a review on micro algae, a versatile source for sustainable

8/8/2019 A Review On Micro Algae, A Versatile Source for Sustainable

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INTERNATIONAL JOURNAL OF ENERGY RESEARCH

Int. J. Energy Res. (2010)

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/er.1695

REVIEW

A review on microalgae, a versatile source for sustainable

energy and materials

K. G. Satyanarayana1, A. B. Mariano2 and J. V. C. Vargas2,,y

1PIPE & Department of Chemistry, Federal University of Parana, Centro Politecnico, CP 19081, Jardim das Americas, CEP:81531-980,

Curitiba, Parana, Brazil2Nucleo de Pesquisa e Desenvolvimento de Energia Auto-Sustentavel-DEMEC-UFPR, Centro Politecnico, CP 19011, Jardim das

Americas, CEP:81531-980, Curitiba, Parana, Brazil

SUMMARY

Increasing energy demands, predicted fossil fuels shortage in the near future, and environmental concerns due tothe production of greenhouse gas carbon dioxide on their combustion have motivated the search for alternativeclean energy sources. Among many resources for this, microalgae have been found to be most promising due totheir high production capacity of vegetable oils. They possess a high growth rate, need abundantly available solarlight and CO2, and thus are more photosynthetically efficient than oil crops. Also, they tolerate high concentrationof salts allowing the use of any type of water for the agriculture and the possibility of production using innovativecompact photobioreactors. In addition, microalgae are a potential source of biomass, which may have greatbiodiversity and consequent variability in their biochemical composition. This paper presents an overview onmicroalgae with particular emphasis as a source for energy (biofuel/electricity) and new materials. Criticalissues involved in production of microalgae and their use, future R & D to overcome these, including the workinitiated by the authors at Federal University of Parana , UFPR, in Brazil are discussed. Copyright r 2010 JohnWiley & Sons, Ltd.

KEY WORDS

biodiesel; biogas; biomass; microalgae; photobioreactor; biodigester; sustainable energy

Correspondence*J. V. C. Vargas, Nucleo de Pesquisa e Desenvolvimento de Energia Auto-Sustentavel-DEMEC-UFPR, Centro Politecnico, CP 19011,

Jardim das Americas, CEP:81531-980, Curitiba, Parana, Brazil.yE-mail: [email protected]

Contract/grant sponsor: CNPq; contract/grant number: 552867/2007-1,574759/2008-5

Contract/grant sponsor: Araucaria Foundation of Parana; contract/grant number: 13470

Received 16 August 2009; Revised 8 January 2010; Accepted 11 January 2010

1. INTRODUCTION

Continuously growing population has led to increasingenergy demands all over the world. The reported

current consumption of petroleum is at 105 times faster

than nature can create [1]. These facts, along with the

limited resources of oil reserves (stocks of fossil fuels)

and its use contributing to the increase of atmospheric

CO2 resulting in global warming [2] are currently

recognized as great threats to mankind. Hence, both

the demanding energy requirement and the ecological

considerations have led to finding substitutes for the

fossil fuels by other resources including renewable

sources derived from biologically based fuels such as

biomass and biofuels (biocombustible, methane and

ethane) [3], which have attracted increased attention asevident from the growing literature [270]. Biofuels have

become increasingly necessary for the global fuel market

[29] with the reported annual estimated world raw

biomass energy potential in 2050 to be 150450 EJ

(E51018) leading to higher net farm incomes [19]. Also,

biomass energy meets the increasing demands in various

countries with Brazil between 23 and 30%, Finland

20.4% and Sweden 17.5% [19]. Such a fuel should also

be biodegradable and non-toxic [16]. Biofuel is a fossil

fuel replacement that is produced from vegetable oils,

Copyrightr 2010 John Wiley & Sons, Ltd.


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recycled cooking fats or waste oils, animal fats, or

microalgal lipids [29] and is known to mankind even

from ancient days [37]. Table I lists some of the

renewable sources of biodiesel including microalgae.

Those oils are renewable since plants and microalgae

produce oils from sunlight and air, and can do so year

after year on cropland [29]. Substitution of the diesel

used in the transport sector by the biodiesel producedstarting from cultivated plants would need the use of

massive lands that are presently used to produce food

[27]. A plant with the largest oil production for culti-

vated area is the Palm [2,38]. Even with the use of palm

oil to produce sufficient amount of biodiesel just to

meet the half of the demand of fuel for transport in the

United States would require about 24% cultivable area

in that country [2]. Currently, the fiscal incentives of-

fered by several governments all over the world for the

production of biofuels from renewable resources are

contributing for the decrease of the land for the pro-

duction of food, which result in higher land costs.

Also, biodiesel derived from oil crops (e.g. soybean,palm) cannot realistically meet existing costs of higher

fraction of the raw materials and competitive demand

of the soil for their growth [29]. This is due to the cost

of raw material accounting 5085% for the total

production cost in the current technique of the

preparation of biodiesel from these sources [9].

Therefore, the cost of material is the dominant factor

in fixing the price of biodiesel. Hence, there are nu-

merous criticisms for such promotion of lands for re-

newable source of energy [23] and also arguments for

and against the biofuels from microalgae and plant

resources [2,3,30,40,41].

One possibility to overcome the problem is the cul-

tivation of microalgae, which is biological fuel source[3] and seems to be a promising source for the pro-

duction of biofuels since they use carbon dioxide for

their energy in addition to sun light and carbon supply.

Also, they have higher photosynthetic efficiency than

terrestrial plants and are efficient carbon dioxide fixers

[3]. Therefore, higher biomass productions along with

faster growth rate over energy crops [15,16,29] are

observed. Additionally, high production of biomass

and some metabolites are achieved by their hetero-

trophic growth [4244]. Microalgae (Dunaliella tertio-

lecta), which was grown under highly saline conditions

produced about 36% oil [17]. Further, depending on its

capability of higher photosynthetic efficiency and other

characteristics mentioned above, microalgae wouldhave cost advantage. One reason for this could be that

the oil content of several microalgae species might

reach up to 80% of its dry weight and their pro-

ductivity can be enhanced by genetic manipulations

making microalgal biodiesel economically competitive

with petrodiesel through large-scale production of ge-

netic microalgal biomass [29].

The utilization of microalgae as a renewable source

for obtaining fuel was an old concept proposed in fif-

ties with follow up in sixties and seventies particularly

for producing biogas [32] and later reported for liquid

fuel in eighties and nineties [2,3], but received increased

attention in recent times due to the reasons mentionedearlier (increasing petroleum and ecological con-

siderations) [12] Also, this seems to be the ideal solu-

tion for total substitution of the diesel used in the

transport [2].

Considering the above facts, this paper gives an

overview on microalgae with particular emphasis as a

source for energy (electricity) and new materials. Pro-

duction of microalgae, their characteristics and appli-

cations in various areas are presented. Perspectives for

microalgae including the work initiated by the authors

at Federal University of Parana (UFPR) are also given.

Therefore, in order to complete this review study, the

application of the ideas collected in the literature review

is also included with a brief description and status of anongoing project by the authors. The main objective is to

provide the reader with an assessment of the feasibility

of innovative microalgae biomass-based projects.

2. MICROALGAE

The microalgae (Figure 1) [71], one of the oldest living

organisms, are the unicellular algae that exist indivi-

dually, or in chains or groups [29] that form the base of

the alimentary chain in the seas and rivers and they are

known as plankton. There are more than 105 types of

microalgae used to produce biodiesel only. Further,

they are known as essential components of coral reefs.

It is reported [32] that in addition to being exception-

ally diverse, they represent highly specialized group of

organisms, which can adapt to various ecological

habits. The current market for microalgae is in the

cosmetics, food industries and also in aquaculture [45].

In the cosmetic industry, the algae are marketed in

frozen condition and they supply the matter, which is

necessary for the preparation of anti-wrinkle cream

Table I. Oil yield of sources of biodiesel (adapted from

Chisti [2]).

