MEASUREMENT OF ALGAL GROWTH RATE BETWEEN HARVESTS IN AN
ARTIFICIALLY LIT PHOTOBIOREACTOR UNDER FLUE GAS CONDITIONS
A thesis presented to
the faculty of
the Russ College of Engineering and Technology of Ohio University
In partial fulfillment
of the requirements for the degree
Master of Science
Viral V. Doshi
November 2006
This thesis entitled
MEASUREMENT OF ALGAL GROWTH RATE BETWEEN HARVESTS IN AN
ARTIFICIALLY LIT PHOTOBIOREACTOR UNDER FLUE GAS CONDITIONS
by
VIRAL V. DOSHI
has been approved for
the Department of Chemical and Biomolecular Engineering
and the Russ College of Engineering and Technology by
David J. Bayless
Professor of Mechanical Engineering
Dennis Irwin
Dean, Russ College of Engineering and Technology
Abstract
DOSHI, VIRAL V., M.S., November 2006, Chemical and Biomolecular Engineering
MEASUREMENT OF ALGAL GROWTH RATE BETWEEN HARVESTS IN AN
ARTIFICIALLY LIT PHOTOBIOREACTOR UNDER FLUE GAS CONDITIONS (73
pp.)
Director of Thesis: David J. Bayless
Carbon dioxide (CO2) is now being recognized as a major pollutant in the
atmosphere. Sequestration and utilization are two ways of reducing CO2 from the
atmosphere. The objectives of the research are 1) to show that enhanced practical
photosynthetic
CO2
mitigation
in
a
photobioreactor
using
cyanobacteria
(Chroogloeocystis Siderophila) with periodic harvestings is a sustainable process and 2)
to measure the cyanobacterial (Chroogloeocystis Siderophila) growth rate between
harvests (g × m-2 × day-1) in an artificially lit photobioreactor under flue gas conditions.
I conducted a six week long experiment in the photobioreactor (called as CRF II)
during which I performed four periodic harvestings. The reactor remained in live
condition throughout the test period. After each harvest I observed regrowth on the
harvested portions of the membrane and I quantified the mass of algae from each harvest.
Once the final results showed a decline in algae growth rate, I determined the potential
factors responsible for the decline, investigated the results, and have made
recommendations based on my findings.
Approved:
David J. Bayless
Professor of Mechanical Engineering
Acknowledgments
I would like to express my deepest gratitude toward those who have helped me
throughout this process and have made my research a worthwhile experience.
My sincere thanks to my advisor, Dr. David J. Bayless, who was an excellent
source of guidance, motivation and encouragement in making this research possible.
Many thanks to my thesis committee members: Dr. Gregory Kremer, Dr. Ben Stuart, Dr.
Mike Prudich, Dr. Morgan Vis Chiasson, and Dr. Mark Stoy for their valuable
suggestions, spirited guidance and most importantly, their valuable time during my
research.
I would also like to thank Shyler Switzer and Micah McCreery for their tireless
efforts and help with getting the experimental setup in place. I sincerely thank all my
colleagues and friends for their moral support and motivation.
Last but not least I am grateful to my parents who have been with me in all times
and without whom this would not have been possible.
5
Table of Contents
Abstract ............................................................................................................................... 3
Acknowledgments............................................................................................................... 4
List of Figures ..................................................................................................................... 7
List of Tables ...................................................................................................................... 8
1.
Introduction............................................................................................................. 9
2.
Literature review................................................................................................... 11
2.1
Sequestration of CO2......................................................................................... 11
2.2
Utilization of CO2 ............................................................................................. 13
2.2.1
Chemical fixation of CO2.............................................................................. 13
2.2.2
Technological use of CO2 ............................................................................. 14
2.2.3
Biological use of CO2. .................................................................................. 14
2.2.4
Photosynthetic CO2 fixation ......................................................................... 15
2.3
3.
Uniqueness of research ..................................................................................... 17
Experimental setup................................................................................................ 19
3.1
Gas system. ....................................................................................................... 21
3.2
Lighting system................................................................................................. 23
3.3
Nutrient system ................................................................................................. 25
3.4
Harvesting system............................................................................................. 29
3.5
Data Acquisition (DA) system.......................................................................... 30
3.6
Safety system .................................................................................................... 31
3.7
Procedure for the experimental section............................................................. 32
6
4.
Results................................................................................................................... 35
4.1
Test parameters ................................................................................................. 36
4.1.1
Light intensity ............................................................................................... 36
4.1.2
Gas velocity .................................................................................................. 36
4.1.3
Temperature .................................................................................................. 38
4.1.4
Gas concentration.......................................................................................... 38
4.2
Productivity testing ........................................................................................... 39
4.2.1
Shake down test ............................................................................................ 40
4.2.2
Uncertainty determination test...................................................................... 41
4.2.3
Growth measurements .................................................................................. 41
5.
Conclusions and recommendations....................................................................... 47
6.
References............................................................................................................. 50
7.
Appendix............................................................................................................... 54
7
List of Figures
Figure 2.1: Coupling the Light and Dark Reactions of Photosynthesis.(Todar,2006) ..... 15
Figure 3.1: Front View of CRF II Showing Reactor Chamber, Ducts and DA System. .. 19
Figure 3.2: Back View of CRF II Showing Nutrient System and Harvesting System. .... 20
Figure 3.3: Components of the Photobioreactor Gas Delivery System. ........................... 22
Figure 3.4 (a, b): Solenoid Valve, Two stage Air Line Regulators. ................................. 22
Figure 3.5: Detailed View of Gas System. ....................................................................... 23
Figure 3.6: Light Panels Inside and Outside the Reactor Chamber.................................. 24
Figure 3.7: Ballast and Junction Box................................................................................ 25
Figure 3.8: Nutrient System with Nutrient Tank and Nutrient Pumps. ............................ 26
Figure 3.9: Membrane Assembly with Components. ....................................................... 28
Figure 3.10: Drain Line with Two Drain Valves for the Harvest and Nutrient System. .. 28
Figure 3.11: Harvest System with Harvest Tank, Harvest Pump and High Pressure Lines.
................................................................................................................................... 29
Figure 3.12: Data Acquisition System with the Nova Gas Analyzer (NGA). .................. 31
Figure 4.1: Light Panel Grid. ............................................................................................ 36
Figure 4.2: Top View of Sampling Locations. ................................................................. 37
Figure 4.3: Front View of Sampling Location’s Depth of Membranes............................ 38
Figure 4.4: Flowchart of Testing. ..................................................................................... 39
Figure 4.5: Harvest Yield.................................................................................................. 44
Figure 4.6: Algal Productivity Rate for Harvests ............................................................. 44
Figure 4.7 (a, b): Membranes 1 and 2. ............................................................................. 45
Figure 5.1: Membrane Design. ......................................................................................... 48
8
List of Tables
Table 4.1: Key parameters and their targeted values…………………………………… 35
Table 4.2: Filter weights for harvesting events…………………………...……………...42
Table 4.3: Mass of algae…………………………………………………………………42
Table 4.4: Algal productivity rate………………………………………………………..43
9
1. Introduction
Since energy is necessary for economic growth and development, it can be said
that the progress of a country can be related to its energy consumption. Energy affects
social, economic, and environmental aspects of development (United Nations
Development Program, 2006). It is used in industries for transportation, public use, etc.
With advances in civilization, energy consumption has increased resulting in increases in
the concentration of pollutants. The process of combustion converts coal into energy and
releases flue gases as byproducts of combustion, carbon dioxide being a major
constituent (Raghuvanshi, 2006).
“The ocean waters contain about sixty times more CO2 than the atmosphere”
(Socha, 2006). If the equilibrium were disturbed by externally increasing the
concentration of CO2 in the air, the oceans would absorb more and more CO2. However,
as more CO2 is released, the process of absorption will eventually falter, leaving more
CO2 in the atmosphere. It is inevitable that such a situation would arise as when water
warms, its ability to absorb CO2 is reduced (Socha , 2006).
While CO2 is a good transmitter of sunlight, it partially restricts infrared radiation
from the earth back into space. This process produces the so-called greenhouse effect and
prevents a drastic cooling of the earth during the night. Increasing the amount of CO2 in
the atmosphere reinforces this effect and is expected to result in the warming of the
earth's surface (Socha,2006). “Carbon dioxide emissions are increasing by 4% a year.”
(Miller, 1990).
Average temperature of earth has been rising (Khandekar, 2005). Several factors
10
contribute to this increase in temperature, but Kerr (1999) concluded that the most
significant factor is the emissions of the "greenhouse" gases, the most prevalent being
CO2. While most of today's CO2 emissions come from the burning of fossil fuels, a
significant portion is derived from the loss of forests (Kerr, 1999). CO2 potentially
contriubtes 60% to the greenhouse effect (Raghuvanshi , 2006).
The objectives of this research are
i)
To show that mitigation of CO2 by photosynthesis in a photobioreactor can be
carried out in a sustainable manner with periodic harvestings.
ii)
To measure the algal growth rates (g × m-2 × day-1) between harvests.
