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Energy Production By Microalgae in Photobioreactors 1
A
Seminar Report On
Energy Production By Microalgae in
Photobioreactors
PRESENTED AND SUBMITTED BY:
PUSHPA BHAGAT
(U07CH135)
Under the Guidance of
Mr. CHETAN PATEL
Assistant Professor CHED
DEPARTMENT OF CHEMICAL ENGINEERING
SARDAR VALLABHBHAI NATIONAL INSTITUTE OF
TECHNOLOGY
Surat (Gujarat) -395007.
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CERTIFICATE
This is to certify that candidates Miss. PUSHPA BHAGAT (U07CH135) has
submitted the TRAINING REPORT for the fulfilment of the requirement for
the degree of Bachelor of Technology in C hemical Engineering B.TECH (2007-
11).
Examiner: Signature
1)
2)
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ACKNOWLEDGEMENT
I express my sincere thanks to Dr. Mousumi Chakraborty, Head of the
department for providing me the guidance and facilities for the
project.
I thank our project guide Mr. Chetan Patel for great help and guidance
in preparing and presenting my seminar report.
I also extend my sincere thanks to all other faculty members of
Chemical department and my friends for their support and
encouragement.
Pushpa Bhagat
U07CH135
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CONTENTS
Abstract
Chapter 1 INTRODUCTION
1.1Macro vs microalgae.61.2Why we need microalgae..61.3Literature Survey on production of oil by microalgae..7
Chapter 2 HOW TO GROW ALGAE
2.1 Open Pond10
2.2 Photobioreactors...10
Chapter 3 TYPES OF PHOTOBIOREACTORS
3.1 Tubular Photobioreactor..12
3.2 Flate Plate Photobioreactor..13
3.3 Vertical Photobioreactor 14
Chapter 4 CONSTRUCTION AND WORKING
4.1 Construction.....17
4.2 Working.18
Chapter 5 PERFORMANCE EVALUATION OF PHOTOBIOREACTORS
5.1 Factors Effecting Growth Rate.20
5.2 Challenges and Future Prospects.22
SUMMARY.23
REFERENCES..24
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ABSTRACT
Current biofuel production relies on limited arable lands on the earth, and is impossible to
meet the biofuel demands. Oil producing algae are alternative biofuel feedstock with
potential to meet the worlds ambitious goal to replace fossil fuels. This report provides an
overview of the biological and engineering aspects in the production and processing of algae
into energy fuels in photobioreactors. This article includes comparision of traditional open
ponds and photobioreactions in production of algae mass. It also discusses different type of
photoreactors, their construction, working and their application.
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Chapter 1
INTRODUCTION:
Algae fuel provides an exciting opportunity. There is strong view among industry
professionals that the algae represent the most optimal feedstock for biofuel production in
long run. It is also widely acceptable that algae alone and no other biostock have ability to
replace entire global fossil fuel requirements.
Algae present multiple possibility for fuel end products-biodiesel, ethanol, methane, jet fuel,
biocrude and more-via a wide range of process routes. Each set of process represents its ownset of opportunities , parameters, dynamics and challenges.
Efforts into algal fuel research have accelerated in past few years. As of mid 2010, over
hundreds of companies and over hundreds of universities have begun serious exploratory
efforts into algal fields.
1.1 Macro vs Micro algae:
1) Microalgae have high oil content but are difficult to cultivate.2) Macroalgae on the other hand present low cost cultivation and harvesting possibilities,
but most of the species are low in lipids and carbohydrates.
3) With processes such as cellulosic fermentation (for deriving alcohol), gasification (forderiving biodiesel, ethanol and a wide range of hydrocarbons) or anaerobic digestion
(for methane or electricity generation), it is possible today to use microalgae as feed
stock for biofuels.
1.2Why we need microalgae?
Continuous use of petroleum sourced fuels is now widely recognized as unsustainable
because of depleting supplies and the contribution of these fuels to the accumulation of
carbon dioxide in environment.
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Microalgae have emerged as one of the most promising sources for biodiesel production. It is
an eco-friendly fuel as the CO2 taken from environment to produce lipids is returned back to
environment when being burnt. Thus no more addition of CO2 to the environment.
Table Showing Capacity to produce oil per unit area per year [8]
Gallons of Oil per Acre per Year
Corn 18
Soybeans 48
Safflower 83
Sunflower 102Rapeseed 127
Oil Palm 635
Micro Algae 5000-15000
From the above table we can see that Micro-algae can produce maximum capacity to produce
oil per unit area per year.