So urce Yi eld o f oil (L h a1) Required land area (Mha)

Corn 172 1540Soyabean 446 594

Canola 1190 223

Jatropha 1892 140

Coconut 2689 99

Oil palm 5950 45

Microalgaey 70 405 7.6

Microalgaez 35 202 15.2

To meet 50% of all transport fuel needs of U.S.A.y40% oil (% dry wt) in biomass.z20% oil (% dry wt) in biomass.

A review on microalgaeK. G. Satyanarayana, A. B. Mariano and J. V. C. Vargas

Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd.

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due to its great concentration in long chain fatty acids

with great regenerative capacities of the skin. That

differentiated composition of long chain fatty acids,

mainly the unsaturated ones such as Omega-3 and

Omega-6, besides the high concentration of proteins

and carbohydrates makes the microalgae as ideal

sources of nutrients for the preparation of functional

foods, food additive or even in nutraceuticals [46].

Microalgae, which are the microscopic organisms,

present possibility for higher oil production capacity

reaching up to 77% of their dry weight [2]. Table II

lists oil content of some of the microalgae.

Besides, microalgae possess a high growth rate with

duplicating the number of cells several times in a singleday [32,47]. The microalgae have advantages over the

cultivated plants such as faster growth, yield of high

amount of oils and possibility of the use of any kind of

water for their culture. They can also generate biomass

in suitable reactors [32,47] many more times per unit

area of land than growing agricultural crops that

double in size over several days or weeks, or trees that

grow on a timescale of years throughout the year. The

microalgae present a very simple cellular structure in

relation to the oil crops that have been supplying

transport systems. Depending on the species, their sizes

can range from a few micrometers (`m) to a few hun-

dreds of micrometers [29]. The accumulated chemical

energy after the photosynthesis process is not diverted

for the construction of complex structures allowing

this way, the best use for the production of new cells.

In addition, they are also potential source of biomass

or specific products (e.g. lipids, pigments, antioxidants)

[18]. Other advantages of microalgae for their becom-

ing as feedstock for biofuels and materials include [32]:

ability to synthesize and accumulate about 2050%

dry cell weight of neutral lipids/oil; use of waste land

(desert, arid and semi arid), which is unsuitable for

agriculture and use of N2 and P as nutrients from

different kinds of waste water sources.

2.1. Market and cost for microalgae and

different products produced by it

Estimated annual world production of biomass is

about 50007500 t [24,48] generating annual turnover

of about US$ 1.25 billion. Meanwhile the market for

microalgae to produce the biomass to be used mostlyin health food, animal feed and aquaculture is fast

growing with an estimated retail value of US$

30004000 million [49]. With an assumption of free

availability of CO2, estimated cost [2] for producing

microalgae by two different methods (raceway ponds

and photobioreactors with identical production capa-

cities of 100 000 kg) are US$ 3.80 and US$ 2.95 per kg,

respectively. These costs could be reduced by increas-

ing the production to 10 000 t. Based on this, cost of 1 l

of biofuel produced by the photobioreactor produced

biomass is estimated to be US$ 2.8 assuming 30% oil

content in the biomass, which is higher than that

produced by vegetable oil such as palm oil (US$ 0.66),

which in turn is 35% higher than the petrodiesel (US$

0.49), both of which are free of tax and transportation

charges and prices as existed in 2006 in USA. Other

cost comparisons of 1 l of petrodiesel and biodiesel-

based waste cooking oil reported are US$ 0.35 and

US$ 0.50, respectively [7]. The world sale of one of the

algae (Chlorella) used in human food, animal feed and

as food additive was higher than US$ 38 billion per

annum, while annual estimated market for docosahex-

aenoic acid, another nutritional supplement or used in

Figure 1. Scanning electron micrograph of a microalgae

(Chlorella) (Zhang et al. [[71] Reproduced with the kind

permission of the Springer Publishers]).

Table II. Oil content in some microalgae.

Species

Oil content

(% dry wt) Referen ce

Botryococcus braunii 2575 [2,36]

Chlorella sp. 2832 [2]

Chlorella emersonii 63 [34]

Chlorella minutissima 57 [34]

Chlorella protothecoides 23 [34]

Chlorella sorokiniana 22 [34]

Chlorella vulgaris 40, 56.6 [34]

Cylindrotheca 1637 [36]

Crypthecodinium cohnii 20 [36]

Dunaliella primolecta 23 [2]

Isochrysis sp. 2533 [2]

M. Subterraneus 39.3 [34]

Monallanthus salina 420 [2]

N. laevis 69.1 [34]

Nannochloris sp. 2035 [2]

Nitzchia sp. 4547 [2,36]

P.incisa 62 [34]

Phaeodactylum tricornutum 2030 [2]Schizochytrium sp. 5077 [2,36]

Tetraselmis sueica 1523 [2]

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aquaculture, produced by microalgae (Crypthecodi-

nium or Schizochytrium) is about US$ 10 billion [48].

Similarly, cost per kg of pigment carotenoids derived

from a microalgae (D. salina) used for human food and

animal feeds is reported to be US$ 3003000 while that

of another pigment, Astaxanthin (used in aquaculture)

is US$ 2500 with an estimated world market of US$

200 million [18,24], which was expected to increaseto US$ 257 million in 2008 [50]. The market for

b-carotene was expected to reach US$ 253 million in

2008, while market for lutein, which is the most

important carotenoid used in human foods and serum

was expected to reach US$187 million by the same time

[50]. Comparison of market and cost of various types

of high molecules derived from microalgae and their

producers are available [48]. Cost of biomass also

depends on the type and region where it is produced

[19]. For example, in USA, the cost of plant biomass is

US$ 515 per barrel of oil energy equivalent compared

with US$ 1139 for solid industrial residues and energy

crops (e.g. soybean, rapeseed), respectively.

2.2. Production of microalgae and photo-

bioreactor design

Microalgae exist in different atmospheres and a lot of

species tolerate high concentration of salts allowing the

use of any type of water for the cultivation medium

[17]. A traditional cultivation of microalgae generating

the biomass for human consumption and aquaculture is

the use of tanks or ponds [51]. This type of reactors

called Raceway ponds are normally open shallow

ponds or channel type systems [52]. A schematic view of

this type of reactor is shown in Figure 2(A). Also,

production through ponds requires large areas despitebeing cheap since it uses very low amount of CO2 of the

air and thus contaminates other organisms such as

mushrooms, bacteria and protozoa. They also show

low photosynthetic efficiency [52], due to low CO2 and

sunlight available only at the pond surface. Hence,

closed type photobioreactors have been proposed,

which not only possess higher photosynthetic efficiency,

but also temperature control of the culture medium,

since temperature normally increases with the exposure

to the sunlight [52], and allow for the use of external

contamination control. A schematic view of this type of

reactor is shown in Figure 2(B). Further, despite several

research efforts for the design and operation of manyphotobioreactors, devising and developing suitable

apparatus, cultivation procedures and algal strains

susceptible of undergoing substantial increases in

efficiency for the use of solar energy and carbon

dioxide is major challenge for the industrial microalgal

culturing. Accordingly, there is no best reactor system

to achieve maximum productivity with minimum

operation costs, irrespective of the available biological

and chemical systems [14]. Accordingly, choice of the

most suitable system is situation-dependent, dictated by

both the available species of algae and the final

intended purpose. The need of accurate control impairs

the use of open-system configurations, so focus hasshifted mostly on closed systems.

Design and operation of the microalgal biomass

production systems have been discussed extensively

[24,7,14,15,18,28,43,44,47,5155,58] with a recent re-

view comprehensively presenting several types of

closed bioreactors for the production of microalgae

based on transport phenomena and process engineer-

ing methodological approaches [14].

Photobioreactors are closed systems that allow the

cultivation of single-species culture of microalgae [2].