In this thesis, Chapter 2 will review relevant literature regarding CO2 control
technologies and photobioreactors. Chapter 3 will give a detailed description of the
experimental setup and the procedure for carrying out the experiment. Discussions of the
test matrix, results, conclusions and recommendations appear in subsequent chapters.
11
2. Literature Review
There are two generally accepted ways to reduce CO2 from the atmosphere:
sequestration and utilization of CO2. This literature review will discuss both the options,
specifically focusing on the application of photobioreactors.
2.1 Sequestration of CO2
Sequestration is the act of removing or separating. Carbon dioxide can be
sequestered in oceans, aquifers, spent gas, or oil wells and deep geological cavities
(Bachu, 2000).
One of the most significant sinks for CO2 disposal provided by nature is the
ocean. The density of seawater at depths greater than 3000 m is less than the density of
CO2, which prevents the CO2 from rising to the top. At such depths, CO2 forms hydrates
or plumes at ocean bottom causing it to sink to further depths. The technology for
disposing CO2 at such depths is evolving (Bachu, 2000). While the use of the ocean as a
disposal site for CO2 is evolving, tides, currents, and ocean processes may be a potential
hindrance for large scale ocean disposal of CO2.
Another potential site for CO2 can be found in geological media. This type of
sequestration is an attractive option in situations for disposal where an ocean is not
readily available. Geological sequestration has two advantages: general public acceptance
and mature technology, the latter has already been developed by the energy industry for
hydrocarbon exploration and production.
Salt caverns are considered a good option for long term CO2 sequestration due to
12
their large storage capacity and because the technology for sequestration has long been
established. Disadvantages include the high cost associated with the sequestration
operation and environmental problems with cavern mining, i.e. rock and brine disposal
(Dusseault, 2001).
Enhanced oil recovery (EOR) operation is already a viable option for CO2
sequestration. CO2 is often used as a medium to displace residual oil in reservoirs. CO2
dissolves in the oil reducing the oil viscosity and thus helps in the extraction of oil. Since
the infrastructure is already present, oil reservoirs are often considered as a good
sequestration option. The aim with the EOR operation is to use as little CO2 as possible
per barrel of oil extracted (Kovscek, 2005).
Carbon dioxide can be adsorbed on coal. When CO2 is injected in the coal bed, it
will adsorb on the coal and displace methane, which can then be easily removed and used
as a fuel. Methane is also a greenhouse gas but is a much cleaner fuel than coal. Though
the adsorption data of CO2 on coal is not widespread, published data shows that CO2 has
higher affinity on coal as compared to methane with the ratio of 2:1 (Gluskoter, 2002).
Deep saline aquifers contain salt water, which is not fit for drinking or agricultural
use. The storage capacity of deep saline aquifers and their availability near power plants
make it a good candidate for CO2 sequestration. It is estimated that CO2 will dissolve and
form rocks giving advantage of permanence. Estimates suggest that all the CO2 emitted
could be sequestered in these saline aquifers until 2050 (Haszeldine, 2005). To store CO2
in the supercritical phase, it needs to be subjected to high pressures. The depth of
aquifers provides enough pressure for CO2 to remain in the supercritical state
(Haszeldine, 2005). As the temperature and pressure are increased along the liquid/gas
13
line, at one point both the phases become identical and this point is called the critical
point. Above this point, carbon dioxide exists in supercritical state (Greener Industry,
2006). But technical assessment of these aquifers need to be done to determine the
solubility of CO2 and the potential reactions between supercritical CO2 and other fluids
present in the aquifer before any sequestration can be attempted.
All of the above listed processes mainly store CO2, trapping the gas in oceans,
geological formation such as deep saline aquifers, salt caverns, oil reservoirs, etc. A good
alternative to disposal is utilization of CO2. “In general, utilization rises a double
beneficial effect, as per each atom of carbon that is recycled, at least one atom is saved as
natural resources.” (Aresta, 1999).
2.2 Utilization of CO2
Chemical fixation, technological use and biological use are the three different
ways in which CO2 can be utilized. In this next section, I will exam each of the utilization
options in detail.
2.2.1
Chemical fixation of CO2
The use of CO2 for reactions can be divided into two classes: the first one in which
the –COO – segment is maintained, e.g. esters, ureas, lactones and the second in which
the molecule is reduced to C1 molecules like HCOOH, CO, etc (Aresta, 1999). Due to
such reactions, the industrial utilization of CO2 has been in place for more than a century.
Industries such as pharmaceutical and other chemical processing industries have started
using CO2 as a less toxic alternative when compared to more traditional solvents, e.g. dry
cleaners or the synthesis of methanol as an additive to CO. The only factor that makes the
14
use of CO2 as a chemical fixation agent questionable is the amount of energy needed for
its conversion (Aresta, 1999).
2.2.2
Technological use of CO2
The use of CO2 without any molecular conversion, is considered technological
and can be used in such areas as refrigeration, cooling, food packaging, soldering, in
beverages, and so forth (Aresta, 1999). CO2 is often classified based on its state as either
a solid, liquid, or gas. Solid CO2, known as dry ice, is used in the food industry for
storage and transportation of ice cream and frozen foods. CO2 in a gaseous state is
typically used in soft drinks and soda water. In a gaseous state, CO2 can also be used in
life jackets, fire extinguishers and for creating an atmosphere for welding (Wikipedia,
2006). Liquid CO2 is a good solvent for many organic compounds. Because of this, CO2
is also being considered by the industries that specalise in dyeing and polymerization
reactions. The major barrier to technological use of CO2 is the cost and maintenance of
equipment. Cheaper technological development is the key to expanded use of
supercritical CO2 (Aresta, 1999).
2.2.3
Biological use of CO2.
Another potential use for CO2 can be found in biological use. One such method is
to utilize sunlight to convert the CO2 to biomass, then reuse the resulting biomass as an
alternative to fossil fuels such as fuel (biodiesel, hydrogen) or cattle feed (Herzog, 1996).
Biological use includes biomass of terrestrial plants, algae or halophytes. The amount of
CO2 fixed per time by terrestrial plants it consistently lowers than that of industrial
emissions. A more time and cost effective alternative to terrestrial plants is algae since
15
they typically have much higher fixation efficiency under natural conditions (Aresta,
1999).
2.2.4
Photosynthetic CO2 fixation
Carbon dioxide fixation in nature occurs through the process of photosynthesis.
Photosynthesis is the physio-chemical process by which photosynthetic organisms use
light energy to drive the synthesis of organic compounds. It is carried out by plants, algae
and photosynthetic bacteria. The schematic diagram below explains the process of CO2
fixation.
X: Ferredoxin , e- - electron
Figure 2.1: Coupling the Light and Dark Reactions of Photosynthesis.(Todar,2006)
Photosynthesis is a form of metabolism divided into light and dark reactions. The
light reactions help in the formation of ATP and NADH, which in turn are used to form
cell carbon from CO2 by the dark reactions (Raven, 1999). Hence photosynthesis results
16
in the consumption of CO2 and production of carbohydrates and molecular oxygen. Some
types of bacteria use anoxygenic photosynthesis to synthesize organic CO2 without the
production of molecular oxygen. The general photosynthesis reaction is given by
(Raven, 1999).
CO2 + 3ATP + 2NADPH2 ----------> CH2O + 2ADP + 2Pi + 2NADP
(2.1)
The photosynthetic reaction process by rooted plants is too slow to significantly
offset the point source emissions of CO2 within a localized area (Miguel, 2001). Algae
have been identified as fast growing species whose carbon fixing rates are higher than
plants. By increasing the CO2 concentration in an aqueous environment, the production of
micro algae can be dramatically increased (Ormerod, 1995). Engineering units that
operate on this principle are called photobioreactors (PBR), where high CO2
concentration is utilized by the algae to grow.
PBRs can be classified into two types: open and closed systems (Pulz, 2001).
Outdoor ponds are an example of open type PBR, but have the disadvantage of having no
control over process parameters and contamination caused by other microorganisms.
However, closed system overcomes these disadvantages by offering precise control over
the process parameters with no intrusion by other microalgae. Additional advantages of a
closed system include the option of being at the source of emission. PBRs can be
modified as per the source requirements. The utilization of CO2 is performed by the algae
with human control over the process parameters (Pulz, 2001).
Though outwardly the start-up of open ponds appear inexpensive and the start-up
cost of photobioreactors is often higher, in the long run the efficiency and higher yields
found in photobioreactors offset the initial costs. (Pulz, 2001).
17
Biological CO2 fixation can take on many forms. Such forms include the flue gas
generated from industry containing a high concentration of CO2 passed to a PBR. In this
situation, precultured microorganisms absorb the CO2 from the flue gas and grow. The
flue gas free from CO2 can then be discharged into the atmosphere or sent for further
processing. The biomass produced in the PBR has multiple uses. It can be used to
produce fine chemicals, as manure feed but the most attractive option is the use of
cyanobacteria as fuels, one of the most useful being hydrogen.(Yoon, 2002)
Hydrogen is generated by the enzyme nitrogenase. Reductants are required to
support the nitrogenase activity. The degradation of fixed CO2 generates reductant for
nitrogenase and hence hydrogen production. (Yoon, 2002)
The researchers (Yoon, 2002) have suggested a two phase hydrogen productionCO2 uptake operation.
