIODIESEL DEMAND

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INCREASED MICROALGAE PRODUCTION METHODS TO MEET
BIODIESEL DEMAND



Jose Cruz Rios, Jr.

B.S., California State University, Sacramento,
2008





PROJECT





Submitted in partial satisfaction of

the requirements for the degree of





MASTER OF
SCIENCE



in



MECHANICAL ENGINEERING



at



CALIFORNIA STATE UNIVERSITY, SACRAMENTO



SUMMER

2012






ii








































©

2012


Jose Cruz Rios, Jr.

ALL RIGHTS RESERVED





iii



INCREASED MICROALGAE PRODUCTION METHODS TO MEET
BIODIESEL DEMAND



A Project



by



Jose Cruz Rios, Jr.

















Approved by:


__________________________________, Committee Chair

Akihiko Kumagai, Ph.D



____________________________

Date










iv












Student:
Jose Cruz Rios, Jr.




I certify that this student has met the requirements for format contained in the University
format manual, and that this project is suitable for shelving in the Library and credit is to
be awarded for the project.





________________
__________, Department

Chair

___________________

Susan Holl, Ph.D






Date




Department of
Mechanical Engineering





v



Abstract


of


INCREASED MICROALGAE PRODUCTION METHODS TO MEET
BIODIESEL DEMAND


by


Jose Cruz Rios, Jr.



There are many advantages to microalgae when used in biofuel production. Compared to
current food or energy crops, micro
-
algal growth for biodiesel production does not need
to compete for arable land. While algae may theoretically be capable of producing 1
0 to
100 times more oil per acre, such capacities have not been validated at the commercial
scale level.
The algal biofuel industry is in need of a
sustainable
solution to overcome
low productivity

of algal cultures
.
A critical review of current production

processes are
identified, including algal growth facilities with a focus on
higher oil yields and algal
culture population.

A system is

proposed

and serves
as one

solution

to the above
-
mentioned problem
.
A
hybrid phototrophic energy manufacturing system i
ntegrates
methods such as nitrogen starvation and cell attachment to improve algal oil production
and harvesting. A
conveyor
-
belt type system
floating on a water surface
has been
proposed in the past
utilizing

flat surfaces as the at
tachment medium for the

algae. A





vi

similar
system

implementing

higher productivity methods

is identified. Although
significant literature exists on mi
c
ro
-
algal growth and biochemistry,
considerably

more
work is needed with regards to
harvesting methods and hybrid closed/open
production
systems.







, Committee Chair

Akihiko Kumagai, Ph.D


______________________

Date




vii

ACKNOWLEDGMENTS


The author wishes to express sincere appreciation to the Department of
Mechanical
Engineering

for their extended long
-
term support and especially to Professor
s,
Akihiko
Kumagai
, Sue Holl, and Timothy Marbach

for
their

patience and knowledge. This
project

would never have been completed without the encouragement and devotion of my
beautiful wife,
f
amily and friends.




viii

TABLE OF CONTENTS











Page


Acknowledgments
................................
................................
.............................


v
i
i

List of Tables

................................
................................
................................
.....


ix

List of Figures

................................
................................
................................
......

x

Chapter


1. INTRODUCTION


................................
................................
.......................

1


1.1 Alternative Energies: A Necessity

................................
.....................
1


1.2 Why Biofuel as an Alternative Energy?

................................
...........
4


1.3 Purpose of Study

................................
................................
................
4

2.

BIOFUEL BASICS

................................
................................
.........................
6


2.1 History of Biofuel

................................
................................
..............
6


2.2 Biomass Sources

................................
................................
................
9


2.3 Conversion Process of Feedstock to Biofuel

................................
...
10


2.4 Positive and Negative Impacts of Biofuels

................................
......
13

3. MICROALGAE

................................
................................
............................
15



3.1 Algae Basics
................................
................................
.....................
16



3.2 Algal

Biodiesel Production Pathways

................................
..............
17



3.3 Improving Oil Yields

................................
................................
.......
17



3.4 Current Production Methods

................................
............................
24

4.

AN IMPROVED ENERGY MANUFACTURING SYSTEM

.....................
29


4.1 Algal Growth and Production Process

................................
.............
29


4.2 Algal Harvesting

................................
................................
..............
30


4.3 Economic and Environmental Su
stainability

................................
...
31


4.4 Discussions and Conclusions

................................
...........................
32

Bibliography

................................
................................
................................
.......
33




ix

LIST OF TABLES




Page



1.

Table 3.3 Lipid C
ontent of
C
ommonly
R
esearched
M
icroalgae

S
pecies


18



x

LIST OF FIGURES




Page


1.

Figure 1
.1

Annual
E
nergy
C
onsumption in
Q
uadrillion Btu…………
..

…….
3

2.

Figure 2
.1 Pathwa
ys for Biofuel Production from D
iffere
nt B
iomass






F
eedstocks
………………………………………………………......
8

3.
F
igure
2.4 Percent R
eduction in
P
ollutants

for Biodiesel(B20)



As Compared to Petroleum

Based Diesel(B100)

….

…………..1
3

4.