The photobioreactors have minimum contamination

while having the advantage of using the solar light and

higher amount of CO2 [2,35,58]. It should be noted that

the objective of the photobioreactor photosyntheticproduction process of microalgal biomass is to obtain

simultaneously the reduction of input energy and the

achievement of high photosynthetic production [52].

Also, these closed photobioreactors may be located

indoors or outdoors, although outdoor location is more

common due to the ease of using free sunlight. Compa-

rison of performance of bioreactors can be done for

fixed time [3] by their volumetric productivity (biomass/

volume) or areal productivity (biomass/occupied area)

or productivity/unit illuminated (biomass) surface.

These productivities vary with type of the system.

For example, the productivity (mg L1 d1) values of

370, 400700 and 900 have been recorded for tubular,

shallow and coiled outdoor tubular ponds, respectively,

compared with 510mg L1 d1 obtained for the indoor

reactor. Table III compares some of the variables/

parameters of two types of bioreactors [2,50]. More

details on these can be seen in the references given in

Table III.

Although microalgae production efficiency is often

mentioned in the literature [272], no consensus was

observed on how to calculate it. Therefore, a definition

for microalgae production efficiency based on theFigure 2. Diagram of raceway ponds (A) and tubular photo-

bioreactors (B).



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products/conversion efficiency definition for fluidized

catalytic cracking reactors in the oil refining industry

[73,74] is suggested as follows:

Yi _mdb;out

_mT;in1

where subscript i accounts for the microalgae growth

process type (control volume) through which the mi-

croalgae biomass was produced (e.g. open pond,

photobioreactor); _mdb;out is the microalgae dry biomass

output mass flow rate [kg d1], and _mT;in is the total

mass flow rate of all substances that enter the defined

control volume (process), including CO2, feedback

water, nutrients and others [kg d1].

Generally, in any photobioreactor design, the system

productivity in continuous operating mode is obtained

by multiplying the steady-state biomass concentrationby the dilution rate used. These are related to the

average irradiance inside the photobioreactor, which in

turn is a function of the irradiance on the reactor

surface, operational variables such as fluid-dynamics

and dilution rate along with the pigment content

[32,47,53,57,58].

Of several geometries of photobioreactors (helical,

vertical and horizontal), the most efficient one is re-

ported [2] to be tubular type, which should maximize

the use of solar light, to avoid large areas of shade and

facilitate the diffusion of CO2 along with the control of

temperature. The microalgae are maintained in circu-

lation with turbulent flow to avoid the sedimentation

and to reduce deposit in the walls of the tubes [2].

Further, time-dependent changes in the culture

medium temperature in every season have been pre-

dicted [52] using a heat balance model of the conical

helical tubular photobioreactor previously established

[4]. Using these results, the energy required to maintain

the temperature of culture medium within an appro-

priate range and the maximum and minimum culture

medium temperatures have been predicted for several

sites with different climate characteristics. This helps to

examine the possibilities for the combinations of the

microalgae used for practically higher photosynthetic

production of microalgal biomass, with less operating

energy consumption throughout the year at various

sites. A large difference in photosynthetic productivity

was caused by the difference in ambient temperature in

each site, if temperature control of the culture medium

was not maintained. This helped to get practically

higher photosynthetic production with less operating

energy consumption throughout the year, using a

combination of various strains that had different

characteristics relative to temperature. Figure 3 shows

the effect of high sunlight intensity on specific growth

rate of microalgae [2].

Studies have also been carried out to find the influ-

ence of various reactor operating conditions such as

temperature, solar irradiance and air flow rate on the

yield of the culture. In one such study, biomass pro-

ductivities up to 1.5 g L1 per day are reported with

photosynthetic efficiency up to 14% by maintaining

the cultures below 30.81C, dissolved oxygen levels less

Table III. Comparison of some parameters of two types of bioreactors (adapted from Chisti [2] and Del Campo et al. [50]).

Parameter

Open system

raceway pond

Closed system

photobioreactor Reference

Area needed (m2) 7828 5681 [2]

Annual biomass production(kg) 100 000 100 000 [2]

Volumetric Productivity (kg m3 d1) 0.117 1.535 [2]

Oil Yield (m3ha1) 56.8 78.2 [2]

Contamination control Difficult Easy [50]

Operation regime Batch or

semi-continuous

Continuous [50]

Area/volume ratio Low High [50]

Light utilization efficiency Poor Excellent [50]

Process control Difficult Easy [50]

Scale up Difficult Easy [50]

Based on 40 % dry wt oil in biomass.

Figure 3. Microalgae specific growth rate as a function of

sunlight intensity [[2] Reproduced with the kind permission of

the Elsevier Publishers].



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than 400% saturation (with respect to air saturated

culture) while controlling the cell density. This has led

to achieve an average irradiance within the culture less

than 250mE m2 s

1 [58].

Production of microalgal biomass may be improved

by specific cultivated conditions such as mixotrophic

and heterotrophic cultivation [58,69]. It is also de-

monstrated that [22,33,56,59] variations in the cultiva-tion conditions such as temperature, concentration of

salts, nitrogen and CO2, for instance, interfere directly

in the biochemical composition of the microalgae.

A modular concept of photobioreactors is expected to

allow verification of these different parameters to ob-

tain high amount of lipid and biomass production.

For using the microalgal fuel to produce electricity

(using stationary diesel engines), microalgae of lipid

content should be grown in large quantities with high

productivity (1.5g L1 d1) [2]. There are a large num-

ber of systems available for the mass cultivation of algae

[42,43] with outdoor systems (open ponds and raceway

types) [3] and closed bioreactors consisting of thin pa-nels or tubes laid horizontally [3]. Growth rate of mi-

croalgae depends on type of pumps used to circulate the

culture. For example, centrifugal and rolling pumps

damaged the algae, while a diaphragm pump showed

very little effect on the growth rate of S. platentis [3].

Advantages of a closed system particularly with he-

lical type are (i) increase in incidence of light energy per

unit volume and reduction of self shading due to the

large surface area to volume of the bioreactor, (ii) easy

control of temperature and contaminants and (iii) ex-

tensive pathways for CO2 absorption leading to better

CO2 transfer from gaseous stage to liquid stage [58].

Further, in recent times, based on increasing focus on

biotechnological potential of microalgae due mainly tothe identification of several substances synthesized by

these organisms, commercial scale production of mi-

croalgae has been drawing the attention of the scientific

community [38]. In fact, the great biodiversity and

consequent variability in the biochemical composition

of the biomass obtained from various microalgal cul-

tures, which can be subjected to genetic improvement

and for massive production possibilities have allowed

various species to be commercially cultivated. Thus, the

biomass production not only for use in the food ela-

boration but also for obtaining natural compounds

with high value in the world market have aimed at

developing microalgae cultivations on large scale [38].

Figure 4 illustrates an innovative integrated multi-

disciplinary process. The first step consists of CO2capturing by the photobioreactors followed by algae

growth in the presence of sunlight, biomass production

and possibilities to produce various useful products,

including CO2 fixation by microalgae and production

of biohydrogen [24].

The microalgae are then transferred to a separate

photobioreactor to produce H2 using energy by a

biophotolytic process without the use of sulfur. Then,

the nutrient-rich algal biomass is collected, which may

be used for different purposes such as health food for

human consumption, as animal feed or in aquaculture.

When the nutrient level goes below the limit for such

applications, the algal biomass may contain large

amounts of valuable biomolecules, which may be of

small percent of the biomass. They can be extracted for

pharmaceutical or industrial retail. The remainingbiomass will still contain good amount of the fixed

CO2. Hence, the residual algal biomass from different

process stages can be used as a fertilizer for agriculture,

wherein retention of fixed carbon for some years is

possible. Otherwise, the fixed CO2 may be stored by

industrial applications like production of plastics.

There is a possibility either to extract biodiesel from

the residual biomass (energy carrier) or its direct con-

version into other energy carriers using biological or

thermo-chemical methods.

