Michael Banco

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22 Φεβ 2013 (πριν από 4 χρόνια και 4 μήνες)

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Microalgae


O
ver 40,000 species have been
already
identified,
algae are classified in multiple
major groupings as follows:

C
yanobacteria (
Cyanophyceae
), Green
A
lgae (
Chlorophyceae
), Diatoms (
Bacillariophyceae
),
Yellow
-
green
A
lgae (
Xanthophyceae
), Golden
A
lgae (
Chrysophyceae
), Red
A
lgae
(
Rhodophyceae
), Brown
A
lgae (
Phaeophyceae
),
D
inoflagellates

(
Dinophyceae
) and ‘Pico
-
Plankton’ (
Prasinophyceae

and
Eustigmatophyceae
)



Microalgae are unicellular species that can exist individually, in
chains or groups.


They have the ability to perform photosynthesis.


All algae have the ability to survive in a wide range of
environmental conditions.


Which has a lot to deal with the tremendous diversity of the organism and the
ability to modify their lipid metabolism efficiently in response to environmental
changes.

Microalgae: The ‘drop
-
in’ substitutes
for petroleum
-
based liquid fuels.


Microalgae can form
triacylglycerols
(TAGs).


Under unfavorable environmental or stress conditions for growth,
algae will alter their lipid biosynthetic pathways towards the formation
and accumulation of neutral lipids, mainly in the form of TAGs.


TAGs are not part of any structural components for the cell. But are
stored for energy in densely packed lipid bodies stored in the
cytoplasm for energy.


TAGs can undergo an
transesterification

reaction to produce alkyl
alcohols.


Shown in the 1980’s.


Alkyl alcohols have properties that are the same as petroleum!

Potential advantages of using algae as
feedstocks

for biofuel and biomaterials.

1.
S
ynthesize
and accumulate large quantities of neutral
lipids/oil.

2.
G
row
at high rates (e.g. 1

3 doublings per day
).

3.
T
hrive
in saline/brackish water/coastal seawater for which there are few
competing
demands.

4.

Tolerate
marginal lands (e.g. desert, arid
-

and semi
-
arid lands) that are
not suitable for conventional
agriculture.

5.
Utilize
growth nutrients such as nitrogen and phosphorus from a variety
of wastewater sources (e.g. agricultural run
-
off, concentrated animal
feed operations, and industrial and municipal wastewaters), providing
the additional benefit of wastewater
bio
-
remediation.

6.
S
equester
carbon dioxide from flue gases emitted from fossil fuel
-
fired
power plants and other sources, thereby reducing emissions of a major
greenhouse
gas.

7.
P
roduce
value
-
added co
-
products or by
-
products (e.g. biopolymers,
proteins, polysaccharides, pigments, animal feed, fertilizer and H
2
).

Assessment of bioenergy and bioremediation potentials of the
microalga
Scenedesmus

sp. AMDD cultivated in municipal
wastewater effluent in batch and continuous mode.

Patrick J.
McGinn
, Kathryn E. Dickson,
Kyoung

C. Park, Crystal G. Whitney, Scott P.
MacQuarrie
, Frank J.
Black, Jean
-
Claude
Frigon
, Serge R.
Guiot
, Stephen J.B. O’Leary


Objectives for the study:

1.
To investigate the used of secondary waste water effluent from a
municipal wastewater treatment plant as a source of nutrition for
intensive microalgae growth.


-

Secondary effluent is the end result of the treatment process and typically
discharged into receiving waters. Drinking water…..

2.
To address the issue of productive and stable cultivation of
microalgae in continuous
chemostats

at a high dilution rate.

Microalgae strain used:
Scenedesmus

sp. AMDD


This is very general algae in freshwater.


The cells
are
arranged in a row to for
4 or 8 celled
colonies.
2
to 16 celled
colonies can occur and very rarely there are more
than 16 cells per colony
.



The cells for this study was
isolated from soil samples and
identified by standard DNA
sequencing (courtesy of the NRC
Plant Biotechnology Institute).


The microalgae cells were
transported in standard Bold’s
Basal medium at 20 C in low light
until inoculation.

Two types of reactors were used!

Diagram A: These are batch reactors called
brite

box
photobioreactors
.

Diagram B: This is the continuous reactor using a
chemostat
.

*Samples for wastewater was collected in April, May and August of 2011 from the Mill
Cove wastewater treatment plant.

Brite
-
Box
photobioreactor


The study's
photobioreactor
:


300L enclosed fiberglass shell


Media: Wastewater from the 3 separate months previously mentioned.


Sterilized by 40W UV irradiation system (on site) and than pass through a
tangential flow ultrafiltration system (at the lab)


CO
2

was used a buffer incase the pH exceeded the 3 set points.


Carbon dioxide was the only nutrient added to the cultures.


Mixing was provided by aeration by a sterilized air.


A cooling mechanism was also installed if
the temperature exceed 25 C


A titanium heat exchange loop
pumped with cool sea water.

Continuous batch (
Chemostat
)


The Features:


2L vessel


Wastewater from August was only used in the
chemostat
.


Same sterilization as
Photobioreactor
, but was also autoclaved.


pH of
chemostat

was maintained at 7.0 only, and monitored with carbon dioxide.


