The document discusses life cycle assessment (LCA) of microalgae-derived biofuels. It begins with an introduction to renewable energy sources and types of biofuels. It then describes the goal of assessing the microalgae cultivation process from an integrated lab-scale system producing biodiesel. The assessment includes microalgae cultivation, biomass harvesting, lipid extraction, and conversion to biodiesel. Key steps involve defining the functional unit, system boundaries, inventory analysis and impact assessment categories to analyze the energy and carbon balance of microalgae biodiesel compared to other fuel pathways.
3. Introduction
With the ever growing world population and technological advances
in all works of life, world energy demand is expected to rise by 44%
while CO2 emissions will see an increase of 39% by the year 2035
(U.S. Energy Information Administration, 2010)
Developments of renewable source of energy
Renewable energy – solar, wind or geothermal; hard to store
Biofuel – biodiesel and bioethanol
Biodiesel advantageous over conventional diesel fuel –
* 4 times faster degradation
* Safer and non-toxic
* Higher flash point (100-170 C)
(NREL, 2009)
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4. Introduction …
1st generation biofuels – bioethanol produced by fermentation of
starch (e.g. wheat, barley, corn or potato) or sugars (e.g. sugarcane
or sugar beet) and biodiesel (FAME) produced by trans-esterification
of oil (e.g. rapeseed, soybeans, sunflower, palm, coconut) and
animal fats
(Chisti, 2007)
2nd generation biofuels – bioethanol and biodiesel produced from the
residual, non-food parts of crops (Jatropha, cassava or Miscanthus),
and from other forms of lingo-cellulosic biomass such as wood,
straw, grasses, and municipal solid wastes
(Inderwildi and King, 2009)
Criticisms – Conversion of food crops into biofuels is unsustainable
(Scharlemann and Laurance,
2008)
– limited energetic and environmental benefits
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5. Introduction …
3rd generation biofuels – algae-derived fuels such as biodiesel from
microalgae oil, bioethanol from microalgae and seaweeds, and
hydrogen from green microalgae and microbes
(Aylott, 2010; Dragone et al.,
2010)
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6. Why algae?
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For production of 60 billion gal/year of biodiesel at a productivity rate
of algae at 50 g/m2/day with 50% triglycerides, the CO2 required for
necessary algae cultivation would be 0.9 billion ton/year which is
36% of the total US power plant emissions
(Pienkos,
2007)
The other nutrients required for cultivation such as nitrogen and
phosphorus can be obtained from organic waste from agri-food
industry
(Cantrell et al., 2009)
Oil yield from microalgae per acre of land used is huge
Plants/ organisms Oil yield (gallons/acre)
Soybean 48
Jatropha 202
Palm oil 635
Algae @ 10 g/m2/day with 15% triglyceride 1200
Algae @ 50 g/m2/day with 50% triglyceride 10000
Biofuels from microalgae are fast attracting international research
interest
* They do not compete for agricultural land
* High photon conversion efficiency
* Metabolic storage of intracellular lipids, carbohydrates and
triglycerides
* They produce 15-300 times more feedstock for biodiesel
production than conventional, terrestrial bioenergy crops
(Chisti, 2007)
Coupling photosynthetic efficiency with biomass production offers
exciting prospects for producing renewable biofuels
(Greenwell et al., 2010; Scott et al.,
2010)
7. Hurdles
Various technological and economic issues (commercial scale
deployment, cost of the biodiesel)
It is important to study in detail the environmental impacts of
implementing such technologies and their sustainability to avoid
„problem shifting‟ or “The displacement or transfer of problems
between different environmental pressures, product groups,
countries or over time”
Need for adoption of a cradle-to-grave perspective and assessment
of several environmental impacts
Life Cycle Assessment/Analysis (LCA) - ISO method: it allows the
detection of pollution transfer from one step to another one or from
one kind of environmental impact to another one
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8. Life cycle assessment
“Compilation and evaluation of the inputs, outputs and the potential
environmental impacts of a product system throughout its life cycle.”