2.3. Biodiesel production

The biodiesel consists of a biodegradable fuel pro-

duced from renewable sources. The synthesis of this

fuel can be accomplished by methodologies such as

cracking, esterification or transesterification using

animal fat or vegetable oils. Table IV shows a

comparison of characteristics of biofuels and petro-

diesel along with ASTM biodiesel standard [15,29].

The methodology mostly used for biodiesel pro-

duction is based on the transesterification reaction, as

follows:

(2)

The transesterification reaction, as stated by

Equation (2), takes place in the presence of either

homogeneous or heterogeneous catalysts (traditional

method). Those alternatives can be compared in search

for the most efficient method of biodiesel production

from microalgae lipids.

2.4. Chemical composition of microalgae

As the microalgae do not possess specialized structures,

except for the presence of the pigments and photo-

synthetizers, their composition basically consists of

carbohydrates, proteins and lipids. They are also

sources for almost all types of essential vitamins

(e.g. A, B1, B2, B6, C, E) although environmental

factors, harvesting treatment and cell drying method

determine their quantity [49]. Table V lists the chemical

composition of some microalgae, which are used to

produce food, cosmetics, big molecules and biofuels.

While Table V(A) compares the composition of some

microalgae with those of other food sources, Table V(B)



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lists some microalgae products used in cosmetics.

Table V(C) summarizes the composition of some

microalgae that are of interest for biofuel production.

Therefore, Table V shows that most of the microalgae

have high protein content, particularly those ones that

are used as food sources. Also, carbohydrates are found

mainly as starch, glucose and other polysaccharides

whose digestibility being high, can be used in dry form

without any limitation [49]. Further, lipid content for use

in food varies between 1 and 35% while that for biofuels

lies between 20 and 80% [29,49] compared with 1530%

in vegetable oils, all on dry weight basis.

In order to use microalgae as a fuel, the algae should

be of high calorific value and must be capable of

growing in large volumes. Main contribution to the

calorific value of cells is from their carbohydrate,

protein and lipid content [3]. Microalgae grown under

normal conditions possess calorific values in the range

Table IV. Comparison of properties of biodiesel from microalgal oil, biodiesel fuel and ASTM biodiesel standard (adapted from Miao

and Wu [15]).

Properties

Biodiesel from

microalgal oil Biodiesel fuel

ASTM biodiesel

standard

Density (kgL1) 0.864 0.838 0.860.9

Viscosity (mm2 s1, cSt at 401C) 5.2 1.94.1 3.55.0

Flash point (1C) 115 75 Min 100

Solidifying point (1C) 12 50 to 10

Cold filter plugging point (1C) 11 3.0 (Max 6.7) Summer max 0;

winter maxp15

Acid value (mgKOH g1) 0.374 Max 0.5 Max 0.5

Heating value (MJ kg1) 41 4045

H/C ratio 1.81 1.81

Figure 4. Schematics of an innovative integrated multidisciplinary process [[24] Reproduced with the kind permission of the Elsevier

Publishers].



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of 1821 kJg1, while the value for petrodiesel is

42kJg1. Some microalgae such as Chlorella vulgaris

and C. emersonii have been shown to grow in a 230 L

pumped tubular photobioreactor in Watanabes med-

ium and a low nitrogen medium. While Chlorella species

can accumulate up to 58% lipid under low nitrogen

conditions [3], the Chlorella emersonii accumulates 63%

lipids in small (2 L) stirred-tank bioreactors, which re-

sulted in 29kJg1 of calorific value [4] although the

growth, productivity and lipid accumulation are yet to

be determined at a larger scale. It is found [3] that this

low nitrogen medium induces higher lipid accumulation

in both algae, which increased their calorific value; the

highest calorific value of 28 kJ g1 was obtained with C.

vulgaris with the biomass productivity of 24 mg dry

wt L1 d1 which was lower than that obtained with

Watanabes medium (40 mg dry wt L1 d1).

3. CHARACTERISTICS OFMICROALGAE

In this section, some characteristics of the microalgae

that have made them to be most promising source

Table V. (A) Chemical composition of some food source microalgae compared with other human food sources (% of dry matter)

(adapted from Miao and Wu [15]), (B) Some of microalgae products with applications in cosmetics (adapted from Derner et al. [38])

and (C) Chemical composition of biofuel source microalgae.

Source Carbohydrates (%) Proteins (%) Lipids (%)

(A)

Anabaena cylindrica 2530 4356 47

Chalmydomonas rheinhardii 17 48 21

Chlorella vulgaris 1217 5158 1422

Dunaliella salina 32 57 6

Porphyidium Cruentum 4057 2839 914

Spirulina maxima 1316 6071 67

Bakers yeast 38 39 1

Meat 1 43 34

Milk 38 26 28

Rice 77 8 2

Soya bean 30 37 20

(B)

Products

b-carotene

Vitamin C and E

Arachidonic acidARA

Eicosapentaenoic acidEPA

Starch

Poly-b-hydroxylbutyric acidPHB

Peptides

(C)

Microalgae species Carbohydrates (%) Proteins (%) Lipids (%) Reference

Chaetoceros muelleri 1119 4465 2244 [33]

[59]

Chaetoceros calcitrans 10% 58% 30 [59]

Isochrysis galbana 725 3045 2330 [61]

[62]Chlorella sp. 3840 1218 2832 [2]

Chlorella protothecoides 10.6215.43 10.2852.64 14.5755.20 [19]

Nannochloropsis sp. n.a. n.d. 3168 [2]

Neochloris oleoabundans n.a. n.d. 3554 [2]

Schizochytrium sp. n.a. n.d. 5077 [2]

Scenedesmus obliquus 1017 5056 1214 [y]

Quadricauda de Scenedesmus 47 1.9 [y]

n.a.not available.Values are for two types of reactors used and not the range.yHomero E Ban ados. Biodiesel de microalgas: part 1. (2007Unpublished).



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compared with other resources of biofuels are hereby

recalled: (i) high production capacity of oils; (ii) high

growth rate and (iii) requirement of abundantly

available solar light and CO2, that make them more

photosynthetically efficient than oil crops. They are

tolerant to high concentration of salts allowing the use

of any type of water (fresh, brackish, highly saline and

marine) for the agriculture and possibility to producethem by photobioreactors [24,18,24,35,52,53,55,56,58].

In addition microalgae are a potential source of

biomass, which may have great biodiversity and

consequent variability in their biochemical composition

[38]. Their size (mean diameter in mm) such as of

Chlorella is about 510mm, similar to that of powdered

coal and cellulose to a few hundreds of micrpmetre.

Quantity of the oil produced by these depends mainly

on their lipid content. Higher lipid content gives higher

calorific value of the fuel produced by the microalgae

[4]. Some microalgae such as cyanobacteria (also called

blue algae) may be cultivated without nutrients from

N2 or C and hence cost-effective as well as manageable.In view of microalgae having a greater capacity for

photosynthesis than plants they are capable of syn-

thesizing a number of valuable substances (e.g. health

foods, food supplement, food color, food for livestock,

feeds for bivalves) [15,52].

4. APPLICATIONS OF MICROALGAE

Since the first use of microalgae in China about 2000

years back and the first concept of microalgae for use

in the production of biogas in fifties, and later proposal

as a source of different types of fuel, namely liquid fuel(from Botyrycoccus sp.) [4], and ethanol and methanol

after degradation of the algae [26], also converting into

a gaseous fuel (methane) [28] as well as to produce

hydrogen [75], a number of application areas have been

identified [24,24,37,38,4850,54,5761,71,72,7679].