Phase 1
CO2 uptake
Phase 2
Cellular sub
Cells cultured
H2 production
(2.2)
cells used
In the first stage, the cells produce cellular substance by taking CO2 from the
atmosphere. In the second stage, degradation of cellular substance takes place generating
the reductant, required by the nitrogenase enzyme, which then produces hydrogen,
thereby completing the process.
2.3 Uniqueness of research
“Despite the large body of research in the area of photosynthesis for carbon
sequestration, little work has been done to create a practical system, one that could be
used with both old and new fossil generating units” (Bayless, 2001).
18
“The scale-up of simple closed container based systems as first generation of
closed PBRs was soon faced with serious limitations.”(Pulz, 2001). In addition to scaling
up the simple closed container based systems, these systems should be tested for their
potential productivity.
At the Ohio Coal Research Center, efforts have been made to construct bench
scale PBR that will be tested for its potential productivity on a continuous basis using a
special cyanobacteria “Chroogloeocystis Siderophila. ” Periodic harvesting will be done
to show that mitigation of CO2 by photosynthesis in a PBR using cyanobacteria is a
sustainable process.
Dr. Keith Cooksey and Dr. Igor Brown isolated 36 primary samples of
cyanobacteria from thermal springs inside and outside Yellowstone National Park and
selected special strain “Chroogloeocystis Siderophila” based on the environment in
which it grew. This environment was similar to the flue gas conditions that would be
encountered in the photobioreactor.
The testing of the scaled up PBR for its potential productivity with special
cyanobacteria under flue gas conditions makes this research unique.
19
3. Experimental Setup
The photobioreactor, known as Carbon Remediation Facility (CRF II), located in
015, Stocker Center, is designed for the CO2 sequestration.
Transition
Reactor Chamber
Circulation Duct
DA system
Figure 3.1: Front View of CRF II showing Reactor Chamber, Ducts and DA System.
The CRF II is 8 feet long, 4 feet wide and 7 feet tall. It consists of a reaction
chamber in the center in which the algae grow as shown in Figure 3.1. Attached to the
reaction chamber on both sides is the circulation duct. It is a flexible duct insulated to
prevent heat loss. The transition piece on both sides ensures smooth transition of gas flow
between the reactor and the duct. The circulation fan, burner and the fin strip heater are at
the bottom of the reactor in the duct. On the right is the data acquisition (DA) system.
20
Located on the other side of the CRFII are the nutrient and harvesting system. The
nutrient system is comprised of the nutrient tank, the nutrient pump, and the flowmeters.
The harvest system includes the harvest tank, the harvest pump, and the high pressure
lines as shown in Figure 3.2.
Harvest Pump
Harvest tank
Nutrient Tank
Nutrient pumps
Figure 3.2: Back View of CRF II showing Nutrient System and Harvesting System.
The reaction chamber is framed with iron, and the lexan sheets form the walls and
top cover of the chamber. Lexan sheet is a strong polymer that can withstand the reactor
temperature, pressure and is inert to the flue gas. Since it is transparent it does not
obstruct light from the outside light panel to the growth surface. To access the reaction
chamber, an opening at the top is provided. This opening aids in normal operation as well
as maintenance of the reactor. A gasket ring has been glued at the top of the reaction
chamber to fill the gap that is created when the top lid is bolted to the reaction chamber.
The control panel consists of two main boxes as shown in Figure 3.3. One box of
the control panel contains an on/off switch for the pump, immersion heater for the
nutrient tank, thermostat for the fin strip heater, the timer switch for the light panels
21
inside the reactor chamber, and fan regulator. The other box of the control panel contains
a timer switch for the outside panel and an on/off switch for all four individual light
panels. Above the control panel are rotameters for gas and air. Maintaining the correct
air/gas ratio is essential for efficient combustion of the gas.
The following is a detailed description of each CRFII system:
3.1 Gas system.
Carbon dioxide is generally created by the combustion of natural gas. The CRFII
system recirculates the by products of combustion into the reactor. A natural gas burner is
used to combust the gas and create CO2. The gas delivery system serves two purposes:
supplying CO2 rich gas to the cyanobacteria and maintaining the temperature of reactor
chamber at 122°F (50°C).
The gas delivery system consists of a fan, Bunsen burner, residential control
valve, and compressed air and natural gas lines delivering the respective gases to the
burner. Three snap disks, the solenoid valve, and the pressure regulators form the safety
circuit. Two snap disks are placed on the duct and the third is placed on the gas line. The
lexan access panel provides easy access to the burner.
22
Air & Gas
Rotameter
Control panel
Gas line
Burner
Fan
Residential Gas
Valve
Figure 3.3: Components of the Photobioreactor Gas Delivery System.
The burner is fed a mixture of natural gas and air (50% excess of the
stoichiometric amount) and can be varied with the help of rotameters. The air supply line
contains two stage pressure regulators shown in Figure 3.4. The pressure is reduced to 40
psig in the first stage and 20 psig in the second stage. Air then passes through the
rotameter and is introduced in the gas line between the gas control valve and the burner.
To create a uniform mixture, the pipe contains a thin spiral strip of metal. This strip spins
with the flow of air and gas thus creating a uniform mixture. The fan mixes the hot and
the cold gas and maintains flow through the reactor chamber.
a)
b)
Figure 3.4 (a, b): Solenoid Valve, Two stage Air Line Regulators.
23
Between the rotameter and the burner is placed a residential gas control valve.
The gas control valve allows the gas supply to the burner when the thermocouple
attached to the burner is hot. The thermocouple is placed next to the burner as shown in
the Figure 3.5. The natural gas line also contains a solenoid valve, which will shut off in
case of an emergency.
Gas line
Air line
Bunsen burner
Residential Gas Valve
Thermocouple
Snap disk
Figure 3.5: Detailed View of Gas System.
3.2 Lighting system.
The lighting system of a PBR plays a vital role in the growth of cyanobacteria.
Figure 3.6 shows the lighting system of CRFII.
24
Inside panels
Membranes
Outside panels
Figure 3.6: Light Panels Inside and Outside the Reactor Chamber.
The CRFII has four light panels, two on the outside of the reaction chamber and
two on the inside of the reactor chamber. Each light panel provides light to one side of
the membranes with cyanobacteria. The distance from the membrane surface to the light
panel is approximately 4 inches. Each light panel is made up of six high intensity light
bulbs. One ballast is needed for two light bulbs therefore the bulbs are wired in pairs. The
number of light bulbs used during the normal operation is determined by the shake down
test. The main control panel contains two timer switches - one for the outside panels and
one for the inside panels along as well as the switch for each light panel. The timer switch
can be set so the lights are on for the desired number of hours. The ballast box at the
bottom contains all the ballast for the four light panels. It also contains a cooling fan used
to cool the ballasts during normal operation. There are three junction boxes, one above
the rotameters and two on the right side shown in Figure 3.7. The wires to the light panels
from the ballast box pass through the junction box.
25
Junction Box 2
Junction Box 1
Junction Box 3
Ballast Box
Figure 3.7: Ballast and Junction Box.
All the light panels have been glued with high temperature silicon sealant so that they are
air and water tight. The sides of the light panel are made of plexi glass, whose mechanical
properties are best suited for this system.
3.3 Nutrient system
The nutrient system disperses the cyanobacteria to the membranes (growth
surfaces) and also provides nutrients (BG 11 growth media) to the cyanobacteria growing
on the surfaces. The nutrient system is comprised of the nutrient tank, nutrient pumps,
rotameters and the membrane seen in Figures 3.8 and 3.9.
26
Transformer
Rotameters
Nutrient Tank
Nutrient Pumps
Figure 3.8: Nutrient System with Nutrient Tank and Nutrient Pumps.
The nutrient tank is connected to the nutrient pumps, which deliver the
cyanobacteria and nutrient solution to the membranes. The three rotameters are placed
between the pumps and the membranes help maintain the desired flowrate onto the
membrane surfaces. During normal operation, the nutrient tank is filled with the required
quantity of cyanobacteria in liquid solution and topped off with nutrient solution until it
reaches the desired level. Two pumps are utilized for circulation with the third pump used
as a standby pump. The standby pump is used in case of pump failure due to excessive
running time. If any of the working pumps fail, the pressure switch mounted on the pump
outlet automatically switches to the standby pump thus maintaining the required flowrate.
Diaphragm pumps are used instead of centrifugal pump because impellers found in
27
centrifugal pump can rupture the cyanobacterial cells. The set point for the pressure
switch is 10 psi. The transformer is located on top of the rotameters and it controls the
speed of the pump. The transformer and the rotameters help to maintain the required
flowrate to the headers.
The nutrient solution temperature (122°F) is maintained by an immersion heater
fitted onto the nutrient tank. The immersion heater contains an inbuilt thermostat that
helps to maintain the desired temperature. The nutrient solution is maintained at 122°F.
The cyanobacteria used in this PBR have been cultivated in the laboratory, on the
surface of large tanks. In the PBR these cyanobacteria are also grown on a surface, but
this surface is Omnisil 1000 fabric. The omnisil membrane is stitched with two loops, one
at the top and other at the bottom as shown in Figure 3.9. The membrane has been dried
and weighed prior to assembling the membrane with the frame to quantify cyanobacterial
growth at the end of the experiment. The top loop slides into the shim of a header pipe
with the help of stainless steel rod. A rectangular stainless steel bar is inserted in the
bottom loop and the membrane is pulled tightly with the help of springs, which are
attached to the rectangular bar and frame.
