growth of micro algae in photo bio reactors

8/8/2019 Growth of Micro Algae in Photo Bio Reactors

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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

growth of micro algae in photo bio reactors

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