They include human and animal nutrition, cosmetics,

high-value molecules such as fatty acids and pigments

as well as natural dyes. In fact, interest in the

development of active biomolecules from microalgae

is rapidly growing [55]. Microalgae have been used to

fix CO2, and hence its growth can be linked to the

removal of carbon dioxide from industrial waste gases

(stack and exhaust gasses) [4], for wastewater treat-

ments, as animal food as human food or to produce

numerous high-value bioactives [57,58].The photosynthetic product (microalgal biomass)

can be used as livestock fodder and as forage crops

substitute [4], while attempts have been made to

develop composite materials using a microalgae

(Chlorella vulgaris) as filler in various polymers such as

polypropylene, PVC, polystyrene and polyethylene

[2,3,71,72,7779]. As these microalgae may putrefy and

decompose, resulting in the release of CO2 to the en-

vironment, they have been used by incorporating them

in polymer matrices up to 50 wt.% and the resulting

composites exhibited interesting tensile properties. For

example, PVC-Chlorella composite prepared by hot

molding process exhibited tensile strength (TS) be-tween 30 and 41 MPa and % elongation of 1.86 for

average particle sizes of 5110mm. With microalgae

content waso20 wt.%, while it was 415 MPa when its

content waso50 wt.%. These values were lower than

that of PVC matrix (TS: 50.4 and % elongation: 180).

Similarly, its composite with polyethylene showed

good thermal plasticity whereby it could be shaped

into plates and dishes [79].

Figure 5 shows scanning electron micrographs of

two polymer composites containing Chlorella micro-

algae [71,72]. Figure 5(A) is the surface of the PVC

composite revealing the reinforcements lying in the

matrix surrounded by air gaps, but without any

changes in their shape due to the processing whileFigure 5(B) is the fractograph of this composite

showing fracture of microalgae. One can see the

bonding between the matrix and the reinforcement

does not exist and hence no increase in the tensile

properties was observed. However, about 22% in-

crease in volume of the composite over the matrix was

observed suggesting the microalgae could be good filler

Figure 5. Scanning electron micrographs PVCChlorellacomposite: (A) Surface; (B) Fracture surface; and (C) Fracture of PEChlorella

composite [[71,72] Reproduced with the kind permission of the Springer and American Chemical Society Publishers].



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for polymers. On the other hand, composite of PE with

the same reinforcement showed improved TS and

modulus when the matrix was modified.

Figure 5(C) is the fractograph of maleic anhydride

modified polyethylene composite containing 40 wt.% of

the same reinforcement. Here also good bonding (che-

mical bonds formed between Chlorella grains and the

PE matrix) between the matrix and the reinforcement isevident from the fracture of the reinforcement itself and

also non-existence of any gap between the matrix and

the reinforcement, which exhibited TS twice that of a

composite with unmodified PE. Some of these proper-

ties suggest these composites can be used as substitutes

for rigid and plasticized PVC and similar products.

Table VI summarizes the products and applications

of microalgae as reported by Rozas and Belli [46]

(Table VI(A)), and effective applications of microalgae

studied by Usui and Ikenouchi [24] (Table VI(B)).

5. CRITICAL ISSUES INVOLVED INTHE PRODUCTION AND USE OFMICROALGAE AND FUTURE R & D

Owing to increasing applications of microalgae parti-

cularly for meeting the energy demands, despite its cost

disadvantage, there is a growing interest to develop

cost-effective processes and to enlarge their application

areas based on various advantages mentioned earlier.

These include bulk biological chemicals and rapidly

growing biofuel industries. There are also limited

reviews in recent years on the perspectives on different

aspects of microalgae including critical issues and

possible remedies [2,24,29,32,34,36,50,6567]. Some of

these are summarized below:

Isolation, culturing and characterization of microalgae:

While isolation and characterization from any uniqueenvironment have been ongoing processes, culturing

still remains a niche area needing continued R&D

efforts towards cost-effective technologies [2,32].

Research efforts towards additional organisms which

may possess unique mechanism for efficient production

of lipid/oil should continue, while innovative develop-

ment of large-scale culture systems through proper se-

lection of algal strains that lead to high and sustained

growth rates of oil-rich biomass should be looked into

[32]. Production of higher biomass yield through the use

of genetic engineering to increase the photosynthetic

efficiency or to produce higher yields of oil, stability of

such strains, identification of new strains capable offaster growth at high cell densities, increasing the

growth rate of biomass and its oil content, reduction of

photooxidation susceptibility which damages cells,

identification of factors including biochemical triggers

and environmental that enhances the oil content are

some of the issues needing greater attention [2,32,50].

Design Aspects of Photobioreactors: This aspect is

an important issue to achieve cost-effective

Table VI. (A) Various products from microalgae with their applications [38] and (B) Microalgae applications considered effective

[Adopted from [55]].

Product Application

(A)

Biomass Biomass Natural health food, Functional food, Food

Additives, Aquaculture

Carotenes and antioxidants Xantophils, lutein, b-carotene, vitamin C and E,

arachidonic acid, eicosapentaenoic acid

Food additives, cosmetics

Fatty acids Docosahexaenoic acid, g-linolenic acid, L dismutase

superoxide linolenic acid

Food additives

En zyme s Phos phog lyc erate qui nas e, l ucip herase and luc iph eri n,

restrictive enzymes, polysaccharides

Natural food, research and medicine

Polymers Starch, polyhydroxybutyrate (PHB), peptides, toxins Natural food, cosmetics and medicine

Special products Istotopes, aminoacids, steroids Research and medicine

(B)

Item Method and application

Fuel Extraction of carbohydrate

Direct liquefaction using coal liquefaction technology

Manure Compost

Animal feed Fodder or feed for domestic animals or fish cultivation

Building materials Plastic filler

Concrete additives for high efficiency concrete

Biodegradable plastic Plastic forming processes, biodegradable polymer

products including biodegradable composites

Physiologically active material Reformation of carbohydrates



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photobioreactors with high efficiency, keeping in mind

that there is no such thing as the best reactor system

to achieve maximum productivity with minimum

operation costs. Efficiency of present day photo-

bioreactors lies between 5 and 10% [65], so that de-

pendence of efficiency with high irradiance intensity

and reactor size is one of the major issues. Particularly

the latter with the retention of high photosyntheticefficiency even at large sizes and at high light intensities

at longer periods should be looked into. Probably,

optimization of photobioreactor for various variables

through separation of reactor and collection system for

light may be one way. Then, performance of micro-

algae culture should be tested. As the efficiency of

photobioreactors depends on irradiance of light,

proper design for motionless mixers inside the reactors

should be thought off to obtain better mixing between

properly lit zone and dark zone in the reactor [2].

Further, process strategy may be changed to get in-

creasing yields at lower costs as reported in the efficient

production of astaxanthin-rich biomass using con-tinuous photo-autotrophic cultures [50].

Downstream processing: This is one of the major

issues in microalgal biotechnology, which includes se-

paration of biomass and concentration of microalgae

culture. Attempts should be made to develop cheaper

and energy conserving processing methods [32,53,58]

including genetic modification and engineering of algal

strains from dilute cultures with optimum photosynth-

esis and product formation [50,65]. Also, development

of economical, quick and efficient processes for har-

vesting and de-watering of biomass depending on the

end use is another area of interest for R&D [32,50,65].

Cost: High cost to produce microalgae, which leads

to high cost of microalgal fuel (biodiesel), is anotherissue. Some of the methods to offset that problem may

be by (i) resorting to production strategy to integrated

biorefinery, where useful products are produced using

every component of biomass [2], (ii) identifying high-

value products particularly big molecules type based on

specific microalgae used [2] or broadening commer-

cially viable product range such as nutraceuticals based

on highly productive heterotrophic type cultures [32,65]

and (iii) sale of generated excess power [2]. Also, pro-

cessing of biomass for oil, wherein lipid extraction is an

important step [32], is another issue to be looked into.

Environmental aspects: Although biofuel is con-

sidered environmentally less harmful than diesel fuel,

its eco-compatibility depends on method of its pro-

duction, use and trade [80]. These in turn determine its

economic, environmental and social aspects since not

much is reported on its eco-toxicological information

of non-regulated emissions, effluents generated during

its production and on its water-soluble fractions

(WSF). These factors have to be considered as they are

important to follow the precautionary principle pre-

scribed by law in many countries that have plans to

increase the production of biofuel, which may lead to

environmental risks by its use. Hence, there is need for

studies including modeling to look into toxic effects

caused by this fuel particularly the WSF of biofuels

although some attempts towards these have recently

initiated [80].