1.3 Literature Survey for production of oil by M icroalgae:
Various steps are involved in production of fuels: [1]
1. Selection of algal strain:Selection of optimal algal strain is a key component of a successful algal fuel venture.
With tens of thousands of strains to choose from this easier said than done. A number
of parameters need to be kept in mind while evaluating algal strains for their
suitability as biofuel feedstock. Strain with high oil content should be chooses for
mass fuel production.
2. Culture of the microalgae in proper medium: Cost effective algal cultivation is a
key requisite of success of biofuel production. However such cultivation of right
strain of microalgae, in the right environment and media is a challenge from algae
fuel production companies. Various methods for growing it in pond or in
photobioreactors are available.
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3. Harvesting of microalgae: Harvesting is by centrifugation, flocculation, froth
floatation. Interrupting CO2 can cause the algae to flocculate its own. Flocculation is
tougher in salt water. Other chemical agents such as alum and ferric chloride are used.
In froth floatation process cultivator aerates the water into froth and algal mass is
skims from the top.[2]
4. Extraction of lipids from microalgae: The first thing here we do is to disrupt the
cells. This is done by.[3]
a) Autoclaving at 125C and 1.5MPa.
b) Bead-beating using bead beater at a high speed of 2800 rpm for 5 min.
c) Microwaves using a microwave oven at a high temperature about 100C and
2450MHz for 5 minutes.
d) Sonification using a sonicator at resonance of 10 kHz for 5 min and
e) Osmotic shock using a 10% NaCl solution with a vortex for 1 minute and
maintained for 48 hours
Second step is to extract the lipids. This may be done by mixing chloroform
methanol (1:1 v/v) with the samples in a proportion of 1:1. The mixtures were
transferred into a separatory funnel and shaken for 5 min. The lipid fraction was then
separated from the separatory funnel and the solvent evaporated using a rotary
evaporator. The weight of the crude lipid obtained from each sample was measured
using an electronic scale.
Table 1 ALGAE TO ENERGY SUMMARY OF EACH ENERGY PRODUCTS:[1]
FINAL PRODUCT PROCESS
Biodiesel Oil extraction and transesterification
Ethanol Fermentation
Methane Anaerobic digestion of biomass, methanation
of syngas produced from biomass
Hydrogen Tiggering biochemical processes in algae,
gasification/pyrolysis of biomass and
processing of biomass and resulting of
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syngas.
Heat and electricity Direct combustion of algae biomass,
Gasification of biomass
Other hydrocarbon fuels Gasification/pyrolysis of biomass and
processing of biomass and resulting of
syngas.
Fig 1 Various pathways to produce energy by algae mass[1]
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Chapter 2
METHODS TO GROW ALGAE:
2.1Open ponds: These are preliminary way of production of microalgae. The open ponds can be natural or constructed. Generally artificial cemented open ponds are
used.
Fig 1 Open pond [4]
2.2 Photobioreactors(closed or open) These are more compact fermenters in which phototrophic microalgae are cultivated where their growth and propagation is
promoted at the same time as the various substances are produced by photosynthetic
cell.
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Fig 2 Tubular Photobioreactor[5] Fig 3 Flat Plate photobioreactor[6]
Table No 2 Difference between open pond and photobioreactors:
OPEN POND PHOTOBIOREACTORS
Lake or ponds are open to the elements. They are mainly closed systems.
Its highly vulnerable to contamination by
other microorganisms such as other algal
species or bacteria.
Its no contamination by other microbes since
its closes.
Difficult to control temperature and lighting. Precise control over nutrient supply,
temperature, lighting and CO2. The grower
provides sterilized water, nutrients, air, and
carbon dioxide at the correct rates. This
allows the reactor to operate for long periods.
Its a batch process. There can not be much
of volume change in production.
It can be batch or continuous depending upon
the requirement. Batch mode requires
restocking the reactor after each harvest.
Continuous operation requires precise control
of all elements to prevent immediate
collapse.
It is cheaper and easily constructed. It is expensive and advanced in design.
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Chapter 3 TYPES OF PHOTOBIOREACTORS:
3.1 Tubular photobioreactors[1]
Among the proposed photobioreactors, tubular photobioreactor is one of the most
suitable types for outdoor mass cultures. Most outdoor tubular photobioreactors
are usually constructed with either glass or plastic tube and their cultures are re-
circulated either with pump or preferably with airlift system. They can be in form
of horizontal / serpentine, vertical near horizontal, conical, inclined
photobioreactor. Aeration and mixing of the cultures in tubular photobioreactors
are usually done by air-pump or airlift systems.