- International Organization for Standards (ISO, 1997)
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9. Types of LCA
Conceptual LCA – Life Cycle Thinking
Very basic level assessment of environmental aspects
presented using qualitative statements, graphics, flow diagrams or
simple scoring systems which indicate which components or materials
have the largest environmental impacts and why
Simplified LCA
Covers whole life cycle superficially by using generic data and
standard modules for energy production
* Screening
* Simplifying
* Assessing reliability
Detailed LCA
Involves full process of undertaking LCAs and require extensive
and in-depth, data collection, specifically focused upon the
target of the LCA
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10. Phases of LCA
LCA generally has 4 phases -
(i) Goal and scope definition
(ii) Inventory analysis (LCI)
(iii) Impact assessment (LCIA)
(iv) Interpretation
All phases are often interdependent in that the results of one phase
will inform how other phases are completed
(ISO 14040-14044:
2006)
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11. Starting key step
* Sets out the context of the study
* Explains how and to whom results are to be communicated
The goal and scope of a LCA should be
* Clearly defined
* Consistent with the intended application
The goal and scope documents:
* The functional unit
* The system boundaries
* Any assumptions and limitations
* The allocation methods used to partition the environmental
load of a process when several products or functions share
the same process
* The impact categories chosen
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Goal and Scope Definition
12. Defines what is being studied
Quantifies the service delivered by the product system
Provides a reference to which the inputs and outputs can be related
Enables alternative goods, or services, to be compared and analysed
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Functional Unit
can be set to different extends depending upon the goal of the study
Variants:
cradle to grave (raw material extraction- usage of the product)
cradle to gate (raw material extraction- production)
cradle to cradle (extraction of raw material- production- distribution-
usage- disposal- recycling)
gate to gate (production process)
System Boundaries
13. Involves creating an inventory of flows from and to nature for a
product system
Development of a flow chart of the system to show mass and energy
flows included in the processes
Compilation of the mass and energy inputs and outputs and their
quantification throughout the life cycle of the system
(Rebitzer et al., 2004)
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Life Cycle Inventory (LCI)
14. Evaluates the environmental and potential human health impacts of
the system
4 mandatory elements:
* selection of impact categories, category indicators and
models,
* assignment of the LCIA results (classification),
* calculation of category indicator results (characterisation),
* data quality analysis
Optional elements:
* Normalization: Comparison of the results of the impact
categories from the study with the total impacts in the region of interest
* Grouping: Sorting and possibly ranking the impact categories
* Weighting: Allowance or adjustments of the different impacts
relative to each other so that they can then be summed to get a single
number for the total environmental impact
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Life Cycle Impact Assessment (LCIA)
Impact categories Category indicators Classification Characterization
Global Warming
Potential
GWP CO2 Kg CO2 eq.
Acidification
Potential
AP SO2 Kg SO2 eq.
Eutrophication
Potential
EP PO4
3- Kg PO4
3- eq.
Ozone Depletion
Potential
ODP CFC-11 Kg CFC-11 eq.
Photochemical
Ozone Creation
Potential
POCP C2H2 Kg C2H2 eq.
Abiotic Depletion
Potential
ADP Oil/mineral Oil/mineral eq.