Figure
3.1 P
roducts of an
A
lgae
C
ell
T
hrough
P
hotosynthesis.…
.
.
……


.
16

5. Figure 3.3.4 Effect of Light I
ntensity on
S
pecific
G
rowth
R
ate of






Microalgae
………………………………………………………….2
1

6. Figure 3.4.1.1 Model of an
O
pen
Raceway P
ond……
…..
……
..
……………
..
25

7.
Figure 3.4.1.2 Model of Closed P
hotobioreactor…
………

…..
…………
..
..
27

8. Figure 4.4 Concept of a
S
ustainable
M
echanical
B
iological




Manufacturing
S
y
stem

..................................................................
.31





1

Chapter 1

INTRODUCTION

With the U.S. being the
largest consumer of energy on the planet, it is imperative
that the U.S. take initiative in discovering more sustainable sources of energy and
decreasing its dependence of foreign oil, coal, and natural gas. The goal set by the U.S.
government is to replac
e 20% of fossil
-
based transportation fuels wi
th biofuels by the
year 2030
. If biodiesel were the sole biofuel used to meet this goal, 5.1 x 10
10

gasoline
-
equiv
alent gallons of biodiesel would

be needed each year at the current rate of
consumption

(Biomass Research and Development Initiative, 2006)
. According to the
United States
Energy Information Administration
, the average price of gasoline in the
U.S. as of
June 4
, 201
2

has reached $3.
612
. This influx in energy prices has bro
ught
increased at
tention to
biofuels as a renewable energy option
.

1.1 Alterative Energies: A Necessity

Political, economic, and environmental pressures have challenged us to look
toward other means of energy. Specifically, energies that are

economically and
environmentally sustainable.

Alternative fuel sources were heavily investigated during
the energy crisis of the 1970’s. At that time, most industrialized economies were highly
dependent on crude oil. The Organization Petroleum Exporting C
ountries (OPEC)
controlled the majority of the oil supply and price. In 1973, the US government decided
to back the Israeli military during the Yom Kippur War. This decision did not bode well
with the Arab nations, thus the Organization of Arab Petroleum E
xporting Countries
2


(OAPEC) voted on an oil embargo against the US. This resulted in escalating gas prices
for the United States. Since this event, the US has invested heavily in alternative energies
in order to be less dependent on foreign oils and more po
litically autonomous
(Horton,
2010)
.

Global economic issues can affect the oil supply through war, terrorist attacks,
and natural disasters, which can drastically affect oil prices in the US. In August 2005,
there was an interr
uption in oil supply due to Hurricane Katrina. Major ports in the
regions affected were not able to receive foreign oil, which resulted in the temporary
shutdown of many US refineries and pipelines. It is apparent that a disruption in the
foreign oil suppl
y of this magnitude may have been averted by having domestically
harvested oil available to the regions in need

(Horton, 2010)
. The availability of
additional fuel sources will also help decrease the effects of depleting oil re
serves and an
increasing demand. Emerging economies such as China and India are now competing for
oil supply. Therefore, it is imperative that the US investigates other avenues of energy so
that we can become less dependent on foreign oil (Figure 1.1).

3



Figure
1
.1:

Annual Energy Consumption in Quadrillion Btu



Source:
(
U.S. Energy Information Administration
)




Environmental factors such as air quality and global climate change are just two
reasons why biofuels need
continu
ed
investigat
ion
. Automotive emissions such as carbon
dioxide and unburned hydrocarbons can lead to ozone depletion. The result is respiratory
and cardiovascular issues among humans. An increase in average temperature around the
world will also cause hi
ghe
r energy consumption and thus,

further deplete world oil
reserves.

0
20
40
60
80
100
120
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006

(Quadrillion (10
15
) Btu)



Annual Energy Consumption

1992
-
2006

United States
Russia
China
Europe
India
4


1.2 Why Biofuel as an Alternative Energy?

Renewable energy is something the world desperately needs to reduce greenhouse
gas emissions. Fossil fuels are not sustainable and are in limited
quantity. The security of
our energy supply lies rooted in biofuels for our growing transportation sector.
In the
United States, the production of biofuel is in limited quantities. The majority of which are
ethanol and biodiesel. Today, ethanol displaces 2
% of all gasoline. Advancements in
technology may allow us to produce ethanol out of cellulosic material, ultimately
reducin
g our dependence on gasoline
(Wenqiao, Cui, & Pei)
.


For now,

c
orn is still the main feedstock of ethanol

production today. Using food
crops as fuel may seem like a convenient short
-
term solution

but the effect is that it
increases the demand of food crops. Assuming supply remains constant, if demand goes
up, then prices will go up as well.
As a result, the p
rice of corn has shot up with the
increased demand for ethanol.
From a moral standpoint, food should not have to compete
with energy when hunger is such a major issue around the world. The right thing to do is
to make alternative fuels from non
-
food crops
and waste
s
.

1.3 Purpose of Study

It takes roughly one gallon of oil to produce one gallon of ethanol using current
technologies
,

w
hereas, it takes one gallon of oil to produce between two to three gallons
of biodiesel.
Biodiesel
produced from agricultural waste and non
-
food crops
is beneficial
to the environment, reduces carbon emissions and does not compete with food crops
.

Therefore, this author
has chosen to

focus
his research
on al
gae as a feedstock for
biodiesel production, b
ased on initial findings and interest in the subject matter
.
An
5


investigat
ion of the

p
roduction pathways for current biofuels

will be conducted
, f
ollowed
by an
overview

of

the production pathway of

microalgae

for

biodiesel

production
.
The
author will also
evaluate

methods of
increased
algal production

and

will c
onclud
e

with

a
proposal

of
an

energy manufacturing system

with the

potential
for

increase
d

yield

of
microalgae
.

Closing though
ts and future

research are
identified.