The
chemostat

was started as a batch reactor first! Once cells were in the late log
phase (day 4) than
chemostat

was started.


The dilution rate was set to 0.94 mL/min.


Once
chemostat

was started, an output for
pumping media out was also turned on.


This is prevent overconsumption of culture
for the system.


Chemostat

was considered to be at a steady
state IF cell biomass measured from output
was consisted for 3 days.


Not greater than 10%.


Temperature was maintained at 21 C by a
circulating water bath


Light was provided continuously from one side by
a bank of fluorescent lights.

Analysis!!


Microalgae growth and biomass analysis:


About 10
-
200mL of culture was taken daily from each culture
and filtered onto on a
preweighed

glass fiber filter (GF filter).


After filtration cells were washed with distilled water and than
freezed

dried overnight in a
lyophilizer
.

Than weighed the next
day.

Specific Growth Rate:

Biomass productivity:

Gas Chromatography used to
analyze fat yields in biomass.

Analysis!! Cont.


Elemental analysis of biomass:


Vario

Microcube

elemental analyzer


Used to calculate elemental C, H, N and S.


Phosophrous

was measured using a
commercial assay.


Samples were
disgested
, cooled with color
developing
regant

added, and than read on a
spectrophotometer at 890nm.


Metal
analysis of
bio
mass using a inductively
coupled plasma
-
mass
spectrometry (ICP
-
MS)


Digesting cells in concentrated
nitric acid and than analysis.

Results/Discussion!


Chemostats

lasted longer however than batch
cultures lasting 12 weeks.

Batch cultures

Chemostats

Results/Discussion!


Batch reaction did have a higher maximum growth rate than the
chemostat

did.
However the
chemostat

had a higher growth productivity.


Both reactors shown complete removal of nitrogen and phosphorus from the
wastewater.


However retention time is higher having the cells intake more of the elements.


Chemostat

was 5 times shorter than the batch cultural.


Fatty acid yields were low as well in both reactors.


However having a high dilution rate could have effected the rate of TAG production.

Batch cultures

Chemostat

Initial concentrations of wastewater

Results/Discussion!

Trace elements were that were also shown to have a significant
uptake as well
.

Problems with study:

1.
Chemostat

and Batch reactor should have been consistent in design and experiments to
compare each other:

1.
The
chemostat

wasn’t tested for all 3 months. It was only tested in the month for
August.

2.
The
chemostat

and the batch reactor needed to be actually the same. What I mean
is that the batch reactor used a aeration system to stir while the
chemostat

used a
stir plate to mix. Small differences can change the data greatly.

2.
For the
chemostat
, it was performed with 7.0
pH.

While in the paper it mentions that
carbon dioxide is best transferred to the cells at pH 6.2 (when it’s higher it’s transferred
as bicarbonate). Since algae are photosynthetic organisms that depend on carbon
dioxide, the
chemostat

should have been set to 6.2 rather than 7.0.

3.
HPLC could have been used instead of GC to measure fatty acids.

1.
A major advantage can be that HPLC operates at ambient temperature so there is
relatively little risk to sensitive functional groups

4.
Try to do a better job at sterilizing their reactors.

1.
Data for the batch reactor might be biased. This is because the reactors were
contaminated with algal grazers.

5.
Low yields of fatty acids or TAGs.

1.
In some studies they suggest that providing environmental stress can create higher
TAGs. There was no form of environmental stress placed on the microalgae.



Work cited

1.
Fresh water life. Web. 3 Dec. 2012.
http://www.freshwaterlife.org/imagearchive/main.php?g2_itemId=1031
5
.

2.
J.T. Sheehan, J.
Dunahay
, J.R.
Benemann
, P.G.
Roessler
, A look back at the
US Department of Energy’s Aquatic Species Program


biodiesel from
algae,
http://www.nrel.gov/biomass/pdfs/24190.pdf 1998
.

3.
Hu,
Qiang
, Milton
Sommerfeld
, Eric Jarvis, Maria
Ghirardi
, and Matthew
Posewitz
. "
Microalgal

triacylglycerols

as
feedstocks

for biofuel
production: perspectives and advances."

The Plant Journal

54.4 (2008):
261
-
693. Web. 3 Dec. 2012
.

4.
Christie, William. "ANALYSIS OF FATTY ACIDS BY HIGH
-
PERFORMANCE
LIQUID CHROMATOGRAPHY."

Lipid Technology

(1997): 124
-
26. Web. 3
Dec. 2012. <http://lipidlibrary.aocs.org/topics/fa_hplc/index.htm
>.

5.
Chen,
Zhuo
,
Yangmin

Gong,
Xiantao

Fang, and
Hanhua

Hu.
"
Scenedesmus

sp. NJ
-
1 isolated from Antarctica: a suitable renewable
lipid source for biodiesel production."

World Journal of Microbiology and
Biotechnology

28.11 (2012): 3219
-
25. Web. 3 Dec. 2012.
<http://link.springer.com/article/10.1007%2Fs11274
-
012
-
1132
-
0>.


But do you have any questions, comments, concerns,
disappointments, or confusion?

Note to self:
Always review a journal article before getting it
approved for a 15 minute presentation! Making sure keywords
of your assigned topic is in the title doesn't mean you've review
it.