15. GHG emissions to the atmosphere retain heat in the Earth‟s
ecosystem by absorbing reflected radiation, resulting in global
warming
GWP is an index to measure the contribution to global warming of a
substance that is released into the atmosphere
E1 = Σ eC1,jBj (kg)
(Bj = Emission of green house gas j
eC1,j = GWP factor for j)
Expressed relative to GWP of CO2
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Global Warming Potential (GWP)
j = 1
J
1
16. Acidification is a consequence of acids being emitted to the
atmosphere and subsequently deposited in surface soils and water
resulting in negative consequences for coniferous trees and the
death of fish in addition to increased corrosion of manmade
structures
AP is based on the contributions of SO2, NOx, HCl, NH3 and HF to
the potential acid deposition in the form of H+ (protons)
E2= Σ eC2,jBj (kg)
(Bj = Emission of gas j
eC2,j = AP of gas j)
Expressed relative to AP of SO2
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Acidification Potential (AP)
j = 1
J
2
17. Eutrophication originates mainly from N and P (such as N, NOx,
NH4+, PO4
3-, P and COD) in sewage outlets and fertilizers
Nutrients accelerate the growth of algae and other vegetation in
water. Degradation of this organic material consumes oxygen
resulting in oxygen deficiency and fish kill
EP quantifies nutrient enrichment by the release of substances in
water or into soil
E3= Σ eC3,jBj (kg)
(Bj = Emission of a species j
eC3,j = EP of species j)
Expressed relative to EP of PO4
3-
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Eutrophication Potential (EP)
j = 1
J
3
18. The ozone layer in atmosphere protects plants and animals from the
sun‟s harmful UV radiation
Some substances in atmosphere (CFCs, halogenated hydrocarbons,
N2O) make the ozone layer decline, resulting in an increased UV
radiation level at ground level
E4= Σ eC4,jBj (kg)
(Bj = Emission of a ozone depleting gas j
eC4,j = ODP factor of j)
Expressed relative to ODP of CFC-11
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Ozone Depletion Potential (ODP)
j = 1
J
4
19. Photochemical ozone (ground level ozone or summer smog) is
formed by reaction of VOCs and nitrogen oxides in presence of heat
and sunlight
Excess ozone can lead to damaged plant leaf surfaces,
discolouration, reduced photosynthetic function and ultimately death
of the leaf and finally the whole plant and in animals, it can lead to
severe respiratory problems and eye irritation
E5= Σ eC5,jBj (kg)
(Bj = Emission of species j participating in
summer smog formation
eC5,j = Classification factor for smog formation)
Expressed relative to the POCP classification factor for ethylene
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Photochemical Ozone Creation
Potential (POCP)
J
j = 1
5
20. ADP includes depletion of non-renewable resources i.e. fossil fuels,
metals and minerals
E6= Σ Bj / eC6,j
(Bj = Quantity (burden) of the resource used
eC6,j = Estimated total world reserves of that resource)
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Abiotic Depletion Potential (ADP)
J
j = 1
Other Impact categories
Human Toxicity Potential (HTP)
Aquatic Toxicity Potential (ATP)
6
22. Systematic technique to identify, quantify, check, and evaluate
information from the results of LCI and LCIA
Interpretation should include:
* Identification of significant issues based on the results of the
LCI and LCIA phases of an LCA
* Evaluation of the study considering completeness, sensitivity
and consistency checks
* Conclusions, limitations and recommendations
Helps to determine the level of confidence in the final results and
communicate them in a fair, complete, and accurate manner
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Interpretation
23. Micro-algal biofuel production consists of 4 processes:
* Microalgae cultivation
* Biomass harvesting
* Micro-algal oil (lipid) extraction
* Oil conversion to final products (e.g. biodiesel)
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Case Study
24. LCA goal and scope
ICES microalgae-to-biodiesel production:
- From cultivation and harvesting (integrated lab-scale),
- Lipid extraction (lab scale with estimated energy requirements),
- Theoretical conversion (from literature),
- Sensitivity analysis.
Comparison of ICES microalgae-to-biodiesel system with five other
case studies
For (II), comparisons will be made against ICES ‘Base Case’
and a projected ‘Optimistic Case’
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The selected functional unit for all cases is 1 MJ as
the high calorific value of biodiesel
Methods
25. It can be quantified by comparing energy inputs required in each LCA
stage and compare the total required inputs with the embodied energy
of that biofuel product
CO2 balance
It is critical to consider the total emissions from fossil energy and
resource consumption Vs. the CO2 intake by the microalgae during
cultivation
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Energy balance
1 tonne of algal biomass is estimated to
fix (or sequester) 1.5-1.8 tonnes of CO2
(Patil et al., 2008)
26. From cradle-to-gate, starting from microalgae cultivation and
ends with biodiesel production as the main product
The ‘cradle’ stage begins with an integrated photobioreactor-
raceway system for cultivating microalgae Nannochloropsis sp.
