1. by
N. AARTHI PRIYANGA

2. What are microalgae?
Microalgae are prokaryotic or eukaryotic photosynthetic
microorganisms that can grow rapidly and live in harsh
conditions due to their unicellular or simple
multicellular structure.
Examples:
Prokaryotic microorganisms: Cyanobacteria
(Cyanophyceae)
Eukaryotic microalgae: Green algae (chlorophyta)
and diatoms (Bacillariophyta)

3. Biology of microalgae
 Algae are recognised as one of the oldest life-forms.
They are primitive plants (thallophytes), i.e. lacking
roots, stems and leaves, have no sterile covering of cells
around the reproductive cells and have chlorophyll a as
their primary photosynthetic pigment.
 Algae structures are primarily for energy conversion
without any development beyond cells, and their
simple development allows them to adapt to prevailing
environmental conditions and prosper in the long
term.

4. Biofuels
cosmetics
Pharmaceuticals
Nutrition
Aquaculture
Food additives
Pollution prevention
Biotechnology areas of microalgae

5. Biodiesel from microalgae why?
 Energy is of vital importance to society and human.
 Biomass energy, as a green and renewable resource,
has been considered to be one of the best ways to solve
the global energy crisis.
 Microalgae is an economical and potential raw
material of biomass energy, because it does not require
a large area of land for cultivation, exhibits short
growth period, possesses a high growth rate and
contains more high-lipid materials than food crops.

6. Biodiesel from microalgae why?
 Recent studies have demonstrated that microalgae has
been widely regarded as one of the most promising
raw materials of biofuels. However, lack of an
economical, efficient and convenient method to
harvest microalgae is a bottleneck to boost their full-
scale application.

7. Technologies for the production of
microalgal biomass production
 Under natural growth conditions phototrophic algae absorb
sunlight, and assimilate carbon dioxide from the air and
nutrients from the aquatic habitats.
 Therefore, as far as possible, artificial production should attempt
to replicate and enhance the optimum natural growth
conditions.
 The use of natural conditions for commercial algae production
has the advantage of using sunlight as a free natural resource .
 However, this may be limited by available sunlight due to diurnal
cycles and the seasonal variations; thereby limiting the viability
of commercial production to areas with high solar radiation.
 For outdoor algae production systems, light is generally the
limiting factor .

8. Open ponds
 Open ponds are the most widely used system for large-
scale outdoor microalgae cultivation.
 Commercially economical.
 Easy to build and operate.
 Depending on their size, shape, type of agitation and
inclination, the open pond systems can be classified
into (a) raceway pond, (b) circular pond, and (c)
sloped pond

9. Figure 1 Three different designs of open pond systems

10. Enclosed PBR
 Two major types of enclosed PBR are tubular and plate
types.
 Due to enclosed structure and relative controllable
environment, enclosed PBR can reach high cell density
and easy to maintain monoculture.

11. Hybrid systems
 Other types of systems are an internally illuminated
photo bioreactor (Helix PBR) developed by Origin oil
company.
 The light array rotates vertically that allows algae
growth in deep media and provides agitation.
 The light array consists of blue, red and white lights,
which are the wavelengths the algae prefer.

12. Harvesting and drying of algal biomass
 There are currently several harvesting methods,
including mechanical, electrical, biological and
chemical based.
 In mechanical based methods, microalgal cells are
harvested by mechanical external forces, such as
centrifugation, filtration, sedimentation, dissolved air
flotation and usage of attached algae biofilms and
ultrafiltration membranes.

13. Harvesting and drying of algal
biomass
 (1) Bulk harvesting—aimed at separation of biomass
from the bulk suspension. The concentration factors
for this operation are generally 100–800 times to reach
2–7% total solid matter. This will depend on the initial
biomass concentration and technologies employed,
including flocculation, flotation or gravity
sedimentation.
 (2) Thickening—the aim is to concentrate the slurry
through techniques such as centrifugation, filtration
and ultrasonic aggregation, hence, are generally a
more energy intensive step than bulk harvesting.

14. Flocculation and ultrasonic
aggregation
 Microalgae cells carry a negative charge that prevents
natural aggregation of cells in suspension, addition of
flocculants such as multivalent cations and cationic
polymers neutralises or reduces the negative charge.
 It may also physically link one or more particles
through a process called bridging, to facilitate the
aggregation.
 Multivalent metal salts like ferric chloride (FeCl3),
aluminium sulphate (Al2 (SO4)3) and ferric sulphate
(Fe2 (SO4)3) are suitable flocculants.

15. Harvesting by flotation
 Flotation methods are based on the trapping of algae
cells using dispersed micro-air bubbles and therefore,
unlike flocculation, do not require any addition of
chemicals.
 Some strains naturally float at the surface of the water
as the microalgal lipid content increase.

16. Gravity and centrifugal sedimentation
 Gravity and centrifugation sedimentation methods are
based on Stoke’s Law, i.e. settling characteristics of
suspended solids is determined by density and radius
of algae cells (Stoke’s radius) and sedimentation
velocity.
 Gravity sedimentation is the most common harvesting
technique for algae biomass in wastewater treatment
because of the large volumes treated and the low value
of the biomass generated.