6. WORK AT UFPR

Increasing global demand for fuels from renewable

energy sources, with motivation by tax exemptions of

biofuels has triggered many initiatives in the federal

and private sectors aimed at producing biofuels,

particularly in Brazil, USA and Europe [23]. For

example, European production of biodiesel was

reported to have increased from about 1.9 billion liters

in 2004 to about 4.9 billion liters in 2006 [66], while

estimated annual production of biodiesel in Brazil is

about 176 million liters, which advocates the first use

of diesel with 2% biodiesel in the current year and then

of 5% by 20122013 [see: http://www.biodiesel.gov.br].It is also interesting to note other advantages accruing

from this, such as increased employment avenues and

useful co-products obtained during the processing of

this new fuel such as about 110 kg of crude glycerin

from 1 t of biodiesel [31]. These require new develop-

ments in technology of biofuels.

As a first example, in a recent work, Gravalos et al.

[81] showed that vegetable oils are one of the alter-

natives utilized by farmers, which can be used as fuel in

diesel engines either in the form of straight vegetable

oil or in the form of biodiesel. The study presented

experimental data by utilization of home and industrial

biodiesel as fuel in an agricultural tractor diesel engine.

The home biodiesel production was made from dif-ferent vegetable oils (crude rapeseed, edible sunflower

and waste oil) with the process of one-stage-based

catalyzed transesterification. According to the results,

agricultural tractor diesel engine operating on home

biodiesel fuels had better performance characteristics

related to industrially produced biodiesel and similar

to conventional diesel fuel.

Physical properties of biodiesel are another im-

portant issue, playing an important role in the injec-

tion, atomization and combustion performance.

A recent work investigated the spray properties of

biodiesel [82]. In sum, the results indicated that, on the

macroscopically view, the shape of biodiesel spray is

similar to that of diesel.

Next, in order to complete this review study, the

application of the ideas collected in the literature re-

view is illustrated in this section with a brief descrip-

tion of an ongoing project by the authors of this study

under implementation at Federal University of Parana,

Curitiba, Brazil along with status of each of the items.

The main objective is to provide the reader with an

assessment of the feasibility of innovative microalgae

biomass-based projects.



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Keeping in sight the current needs of technology

development in the area of biofuels elsewhere and va-

lue addition to renewable resources, the Center for

Research and Development of Sustainable Energy

(NPDEAS) was created at UFPR in Curitiba, Parana,

Brazil. The main objective of this center is to demon-

strate the concept of energy sustainable plants powered

by renewable fuels in a possible future scenario ofdistributed power generation. Specific objectives in-

clude: (i) design and fabrication of compact photo-

bioreactors for microalgae cultivation; (ii) obtaining

biodiesel and other co-products and possible uses of

byproducts particularly residues; (iii) mathematical

modeling, experimental validation and thermodynamic

optimization of the components and processes, as well

as of the entire system, and finally (iv) divulgation of

the results of the project, improvement of the current

technology of microalgae cultivation, evaluation of

system functionality and the possibility of general re-

plication.

6.1. Photobioreactor development

An important step of this project is the development

and improvement of compact photobioreactors for

microalgae cultivation. Aiming to reach compatible

efficiency with the target plant needs and taking into

account the various parameters that affect the effi-

ciency of the bioreactor, the photobioreactor design

has an innovative geometric conception. The objective

is to achieve high biomass productivity through the

best use of the solar light under a fixed volume

constraint. The volumetric productivity (kg m3 d1)

and surface (kg m2 d1) will be analyzed and com-

pared with data available in the literature for tradi-tional methods of microalgae cultivation in tubular/

helical photobioreactors and ponds.

With a view to have freedom to vary several para-

meters allowing for appropriate flexibility of the sys-

tem, the proposed photobioreactors will be built in a

modular way. The modular construction will make it

possible to study different types of microalgae in par-

allel, as well as comparison of different ways for their

cultivation. The possibility to alter several parameters

in parallel allows the determination of the best condi-

tions for the cultivation with the proposed specific

objective of obtaining great biomass production and

high amount of fat. Considering the effect of the use of

inoculum, the Integrated Group of Aquaculture and

Environmental Studies at UFPR will produce in-

oculum and supply the required amount of microalgae

for this project taking into account the minimum time

to get the maximum productivity in the photo-

bioreactor. The processes of cultivation of unicellular

organisms usually begin with the addition of a stan-

dardized amount of cells called inoculum. As it could

be presumed, the quality of the growth process is di-

rectly dependent on the quality of the inoculums.

Sometimes, smaller amounts of additions may result in

slow growths and consequently low productivity.

A new design conception for compact photo-bior-

eactors for the cultivation of microalgae has been de-

veloped. The photo-bioreactor design has the

innovation of the maximization of the cultivation and

sun exposed area in a given volume, by utilizing cir-

cular transparent polymeric staggered tubes (crystalPVC). The geometric conception is based on the

compact heat exchangers technology [83].

Although attempts have been made to achieve cost-

effective photo-bioreactors with high efficiency, not

much success has been reported and photo-bioreactor

technology is still in its early steps as discussed earlier

in the text. In that direction, Prakash et al. [84] de-

veloped a transient thermal analysis and estimated the

incident solar energy for two designs of tubular photo-

bioreactor installed outdoors arranged in one and two

planes, respectively. The model was validated by

comparing the experimental data and predicted values

of culture temperature. The performance of the twophotobioreactors for mass culture of Spirulina was also

studied with respect to their design and culture tem-

perature. Among several important conclusions, it is

interesting to note that the average biomass yield ob-

tained in one-plane and two-plane photobioreactors

were (dry weight) 23.7g m2 day1 and 27.8g

m2 day1, respectively, giving a clear indication that

superimposing planes could increase density produc-

tion, therefore exploring design compactness.

Figure 6 shows the flowchart of the proposed sus-

tainable energy plant with the details of the integration

of all engineering subsystems. The main components

are described in the next subsections.

6.1.1. Gasser/degasser system. During the photosynth-

esis process, conversion of CO2 and H2O in sugar

(glucose) will take place along with oxygen (O2)

release. Therefore, there is no limitation for the growth

of the microalgae provided that CO2 is injected during

the growth process through a gasser/degasser system.

Injected CO2 may be originating from the atmospheric

air or from external gas sources (exhaust gases from

thermal plants, motors or industrial processes) [63].

The larger the concentration of CO2 in the injected air,

the better will be for the microalgae. In this project,

exhaust gases from a biodiesel powered motogenerator

as source of CO2.

The biodiesel produced from the microalgae-ex-

tracted oil as well as gases generated in biodigester will

feed a motogenerator, a multifuel (biodiesel/biogas)

internal combustion engine. The hot exhaust gases

coming from the engine will be the heat source for an

absorption refrigerator in order to produce cooling for

utilization by the plant processes and climatization. In

this way, the motogenerator will have three functions,

i.e. as supplier of electrical energy, heating and cooling,

namely a trigeneration system. Additionally, the



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system will supply CO2 that will be directed to the

photobioreactors, acting as substrate for the micro-

algae in the photosynthesis process.Another function of the gasser/degasser system

is the removal of O2 generated by the photosynthesis.

The excess oxygen is poisonous to the algae because

it promotes oxidative stress leading to death of cells.

On the other hand, small amount of O2 leads to in-

hibition of the photosynthesis, therefore impeding

the microalgae growth. The modular concept of

gasser/degasser system allows the adaptation of the

photobioreactors to operate with: (a) any type of

microalgae, (b) appropriate growth rate and (c) avail-

ability of solar light during the year. Alteration of

any one of these parameters alters the use of CO2and consequently, the production of oxygen. To in-

crease the solubility of CO2 during microalgae growth,

the medium will be artificially cooled. The cold

water used in the process will be supplied by the

absorption refrigerator powered by the tri-generation

system.

