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Microalgae Route to Biodiesel:Microalgae Route to Biodiesel:
Prospects, Potential and ProcessProspects, Potential and ProcessDesignDesign
Dr. V. S. MoholkarDepartment of Chemical Engineering
Indian Institute of Technology Guwahati
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In the beginning, there were algae, but there wasno oil
Then, from algae came oil.
Now, the algae are still there, but oil is fastdepleting
In future, there will be no oil, but there will still bealgae
So, doesnt it make sense to explore if we canagain get oil from algae?
This is what we try to do explore the potentialof getting oil from algae
Biodiesel From Algae
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Biodiesel Feedstock Tree
Source: African Biofuels 200
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Lipid Content of Algal species Some algae naturally manufacture hydrocarbonsthat are suitable as high energy fuels.
Botrycoccus braunii, a common species, cancontain more than 50% oil, mostly in form ofhydrocarbons.
Genetically engineering species of Botrycoccusbraunii can be made to grow faster.
1 1Sy nechoccus sp.
9 - 1 4Porphy r id ium sp .
2 2 - 3 8Pry m nesium sp .
1 4 - 2 0Eug lena sp.
6 - 8Dun al ie l la sp.
1 1 - 2 1Sp i rogy ra sp .
1 4 - 2 2Clor el la sp.
2 1Chlam yd om onas sp.
1 2 - 4 0Scenedesm us sp.
% Lip id
( b y m ass o n d r y b asi s)
St r a in or Spec ies
1 1Sy nechoccus sp.
9 - 1 4Porphy r id ium sp .
2 2 - 3 8Pry m nesium sp .
1 4 - 2 0Eug lena sp.
6 - 8Dun al ie l la sp.
1 1 - 2 1Sp i rogy ra sp .
1 4 - 2 2Clor el la sp.
2 1Chlam yd om onas sp.
1 2 - 4 0Scenedesm us sp.
% Lip id
( b y m ass o n d r y b asi s)
St r a in or Spec ies
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Microalgal Oil
Composition of microalgae (dry basis): protein(1235%); lipid (7.223%); carbohydrate (4.623%).
Algal-oil is very high in unsaturated fatty acids,like the canola oil. Some UFA's found in differentalgal-species include:
Arachidonic acid(AA)
Eicospentaenoic acid(EPA)
Docasahexaenoic acid(DHA)
Gamma-linolenic acid(GLA)
Linoleic acid(LA)
Catalytic hydrogenation of oil prior totranesterification is a possible solution.
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Microalgal Biodiesel
Not significantly different than the biodiesel
produced from vegetable oil. Microalgal oil contains high levels ofpolyunsaturates which can pose stabilityproblem due to possibility of oxidation.
Due to lower melting point of polyunsaturates(than mono-unsaturates or saturates), algalbiodiesel possesses better cold weather
properties. Growing algae using exhausts of power plants
for CO2 source can help reduce carbon and NOxemissions.
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What Effects Algal Growth?
Selected Algal strain Light conditions
Temperature Water flow rate Supply of carbon dioxide (use exhaust of power
plants) Macronutrients: C, N, P, Mg, Ca, K, Na, Cl Micronutrients (Trace elements): Fe, B, Zn, Mn, Mo,
Cu, SO4, Co, Cd, Va, Al, Br, Etc..
Vitamins Marine microalgae: Seawater supplemented with
commercial fertilizers
Biodiesel is carbon neutral no net accumulation ofCO2 in atmosphere.
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Bag culture
Tubular ReactorAirlift Bioreactor
Stirred Tank Reactor Bag Culture
PHOTOBIOREACTORS
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Features of Raceway Ponds
Closed loop recirculation channel; mixing achievedwith paddle wheel.
MOC: concrete, compacted earth or lining with
white plastic to reduce seepage losses. Typical dimensions: Depth 20-30 cm; Area
100-250 hectare, production 0.1 to 0.5 g dryweight per liter.
Limitations: Significant evaporation losses.
Poor thermal or temperature control.
Poor utilization of CO2 due to evaporation orstripping.
Contamination from unwanted algae and micro-organisms.
Low biomass concentration due to poor mixing andoptically dark zones.
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Features of Photobioreactors
Known as closed systems and permit cultivation ofsingle species for longer duration.