Fig 4 Tubular photobioreactor[1]
Tubular photobioreactor are very suitable for outdoor mass cultures ofalgae since
they have large illumination surface area. On the other hand, one of the majorlimitations of tubular photobioreactor is poor mass transfer. It should be noted that
mass transfer (oxygen build-up) becomes a problem when tubular photobioreactors
are scaled up. For instance, some studies have shown that very high dissolved oxygen
(DO) levels are easily reached in tubular photobioreactors.[13]
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Tubular photobioreactors consist of straight, coiled or looped transparent tubing
arranged in various ways for maximizing sunlight capture. Properly designed tubular
photobioreactors completely isolate the culture from potentially contaminating
external environments, hence, allowing extended duration monoalgal culture.
Also, photoinhibition is very common in outdoor tubular photobioreactors .When a
tubular photobioreactor is scaled up by increasing the diameter of tubes, the
illumination surface to volume ratio would decrease. On the other hand, the length of
the tube can be kept as short as possible while a tubular photobioreactor is scaled up
by increasing the diameter of the tubes. In this case, the cells at the lower part of the
tube will not receive enough light for cell growth (due to light shading effect) unless
there is a good mixing system.
Also, it is difficult to control culture temperatures in most tubular photobioreactors.Although they can be equipped with thermostat to maintain the desired culture
temperature, this could be very expensive and difficult to implement. It should also be
noted that adherence of the cells of the walls of the tubes is common in tubular
photobioreactors. Furthermore, long tubular photobioreactors are characterized by
gradients of oxygen and CO2 transfer along the tubes . The increase in pH of the
cultures would also lead to frequent re-carbonation of the cultures, which would
consequently increase the cost of algal production.
y ProspectsLarge illumination surface area
Suitable for outdoor cultures,
Fairly good biomass productivities
Relatively cheap.
y LimitationsGradients of pH,
dissolved oxygen and CO2 along the tubes,
Fouling, some degree of wall growth,
Requires large land space.
3.2 Flat plate bioreactors[1]
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Generally, flat-plate photobioreactors are made of transparent materials for maximum
utilization of solar light energy. Accumulation of dissolved oxygen concentrations in flat-
plate photobioreactors is relatively low compared to horizontal tubular photobioreactors.
It has been reported that with flat-plate photobioreactors, high photosynthetic efficiencies
can be achieved.[13] Flat-plate photobioreactors are very suitable for mass culture of algae.
Prospects
y Large illumination surface areay Suitable for outdoor culturesy Good for immobilization of algaey Good light pathy Good biomass productivitiesy Relatively cheapy Easy to clean upy Readily temperedy Low oxygen buildup.
Limitations
y Scale-up require many compartments and support materialsy Difficulty in controlling culture temperaturey Some degree of wall growthy Possibility of hydrodynamic stress to some algal strains.
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3.3 Vertical column bioreactors:
Various designs and scales of vertical-column photobioreactors have been tested for
cultivation of algae. Vertical-column photobioreactors are compact, low-cost, and easy to
operate monoseptically . Furthermore, they are very promising for large-scale cultivation ofalgae. It was reported that bubble-column and airlift photobioreactors (up to 0.19 m in
diameter) can attain a final biomass concentration and specific growth rate that are
comparable to values typically reported for narrow tubular photobioreactors. Some bubble
column photobioreactors are equipped with either draft tubes or constructed as split cylinders.
In the case of draft tube photobioreactors, intermixing occurs between the riser and the
downcomer zones of the photobioreactor through the walls of the draft tube.
Fig 6 Vertical Photobioreactors[9]
Prospects
y High mass transfery Good mixing with low shear stressy Low energy consumption,y High potentials for scalability,y Easy to sterilize, readily tempered,y Good for immobilization ofalgae,y Reduced photoinhibition and photo-oxidation.
Limitations
y Small illumination surface areay Their construction require sophisticated materialsy Shear stress to algal cultures
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y Decrease of illumination surface area upon scale-up.
For the successful outdoor algae mass cultivation, photobioreactors should posses the
following characteristics/properties:
y High surface to volume ratioy High mass transfer ratey High surface illumination
Following are the advantages of photobioreactor:
y Variable volume and dynamic conditions are available.y Prevent contamination by hostile species.y Accelerates the growth
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Chapter 4 CONSTRUCTION AND WORKING OF PHOTOBIOREACTOR:
4.1.Construction
Fig 7 Tubular Reactor:[19]
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Fig 8 Flat plate Reactor:[19]
Fig 9 Vertical Aerated Photobioreactor:[19]
The following problems must be resolved while constructing a photobioreactor :[12]
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1. The reactor design should be universal and permit the cultivation of variousunicellular photosynthesizing organisms.