The header is a specially fabricated stainless steel pipe, 2 feet long and 2 inches in
diameter with an opening at the top to allow the nutrient solution to flow into the header.
Two openings on the header pipe and a small opening in the middle of header are
provided for the nutrient solution. Two larger openings are also available for greater
harvest liquid volume as shown in Figure 3.9. The header is sealed on both the ends with
a plate and gasket to make the fitting leak tight. The nutrient solution flows on a pressure
28
shim placed inside the header. This shim distributes the nutrient evenly on both the sides
of the membrane.
Nutrient inlet
Harvest inlet
End plate
Header pipe
Omnisil growth surface
Gasket
Rectangular rod
SS rod
Spring
Pressure shim
Frame
Figure 3.9: Membrane Assembly with Components.
The nutrient solution flows over the membrane surface and drains from the
bottom of the reaction chamber into the nutrient tank. There are three drain holes through
which the water from the chamber is collected. The drain line is used for both the nutrient
and harvest systems. Two valves shown in Figure 3.10 on the drain line switch between
the nutrient and the harvest tank.
Drain Valve for
Drain Valve for
Harvest Tank
Drain points
Figure 3.10: Drain line with Two Drain Valves for the Harvest and Nutrient System.
29
3.4 Harvesting system
Harvesting is the removal of excess cyanobacteria from the growth surface. The
harvesting system is comprised of the harvest tank, the harvest pump, and the high
pressure lines seen shown in Figure 3.11. The Reverse Osmosis (RO) water from the
harvest tank is pumped through the harvest lines at higher pressure and flowrate over the
membranes than during normal operation and is carried back to the harvest tank through
the drain line. During harvesting, the nutrient drain valve is closed and the harvest drain
valve is opened. The force created by high pressure and flowrate shears off some of the
cyanobacteria not tightly adhered to the membrane surface. These organisms are
collected using 100 µm and 0.5 µm filters for weight measurement and further analysis.
Harvest pump
High
Valves for the
membranes
pressure
lines
Harvest Tank
Figure 3.11: Harvest System with Harvest Tank, Harvest Pump and High Pressure Lines.
The setup of the harvest system consists of a conical bottom harvest tank attached
to the harvest pump. The conical bottom does not allow the algae to settle down in the
tank and thus helps to keep the algae in circulation. The outlet line from the pump is
30
divided into two parts. The first part is the filter line which passes through the filters.
The other line, which does not pass through the filters, is called the filter bypass line. The
filter bypass line goes back to the harvest tank. The flow is distributed between the
bypass filter line and the filter line to keep the desired flowrate and pressure throughout
the filter line. The filter line is distributed to all the membranes with valves on each line
as seen in Figure 3.11. During harvesting, only the valve of the membrane being
harvested remains open.
3.5 Data Acquisition (DA) system.
The DA system is located next to the reactor. The DA system not only records
data from the PBR but also serves as a crucial component of the safety system. This
system is comprised of the DA panel, Nova Gas Analyzer (NGA), and a computer to log
the data. The sampling port on the right transition piece is connected to the NGA with the
help of stainless steel piping as shown in Figure 3.12. The NGA continuously monitors
gas from the burner and has a display for CO, CO2 and O2. The NGA is connected to the
DA system to maintain a log of all the process parameters.
31
Sampling point
DA rack
Nova Gas Analyzer
DA Computer
Baldwin Condenser
Figure 3.12: Data Acquisition System with the Nova Gas Analyzer (NGA).
The DA panel has provision for the following type of inputs
i)
Li-Cor sensors to measure light intensity
ii)
Thermocouple inputs to measure temperature
iii)
Channels to connect the Nova GA
iv)
Relay for the safety circuit.
The DA panel has an interface, which connects it to the computer. LABVIEW
software is used to monitor and record data and displays the CO level. The CO level is
monitored with a bar while the CO2, O2, and temperature levels are displayed using
graphs. A light is activated when data is being acquired. A separate panel has an alarm
light which is activated when the CO level exceeds the set level. A stop button can be
used to terminate acquisition of further data when necessary.
3.6 Safety system
The solenoid valve, snap disks, and the DA system along with the Nova Gas
Analyzer form the safety system. The solenoid valve is an electrically actuated valve. The
32
electrical coil inside the valve generates a magnetic field when powered. This magnetic
field pulls the valve pin and the valve allows the fluid pass through it. When the power
supply is stopped, the solenoid valve pin drops and the valve closes.
The snap disk is a heat sensitive device and if exposed to excessive temperature,
the snap disk breaks the electrical circuit.
The Nova Gas Analyzer is a portable instrument that takes samples from a gas
stream and measures the amount of CO2, CO and O2 in the gas. Samples are drawn from
the gas stream into the analyzer through a series of filters by a built-in vacuum pump.
NGA uses an infrared detector for CO2 and electrochemical sensors for O2 and CO. It has
a display unit which indicates the levels of all three gases. Electrical signals are sent from
the analyzer to the DA system.
The safety system operates as follows: when CO level rises above the set point,
the DA system stops power to the solenoid valve, thus closing the supply of the gas to the
burner. The flame extinguishes, immediately stopping the increase in the CO. At the
same time, the thermocouple in front of the burner gets cold due to the absence of the
flame and the residential control valve stops the supply of gas. With this system, the CO
level remains within the allowable limit and the flow of gas is stopped completely.
3.7 Procedure for the experimental section.
The procedure consists of two parts: a) pretest and b) main experiment.
a) Pretest: Different components of the reactor such the burner, fan, safety system, etc.
are tested during this phase. This is followed by fixing the various parameters like the
light intensity, velocity, gas concentrations, and the temperature.
33
i)
Light intensity - Light panels have six bulbs and a maximum light intensity of 180
µmoles. The light intensity can be varied by having 2, 4 or 6 bulbs operating at
any given time. Once the target range is reached, the light profile is made. If the
light distribution is uniform and the values within the profile meet the criteria as
per the test plan, then the required setting for the light intensity is achieved.
Otherwise, the procedure is repeated by switching on a different combination of
light bulbs.
ii) Velocity - The velocity can be varied with the help of variable speed control
located on the control panel. The velocity profile is made by measuring velocity at
12 different locations and at two separate depths. If the gas velocity values within
the profile meet the criteria as per the test plan, the required setting for the gas
velocity is achieved. Otherwise, the procedure is repeated by changing the speed
of the circulation fan.
iii) Gas - The gas concentration is measured with the NGA. The gas concentrations
can be changed with the help of air and gas rotameters. The reactor is checked
thoroughly prior to the experiment to ensure that there are no gas leaks.
iv) Temperature - Temperature of the nutrient solution is maintained with the help of
the immersion heater and can be adjusted with the help of a knob located on the
immersion heater.
After all the parameters are set, the reactor is observed for a week. During that
time, all parameters are observed and recorded. If the parameters are in the targeted
range, then the main experiment is started. In the case of any deviation, the parameter
is re-tested and changes are made until the targeted values are achieved.
34
b) Main experiment: After the pre test is completed, the membranes are stitched,
weighed, and loaded onto the frame work. All three membranes are placed in the
reactor, the nutrient tank is loaded with RO water, and the reactor is started. The
parameters are monitored for a full day to ensure that they are at their target values.
If the parameters are at their target values, the algae is loaded in the nutrient tank.
As the nutrient solution flows over the membrane, the cyanobacteria adhere to the
surface and begin grow. The initial growth period is around fourteen to sixteen days.
Once the initial growth period is complete, the first harvest is carried out. After the first
harvest, a second growth period lasting eight to ten days is completed followed by a
second harvesting. The cycle of growth period and harvesting continues depending on the
number of harvests determined in the test plan. This process is the normal operating
procedure of the photobioreactor (Refer Appendix F for detailed procedure).
35
4. Results
The first objective of this research is to show that enhanced practical
photosynthetic
CO2
mitigation
in
a
photobioreactor
using
cyanobacteria
(Chroogloeocystis Siderophila) with periodic harvesting is a sustainable process.
The second objective is to measure the cyanobacterial (Chroogloeocystis Siderophila)
growth rate per unit area between harvests (g/m2/day) in an artificially lit photobioreactor
under flue gas conditions. These objectives can be achieved by completing periodic
harvests in a sustainable manner and measuring the cyanobacterial growth rates between
harvests.
Testing consisted of four phases: Initial loading phase, growth phase, harvesting
during operation, and final harvesting. Before the first phase, the reactor needed to
achieve a steady state. Steady state is characterized by the key parameters reaching the
target values as listed in Table 1.