6


Chapter 2


BIOFUEL

BASICS

There
are many renewable energy sources; biomass is one of the fe
w biofuels that
converts

directly into a liquid fuel. In order to gain a better understanding of
how
b
iofuels

are manufactured
,

their histor
ical use
,
biomass sources
,
and conversion process
es

must
be
investigated.
An e
xploration of traditional pathways of biofuel
s

is

also
necessary

in order
to understand how biomass
is
convert
ed

in
to biofuels.

2.1 History

of Biofuel



Biofuel

is defined as fuel derived from biological materials, including materials
from organisms that died relatively recently and from the metabolic by
-
products of living
organisms

(Demirbas, 2009)
. Biofuel can come in the form of so
lid or liquid fuels, as
well as various biogases. Some examples include low nutrient input with high per acre
yield crops, agricultural or forestry waste, and other sustainable biomass feedstock like
algae.


Early applications of biofuels in the solid form

have been used since man
discovered fire. Wood was the first form of biofuel that was used even by the ancient
people for cooking and heating. Liquid biofuels such as olive oil soon followed. Other
oils were derived from plants and animals and used for la
mp oil

(Sussman, 1983)
. Whale
oil was also commonly used until the modern methods of refining kerosene were
develo
ped in 1846 by Abraham Gesner
(Russell, 2003)
.

7



By the 19
th

century, gasoline and pe
trol
-
fueled engines were being invented.
Rudolf Diesel was a German inventor who invented the diesel engine. He designed his
diesel engine to run on peanut oil
(Knothe, 2001)
.

The Model T car was invented by
Henry Ford in 1903.

His car was completely designed to use hemp derived biofuel as a
fuel
source
(New York Times, 1925)
. World War II saw an increase in demand for
biofuels because participating countries found it more cost
effective

over

importin
g fuel.
Germany had developed the use of a gasoline mixture
that

included

alcohol that was
derived from potatoes.

Great Britain soon followed and discovered a way to mix grain
alcohol with petroleum
(Nag, 2007)
. After WWII, cou
ntries in the Gulf and Middle East
supplied western countries with cheap oil, which had a negative effect on the further
development of biofuels.


It was not until the 1970’s, after the oil crisis, that man renewed his interest in
biofuels. Growing realiza
tions of the world’s environmental problems and critical
instabilities in the Middle East have brought biofuels back on the table and have become
the center of attention of world governments.


Interest in biofuel began to reemerge
in 2004 with policies in
the US to increase
biofuel consumption in its economy. The two main types of liquid biofuels in use are
ethanol and biodiesel. Ethanol is used in gasoline engines and is der
ived from grains and
sugarcane crops

while biodiesel is used in diesel engines and
is derived from oil
producing crops, such as
rapeseed and
oil palm.
Figure
2.1 illustrates

the most current
biofuel pathways

for various biomass feedstocks
.
It is also worthy to note that there is a
differences between “first generation” biofuels

and “advanced” biofuels. First generation
8


biofuels
originate
from

agricultural crops and processes. Production processes for these
biofuels are established. For example, producing ethanol requires fermentation or
distillation additionally biodiesel requir
es a process known as transesterification.
Advanced biofuels come from non
-
food crops or residues, such as trees
,

grasses,
agricultural
or
forestry residues,
and

algae.
The next few subchapters will attempt to
explain each step in the biofuel pathways flow
chart.



Figure
2
.1:

Pathways
f
or
B
i
ofuel

P
roduction from
D
ifferent
B
iomass
F
eedstocks



Source:
(
Pena and Sheehan, 2007, in USAID, 2009
)



9


2.2
Biomass Sources



Biofuels

begin as biomass, biological material consisting of living or recently
living things.
There are two key
types of biomass sources
,
energy crops and biomass
waste. Energy crops
not used for human consumption
are

grown for immediate use as
fuel or transforme
d into biofuels through a conversion process

discussed later
. The main
crops that fall into this category include
o
ilseed, grains, and sugar crops
.
These f
irst
generation

biofuels are obtained using conventional techniques of production
. Each
feedstock con
sist
s

of oils, starches and sugars. Some of the most
prevalent

types of first
generation biofuels include biodiesel, vegetable oil, biogas, bioalcohols, and syngas.

(First Generation Biofuels, 2010)
.


Second generation biofuels

are derived from biomass waste.
According to the US
Energy Information Administration, biomass waste is an organic non
-
fossil material of
biological origin that is a byproduct or a discarded product. Biomass waste includes
municipal solid waste from bioge
nic sources, landfill gas, sludge waste, agricultural crop
byproducts, straw, and other biomass solids, liquids, and gases; but excludes wood and
wood
-
derived fuels (including black liquor), biofuels feedstock, biodiesel, and fuel
ethanol
(U.S. Energy Information Administration)
.


C
rop
s

grown outside of tropical regions around the globe produce wastes
exceeding one billion tons per year. These
wastes
primarily come from

wheat and corn

residues, which remain largely unused
.
Biologi
cal wastes such as manure, sewage sludge,
and municipal solid wastes are treated and converted into biofuels. Landfill gases
generated by garbage consisting of biomass, are also a source of bioenergy
(Boyle, 2004)
.

10


2.3
Conversi
on Process of Feedstock to Biofuel


A number of different conversion processes exist for the conversion of cellulosic
biomass to biofuels. The predominant differentiation between the conversion options is
the primary catalysis system.
Biomass can be
converted

into biofuel through three
different conversion processes
, chemical, biological, and thermochemical.


2.3.1 Chemical Conversion


A chemical conversion process usually consists of a sequence of steps, each of
which involves making some sort of cha
nge in either chemical makeup, concentration,
phase state, energy level, or a combination of these, in the materials passing through the
particular step. Transesterification and hydrotreating are among the more common
chemical conversion processes which
ma
kes
biodiesel production possible.