Basic designs: Flat plate reactors and tubular reactors.
Principle is to reduce path length of light. Tubular array with each tube of 3-4 in. dia.
Microalgal broth is circulated through a degassing tankwith either mechanical pump or airlift pump.
Either horizontal or vertical array is possible.Illumination could be natural or artificial.
Temperature control of broth by placing a coil indegassing tank or circulation of water through a jacket
around tube. Operational difficulties:
Growth of algae in tube walls blocking light.
High oxygen concentration that can inhibit
photosynthesis. Limit on the length of the tube in single run.
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Raceway Ponds vs.
Photobioreactors 13-fold high biomass
productivity and higher oil yieldper hectare in photobioreactors.
Recovery of biomass is also animportant issue.
Recovery cost in
photobioreactor is a minorfraction of total processing costdue to high biomassconcentration.
Total area need forphotobioreactor is smaller.
Effective utilization of area canbe achieved with BIOCOIL.
Typical volume of BIOCOIL:1000 Liter
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Comparison of Large Scale Systems
EasyAchievableEasyLow-highLow-high
ExcellentExcellentUniformTubularreactor(Biocoil)
ReasonableAchievableEasyLow-highLow-high
ExcellentExcellentUniformTubularreactor(serpentine)
DifficultAchievableEasyLow-highHighExcellentExcellentUniformFlat platereactor
DifficultEasilyachievable
EasyLowLow-high
Good(indoors)
Fair-GoodVariableBag culture
DifficultEasilyachievable
EasyLowHighExcellentGoodGenerallyuniform
Airliftreactor
DifficultEasilyachievable
EasyHighLow-high
ExcellentFair-GoodLargelyuniform
Stirred tankreactor
Very difficultNoneDifficultLowPoorNoneFair-GoodFair-goodPaddlewheel
Raceway
V.difficultNoneDifficultLowPoorNoneFair-GoodFairCircularstirred pond
V.difficultNoneDifficultV. PoorPoorNoneV. poorPoorTanks
V.difficultNoneDifficultV. lowPoorNonePoorV.poorUnstirredshallow
ponds
Scale upSterilitySpeciescontrol
Hydrodynamicstress on algae
Gastransfer
Temperaturecontrol
LightutilizationEfficiency
MixingReactorType
EasyAchievableEasyLow-highLow-high
ExcellentExcellentUniformTubularreactor(Biocoil)
ReasonableAchievableEasyLow-highLow-high
ExcellentExcellentUniformTubularreactor(serpentine)
DifficultAchievableEasyLow-highHighExcellentExcellentUniformFlat platereactor
DifficultEasilyachievable
EasyLowLow-high
Good(indoors)
Fair-GoodVariableBag culture
DifficultEasilyachievable
EasyLowHighExcellentGoodGenerallyuniform
Airliftreactor
DifficultEasilyachievable
EasyHighLow-high
ExcellentFair-GoodLargelyuniform
Stirred tankreactor
Very difficultNoneDifficultLowPoorNoneFair-GoodFair-goodPaddlewheel
Raceway
V.difficultNoneDifficultLowPoorNoneFair-GoodFairCircularstirred pond
V.difficultNoneDifficultV. PoorPoorNoneV. poorPoorTanks
V.difficultNoneDifficultV. lowPoorNonePoorV.poorUnstirredshallow
ponds
Scale upSterilitySpeciescontrol
Hydrodynamicstress on algae
Gastransfer
Temperaturecontrol
LightutilizationEfficiency
MixingReactorType
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Algal Production andEconomics Model
WaterA. Net make up
B. Supply system cost
Media Recycle
Algal ProductionA. Yield (gross)
B. Efficiency on ParC. Facility designD. Facility costE. Flow/mass balanceF. Power requirementG. Module hydraulics
H. Energy requirementI. Salinity tolerance
HarvesterA. Capital costB. Energy cost
EconomicsA. Annual operating cost
B. Capital investmentC. Lifecycle revenue required
D. Product pricing
Processing and Storage
Product State
A. Net biomassB. Lipid quantityC. Carbohydrate quantity
D. Protein quantity
Nutrient Recycle
Nutrients for N,K,PA. QuantityB. CostC. System cost
CarbonA. QuantityB. CostC. System cost
WaterA. Net make up
B. Supply system cost
Media Recycle
Algal ProductionA. Yield (gross)
B. Efficiency on ParC. Facility designD. Facility costE. Flow/mass balanceF. Power requirementG. Module hydraulics
H. Energy requirementI. Salinity tolerance
HarvesterA. Capital costB. Energy cost
EconomicsA. Annual operating cost
B. Capital investmentC. Lifecycle revenue required
D. Product pricing
Processing and Storage
Product State
A. Net biomassB. Lipid quantityC. Carbohydrate quantity
D. Protein quantity
Nutrient Recycle
Nutrients for N,K,PA. QuantityB. CostC. System cost
CarbonA. QuantityB. CostC. System cost
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Parameters Affecting Microalgal
Production Economy
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Economic Analysis of
Microalgae Production
Product Cost Contributions by
General Category
Total capital,23.30%
Maintenance
costs, 8.80%
Operating
costs, 67.90%
Economic potential can bejudged by assessingindividual cost centers.