Table 4.1: Key parameters and their target values
Parameters
Target Value
Light intensity
Gas velocity
50 - 100 µmols
> 0.4 m/s
Temperature
Nutrient solution
Reaction Chamber
50 ± 5 °C
CO concentration
CO2 concentration
<40 ppm
8 - 10 %
36
4.1 Test parameters
4.1.1
Light intensity
The light intensity in the bioreactor was established in the range 50 to 100
µmols/m2/sec. I selected this range because the cyanobacterial strain doubles in a period
of 8 h at 48µmols (Brown, 2005). A grid of eight points by three points seen in Figure 4.1
was chosen to measure the light levels on each side of the membrane. As the light panels
inside the reactor were not obstructed, 90% of the values in the light profile needed be in
the specified range. When testing the outside panels, the specific range of values needed
to be adjusted to 70% as some parts of the light panels were obstructed.
Figure 4.1: Light Panel Grid.
Light levels were measured before and after the test run to ensure they satisfied
the previously mentioned criteria. (Refer to Appendix A) Since the light levels were
maintained within the targeted range throughout the test, the effect of variation in light
levels on the growth efficiency was assumed to be negligible.
4.1.2
Gas velocity
The gas velocity in the reactor was targeted to be 1m/s for simulation of flue gas
conditions. The minimum value of the velocity was set to 0.4 m/s to ensure the absence
37
of any dead zones in the reaction chamber, because the gas flow was parallel to the
membranes. A gas velocity profile was made before and after the test by measuring the
gas velocity with the help of pitot tube at twelve points across the cross section as shown
in Figure 4.2 and at two different depths as shown in Figure 4.3. The measurements were
used to ensure that the gas velocity remained constant throughout the test (Refer to
Appendix B). Since the gas velocity was kept constant throughout the test, the effect of
velocity fluctuations on cyaonbacterial growth was assumed to be negligible.
Front Edge
1
7
2
8
3
9
4
10
5
11
6
12
Reference
Figure 4.2: Top View of Sampling Locations.
38
Side of
reactor
8” depth
14” depth
Bottom
of reactor
Figure 4.3: Front View of Sampling Location’s Depth of Membranes.
4.1.3
Temperature
The natural habitat temperature of the thermophilic bacteria is 50°C-55°C
(Brown, 2005). Because of this, it is important that the temperature in the reactor is
maintained at 50°C ± 5°C. A temperature profile was made by measuring temperature at
the same points where velocity measurement was completed. (Refer to Appendix C)
Temperature was continuously monitored and maintained at the desired value throughout
the test. Variation in this parameter will not affect the test results.
4.1.4
Gas concentration
Carbon dioxide concentration in the stack gas from a typical power plant is 12 %
and hence maintaining concentration of CO2 greater than 10% in the reaction chamber
was desirable. CO, which is produced as a result of incomplete combustion, inhibits the
39
cyanobacterial growth when its concentration exceeds 60 ppm. Because of this, the
concentration of CO at all times should not exceed 40 ppm. To ensure that the CO did not
exceed 40 ppm, CO2, CO and O2 were constantly measured during the test by the Nova
Gas analyzer (see section 3.5) and these data were recorded on the computer. Throughout
the experiment, CO2 was maintained in the range of 8% to 10% and CO below 40 ppm.
4.2 Productivity testing
In order to quantify the amount of cyanobacteria (Chroogloeocystis Siderophila)
that can be grown per unit area per unit time in the CRFII bioreactor, a test, consisting of
multiple periodic harvests was performed. The sequence of phases that took place during
the productivity test is shown in Figure 4.4.
Uncertainty
Determination Test
Shake Down Test
15 to 20
days
Initial Loading
8 to 10 days
First Harvest
8 to 10 days
Second Harvest
8 to 10 days
Third Harvest
8 to 10 days
Fourth Harvest
Figure 4.4: Flowchart of Testing.
40
The experiment was carried out for a period of six to eight weeks and began with
the initial loading of the algae followed by an initial growth period lasting fourteen to
sixteen days. Once algal growth was observed on the membranes as determined optically
by Dr. Vis, the first harvest was carried out. It took around eight to ten days before the
next harvest was performed. Once the time period for the second harvest had been
determined, then the same time interval was followed for all other harvesting events in
this experiment.
4.2.1
Shake down test
To achieve the desired values of the parameters found in Table 4.1, these
parameters were measured with the current setup and then changes were made e.g. flow
directors, light diffusers, and so on to adjust the values into the desired range. The test
also included setting the proper air / fuel ratio for the burner, setting the temperature on
the immersion heater, and establishing a nutrient flow rate to achieve uniform flow from
the headers on the membrane surface. All these settings were necessary to achieve the
desired steady state in the reaction chamber.
To ensure that the values of the velocity and temperature profile were repeatable
and representative of the actual conditions in the reactor, five random points from the
velocity/temperature profile were measured again. Light and velocity profiles were made
before and after the test to ensure that these parameters remained within the targeted
range throughout the duration of the test.
41
4.2.2
Uncertainty determination test
When the cyanobacteria was initially loaded in the reactor, a sample of slurry was
collected along with the initial loading and the mass in the sample was determined. Based
on this mass, the total initial loading mass was estimated for the experiment. To find the
uncertainty associated with this approximation, a separate test was carried out. This test
consisted of withdrawing five samples from the algae cultural tank and running each
sample through the harvesting operation. This harvesting operation replicated the actual
harvesting operation. All these samples were run consecutively to ensure that each
sample was subjected to the same conditions. Uncertainty associated with the operation is
±14 % using the t test method (For the detailed calculations refer to Appendix A).
4.2.3
Growth Measurements
Algal productivity between harvesting events was measured during a six week
test. During that time, all the test parameters were maintained in their determine ranges.
Regrowth on the membranes was observed after each harvest. 17 g ± 2.4 g of algae was
initially loaded. A net 30 g of algae was obtained at the end of the test, suggesting that the
algae doubled over the course of the experiment.
No attempt was made to find an overall productivity rate. This is due to some of the algae
building up and becoming embedded in the header assembly. Four periodic harvestings
were carried out. The duration between each harvest was one week. To quantify the mass
of algae harvested, the following measurements were made: initial weight of coarse filter
and fine filter (predried in the oven for seven days), initial weight of whatman filter
paper, final weight of coarse filter and fine filter (after they dried in oven for seven days),
42
and final weight of whatman filter paper. Whatman filter paper was used to filter out the
residual algae in the filter casings. Table 4.2 shows the values of the filters during each
harvest.
Table 4.2: Filter weights for harvesting events.
Harvest 1
Harvest 2
Harvest 3
Harvest 4
Initial weight (g) Final weight (g) of Initial weight
of filters
filters
(g) of
whatman
filter
CF
FF
CF
FF
332.24
393.18
334.74
395.27
3.12
322.19
387.47
323.56
388.43
3.15
328.99
395.59
329.67
396.27
3.17
325.47
392.75
326.11
393.35
3.09
Final weight
(g) of
whatman
filter
3.16
3.19
3.2
3.12
The mass of algae was determined by adding the net weight of the coarse filter,
fine filter, and Whatman filter. The net weight of the various filters was found by
subtracting the initial weight of the filter from the final weight of the filter as shown in
Equation 4.1 below:
Mass of algae = Net weight of coarse filter + net weight of fine filter +
net weight of Whatman filter paper
(4.1)
Table 4.3 below shows the net weight of the various filters and the mass of algae during
each harvest.
Table 4.3: Mass of algae
Harvest 1
Harvest 2
Harvest 3
Harvest 4
Net wt (g) on Net wt (g) on Net wt (g) on
Coarse filter
Fine filter
Whatman filter
2.5
2.09
0.04
1.39
0.96
0.04
0.68
0.68
0.03
0.67
0.6
0.03
Mass
of
algae (g)
4.63
2.37
1.39
1.27
43
To determine algal growth rate, mass of algae (g) obtained during each harvest
was divided by the growth surface area (m2) and the time (days) between the harvests.
Algal growth rate between initial loading and harvest can be found using Equation 4.2
Growth Rate
=
Mass of algae
(4.2)
Surface area × Time
Table 4.4 below shows the calculated algae productivity rate.
Table 4.4: Algal productivity rate
Initial loading and First Harvest
First Harvest and Second Harvest
Second Harvest and Third Harvest
Third Harvest and Fourth Harvest
Algal productivity rate (g × m-2
× day-1)
0.59
0.61
0.36
0.33
Figure 4.5 shows the harvest yield for the experiment. Figure 4.6 shows a plot of
algal growth rate versus the harvesting event. The first harvest was performed fourteen
days after the cyanobacteria were initially loaded into the reactor. The second, third and
fourth harvests were carried out at interval of seven days after their previous harvests.
The growth rate can be calculated assuming that the harvested mass is equal to the new
growth since the last harvest. A decreasing trend is observed in both the measured yield
and the calculated growth rate after the second harvest. The potential factors for the
decreasing trend after the second harvest are the non-uniform flow of the growth solution
over the membranes during the growth stage and the highly variable flow during the
harvesting operation.
44
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Harvest 1
Harvest 2
Harvest 3
Harvest 4
Harvests
Figure 4.5: Harvest Yield
Algal Productivity Rate for Harvests
0.7
Algal productivity rate(g*m-2*day-1)
Mass of algae(grams)
Harvest Yield
0.6
0.5
0.4
0.3
0.2
0.1
0
Harvest 1
Harvest 2
Harvest 3
Harvest 4
Figure 4.6: Algal Productivity Rate for Harvests.