From here, wet biomass is harvested and dewatered to
produce dry biomass
Lipid extraction is carried out with the use of solvents which
are assumed to be fully recycled
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Modelling parameters
27. The production of biodiesel from lipid is carried out via trans-
esterification with the help of methanol
Main energy inputs and CO2 emissions/absorption by
microalgae will be included throughout the life cycle
Emissions of wastewater and other types of air pollutants are
not covered in the LCA
Any by-products (glycerine) are also not taken into account
Waste (solids or wastewater) treatment is not covered in the
LCA
The final heat energy content of the biodiesel product is 40
MJ/kg (base case)
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Modelling parameters …
29. Microalgae: Nannochloropsis sp.
Culturing system: Integrated PBR and raceway pond
Doubling time: 12 hours
Cell density: 0.5 g/L
2000 L culture volume needed to produce 1 kg biomass
Growth medium provided with elements (N and P) in PBR
Energy requirement for CO2 pumping (2%) for mixing: 0.0222 kWh
per kg CO2
(Kadam, 2002)
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Microalgae cultivation
31. Coagulant: FeCl3.6H2O @ 250 mg/g biomass
Air sparging assisted coagulation flocculation (ASACF) process
Biomass content: 3%
Energy consumption in ASACF: 16.7 kJ
Dewatering by centrifugation
Biomass content: 15% energy consumption by centrifuge: 360 kJ/kg
of biomass (dry equivalent)
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Biomass harvesting
32. Microalgae contains 15-60% lipids per dry biomass weight
(Demirbas et al., 2011)
Lipid content of 25% to be extracted from the dry microalgal biomass
Solvent extraction: hexane: methanol (3:1 by volume)
Solvent-to-dry biomass: 20:1
Lipid-depleted biomass settles at the bottom
Extract was decanted and filtered
Evaporation and recycling
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Microalgal oil (lipid) extraction
33. Total energy demand (lipid extraction process + evaporation step):
3.8 MJ per MJ biodiesel (or 152 MJ/kg)
A simple mass balance is applied as:
From the content of 25% lipid in algal biomass, 1 kg of dry micro-
algal biomass can produce a theoretical maximum of 0.25 kg of
lipids. This further translates to 4 kg dry biomass per kg lipid
From 1 kg lipid produced, 90% is converted to biodiesel. Therefore
the total amount of dry algal biomass required to produce 1 kg
biodiesel = 4.44 kg dry biomass
Heat of combustion of the microbial oils can be 38-42 MJ/kg.