2. In order to ensure a high efficiency of light use by the culture, the cultivator designmust provide for the uniform illumination of the culture surface and the fast mass
transfer of CO2 and O2.
3. Cells of microalgae are highly adhesive, which results in the rapid fouling of the light-transmitting surfaces of reactors. This necessitates photobioreactos to be frequently
shut down for their mechanical cleaning and sterilization. The reactor, particularly of
this light-transmitting surfaces.
4. High rates of mass transfer must be attained by means that neither damage culturedcells nor suppress their growth.
5. The photobioreactor must fuction normally under conditions of intense foaming, asoften occurs in reactors with high rates of mass transfer.
6. In order to attain high productivity, the volume of the nonilluminated parts of thereactor should be minimized.
7. For the industrial-scale production of biomass, the energy consumption required formass transfer and the arrangement of the light-receiving surface of the algal
suspension must be reduced to its minimum possible level.
4.2 Working of typical Photobioreactor:[7]
Culture medium was pumped into the tubings at set at fixed flow rate. These tubes provide a
large area exposed to the fluorescence light. Air compressor supplies air to the system for
aeration and to serve as a source of carbon dioxide. The air flow rate is set in the range of 193
210 gal/hr. Culture flow rate is maintained in turbulent regime with a Re >2000 to assure a
good mixing and agitation. This TPBR could be used indoor with artificial source of photonic
energy such as fluorescence lamps with low light intensity compared to sunlight. If weather
permitted, the system could be set outdoor using sunlight as a source of photonic energy to
minimize production cost.
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Fig 10 Working of tubular photobioreactor[7]
Chapter 5: PERFORMANCE EVALUATION OF PHOTOBIOREACTOR:
5.1 Factors effecting growth rate:
Many factors effect the growth of mircoalgae in photobioreactor:
1) Light - Light is needed for the photosynthesis process. It accelerates the growth ofmicroorganism. So most of the photobioreactors are designed out of transparent
material. When culture densities are low during early stages of logarithmic growth,
light effectively penetrates through the entire culture medium, and a low light flux is
adequate. In dense suspensions, higher intensity light is required to penetrate deeper
and be more available to growing cultures. Studies have shown that light control in
photobioreactors can serve to improve growth rates [9,10] as well as final biomass
concentrations [10,11]. However, these studies utilize sophisticated control methods
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that include frequent changes in light intensities. In large-scale systems processing
several million gallons of algal cultures for biofuel production, such precise controls
are likely to be difficult to implement, and perhaps unnecessary. Simpler methods that
involve only periodic alteration of growth parameters are more practical.
2) Temperature: There is an ideal temperature range that is required for algae to grow.Below and above this range the enzymes in the micro-organisms do not function
properly and the growth is inhibited.
Fig10 : Optimum Temperature curve [15]
3) Medium/Nutrients composition of the water is an important consideration(including salinity)
4) pH algae typically need a pH between 7 and 9 to have an optimum growth rate.
The gas exchange between the atmosphere and the culture medium is dependent on
gradient of the partial pressure of the gases across the gas-liquid boundary layer. The
higher the pH, the higher the CO2 gradient under a given carbonate alkalinity and the
higher the possible contribution of free carbon from the atmosphere,(Lee and Pirt,
1984) [14]. Further increase of pH will limit the growth.
5) Agitation- When environmental conditions are not growth limiting, agitation done tocreate a turbulent flow in the photobioreactor constitutes the most important requisite
for constant high yield of algal mass. One basic reason for mixing is to prevent the
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microalgal cell from sinking, this being, particularly severe in those area where the
turbulence is very low. Also high turbulence relates to the nutritional and gaseous
gradients formed around the algal cells in the course of metabolic activity. Such
gradients impose restrictions on the growth rate and are alleviated with high
turbulence. Another relevant point is that the high density of actively
photosynthesizing cells creates an extremely high concentration of dissolved oxygen
which, in large commercial pond, may reach at midday concentration of over 400%
saturation. The more vigorous the mixing, the less would the O2 build-up in the
culture [16]. The major objective for creating a turbulent flow in cultures, however,
relates to the phenomenon of mutual shading [17]. The turbulent flow induces a
continuous shift in the relative position of the cells with respect to the photic zone,
causing the solar radiation impinging on the surface of the photobioreactor to be
distributed more evenly to all the cells in the culture [16].