45
Figure 4.7 shows that while certain parts of the membranes populated very well,
some surfaces had no growth at all. The membrane in Figure 4.7(a) is very well
populated particularly on the sides and the bottom. The area between the ends had a
channelized flow with the algae density higher in the center. The membrane in Figure
4.7(b) has growth only in the center of the membrane.
Good harvest area
Highly populated areas
that
couldn’t
be
harvested
a) Membrane 1 side 1
Algae growing only in
the center of the
membrane
b) Membrane 2 side 1
Figure 4.7 (a, b): Membranes 1 and 2.
During harvesting, the high pressure flow did not extend to the ends of the
membrane to harvest the algae with high density. Good harvesting was observed below
46
the two portions from where the harvest flow entered the header and was distributed
throughout the header. The harvesting flow did not spread evenly through the membrane
leaving the algae in the center portion unharvested. The two portions below the
harvesting port inlets shows good harvesting and regrowth after each harvest as seen in
Figure 4.7(a).
Scotch tape was used to ensure that the omnisil fibers remained intact during and
after stitching each membrane. The portion that had the tape remained void of algae. The
stitch with the tape at the top of the membrane posed problems during harvesting. Jets
formed at the stitch and the area below the stitch could not be harvested effectively. On
some areas of the membranes, the jets hit the reactor chamber walls and reflected back on
the membrane. Those portions of the membrane showed harvesting.
As seen from the results, there was an uneven growth of algae on the membranes.
After the test, it was found that all the membranes had a good amount of algae on the
portion of the membrane that remained inside the header. This algae remained unexposed
to the light. After a few hours of the initial loading operation, the nutrient solution
became a clear liquid. But it is difficult to predict the amount of the algae that was
exposed to the light as some of the algae was found in the header, some circulating with
the nutrient liquid, and some at the bottom of the reactor chamber. It is therefore not
possible to calculate the overall algal productivity rate for this experiment. The harvested
algae could be from any of these areas and it is not recommended to report such algal
growth values per area of the growth surface.
47
5. Conclusions and Recommendations
The first objective of this research was to investigate whether periodic harvestings
can be performed in a photobioreactor in a sustainable manner. A six week long
experiment was carried out and four periodic harvestings were done successfully
completing the first objective of the research was completed.
The second objective of the research was to determine the algal growth rate
during each harvest. This was completed successfully and the values indicate a decline in
the harvest yield. A number of factors that possibly contribute to the declining trend in
the harvest yield are as described below.
The results of the experiment showed that the distribution of algae on the
membrane during the experiment was not uniform. The nutrient flow channelized on the
membrane surface with some areas receiving no flow at all. Uniform distribution of the
nutrient flow with maximum membrane coverage is essential for even distribution of
algae on the membranes.
The results indicate that there was no control over harvesting flow. Harvesting
flow coverage had to be limited to only a few portions on the membranes where good
harvesting could be observed. Controlled harvesting operation and maximum harvesting
flow coverage is necessary for continued algal growth on the membranes.
Results indicate that the uncertainty with the initial loading operation is 14%
(Refer to Appendix D). The uncertainty with the initial loading operation is generally in
this range (Kremer,2001).This uncertainty is high for bench scale photobioreactor as
small amounts of cyanobacteria are normally loaded and it becomes difficult to compare
48
experiment results with uncertainty in the higher range. To achieve better results, the
uncertainty in the initial loading operation should be reduced.
Recommendations
The following recommendations aim at maximizing the nutrient flow coverage,
having controlled harvesting to achieve a steady or increasing harvesting yield.
Membrane Stitch design modification. Current membrane design has a closed
loop at the top that extends out of the header. As shown in the Figure 5.1, this loop
creates an uneven gap between the header and the membrane resulting in an uneven algae
distribution.
Header
Shim
S.S Rod
Big Loop
Small Loop
Gap between header
Wider gap
Old Design
New Design
Figure 5.1: Membrane Design.
The new design has a smaller loop at the top thus increasing the gap between the
header and the membrane. This decreases the resistance offered to the nutrient solution
resulting in a more even distribution.
Header modification: To ensure even flow distribution, it is essential to center the
membrane in the header gap with the help of spacers or similar attachment. This would
ensure that the gap between the header and the membrane is even at all times avoiding
channelised distribution.
49
Nutrient flow and Harvest flow testing: This testing should be performed prior to
the experiment. This test would replicate the actual operation indicating the nutrient flow
coverage, control over the harvesting operation and highlight any problems that could be
encountered during the actual operation. This test should be done using nutrient solution,
as water does not replicate the actual conditions.
Modify Initial Loading Operation: The first step of the initial loading operation is
to mix the algae in the cultural tank and stir the algal solution to break-up big lumps of
algae. Samples are then withdrawn from the tank. The algae has a tendency to settle
quickly. If a stirrer or an agitator is installed in the tank, the solution will be continuously
stirred resulting in a well mixed algae solution. The agitator would always maintain the
algae in suspension. This would reduce the 14 % uncertainty as uniform samples will be
withdrawn from the tank.
The Scotch tape did not support the growth of algae and those areas of the
membrane were unavailable for the algae growth. Control over harvesting was lost due to
the formation of jets at the junctions of the Scotch tape. The use of Scotch tape on the
membranes should be minimized.
50
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54
7. Appendix
A. Light Measurement
Before Test
Membrane 1Side 1
1
2
3
57
56
46
67
65
56
73
69
59
74
72
60
74
73
60
74
72
61
72
71
60
67
66
57
Side 2
4
5
6
71
74
71
80
79
71
83
81
75
80
85
81
84
83
85
83
81
82
79
78
77
68
69
70
Membrane 2Side 1
7
8
9
67
80
87
74
84
94
72
87
96
78
90
98
77
90
98
73
89
99
72
86
98
63
79
93
Side 2
10
11
12
72
79
85
79
84
90
82
87
91
83
89
93
82
89
92
80
85
88
76
83
82
69
76
83
Membrane 3Side 1
13
14
15
73
81
73
82
89
85
86
92
86
88
93
87
89
94
85
83
92
84
83
88
83
73
77
77
Side 2
16
17
18
67
69
61
70
69
61
71
69
63
71
72
64
68
70
62
63
65
55
43
54
48
35
35
33
Note: All light measurements are in µmols.
55
After Test
Membrane 1Side 1
1
2
3
52
51
45
63
61
53
67
66
57
69
67
58
70
68
59
69
68
59
66
66
57
62
62
55
Side 2
4
5
6
75
74
71
85
84
78
85
88
83
90
91
88
88
91
88
87
88
84
82
83
79
71
73
69
Membrane 2Side 1
7
8
9
69
81
57
77
86
98
80
88
99
82
91
112
83
90
114
82
87
99
77
80
97
71
71
95
Side 2
10
11
12
73
81
85
82
88
93
80
90
95
85
87
94
82
86
99
76
87
90
76
81
92
66
75
86
Membrane 3Side 1
13
14
15
79
83
79
86
93
88
89
96
91
90
98
93
90
97
94
87
93
92
80
88
84
73
78
77
Side 2
16
17
18
64
64
58
66
64
59
66
67
61
67
67
61
64
65
58
57
61
55
49
51
47
30
32
28
Note: All light measurements are in µmols
56
B. Velocity Measurement
Before Test
Location\Depth
1
2
3
4
5
6
7
8
9
10
11
12
After Test
8"
1.53
1.6
1.75
1.7
0.96
0.83
1.29
1.37
1.46
1.36
0.6
0.7
14 "
1.43
1.38
0.75
1.15
0.86
0.88
1.37
1.39
0.75
0.75
0.89
0.6
Note: All velocities are in m/s.
C. Temperature Measurement
Location
1
2
3
4
5
6
7
8
9
10
11
12
Temperature ( °C)
46.9
47
47
47
47
47
47
47.1
47
47.1
47.2
47
Location\Depth
1
2
3
4
5
6
7
8
9
10
11
12
8"
1.34
1.65
1.65
1.53
0.71
0.96
1.11
1.1
1.03
0.81
0.48
0.86
14 "
1.14
0.95
0.46
1.05
0.76
0.62
0.95
1.35
0.45
0.5
0.52
0.6
57
D. Uncertainty Calculations
Initial filter weights
(g)
Final filter weights
(g)
Algae collected
(g)
Fine
Coarse Whatman
Fine
Coarse Whatman Fine Coarse Whatman
388.43 314.87
3.15
390.08 317.35
3.17
1.65
2.48
0.02
390.42 320.55
3.18
392.43 322.36
3.19
2.01
1.81
0.01
379.62 324.68
3.21
381.26 327.18
3.25
1.64
2.5
0.04
378.04 329.39
3.19
379.82 332.23
3.22
1.78
2.84
0.03
390.98 330.29
3.23
392.92 332.83
3.26
1.94
2.54
0.03
Mean
Standard Error
Median
Mode
Standard Deviation
Sample Variance
Kurtosis
Skewness
Range
Minimum
Maximum
Sum
Count
Largest(1)
Smallest(1)
Confidence
Level(95.0%)
4.264
0.1445545
4.18
#N/A
0.3232337
0.10448
-0.9509134
-0.1409149
0.82
3.83
4.65
21.32
5
4.65
3.83
0.4013476
Uncertainty = ± 14.45 %
Total
dry
Wt.