6.1.2. Composition of the medium. The composition of

the medium of culture is defined by the microalgae and

the cultivation conditions. As mentioned earlier in the

text, microalgae are capable of growing in different

ways including waters with high concentration of

pollutants such as in ponds and in treated industrial

wastewater. Hence, the project predicts the use ofdifferent types of water.

The utilization of sea and fresh water in the photo-

bioreactors are discussed separately, as follows:

6.1.2.1. Sea water. The use of algae that grow in

seawater allows for a biodiesel production that does

not compete with food-oriented agriculture since it

uses water that is not used for irrigation. The use of

such a system is best suited for coastal areas where

seawater is cheaply available and the production of a

residue containing high amounts of salt does not

matter. The seawater possesses mainly sodium chloride

with an average mass concentration of approximately

3 5 g l1. Besides CO2 and the sunlight, these organisms

need several other ions that are present in the sea. With

the objective of obtaining the best microalgae growth

conditions, besides seawater, other low-cost additives

are needed such as those used in agriculture, i.e. urea

(source of nitrogen) and superphosphate (source of

phosphate).

6.1.2.2. Fresh water. At places distant from the coast,

use of salty water becomes somewhat unfeasible for the

Figure 6. Flowchart of the sustainable energy plant under construction at UFPR, Curitiba, Brazil.



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cultivation of sea microalgae in view of the cost

involved for the transport of seawater or sea salt.

Additionally, a problem would be created with the

production of residues with high amount of salt.

The cultivation of algae with fresh water consumes

higher amounts of water than with seawater initially.

After the establishment of the culture, the amount of

water eliminated by evaporation in the gasser/degasser

system has to be replaced. This water can be recycled in

the system with the need for addition of the elements

consumed by the algae. The cultivation medium in

fresh water also needs the addition of nitrogen, phos-

phate and some of the ions used by the metabolism of

the microalgae.

6.2. Biodiesel production

The project will use oil extracted from microalgae

biomass cultivated in compact tubular photobioreac-

tors to produce biodiesel and possibly other valuable

products, as discussed earlier in the text. Next, thesubcomponents utilized for biodiesel production ac-

cording to the flowchart shown in Figure 6 are

discussed.

6.2.1. Unit operations. A fundamental point in the

biodiesel production from microalgae consists of

the choice of the methodologies to be used in the

separation and drying of the microalgae biomass and

also in the oil extraction process. Methodologies that

are high energy consuming make the biodiesel produc-

tion process commercially unattractive. Further, since

the project is aimed at developing sustainable electric

power plants, it is mandatory to minimize energy

consumption at every stage of the biodiesel productionprocess, as follows.

6.2.1.1. Separation and drying of the microalgae. Dif-

ferent methodologies such as flocculation, centrifuga-

tion or filtration can be used for the separation of the

microalgae biomass from the culture medium.

After the separation, drying of the material takes

place through sun drying, liofilization, spray-drying or

even competitive flow, since the possibility of free

heating exists by burning natural gas produced in the

biodigester, as shown in Figure 6 which uses residues

generated by the system.

The choice of the methodologies to be used in the

microalgae biomass separation and drying will be

based on efficiency and cost, whichever produces the

most favorable results in operation.

The culture medium can be recycled after the re-

moval of the algae taking into account the necessary

corrections for consumed nutrients and also elimina-

tion of possible chemical or biological pollutants as it

has been reported by Hu et al. [32].

A study was developed by the UFPR team [85]

with the purpose of demonstrating the efficiency of the

increase in pH of a Nannochloropsis oculata microalgae

solution, by sodium hydroxide (NaOH) addition, to

the flocculation, making possible a simple harvesting

of the cells. The results suggest that increase of pH of

the culture broth is a suitable methodology for mi-

croalgae separation from the growth solution. Similar

results were obtained with cultures of Phaeodactylum

tricornutum.Another work by the UFPR team [86] was con-

ducted to produce dry Nannochloropsis microalgae

biomass with a spray dryer system before oil separa-

tion and biodiesel production. With this process it was

obtained, in the end, powdered N. oculata biomass,

which was submitted to lipid extraction with solvent,

and thereafter to biodiesel synthesis. The experimental

results suggest that the proposed process is a suitable

and low energy consumption methodology for micro-

algae drying.

6.2.1.2. Oil extraction and biodiesel. Separation meth-

ods used in plant oils can be used for microalgae. Thetechniques commonly used include: pressing, solvent

extraction and supercritical extraction [68]. Each one

of these processes requires energy and gives different

yield. With a view to get almost 100% yield, a

combination of two techniques can be used such as

pressing and solvent extraction. However, new ap-

proaches in the extraction of microalgae lipids are

necessary so that the total cost of biodiesel production

will become commercially competitive. Accordingly, it

is planned to have new approaches in this work for the

separation of microalgae lipids. These studies will be

taken up after the start of the photobioreactor

operation and consequently after the production of

biomass.It is proposed to synthesize the biodiesel using the

microalgae produced by the photobioreactors by em-

ploying cracking, esterification or transesterification

normally used with animal fat and vegetable oil. Also,

innovative chemical in situ transesterification process

will be proposed and tested in two different ways. In

the first, simultaneous extraction and transesterifica-

tion is being carried out with new catalysts by the

UFPR team [87]. The work consists of the develop-

ment of a new heterogeneous catalyst for the ester-

ification of free fatty acids and the transesterification

of vegetable oils. The layered compound zinc hydro-

xide nitrate (Zn5(OH)8(NO3)2

2H2O) was very effec-

tive in the alcoholysis of palm oil and the esterification

of lauric acid with m(ethanol), even when hydrated

ethanol was used. Over the range of 1001401C, the

ester yield was the highest at 1401C, while the catalyst

concentration had a much greater effect on ester yields

than the molar ratio of alcohol to acid did. Total ester

contents above 95 wt.% were obtained in both reac-

tions and 93.2 wt.% glycerin streams were recovered as

a result of methanolysis. Such process which has not

been reported till now with microalgae, although 98%



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oil yield has been reported with sulfuric acid or hy-

drochloric acid as catalyst [21]. On the other hand, in

the second, alkaline catalysis is being substituted by

enzymatic catalysis, which has yielded conversion of

98% of oil in 12h in low temperatures with im-

mobilized lipase of Candida sp. [22]. Recently, a tech-

nique to minimize the cost of production of the

enzymatic catalyst was developed. It was demonstratedfor the first time that it is possible to produce a lipase

in fermentation in the solid state and directly apply the

dried and fermented solid in an organic reaction to

catalyze the transesterification reaction. In that way,

necessary extraction and immobilization of the enzyme

is avoided [60].

In a recent development by the UFPR team [88],

three methods for the extraction of lipids from two

different microalgal species were evaluated: N. oculata

and P. tricornutum. The methods were adaptations of

the Folch and the Bligh and Dyer methods [89,90],

both of which are based on the use of a monophasic

mixture of chloroform, methanol and water(CHCl3:CH3OH:H2O). The extraction mixture was

varied showing the best results with Method 1 which

consisted of CHCl3:CH3OH (2:1, v:v).

An evaluation of the potential performance of mi-

croalgae as a raw material for the production of bio-

diesel was conducted experimentally by Carvalho et al.

[91]. For that, organic solvent extraction of lipids from

microalgae that does not have dependency on petro-

leum was investigated as an alternative technique. The

microalgae-extracted oil had its chemical structure

checked via the Fourier Transform Infrared spectro-

scopy method, confirming that indeed triacylglycerol

was obtained. The main conclusion was that the pro-

duction of biodiesel through the proposed system, inview of the high production of ethanol in Brazil, has

the potential to be independent of exports such as

solvents of fossil origin, therefore allowing for a sus-

tainable microalgae derived biodiesel production. As a

sequence of this study, the in situ transesterification

process is currently being investigated, i.e. the direct

conversion of microalgae biomass into biodiesel, i.e.

without having to convert or extract oil from biomass,

to avoid unnecessary steps in the process, therefore

increasing energetic and productivity efficiency.