The pump to circulate the culture represents an integral part of any photobioreactor,
and special attention should be given to ascertain that circulating the culture volume is
carried out with minimal shearing forces. For this reason peristaltic pumps and air-
lift which are used for photobioreactor are superior to centrifugal or rotary positive
displacement pump in supporting maximal growth rate in microalgae[18].
6) Aeration: One of the important factors in large scale production of algae is aeration.It ensures the uniform supply of CO2 in the photobioreactor and enhances the growth
rate.
7) Photoperiod: Light & dark cycles play important role in the growth of microalgae.The growth rate can be altered easily by changing the light/dark period.
5.2Challenges faced and Future Prospects of Photobioreactors:
One of the major challenges is the scale up of the photobioreactors. With increasing the
capacity , the growth rate goes on decreasing. Most of the research work is going on the scale
up and optimization.
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Once the these problems are tackled the photobioreactors can be commercialised in future
and can become a base for the alternative source of fuel.
SUMMARY
Microalgae can fulfil the need of fuels. This is the most preferable alternative to fuels as it
has high capacity per unit area per unit time, it is eco-friendly and can be cultivated easily.
Micro-algae can be cultured in both open pond and photobioreactors. But as the
photobioreactors have lots of advantages over open pond, we prefer photobioreactors. There
are three types of photobioreactors viz tubular, flat plate and vertical aerated
photobioreactors. The construction of the photobioreactors are such that it will be exposed to
maximum light. Mixing and aeration is provided to increase the growth rate along with the
varying light intensities. No doubt the photoreactor are one of the most researched and
burning topic as it provides a base for the large scale production of biofuels.
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REFERENCES
[1]Comprehensive algae report. www.oilgae.com
[2] www.wikipedia.org
[3] Jae-Yon Lee, Chan Yoo, So-Young Jun, Chi-Yong Ahn, Hee-Mock Oh, Comparison of
several methods for effective lipid extraction from microalgae, Environmental Biotechnology
Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 111
[4]www.altdotenergy.com
[5] http://www.mvm.kit.edu/english/349.php
[6] www.pubs.ext.vt.edu
[7]Nkongolo Mulumba, Ihab H. Farag,Biodiesel Production from Microalgae
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[8] Riesing Thomas F., Cultivating Algae for Liquid Fuel Production
[9] Meireles, L. A., Guedes, A. C., Barbosa, C. R., Azevedo, J. L., Cunha, J. P., & Malcata,
F. X. (2008). On-line control of light intensity in microalgal bioreactor using a novel
automatic system. Enzyme and Microbial Technology, 42, 554559.
[10] Yoon, J. H., Shin, J. H., Ahn, E. K., & Park, T. H. (2008). High cell density culture of
Anabaena variabilis with controlled light intensity and nutrient supply. Journal of
Microbiology and Biotechnology, 18, 918925.
[11] Wijanarko, A., Dianursanti, Sendjaya, A. Y., Hermansyah, H., Witarto, A. B., & Gozan,
M. (2008). Enhanced Chlorella vulgaris Buitenzorg growth by photon flux density alteration
in serial photobioreactors.Biotechnology and BioprocessingEngineering, 13, 476482.
[12]Closes Photobio reactors for Microalgal cultivation L.N. Tsoglin, B.V.Gabel,
T.N.Falkovich and V.E.Semeneko Timiryazev Institute of Plant Physiology, Russican
Academy of Sciences, ul, Botanicheskaya 35, Moscow,127276 Russia, Received June 9,
1995
[13] Torzillo et al., 1986; Richmond et al., 1993; Molina et al., 2001).
[14] Lee, Y.K. and Pit-t, S-J., 1984, CO2 absorption rate in an algalculture: Effect of pH,
Journal of Chemical Technology and Biotechnology, Vol. 34B, No. 1, pp. 28-32.
[15] www.microcourse.info
[16] Richmond, A. and Grobbelaar, J.U., 1986, Factors affecting the Output Rate of
SpiruIina Platensis with Reference to Mass Cultivation, Biomass, Vol. 10, No. 4, pp. 253-
264
[17] Tamiya, H., 1957, Mass culture of algae, Annual Review of Plant Physiology, Vol. 8
pp. 309-334.
[18] Pirt. S-J., Lee, Y-K., Walach, M.R., Pit-t, M-W., Balyuzi H.H.M. and Bazin, M.J., 1983,
A tubular bioreactor for photosynthetic production of biomass from carbon dioxide: design
and performance, Journal Chemical Technology and Biotechnology, Vol. 33B, No. 1, pp.
35-38.
[19] http://biofuels2010.blogspot.com/2010/11/mit-algae-photobioreactor.html