2.3.1.1 Transesterification


Biodiesel
is produced through transesterification. It
is an environmentally friendly
diesel substitute that is made up of fatty acid methyl

esters (FAME). R
enewable
biological sources such as
vegetable oil and animal fats
are mixed with

alcohol, in the
presence of a homogeneous and heterogeneous catalyst. The product consists of two
components, biodiesel and glycerol
(Meher, Vidyasagar, & Naik, 2006)



11


2.3.1.2 Hydro
treating


Hydrotreating is a chemical process applied to natural gas and refined petroleum.
The process is also known as hydrodesulfurization. The goal of the process is to decrease
the amount of sulfur in the petroleum by increasing the amount of hydrogen

in the
p
roduct.
The end result is a fuel that has less environmental impact after combustion
(Newth, 2003)
.

2.3.2 Biological Conversion


Biological or
Biochemical conversion routes

rely on biocatalysts, such as
enzymes and mic
robial

cells, in addition to heat and chemicals to convert

biomass first to
an intermediate mixed sugar stream

and then to ethanol or other fermentation produced

biofuel.

2.3.2.1 Alcohol Fermentation


The term fermentation can generally be defined as the
metabolic process in which
an organic substrate

goes under chemical changes due to activities of enzymes secreted
by micro
-
organisms.

2.3.2.2 Anaerobic Digestion


Anaerobic digestion is a series of processes where microorganisms break down
biomass in the
absence of oxygen.
The product is a gas such as methane which can be
used to generate power.
It is a common process in waste management plants and is also
an effective way to release energy

(Kaltschmitt, 2007)
.




12


2.3.2.3 Enzym
atic Hydrolysis and Fermentation


Enzymatic hydrolysis is a process that occurs when
bacteria release enzymes that
break down cellulose into glucose. This process occurs naturally in cows when they
consume straw or other cellulosic matter. Glucose is a sug
ar molecule that can be
converted into ethanol for use as an automotive fuel
(Lynd, 1996)
.

2.3.3 Thermochemical Conversion


Thermochemical

conversion technologies rely on heat and physical catalysts to
convert biomass to an intermediate gas or liquid, followed by a conversion step to
convert that intermediate to a biofuel. Thermochemical conversion technologies tend to
be grouped in two dist
inct categories for fuel production: gasification and pyrolysis

(Energy Production From Biomass, 2002)
.

2.3.3.1 Gasification


Gasification is a complete depolymerization of biomass with limited oxygen at
high temperatures, typi
cally greater than 850˚C, to a gaseous intermediate fuel known as
syngas, which consists of H
2

and CO.

Syngas or synthetic gas can be used for heat and
power generation
(Boyle, 2004)
.

2.3.3.2 Pyrolysis


Pyrolysis is the milder
depolymerization of biomass producing a liquid
intermediate known as bio
-
oil

in the ab
sence of oxygen at lower temperatures, typically
in the range of 400
-
650
˚C

(Bridgwater, 2000)
.

Bio
-
oil typically has about half the energy
va
lue of crude. Further processing is also required in order to remove contaminants.
Bio
-
oils can be utilized for heat and power generation as well as fuel for transportation.

13


2.4 Positive and Negative Impacts of Biofuels


Biofuels have several benefits and

i
mpacts
. The most important
being its low
environmental

impact
. Photosynthesis of carbon dioxide with water creates biomass. This
process extract
s
carbon dioxide from
the
atmosphere. However, as biomass burns during
combustion, CO
2

is
release
d

back into th
e atmosphere.
Unlike biofuels, f
ossil fuels
are
the
result
of man
tapping into

resources

sequestered in the ground for millions of years
.

As fossil fuels burn during combustion, previously sequestered carbon dioxide
is
release
d

into the atmosphere
(Deng, Li, & Fei, 2009)
. Emission studies of
the
combustion of
biodiesel as compared to petroleum diesel show significant reduction in pollutants
(Figure 2.
4
).


Figure
2.4
:

Percent Reduction in Pollutants f
o
r Biodiesel
(B20)

as
Compared to
Petroleum Based Diesel
(B100)

Source:
(Drapcho, Nhuan, & Walker, 2008)

14



The data indicates that there is
up to 100% reduction in sulfur dioxide, 80%
reduction in carbon monoxide, 67% reduction in unburned hydrocarbon
s, 47% reduction
in particulate matter, and up to 90% reduction in mutagenicity
(Drapcho, Nhuan, &
Walker, 2008)
. Biofuels are renewable as new crops are grown and waste material
s

collected. Political and economic relief are

other benefits of biofuels.
Biofuels help
reduce

our reliance on foreign oil and insur
es

the country’s political autonomy.
More jobs

are also created

from

the
manufactur
ing

of
biofuel
s and

acts as an economic stimulus.


Some
drawbacks to

biofuels
include
competition for
land use
among

energy
crops. Since large amounts of crops are necessary to create significant quantities of
biofuels,

land is required to meet growing demands
. Land previously allocated towards
growing
food
crops
are replaced for energy pro
ducing crops
.
This will result in a shortage
of food and will lead to a starving population
.

Thus
,
land use between food crops and
energy crops need to be optimized in order to keep demand under control

and prices
down
. High yield crops are ideal for biofu
els

therefore;

n
ew fuels based on algae
need to
be

res
earched and developed in order to

minimize land competition
.