17. Biomass filtration
 A conventional filtration process is most appropriate for
harvesting of relatively large (>70 mm) microalgae such as
Coelastrum and Spirulina.
 It cannot be used to harvest algae species approaching
bacterial dimensions (<30 mm) like Scenedesmus,
Dunaliella and Chlorella.
 Conventional filtration operates under pressure or suction,
filtration aids such as diatomaceous earth or cellulose can
be used to improve efficiency .
 For recovery of smaller algae cells (<30 mm), membrane
microfiltration and ultra-filtration (a form of membrane
filtration using hydrostatic pressure) are technically viable
alternatives to conventional filtration.

18. Drying
 Harvested algae contain 97%-99% water.
 Removal of most of the water is necessary for long term
storage of the algae feedstock and is required for many
downstream processes.
 To keep algae from prolonged microbial growth, the
moisture level of the harvested algae should be kept below
7%.
 Drying is an energy intensive process and can account for
up to 30% of the total production costs.
 Natural drying (solar and wind) is the most economical
way; however, its weather dependent nature could easily
put the operation at risk of spoilage.
 It also requires a large space.

19. Processing
 Extracting the oil and converting the oil from algae to
biodiesel are the primary driving force for algae to
fuels technology development.
 The oil extracted can be converted to biodiesel via
transesterification reaction.
 Nevertheless, the whole algae or the residues from oil
extraction are excellent feedstock for making other
fuels and products via different processes.
 For example, the starch and cellulose components are
suitable for ethanol fermentation.

20. Oil extraction
 Extraction of oil from algal biomass has proven to be
difficult and expensive.
 Organic solvent extraction is a widely used method for
lipid extraction from traditional oilseed plants, and
different extraction systems have also been tested with
algae cultures .
 In order to maximize the lipid extraction efficiency,
the organic solvent used has to match the lipid polarity
profile in the cells.

21. In situ transesterification
 Conventional transesterification process requires
costly oil extraction and separation.
 If fatty acid containing lipids are simultaneously
extracted and transesterified, it would eliminate the
need to extract and separate the lipids and fatty acids
contained in the algae.
 Direct or in situ transesterification has been proven in
a number of feed stocks including marine tissues,
yeast and fungi, bacteria, microheterotrophs, algae
fatty acid, and municipal primary and secondary
sludge.

22. Ethanol fermentation of starch and
cellulose in Algae
 Algae contain substantial amounts of starch and
cellulose which, in theory, can be fermented to ethanol
using existing technologies.
 The concept appears to be straightforward and has
attracted business attention.

23. Thermochemical conversion
 Algal biomass, either whole algal cells or extraction
residues, are suitable feedstock for thermochemical
conversion such as gasification, pyrolysis, and
hydrothermal liquefaction and gasification to produce
syngas, bio-oil, biopolyols, and biochar.

24. Gasification
 In gasification, biomass is converted to a combustible
gas mixture called “synthesis gas (syngas)” or
“producer gas” through partial oxidation reactions at
high temperature typically ranging from 700 to 1
100°C.
 Syngas may vary in composition with type and
moisture content of feedstock, type of gasifiers,
gasification conditions, etc.
 Syngas can be burned to produce heat or used in gas
engines or gas turbines to produce electricity.

25. Pyrolysis
 Pyrolysis is another important thermochemical
conversion process in which biomass is degraded to
bio-oil, syngas, and biochars at medium high
temperature (300-600°C) in the absence of oxygen.
 Biomass is usually heated through heated surface or
sands.
 The pyrolysis products generally include bio-oil, gas
and char, and nowadays bio-oils are preferred because
they have the potential to be upgraded to liquid
transportation fuels.

26. Hydrothermal liquefaction and
gasification
 Hydrothermal liquefaction refers to decomposition
reactions taking place in water media at high temperature
and high pressure.
 The high temperature and high pressure create a unique
condition termed “supercritical water” in which chemical
reaction rates are significantly enhanced.
 At lower temperature range (200–400°C) the reactions
produce more liquid products (bio-oil or bio-crude), and
therefore termed hydrothermal liquefaction.
 Hydrothermal gasification processes generally take place at
higher temperatures (400–700°C) and produce methane or
hydrogen gases.

27. Anaerobic digestion
 The harvested algae biomass, under anaerobic
condition and inoculation of certain groups of
bacteria, i.e. hydrolytic and fermentative bacteria,
acetogenic bacteria, methanogenic bacteria, can be
fermented to methane, which is another way to
produce renewable energy.

28. Value added co products of biodiesel
 Biodiesel production will generate about 10% (w/w)
glycerol as the main byproduct.
 Omega 3 fatty acids are polyunsaturated fatty acids
(PUFAs) and essential components for the growth of higher
eukaryotes.
 Nutritionally, eicosapentaenoic acid (EPA, 20:5) and
docosahexaenoic acid (DHA, 20:6) are the most important
fatty acids belonging to this group of bioactive compounds.
 These long chain omega 3 fatty acids provide significant
health benefits to the human population, particularly in
reducing cardiac diseases such as arrhythmia, stroke and
high blood pressure

29. Other uses of microalgae
 Microalgae are used as human nutrition, animal feed,
aquaculture etc.
 Algal biomass contains 20%-40% protein, 30%-50%
lipid, 20% carbohydrate, and 10% other compounds.
 Depending on the conversion processes, a range of
products can be obtained from algal biomass.

30. Biodiesel future!!!
 Biodiesel has become more attractive recently because
of its environmental benefits and the fact that it is
made from renewable resources.
 With the increase in global human population, more
land may be needed to produce food for human
consumption (indirectly via animal feed).