General cost distribution
for total product cost: Operating costs: 68%
Capital costs (depreciable
and non-depreciable): 23% Maintenance costs: 9%
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Capital Costs(Depreciable and Nondepreciable)
Fixed costs: 23.3% withdepreciable equipment
costs: 51% of presentvalue of capital. Culture system (37.7%)
includes moduleconstruction, internaldistribution systems,pond lining, mixingsystem etc.
Other major factors
include site preparationand surveying (26.2%),harvester system (13%)and contingency (12%).
Contributions to Capital Cost
Categories
Harvest
system, 13%
Site
preparation,
26.20%
Culture
system,
37.70%
Contingency
allowance,
11.70%
Engineering
fees, 7.60% Land, 3.80%
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Depreciable Investment
Specific life time foreach equipment
differs but average lifeis ~ 15 years.
Highest contribution
by the harvestingsystem.
Lining of pondbottoms, construction
of piping system,mixing system areother components
contributing todepreciation.
Contributions to DepreciableCapital Investment
Harvesters,
25.70%
Lining,
26.20%
Buildings,
1.70% Carbondioxide
transfer
system,
4.20%
Electric
services,
9.10%
Mixing
system,
13.10%
Culture
system, 14%
Water
system, 6%
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Summarization
Hills analysis gives an idea of economic potentialof microalgal biodiesel:
Production of 33,171 tpa of microalgae incurs totalannualized production cost of $13 million.
This gives cost of algal biomass as $393 per ton or$0.35 per kg with approx lipid content of 30%.
Thus, annual lipid yield is 71072 bbl with production costof $1.2 per liter.
Compare to this, the cheapest vegetable oil costs $465per ton or $0.52 per liter.
Petrodiesel costs approx $0.75/liter (inclusive of taxes at20%, crude oil cost 52%, refinery expenses 19% anddistribution and marketing 9%).
Target price for microalgal oil should be $0.5 per literassuming it is tax free!
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Improvement of MicroalgalBiodiesel Economics
Biorefinery based strategy to utilize everycomponent of biomass raw material. Residual biomass can be animal feed. Anaerobic digestion of biomass for methane production
which can be used for producing electricity.
Revenue earned out of side products can improveeconomics of production.
Other strategies would be genetic and metabolicengineering. Possible methodologies are: Increase photosynthetic efficiency. Enhance biomass growth rate. Increase lipid or oil content of biomass. Elimination of light saturation phenomena, photo-
inhibition effect, susceptibility to bio-oxidation.
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Conclusion
Microalgal route to biodiesel is a potentialalternative to vegetable oil.
Overall economics of the process needs
improvement to be competitive substitute topetrodiesel.
Roots of improvement in economy lie in bothscience and technology of microalgae.
Enhancement in lipid content through geneticmodification is one route.
Much simpler and effective way to achieve the
same goal would through photobioreactorengineering. Extensive research on diverse aspectsof photobioreactor is needed.
Biorefinery approach can also improve the
economics significantly.
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ACKNOWLEDGMENTS
The microalgal biodiesel project atI.I.T. Guwahati has been sponsored
by Defense Research Laboratory(DRDO) at Tezpur, Assam.
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