15


Chapter 3


MICROALGAE


Global climate change, population growth and limited oil supplies

have motivated
countries to search for sustainable energy supplies. Renewable energies like wind, wave,
tidal and geothermal have the potential to supplement the
high
-
energy

needs of the US.
Unfortunately,

these types of energies are not easily converted
into liquid fuels for use in
the transportation sector. Although biofuels have the potential to supply
transportation

fuels, first generation energy crops are restricted to agriculturally productive areas and
most likely depend on freshwater source
s

for irrigation. Studies have shown that further
expansion of these types of energy crops will be unsustainable in the future. Therefore,
additional strategies are necessary if biofuel production is to be
sustainable at a
commercial level.

Microalgae can
be advantageous over higher plant forms. For example, algae are
able to grow at very high rates and are able to make use of a large fraction of energy from
the sun. Some algal strains can convert about 10% of the total solar energy into biomass
and grow in

conditions unsuitable for

land energy crops
(Carlsson, Beilenvan, Moller, &
Clayton, 2007)
. It is also possible to cultivate marine microalgae in a
commercial sized
operation where salt water or brackish water can be utilized.
Although microalgae has
many benefits, it currently struggles to be economically feasible with respect to
cultivation, harvesting and extraction processes
(Brennan & Owende, 2010)
.

Additionally, as with agriculture, a nutrient
supply in the form of fertilizers or organic
waste would still be required for algal culture.

T
his chapter will
investigate the
16


production pathway of algae
,

primarily focusing on cultivation and lipid content
optimization
for biodiesel production and ident
ify cultivation methods that can increase
oil yields
.

3.1 Algae Basics


Algae are a large and diverse collection of simple, usually autotrophic organisms,
varying from single
-
cellular to multi
-
cellular forms. Seaweeds are among the largest and
more intric
ate marine forms. Like plants, algae can consume water and carbon dioxide
along with sunlight to produce organic compounds such as sugar. The chemical reaction
is illustrated below:

6CO2 + 6H2O + light energy → C6H12O6 + 6O2

This reaction shows how biolog
ical material or biomass is able to gain water,
carbon dioxide and sunlight then convert it to glucose and oxygen. When these products
ignite, combustion occurs and energy
is
releases in the form of heat (Boyle, 2004).Most
algae are somewhat flat, which
ma
ximizes the surface area for
absorbing water, minerals, and
sunlight. Through this process,
most species of algae are able to
produce cellulose, starches, and
oils as shown in Fig. 3.
1



Figure 3.1:
Products of an Algae Cell

T
hrough Photosynthesis

17


3.
2
Algal
Biodiesel Production Pathways


To determine the most favorable pathway for algal biodiesel production based on
current technologies,
a
life cycle assessment (LCA) analyz
ing

the advantages and
disadvantages of different production methods

must be impl
emented.

F
actors such as
energy input, energy output, and environmental impact

should be considered
.
One
study
identified a pathway for biodiesel production with a net energy savings 85% greater than
the average biodiesel pathway used today (Stephenson, Ka
zamia, Dennis, Howe, Scott, &
Smith, 2010).

Th
e

production of
a
lgal biodiesel
can be modeled in

five

stages. F
irst
,

cultivation of an ideal

strain
of algae
that ha
s high areal productivity

and good
oil content

must be identified
. Once
the
algae are

cultivated,
a harvesting
method
is

implemented.
After the algae
has

been harvested,
lipid extraction
is

necessary.
Afterwards, t
he bio oil

produced
is

then
converted into biodiesel through

the

transesterification process.

Lastly,
options to
reuse or dispo
sal of the leftover biomass

should be

considered to minimize
environmental impact
.


3.3 Improving Oil Yields


Numerous algae
strains can
produce substantial

levels of bio oil or lipids.
Botryococcus braunii
can achieve lipid

contents as high as 75%, but th
e to
tal lipid yield
depends mainly on both, the area of

productivity and lipid content
(Mata, Martins, &
Caetano, 2010)
. Although some strains may produce more lipids, they may not be ideal
candidates as the main population cul
ture because of their

low growth rates and/or
inability to produce dense cultures.
Most

microalgae
strains
usually

used in research
laboratories are model strains
,
f
or their ease of
growth

and availability of previous
18


research,

not for their lipid producti
on, or their
likeliness

for biofuels production.

Table
3.3 lists commonly researched microalgae species and their respective lipid content.


Table 3.3
:

Lipid Content of Commonly Researched Microalgae Species


Source:
(Deng, Li, &
Fei, 2009)


A
key

restriction

in the production of algal biomass for
the
conversion to
biodiesel is that
algal growth and photosynthesis are greatly reduced when the production
of lipids in algae are
exploited
.

One solution to this problem could be
th
rough the genetic
engineering of microalgae in order to
increase

lipid production without
sacrificing over
all
productivity. Steps in this direction have been made using Chlamydomonas and Chlorella
mutants that block starch synthesis leading to increased oi
l
(Ramazanov & Ramazanov,
2006)
.

19


3.3.1 Species Selection

Currently, t
here is a
n extensive
amount of
continuing
work aim
ed

at enhancing

the
understanding of how lipid synthesis
in algae may
be genetically engineered

to
increase
lipid
productivity. It is thought that lipid biochemical pathways in algal cells are
similar to those of terrestrial plants, but evidence is still somewhat limited i
n this respect
(Hu, et al., 2008)
.
T
his type of approach would

complement efforts to increase fatty acid
synthesis in algae.