Additionally, biofuels present new challenges con-

cerning the engine adaptation and the pollutant emis-

sions. In this context, Torrens et al. [92] developed a

study in an attempt to clarify the relation between fuel

properties of microalgae biodiesel and pollutant emis-

sions, studying which properties are desirable in these

new fuels to guarantee engine operation without de-

gradation of performance in comparison to conven-

tional diesel. The methods used were accurate enough,

for a first estimative. Viscosity estimation should be

refined. As the method applied is very complex, the

deviation may be affected by an error. Other method,

based on experimental data might perform better in

such estimations. The simulation of microalgae bio-

diesel allowed a better understanding of the potential

of this feedstock. As the synthetic algae oil had high

amounts of oleic acid and palmitic acid, their esters

presented properties that were intermediary between

Soy/Canola and Palm oil ethyl esters, and might per-

form very well. Microalgae cultivation also allows a

better control on the fatty acid profile, which is espe-cially important for fuel optimization. Many fuel

properties affect directly the engine performance and

pollutant emissions, what makes the importance of

knowing and optimizing the fuel composition clear.

Even if many plants or microorganisms may produce

oils, not necessarily the biodiesel produced from it

have the quality necessary for the operation of modern

engines. With the improvement in biodiesel produc-

tion, it may be possible to produce high-quality fuel

that complies with international standards and helps

limiting the pollutant emission and has the potential to

replace conventional diesel.

6.3. Biodigester

During the process of biodiesel production from

microalgae, biomass residues will be generated at

different stages, which may contain some commercially

valuable substances [70]. The remaining substances will

be sent to a biodigester for anaerobic decomposition to

produce biogas (methane) in a modular biodigester

developed by the authors [93]. The equipment for

biogas production consists of a cylindrical and

hermetic reactor where the residues will ferment

producing the biogas that is captured at the top. The

process has approximately a 40 days retention time.

The gases generated in the biodigester are meant to beused by the tri-generation system or other heat-

demanding processes in the plant.

Recently, Ferna ndez et al. [28] reported the pro-

duction of about 180 mL g1 of dry microalgae d1 of

biogas, with 65% methane concentration, which de-

monstrates the energy potential of microalgae biomass

as substrate in biodigesters.

6.4. Biomass and residues

Residues are produced during microalgae derived

biofuel production as discussed throughout this study.

Currently, in the project, they are being analyzed to

evaluate their characteristics such as chemical compo-

sition, morphology and thermal stability. For example,

the morphologies of microalgae produced by the

authors in different conditions (triglyceride extracted,

sun and air dried, spray dried and P. tricornutum salt

water medium) have been observed in a scanning

electron microscope. Figure 7(A)(D) shows the

micrographs of two types of microalgae samples with

different drying processes indicating the morphological

details of these samples. This suggests that their



DOI: 10.1002/er


16/21

morphology such as shape, size, porosity, etc. depends

on the way they are obtained and dried. Further

studies on their chemical composition and thermal

properties are being carried out. Based on this,

possibility for their use as fillers in polymers to develop

composite materials, as fertilizers or possibly for other

uses including as additives to soil after carbonizing will

be explored.

6.5. Software

A complete mathematical model of all components

shown in Figure 6 is currently under development,

with the objective of producing a software for the

simulation of the entire sustainable energy plant. The

idea is to produce a low computational time-demand-

ing graphical application through a thermodynamics-

based simplified mathematical model to analyze the

transient and spatial behavior of the plant using a

volume element methodology [94]. After experimental

validation of the numerical results obtained with the

mathematical model, the software will be available for

the thermodynamic optimization of design (geometric)

and operating parameters for maximum system global

performance.

Initial modeling attempts have been started by the

authors in two studies [83,95]. In the first study, a

simplified physical model was introduced [81] for one

pipe photo-bioreactor operating in a closed circular

mode, which combines fundamental and empirical

correlations, and principles of classical thermodynamics,

biochemistry, mass and heat transfer. The model is

expected to be a useful tool for simulation, design and

optimization of compact photo-bioreactors. In the

second study [95] the microalgae growth was modeled

based upon a mathematical relationship with the lightintensity. The numerical solution of this computational

model allows for the prediction of photobioreactor

biomass concentration and production per unit volume.

7. CONCLUDING REMARKS

The main objective of this overview is to provide the

reader with an assessment of the feasibility of

Figure 7. Scanning Electron micrographs showing the morphology of two different microalgae: (A) Nannochloropsis oculata

triglyceride extracted; (B) Nannochloropsis oculatasun and air dried; (C) Nannochloropsis oculataspray dried; and (D) Phaeodactylum

tricornutum spray dried.



DOI: 10.1002/er


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innovative microalgae-based projects including the one

being initiated in authors University, which address

important aspects of energy (biofuel) and materials. It

is now known that only renewable biofuel can

potentially replace non-renewable and limited sources

of petroleum-derived liquid fuels. Although microalgae

are known to be one such alternate source for biofuel

since fifties, its technical feasibility is underlined by thestudies carried out thereafter by many including the

authors, with increased attention being given in recent

times due to increasing problems posed by the

conventional petroleum-based fuels and ecological

considerations. It is also clear that microalgae are the

only biofuel source that could be grown without

competing with agricultural land, due to the possibility

of using photobioreactors that can grow vertically and

that can also be made compact whereby biomass

production per unit volume can be maximized.

Accordingly, design of suitable photobioreactors to

produce microalgae, their characteristics and applica-

tions in various areas are well documented. Whilecomparison of market with its fast growth and cost of

various types of high molecules derived from micro-

algae and their production are available, design and

operation of the microalgal biomass production

systems have been extensively discussed. Reported

characteristics including chemical composition of

microalgae indicate their high growth rate with high

production capacity of oils along with them being

more photosynthetically efficient than oil crops in

addition to being a potential source of biomass.

Successful attempts have been reported on their

application to develop new materials. However, to

make them more attractive source for energy and

materials, some critical issues such as their isolation,culturing and characterization, design of cost-effective

photobioreactors with high efficiency, downstream

processing for the separation of biomass and concen-

tration of microalgae culture along with modeling

studies to look into toxic effects of the fuel produced

need to be addressed. Also, genetic and metabolic

engineering should be associated to the scientific effort

for obtaining increased algae growth rates and lipid

content.

A brief description of an ongoing project carried out

by the authors along with its current status addresses

some of those issues. In the authors opinion, eco-

nomically this fuel may not be competitive to petro-

leum-based fuels, but other microalgae products such

as food for human and animal consumption and pro-

duction of various high-value bioactive molecules may

make it economically competitive. This may be feasible

by utilizing the remaining amount of biomass rather

than not being either discarded or overlooked since

only 40% (of the dry biomass) lipid content would be

used in the fuel production. An innovative cogenera-

tion biorefinery concept is suggested, which along with

advances in compact photobioreactor engineering are

expected to lower the cost of production. Indeed,

economically attractive biofuel associated with new

materials production have the potential to turn mi-

croalgae-based industry from a future possibility into a

present reality.

ACKNOWLEDGEMENTS

The authors sincerely acknowledge the publishersCopyright Clearance Centers Rightslinks service,Elsevier, Springer and American Chemical Society whohave given permission to reproduce figures and tables.The authors thank the Brazilian funding agencies,CNPq (projects 552867/2007-1 and 574759/2008-5)and Araucaria Foundation of Parana (project 13470)for the Fellowships and funds provided to carry outthis work. They also thank Director of AdvancedMaterials and Processes Research Institute (AMPRI),Bhopal (M.P. India) for permitting to use theirscanning electron microscope (SEM) and Mr TSV

Chakradhar Rao, Technical officer, who helped inobtaining the SEM photographs of our samples.

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a review on micro algae, a versatile source for sustainable

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