(g)
4.15
3.83
4.18
4.65
4.51
58
E. Algal Growth Rate
The surface area for algal growth rate is calculated as follows:
The algal growth rate is a function of the mass of algae, time and surface area available
for the algae. Since all the membranes were not completely covered during the test, only
the area with good algal density is considered for the purpose of calculations.
Membrane 1 had one side completely covered with algae with no growth on the other
side. Hence the surface area of membrane 2 is 2 ft2. Membrane 2 had 50% coverage on
both sides. Hence, the surface area of the membrane 2 is 2 ft2. Membrane 3 also had only
50% coverage on both sides. Hence, the surface area of the membrane 3 is 2 ft2.
Therefore, total surface area = 6 ft2. The total surface area if all the membranes had been
covered completely would be 12 ft2.
Mass of algae from Harvest 1 = 4.63 g.
Algal growth rate between Initial loading and Harvest 1
=
=
Massofa lg ae
harvested
SurfaceArea × Time
4.63
= 0.5933 g /m2× day
0.5574 × 14
Mass of algae from Harvest 2 = 2.37 g.
Algal growth rate between Harvest 1 and Harvest 2
=
2.37
= 0.6074 g /m2× day
0.5574 × 7
59
Mass of algae from Harvest 3 = 1.39 g.
Algal growth rate between Harvest 2 and Harvest 3
1.39
= 0.3562 g /m2× day
0.5574 × 7
=
Mass of algae from Harvest 4 = 1.27 g.
Algal growth rate between Harvest 3 and Harvest 4
=
1.29
= 0.3306 g /m2× day
0.5574 × 7
60
F. Operation of CRFII
This procedure has been extracted from internally published document at Ohio Coal
Research Center. SOP_ CRFII Operation_060131 (Doshi, 2006).
A.
CRF-II Test Rig Preparation:
Ensure that the work area is clean and clutter free. Make sure that the surroundings
of the rig are free from unnecessary tools and equipment. The OCRC Chemical
Hygiene Plan applies to all aspects of the operation. Get confirmation from lab
personnel before running the test.
1) Check the Nighthawk Carbon Monoxide / Explosive Gas detector. It should
initially be at a value of 0.
2) Supply power to the subsystems of the CRF-II.
Make sure all subsystems are shut off, most of the subsystems are controlled from
the main control panel through switches, dials and knobs. Supply power to all the
subsystems by plugging the power cords into the 120VAC GFCI outlet.
3) Light system check
Check the lighting system for proper operation i.e. loose wiring, operation of all
the bulbs, moisture formation on the inside of the panels and the timer switch
operation.
4) Gas system check
a) Check the Fantech flue gas recirculation blower for proper operation.
i. The variable speed control switch is located on the main control panel for the
CRF-II. The speed can be controlled by setting the speed control dial in
61
different locations. Initially set the blower at its minimum speed and let it
run for 10 seconds.
ii. Set the blower at an intermediate speed and let it run for 10 seconds.
iii. Set the blower at full speed and let it run for 10 seconds.
iv. Turn the blower off.
b) Check all natural gas supply lines and connections for leaks by performing the
snoop test.
c) Check all air supply lines and connections for leaks by turning all the air
valves on and applying the leak checking solution to all connections in the
same manner as for the gas lines and visually inspecting the connections.
Once all connections have been checked and all leaks have been fixed, turn
off all air valves including the rotameter.
5) Nutrient and Harvest system check.
a)
Check the nutrient tank and harvest tank for leaks.
b)
Check the immersion heater for proper operation.
c)
Check the nutrient and harvest pump for proper operation and check the
plumbing for leaks.
d)
Check the fin strip heaters for proper operation.
6) DA system
a)
Calibrate the Nova Gas Analyzer by following the users manual
b)
Compare the values the NGA displays with the values recorded by the
computer. Check if the burner is turned off by the DA system.
62
7) Dry at least seven sets of 100 micron and 0.5 micron filters in the oven at 250°F
(120°C). Along with these filters, dry three omnisil fabric membranes which have
been pre-stitched with an additional half inch allowance for shrinkage. Use high
temperature gloves and other PPE while handling these items in the oven.
8) For post harvesting operation, the filters will be placed in the beakers and they
will be dried for 7 days prior to weighing. The beakers must also be predried in
the oven at the same temperature and weighed.
B. Initial Loading and Startup
1) Check all connections for leakage. Open Valves 1 and 2 and add one gallon of RO
water to the nutrient tank
2) To select a culture tank with enough cyanobacteria to complete desired tests
contact Dr. Vis from the Plant Biology department.
3) The stirrers/scrapers are located on the front of the rectangular culture tank.
4) Select a stable step stool to stand on in order to access the culture tank. Then
unplug the electrical connection of the immersion heater and the light on the lid.
Remove the lid, allow the condensate to drain into the tank and then place it at a
safe location. In case of the rectangular tank, open the lid by pulling the rope and
tie the rope off appropriately.
Note: Please do not contact the immersion heater with the stirrer/scraper while
stirring the tank. Scrape the walls of the tank using the S-2 or S-3 scraper
depending on the tank configuration until all possible cyanobacteria is removed
and is floating in the solution.
63
5) Stir the solution using the S-1 or S-2 stirrer. Continue stirring the solution until
all the clumps of cyanobacteria are broken up into small pieces (1inch or smaller)
and the solution appears to be homogenized. Clean the stirrer with tap water and
wipe it with paper towel before placing it back to its original place.
6) Sampling is done by two methods. Half of the samples will be collected by
method one and the rest by method two. If either of the two methods is not
applicable all the samples are collected by the applicable method.
a)
Method one consists of using a pitcher/scooper. Dip the scooper partially into
the tank (do not immerse the handle into the solution), sample solution from
the top of the tank and pour it in the 2 L beaker which is placed on the
adjustable platform. Once the 2 L mark is reached, empty the sample into the
5 gallon bucket.
b)
Method two consists of opening the spigot at the bottom of the tank and
collecting a sample of the same volume as the first method. When opening
the spigot valve, hold the spigot assembly with one hand (preferably the
spigot stem behind the spigot valve) and rotate the valve with the other hand.
Refer Figure 3.13 (b). In case of a rectangular tank only method one is used.
Both sampling operations will require two people. One person should be
intermittently stirring the solution to ensure that the algae are evenly
distributed throughout the tank when collecting samples from the tank. After
the desired sample volume is obtained in a 5 gallon bucket, the algae solution
is transported to the test facility. Multiple samples can be placed in the same
bucket and multiple buckets can be used. Do not overfill the buckets.
64
Spigot Valve
Pitcher/Scooper
Spigot Stem
Figure 3.13: a) Pitcher/Scooper
b) Spigot
7) Close the lid of the algal tank after making sure that there is atleast 4 inches of
solution above the immersion heater. Contact Dr. Vis to determine which media
to add and how much to add if the level is less than 4 inches. Then plug both the
electrical connections in the wall socket.
8) Pour the solution from the 5 gallon bucket(s) into the conical nutrient tank. To
ensure that all the algae is transferred to the nutrient tank, rinse the
scooper/pitcher and the bucket with small amounts of RO water and add that
rinsed solution (RO water and any algae left in the bucket) into the nutrient tank.
9) After all the algae is rinsed off the bucket, add BG11 with extra HEPEZ solution
until the level in the tank reaches 16 gallons. This 16 gallon level is marked on the
nutrient tank.
10) Start the immersion heater to heat the nutrient solution to 122°F.
11) Install the predried omnisil membranes on the membrane frame and header pipe.
Install the membranes into the CRF-II.
i.
Ensure that three membranes are loaded in the framework inside the
reaction chamber.
The flange on the header pipe should rest on the
framework when properly installed. Make sure that each membrane is in
65
the frame holder on the upper and lower part of the membrane on both
sides. Make sure each that each membrane is placed securely in the frame
holder and cannot rotate or move easily.
ii.
Connect each of the three nutrient supply lines to the nutrient inlets and the
three harvest lines to the harvest inlets on the header pipes. This is done by
pushing each of the nutrient supply lines into the fitting for the header pipe
inlets until they are securely attached. For the harvest lines, twist the male
and female union ends together.
12) Starting the natural gas burner system.
i.
Connect the Nova gas analyzer to the sampling port on the CRF-II and
follow the users manual for proper operation of the Nova gas analyzer.
This will allow for the gas levels inside the CRF-II to be measured while
the natural gas burner is being run. Record the initial measurements for
CO, CO2, and O2 on the Steady State Measurement Data Sheet which can
be found in the Appendix. Also record the temperature of the water inside
the nutrient tank
ii.
Remove the access panel for the natural gas burner and place it in a safe
location.
iii.
Turn all gas valves on except for the ignition module and make sure the
natural gas rotameter is set at the desired value.
iv.
Open all air supply valves. Set the air rotameter to desired flow rate.
v.
Turn the recirculation blower on and set it to its minimum speed setting.
66
vi.
Purge the natural gas lines by turning the knob on the ignition module to the
“pilot” position and push the knob down multiple times.
vii.