Nonetheless
,
a selection of species needs

to be
identified

that are capable of
accumulating the largest amount of lipids and optimized culture conditions

before genetic
alterations begin
. When

growing algae to achieve high yields, one needs to allow them
access to basic nutrients: light, carbon dioxide, water and inorganic nutrients. The
biochemical composition of algae can be modified by manipulating their environment,
this includes nutrient a
vailability. Several studies indicated that lipid concentrations in
algae can vary depending on changes in growth conditions or nutrient concentrations
(Converti, Casazza, Ortiz, Perego, & Del Borghi, 2009)
.

One study has
ident
ified a
marine strain known as
Nannochloropsis salina

that can yield a lipid content of 69%
under a
two
-
stage

growth condition
.

CO
2

and Nitrogen are provided in the first phase

to
promote growth of the algae

followed by a phase of nitrogen starvation
,

whic
h
induces

an
increase in lipid content

within the algae cells

(Sforza, Bertucco, Morosinotto, &
Giacometti, 2010)
.



20


3.3.2 Nitrogen Starvation


Reports indicate that photoautotrophic microalgae under nitrogen starvation have
sh
own increased lipid accumulation
. Nitrogen starvation is one of the more reliable
methods
for

increasing lipid content

(Hsieh & Wu, 2009)
.

However, implementation of
nitrogen starvation commonly causes a decrease in algal growth rates, resulting in lower
lipid production.

3.
3
.
3

Temperature

Water temperature can affect algal growth depending on algal species.

The
optimal temperature for phyto
plankton cultures is generally between 20˚C and 30˚C

(Converti, Casazza, Ortiz, Perego, & Del Borghi, 2009)
. Temperatures below 16˚C can
dramatically decrease growth while temperatures higher than 35˚C can be lethal for most
sp
ecies.

3.
3
.
4

Light
Saturation

L
ight
i
s necessary for healthy growth and production. Light must not be too
strong or too weak. In most algal
-
cultivation systems light only penetrates the top 3 to 4
inches of water. This is due to the growth and multiplicati
on of the algae. They become
so dense that they obstruct light from reaching the deeper parts of a pond or tank. Algae
requires about 1/10th the amount of light they receive from direct sunlight, which can
often be too stron
g
(Chist
i, 2007)
.

Light saturation
is characterized by a light saturation constant, which is the
intensity of light at which the specific biomass growth rate is half its maximum value,
µ
max
.

Light saturation constants for microalgae tend to be much lower than

the maximum
21


sunlight level that occurs at midday.

The biomass growth rate is much lower near the
equator because light saturation is much more intense. Above a certain value of light
intensity will result in a reduction in algal growth

(Fig. 3.2.2)
.
This occurrence is known
as photoinhibition. Algae become photo inhibited when light intesities reach beyond the
light level at which the specific growth rate peaks

(Chisti, 2007)
. Minimizing the effects
of photoinhibition
can
greatly increase the average daily growth rate of algae.



Figure
3
.
3.4
:
Effect of L
ight
I
ntensity

O
n
S
pecific
G
rowth
R
ate of
M
icr
o
algae

Source:

(Chisti, 2007)



22


3.3.5 Carbon Dioxide Fixation


Microalgae need carbon dioxide
fixation
during the photosynthesis process

in
order to produce the sugars necessary to produce bio
-
oil
. Therefore, a steady supply of
CO
2

is required to

grow algae for biodiesel production. Methods to harness CO
2

waste
from g
as burning power generation stations are currently being researched. The benefit
being that the previously harmful greenhouse gases can now be redirected into an algal
oil production facility as nutrients for algal growth.


The amount of CO
2
fixation neces
sary to promote algal growth can be calculated
based on the carbon fraction of
the specific species of
micro algal

biomass

using an
elemental analyzer. The cumulative CO
2

fixation amount (FA
CO2
) can be determined
using the equations below

(de Morais & Costa, 2007)
.





23


3.
3
.
6

Suspended
Growth


Suspended algae production using open or closed systems produce low algae
concentrations in the medium. A usual concentration for these methods is one gram of
dry algae per liter of water.

This equates to a mass ratio of about one to 1000(algae to
water). Minimal algal concentrations require large volumes of water, which may not meet
the goals set by the US Department of Energy. One of the key factors in designing an
open or closed system i
s that large water volume means large system sizes. A large
system size will unequivocally result in high overhead costs and more acreage demand

(Hoffman, 1998)
.

3.
3
.
7

Immobilized

Growth On
Textured Surfaces


All existing alga
l production systems
harvest

suspended algae
that is

allowed to
float freely in a medium
whether in

open pond systems or closed photobioreactor
systems.
T
he process of removing the algae from the medium

can be costly and energy
demanding
. This is due in

pa
rt to low concentrations of algae in the medium.
Flotation,
sedimentation, filtration, centrifugation, and flocculation are methods that will need
further investigation to make algae harvesting more feasible for large
-
scale algal
production. Results have f
ound no simple or cost
-
effective solution suitable to large
-
scale
algae production
(Wenqiao, Cui, & Pei)
.

Research now
indicate
s

that
micro scale
textured

stainless steel
sheets submerged in an algal medium
can
enhance the attach
ment
of algae cells
, resulting in
a potential increase of algae concentrations.



24


3.
4

Current Production Methods


There are three different types of technologies currently capable of algal
production. These
technologies
include p
hotoautotrophic,
h
eterotrophic, and
m
ixotrophic
production. This
subchapter

will further explore these technologies and assess
their
viability
.

3.
4
.1 Photoautotrophic Production


Photoautotrophic production is
cu
rrent
ly, the only

production method that
is
economically

and t
echnically feasible for large
-
scale biomass production.
The author will
investigate
three
key

types of photoautotrophic production of microalgae. They are Open
Pond Production Systems, Closed Photobioreactor Systems, and Hybrid Production
systems. The perf
ormance and viability of these systems depend on the type of
microalgae strain selected for production as well
other factors such as

climatic, economic,
land, and water considerations.