(Sorguven and
Özilgen,2010)
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Micro-algal oil (lipid) extraction …
34. Chemical conversion of oil by trans-esterification
Total energy input: 540 MJ/tonne biodiesel
(Janulis,
2004)
30.3 MJ of energy required to produce 1 kg methanol (methanol :
lipid = 6.5:1)
(Pleanjai and Gheewala,
2009)
50% methanol recycled
Total energy consumption per kg biodiesel = 0.054 MJ/kg (electricity
input) + 3.15 MJ/kg (methanol input) = 3.2 MJ/kg
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Biodiesel production
35. Preliminary energy and CO2 results
Energy requirement: 0.56 MJ Energy requirement: 3.88 MJ
per MJ biodiesel per MJ biodiesel
Total energy demands: (0.56 + 3.88) = 4.44 MJ (13% = biomass
production, 85% = lipid extraction and 2% = biodiesel production)
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Results and discussions
36. Sensitivity analysis
Increase of lipid content from 25% to 35% and 45%
Manipulation of micro-algal lipid metabolisms
(i) Induce nutrient stress during cultivation
(ii) Selection of species with high lipid content
(Greenwell et al.,
2010)
Lower energy requirements for lipid extraction by 1.5 MJ and 2.5
MJ per MJ biodiesel
Nannochloropsis sp. contain very rigid cell walls
(Wijffels et al., 2010)
* Lipid extraction is a big challenge
* Energy decrements as small steps
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Results and discussions …
37. Sensitivity analysis
Heat of final biodiesel product value of 38 and 42 MJ/kg
Energy content of biodiesel ranges between 38 and 42 MJ per
kg biodiesel
(Sorguven and Özilgen, 2010)
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Results and discussions …
38. LCA comparisons with other case studies
Comparison of energy and environmental performance based on
both laboratory and projected (hypothetical) industrial scale
(Stephenson et al., 2010; Lardon et al.,
2009)
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Results and discussions …
39. LCA comparisons with other case studies
Parameters: (i) lipid content of 45%
(ii) 1.8 MJ per MJ energy demands for lipid extraction
(iii) final heating value of product 42 MJ/kg
Total life cycle energy demand for ICES „Base Case‟: 4.44 MJ per MJ
biodiesel (25% efficiency)
LCA carried out by NREL in 1998 reported an input of 1.2 MJ of fossil
energy to produce 1 MJ conventional petro-diesel (83.3%efficiency)
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Results and discussions …
40. Further discussions (limitations)
Quantitative investigations of different LCA systems and results are
not straightforward
Cases differ in species variation, cultivation methods, operating
conditions and use of biomass to make different products
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Results and discussions …
41. Further discussions (limitations)
No internationally agreed conclusion on the environmental burdens
or benefits from this seemingly green renewable energy alternative
This case study was investigated to emphasize the main challenges
of the microalgae-to-biodiesel value chain
„Base Case‟ results highlighted that the main energy burdens were
from lipid extraction (primarily) and next, biodiesel production
From the „Base Case‟, sensitivity analysis was performed by making
adjustments to the energy requirements, percentages of lipid
contents, and lower and higher heating product value
In „Optimistic Case‟, total life cycle energy requirements dropped
significantly – by nearly 60%
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Results and discussions …
42. LCA is used to analyse various microalgae-to-biofuel production
Main bottleneck for most systems lie in the energy intensive
processes of lipid extraction, and next, biodiesel production
Highly favourable results can be generated when the energy
requirements for the extraction of lipids or biodiesel production were
excluded from the study
Each unique case is modelled with different LCA assumptions or
conditions, making a justified comparison rather difficult
However, this does not undermine the importance of using LCA to
set an overall benchmark and test the feasibility of any biofuel
production system
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Conclusions
43. Systematically estimate the environmental consequences and to
analyse the exchanges that take place to the environment and are
related to the examined product or process
Quantify the emissions into air, water and land that take place in
every life cycle phase
Detect significant changes in the environmental effects between the
life cycle phases
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Advantages of LCA
Estimate the effects of materials consumption and environmental
emissions on human and the eco-system
Compare the consequences to human and to the eco-system of two
or more competitive products or processes
Allocate the impacts of the examined product or process in one or
more items of environmental interest
44. A holistic LCA is a very data-intensive and time-consuming
procedure
There is not a generally acceptable LCA methodology
The selected and analysed system in some of the studies does not
include the overall life cycle of the examined product or process, but
it is only confined to specific stages
The assumptions made in such studies might be subjective
The results of such studies are focused on national and regional
level and they might not be suitable for local applications
The accuracy of a LCA study depends on the quality and the
availability of the relevant data
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Disadvantages of LCA
45. LCA for algal biofuel production demand a careful design of
reference system, system boundary and inventory establishment
Contemplating the next decade of LCA involves considering the
dynamic processes in the human and natural environments that may
drive the need for assessment of environmental burdens
Utilization of biological nitrogen, CO2 and NO2 for some special
purpose
Co-products, by products and residues can enhance energy and
GHG savings through substitution of fossil fuel use
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Future prospects