Turn the knob on the ignition module to the “on” position. This will allow
the natural gas to be supplied to the burner when it is ready to ignite.
viii.
Using a propane torch, heat the thermocouple for the burner system. Be
careful not to overheat it. The torch is lit by turning the knob on the torch
clockwise and pressing the spark ignition button. Hold the flame from the
torch near the end of the thermocouple until the burner ignites. The burner
will ignite when the thermocouple has heated up to a specific temperature.
The propane torch can then be extinguished by turning the knob to its
counterclockwise limit.
ix.
Once the burner is lit increase the recirculation blower’s speed to 50%.
x.
Reseal the CRF-II. Make sure the top cover is securely fastened down and
the fin strip heater access panel is securely fastened. Replace the natural
gas burner access panel and securely fasten it to the ductwork.
xi.
Adjust the air/fuel mixture to obtain a stable flame that is nearly all blue
with very little or no yellow/orange flame.
The flame can safely be
observed by looking through the access panel.
xii.
Increase the recirculation blower’s speed to 50% of its maximum setting.
xiii.
After the burner is lit, one person should monitor the CO levels inside the
reaction chamber using the Nova Gas Analyzer and the same can be
observed on the DA computer. The Levels should be checked every 10
minutes for the duration of the test. Make sure the levels are within the
67
specified limits. The CO level should not exceed 40 ppm at any given
time. If the CO level is approaching the specified limit, adjustments should
be made to the burner system by changing the air/fuel mixture using the air
and natural gas rotameters until the desired levels are maintained inside the
CRF-II. If the level reaches or exceeds 40 ppm at any time or the gas
monitor fails to operate properly the burner system should be immediately
shut off by turning the main natural gas valve to the off position and record
the incident in your lab notebook.
xiv.
Start the labview program which will record all the values and activate the
safety circuit.
c)
Adjusting the systems to achieve a desirable steady state.
i.
Turn the lighting panels by using the two timer switches located on the
main control panel.
ii.
Turn the fin strip heaters on by setting the dial located on the main
control panel to 120.
iii.
Based on the readings from the Nova gas analyzer, adjust the air/fuel
mixture using the rotameters for the natural gas and air to maintain the
CO levels in the CRF-II below 40ppm.
iv.
Adjust the fin strip heaters and air/fuel rotameters if necessary to
maintain proper temperature inside the CRFII reaction chamber. The
temperature should be in the range of 47oC to 53oC.
v.
If any of the parameters have been changed, continue measuring all
parameters every ten minutes until they have all converged to a steady
68
state value. Adjustments can then be made and the parameters can be
remeasured and recorded in the same manner until all parameters are in
the proper range.
vi.
Record the settings for the natural gas and air rotameters, the fin strip
heaters, and the immersion heater once a desirable steady state has been
reached. These settings should be recorded on the Steady State
Measurement Data Sheet.
vii.
Once the temperature in the reactor becomes steady at 50°C and the
temperature of the nutrient solution is also in the same range, turn the
nutrient pumps on using the switch on the main control panel and then
set the transformer to 120 V.
viii.
Slowly turn the transformer’s dial clockwise to increase the pump’s
speed until it has reached its maximum speed.
ix.
Check the flow rate for each nutrient supply line; it should be set at 0.8
gpm.
x.
If the steady state temperature in the nutrient tank is not in the range of
47oC to 53oC, the temperature will have to be adjusted.
The
temperature can be adjusted by turning the dial on the back of the
immersion heater. Turning the dial counterclockwise and clockwise will
decrease and increase the temperature respectively.
C. Routine checkup during run
1) Leak check: The best method to trace a leak is the snoop test. A soap
solution containing 20% soap and 80% water is prepared and sprayed at
69
the joints on the gas and air line. Paper towels or beaker can be held to
avoid the spillage. At joints where there is leakage, bubbles form.
2) Burner and Gas level check. : The quality of the burner flame dictates the
gas level (CO/CO2/O2). If the levels are above the desired limits, then
change the air/gas ratio to obtain the desired values (< 40 ppm ).
3) Temperature check: The temperature of the nutrient solution and the
reactor chamber should be checked periodically. If the temperature of the
reactor is less than desired, then switch on the fin strip heaters.
4) Liquid level and ph: If the liquid level in the nutrient tank drops, then fill it
up to the initial level with BG11 solution. Also check the level of the
nutrient solution in the reactor chamber. If the level is building up, then
completely open the drain valve and if necessary, reduce the flowrate of
the nutrient solution so that the liquid in the reactor drains out.
5) If the reactor chamber needs to be accessed when its in operation, then
follow the steps below:
i)
Shut off the burner by closing the inlet gas valve
ii)
Wait till the temperature of the reactor drops to 40°C
iii)
Quickly unbolt the top cover and remove it.
iv)
To avoid thermal shock to the micro organisms, reseal the PBR
quickly.
70
D. Harvesting Procedure.
1) The harvest pump is connected to the harvest tank by screwing valve 2,
which is connected to the pump inlet and the harvest tank drain line. The
outlet filter bypass line is inserted to the top of the harvest tank lid.
2) Check all connections for leakage. Open Valve 1 and Valve 2 and add 1
gallon (approx) of RO water in the harvest tank.
3) Unscrew and remove filter casings 1 and 2. Ensure that the filter casing oring is intact and at its proper location. Insert the predried 100 micron and
0.5 micron filters in filter casings 1 and 2, respectively. Replace the filter
casings and hand tighten.
4) Turn Valves 1 to 3 to the open position. Please note the handle of the
valves should be parallel to the fluid flow when the valves are in the open
position. Valve 4 must be in the closed position.
5) Stop heating the nutrient solution by turning off the immersion heater
from the control panel. Open the drain valve to harvest tank and close the
nutrient tank drain valve.
6) When water level in the harvest tank is sufficient to run the harvest pump,
turn off the nutrient pumps by switching the transformer off and then the
control panel pump switch. Turn off the valves on the nutrient lines
between the pump outlet and the membranes.
7) Loosen the priming bolt located on the front of the pump using a crescent
wrench. The pump is primed and ready when water flows freely from the
71
bolt hole. Next, hand tighten the bolt. Flow should stop when the bolt is
tightened (Refer Figure 3.14a).
Note: Do not use a wrench to tighten the priming bolt.
a)
b)
Pump switch
Priming bolt
Figure 3.14 a, b: Priming Bolt, Pump Switch
8) Plug the harvest pump electrical connection into a 208 VAC wall socket.
After inserting the plug into the wall socket twist it clockwise until the
plug is securely locked in.
9) Harvesting will be done starting with membrane one and then proceeding
onto other membranes. Open the valve to let the harvesting solution pass
to membrane one. Make sure the valves to the other membranes are
closed.
10) One operator will hold the hoses and the second operator will start the
pump by turning the pump switch to the on position (Figure 3.14b). Check
for leaks after the pump is started.
Note: Hold all lines to and from the harvest tank. Pressure can cause them
to blow out resulting in spillage. If this occurs, first turn the pump switch
off, unplug the pump’s electrical connection and clean up the spillage.
11) The pump will circulate the solution from the harvest tank through the
filter bypass line back to the harvest tank. Now slowly open valve 4 until
72
the desired flowrate is reached. In case filters of different micron size are
used, the flowrate can be decided by using the flowrate determination test.
The minimum flowrate is 3 gpm and the maximum flowrate is 5 gpm for
the current set of filters. Pressure should be fixed once the flowrate is
fixed as both of them are interdependent.
12) Once the desired level of harvesting has been achieved, switch to the other
membrane by opening the valve to the other membrane and closing valve
one. Follow the same procedure for the third membrane. Once harvesting
is complete, switch off the harvest pump.
13) Shut off all the valves on the harvest line. Open the drain valve to the
nutrient tank and then close the drain valve to the harvest tank.
14) Fill the nutrient tank upto the initial level with BG11 solution. Open all the
valves on the nutrient lines and start the immersion heater. Once the
temperature reaches 122°F, start the nutrient pumps.
E. Shutting Down the CRF-II:
1) After testing is complete, turn off the fin strip heaters and the immersion heater
using the switches on the main control panel. Turn the main gas supply valve off,
to allow residual gas in the piping to burn off. Then close the remaining gas and
air valves. The rotameters for the natural gas and air can remain on at their
adjusted flow rates.
2) Once the temperature in the reactor chamber is reduced to ambient temperature,
divert all the nutrient solution in the harvest tank. Slowly decrease the pump’s
73
speed using the dial on the transformer until it stops. Turn off the switch for the
pumps on the main control panel. Then shut off all the valves on the nutrient line.
The rotameters can remain at the preset flow rate(0.8 gpm).
3) The blower can then be shut off using the dial on the main control panel. Then
disconnect all the electrical supply to the PBR.
4) Open the reactor chamber top cover, remove the membranes and then remove the
nutrient surface (omnisil). Fold the omnisil and place them in the predried and
weighed beaker.
5) Clean the PBR with RO water and collect it in the harvest tank.
6) Filter out all the algae in the harvest tank by running it through the filters.
7) Dry all the omnisil cloth and filters in the oven for seven days at 250°F.