3.
4
.
1.1
Open Pond Production System
s


Algae can be grown under

natural
or
artificial

conditions
. Raceway ponds are the
most common of open pond production systems.
They
are oval shaped
,

closed loop
recirculation channels typically

operati
ng at water depths of 0.2
-
0.
3

meters
. Areal
dimensions range from 1 hectare for circular
ponds to 200 hectares for large ponds used
in Australia for
D. salina

produciton
.
Water management procedures include direct
CO
2
fixation under automated pH
-
stat control in shallow raceways

(Del Campo, Garcia
-
Gonzalez, &

Guerrero, 2007)
. M
ixing
and circulation of the algae occurs with the help of
25


a paddle wheel continuously driv
ing

the medium

around the channel to prevent biomass
sedimentation

and stagnation

(Brennan & Owende, 2010)
.


Figure
3.
4
.1.1
:

Model of an Open Raceway Pond


Advanta
ge
s

of open pond production systems
include cost effectiveness and ease
of operation
. Open pond production systems require less capital equipment

than other
production methods.

Unfortunately, o
pen pond
production systems
need a steady inflow
of clean water due to evaporative losses. Cont
amination is also a large issue, open ponds
are
susceptible to unwanted
algal
species,
bacterial growth, grazers
and
sudden
environment

changes

such as
harsh weather conditions and large
temperature
swings.
These variables are more difficult to

control in open pond production systems

(Brennan
& Owende, 2010)
.



26


3.
4
.
1.2

Closed Photobioreactor System
s


C
losed photobioreactor pro
duction systems
offer many theoretical advantages to
the inherent
problems associated with open pond production systems. Closed
photobioreactors can
more readily avoid contamination and yields higher culture
densities while providing closer control over ph
ysical and chemical conditions. They also

do not

suffer from evaporative losses nor do they take up extensive areas of land.

There
are three types of photobioreactors; they
include

tubular reactors, plate reacto
rs, and
bubble column reactors.

T
ubular reac
tors
are generally designed to feature shorter optical paths under
external illumination

constructed of an array of glass or plastic
tubes

(
Figure 3.3.1.2)
.
Flat plate reactors are typically thin rectangular chambers oriented vertically or inclined
towards

the sun. These designs are intended to mini
mi
ze light attenuation between the
wall and the center of the cu
l
ture vessel, with typical
tube/plate thicknesses of 0.05m
(Greenwell, Laurens, Shields, Lovitt, & Flynn, 2010)
.
Th
is
t
ype of
production system

uses

typically uses a
mechanical pump or an airlift system
to
re
-
circulate the microalgae
medium
.
Efficient gas transfer is critical to closed photo bioreactors because the system
needs to both sufficiently provide
CO
2

as the source of inorganic carbon for algal growth
and remove synthetically generated
O
2
,

which can inhibit photosynthetic efficiency or be
directly toxic to algae at high concentrations

(Carvalho, Meireles, & Malcata, 2006)
.

27



Figure
3.
4
.1.2
:

Model of Closed Photobioreactor



Large
-
scale commercial closed photobioreactors are currently not economically feasible.
The problem lies with high initial construction and operating costs.
Several kilometers of
tubes are necessary to pr
oduce significant amount of fuel
.

D
esign
ing an economical
photobioreactor system
is
limited to

the length of the
costly
tubes
with other potential
problems arising such as,

potential oxygen accumulation, carbon dioxide depletion, and
pH disparity in the sy
stem

(Deng, Li, & Fei, 2009)
.
Further research and development is
required to make this system

economically feasible.

3.
4
.
1.3

Hybrid Production System

A
h
ybrid production system consist
s

of a combination of
the
o
pen
p
ond
p
roduction
s
ystem and
c
losed
p
hotobioreactor
s
ystem. It is a cost effective
solution to

cultivating high yielding strains of microalgae for production of biodiesel. The
hybrid
p
roduction
s
ystem
has t
wo
components
;

the first
component is to cultivate a

micro
algae
strain

with a high lipid content

in

a
c
losed photobioreactor

system for biomass
28


production. The

second
component is to
deliver

the
concentrated

microalgae
medium
into

an
o
pen
p
ond
p
roduction
s
ystem, which

applies
nutrient restrictions and other stressors to
promote biosynthesis of oil
(Brennan & Owende, 2010)
.

3.
4
.2

Heterotrophic Production


Heterotrophic production system
s

grow

microalgae with

carbon substrates inside
stirred tank bior
eactors or fermenters. During
which
the growth of the microalgae is
independent of light. Therefore, this system provides more control over the growth of the
microalgae and lowers the cost of harvesting due to higher cell density of the microalgae.

H
eterot
rophic production system
s

ha
ve

much lower set
-
up costs th
a
n
p
hotoautotrophic
production system
s
. However, heterotrophic production system uses more energy th
a
n
photoautotrophic production systems. Several studies have concluded that heterotrophic
productio
n systems have higher technical viability for large
-
scale biodiesel production
than photoautotrophic production systems
(Brennan & Owende, 2010)
.

3.
4
.3

Mixotrophic Production


Some microalgae strains can be grown

using either photoautotrophic or
heterotrophic production systems. In this process the algae is able to photosynthesize as
well as ingest organic matter. For this process, light is not a constricting factor since
mixotrophs are not completely dependent on

photosynthesis
.

O
rganic substrates can also
support the growth of the microalgae. The photoautotrophic process uses light to grow
the microalgae while the heterotrophic part of the process such as aerobic respiration uses
carbon substrates to grow the pla
nt
(Brennan & Owende, 2010)
.



29


Chapter
4

A
N

IMPROVED

ENERGY MANUFACTURING SYSTEM

The projected mechanical
-
biological energy manufacturing system is
conceptualized

for theoretical purposes

in Fig.
4.4. The proposed system

is
intended to be
a guideline to
produce a sustainable algal production facility that
intensif
ies

algal lipid
content and population concentrations in a growth medium

with current available
technologies
.
The system

conta
ins three

components, which

integrate

m
ethod
ologies

for
increasing
micro algal

production

as
discussed in Chapter 3
.

They include an ideal algal
growth
production process,
better harvesting
practices
, and methods to make this system
more economically and environmentally sustainable.

4
.
1

Algal

G
rowth and
Production Process

Algae growth will
begin with a carefully screened algal strain, capable of high lipid
produ
ction. A marine species should be selected to minimize freshwater use and
eliminate unnecessary demand of the world’s limited source. Se
lection of a freshwater
strain could lead to price increases in drinking water. The production system will be a
hybrid
photo
trophic
production
system

where two stages will ensure high algal
production and lipid content.

The first stage includes

a closed p
hotobioreactor
system
where algae can grow
without unwanted contaminants. It will be fixed with ideal amounts of CO
2

based on the
algae strain selected along with proper O
2

removal.
Light intensity and nutrients will also
be supplemented

based on the algae strain selected.

30


The second stage will include the transferring of the concentrated algal medium to
an open pond system where nitrogen will be restricted, inducing algal cells to accumulate
high lipid contents. The open pond will featu
re a stainless steel conveyor belt like system
where algae can attach and continue to grow.
The entire production system will be
contained in an indoor facility to minimize contamination and increase water temperature
control. Increased facility costs will

be supplemented with
photovoltaic

and smart
lighting systems along with roof
windows, which

can allow for natural lighting.

4
.2

Algal
Harvesting

Th
e proposed
system
will use corrosion resistant cylindrical steel surfaces,
submerged under
salt or brackish

water to the ideal depth determined by the algal species.

The steel surfaces will

promote further growth in the

medium
during the nitrogen
starvation phase
.
These cylindrical sheets will feature
micro dimples to promote strong
cell attachment of the algae
. The c
ylinders will
rotate about their center axis
simultaneously

being
driven forward
much like

a conveyor belt.
The r
otati
on

rate
and
light exposure
of the cylinder

surface

will be optimized

for the specific
algal
strain
selected
.
Once a layer of algae
has grown on the cylinder surface, a mechanical arm with
a rubber end similar to a squeegee will ge
ntly scrape off the excess biomass for biodiesel
production
. While the cylinder rotates, small amounts of algae in the micro dimples will
be left behind
acti
ng as inoculum,
which will jumpstart new growth.
Centrifugation of the
low concentration
algal medium may be necessary to prevent biomass sedimentation.
This system
has the potential to be de
signed

at a large enough scale where continuous
algae growth and harvesting is possible.


31


4
.
3

Economical and Environmental Sustainability

A

renewable, sustainable power source will be used to operate this energy

manufacturing system. Possible energy sources th
at meet
these criteria

are

hydroelectric
,
hydrothermal vents,
photovoltaic

systems, or wind
turbines.

Since a marine algae strain




would be

selected as the ideal algal population, it may be reasonable to position this
facility near a salty body of water.

A gas burning power generation station located near
the facility can act as a cogeneration plant supplying its waste CO
2

gases. This will
mi
nimize greenhouse gases and lower the cost of algal carbon fixation. Nitrogen rich
waters such as the effluent medium that comes from a regional water treatment facility
can be redirected to

the
proposed system

and act as nutrients for the growing algae

th
rough anaerobic digestion
.

Biomass wastes and biproducts
from this system
can also be
recycled as nutrients for algae growth. This can not only save production costs on
expensive manufactured nutrients, it can also reduce greenhouse gases
. Integrating
envi
ronmentally friendly ideas such as the ones proposed above can lead to a fully
s
ustainable

system in the near future


Figure 4.4:
Concept of a Sustainable Mechanical Biological Manufacturing System

32


4
.4

Discussion
s and Conclusions

A system such as the one proposed above allows for the integration of multiple
disciplines of study

includ
ing

mechanical
engineering,

chemical
engineering, biology,
and
mass/continuous manufacturing concepts
.

Further research and development is
required to identify other r
enewable energy sources
and processes that can potentially
increase algal production.

Bas
ic biology of microalgae, species selection, genetic
manipulation, molecular characterization of control for carbon sequestering and storage
still need further investigation.


Economic feasibility of this energy manufacturing system will depend on
lowering

costs and increasing the efficiency of the following:

1.

Production systems, including land, water, nutrient and CO
2

requirements.

2.

Modification of the photosynthetic capability and productivity of microalgae.

3.

Algal cell harvest methods

4.

Lipid extraction

methods

5.

Transesterification methods

6.

Recycling byproducts from algal biomass

This study identifies

effective methods to increase algal production and lipid
content.
Futur
e research

include
s

a
djustment of both environment and nutritional
conditions of optim
al algal strains for biodiesel production
.

Continued research in algal
cell production and other alternative energies will help decrease our need for foreign oil
and help us meet the goal of replacing 20% of fossil
-
based transportation fuels with
biofuels
by the year 2030.

33


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