**4. Algal basics**

Algae grow almost everywhere in the world. They live all over the world from the ocean to the desert and from hot springs to snow and ice. Algae are important for aquatic ecosystem because they provide food and shelter to other organism. Algae are also important because they have ability of an aquatic ecosystem to absorb nutrients and heavy metals. Algae use sunlight and chlorophyll to make food. Algae are organisms that are like plants and vegetables. Algae grow in almost any aquatic environment and use light and carbon dioxide (CO2) to create biomass. Algae range in size from a few micrometers to over 30 m in length.

One most important benefit of algae over conventional crops is algae can be grown under conditions which are unsuitable for conventional crop production.

### **4.1. Microalgae vs. macroalgae**

There are two types of algae, Macroalgae and Microalgae. The word "Macro" means big so microalgae are large in size (in size of inches and greater) and multi cellular. Seaweed is example of largest Macroalgae which can be well over 25 m in length. The largest seaweed, giant kelp, is known to grow as fast as 50 cm/day, and can reach a length up to 80 m. Microalgae cells can double every few hours during their exponential growth period Macroalgae have some advantages. Mainly because of their relatively larger sizes than micro, these can be harvested more easily.

On other side "Micro" means very small (in size of micrometers) and contain one cell so called "Unicellular" organisms. Microalgae are more preferred because of the fact that they grow very quickly and also because they have much higher lipid content than Macroalgae.

The main advantages of using microalgal organisms in a variety of industrial applications are:


### **4.2. Major compositions of microalgal biomass**

**4. Algal basics**

106 Biofuels - Status and Perspective

**4.1. Microalgae vs. macroalgae**

harvested more easily.

ture;

atmosphere; and,

and valuable co-products.

**•** biodegradable biofuels and valuable co-products.

Algae grow almost everywhere in the world. They live all over the world from the ocean to the desert and from hot springs to snow and ice. Algae are important for aquatic ecosystem because they provide food and shelter to other organism. Algae are also important because they have ability of an aquatic ecosystem to absorb nutrients and heavy metals. Algae use sunlight and chlorophyll to make food. Algae are organisms that are like plants and vegetables. Algae grow in almost any aquatic environment and use light and carbon dioxide (CO2) to create

One most important benefit of algae over conventional crops is algae can be grown under

There are two types of algae, Macroalgae and Microalgae. The word "Macro" means big so microalgae are large in size (in size of inches and greater) and multi cellular. Seaweed is example of largest Macroalgae which can be well over 25 m in length. The largest seaweed, giant kelp, is known to grow as fast as 50 cm/day, and can reach a length up to 80 m. Microalgae cells can double every few hours during their exponential growth period Macroalgae have some advantages. Mainly because of their relatively larger sizes than micro, these can be

On other side "Micro" means very small (in size of micrometers) and contain one cell so called "Unicellular" organisms. Microalgae are more preferred because of the fact that they grow

The main advantages of using microalgal organisms in a variety of industrial applications are:

**•** they grow rapidly and have a higher solar conversion efficiency than most terrestrial plants;

**•** algal production facilities can be collocated on otherwise non-productive, non-arable land;

**•** they can utilize salt and waste water sources that cannot be used by conventional agricul‐

**•** they can use waste CO2 sources thereby potentially mitigating the release of GHG into the

**•** they can produce a variety of feedstocks that to generate nontoxic, biodegradable biofuels

very quickly and also because they have much higher lipid content than Macroalgae.

**•** they can be harvested batch-wise or continuously almost all year round;

biomass. Algae range in size from a few micrometers to over 30 m in length.

conditions which are unsuitable for conventional crop production.

Microalgae are one of the best alternatives to traditional forms of biomass for biofuels pro‐ duction, due to its ability to be cultivated on marginal lands, fastest growing biomass, high productivity, and potential to utilize carbon dioxide (CO2) from various sources.

Microalgal biomass is unicellular organisms which mean they have only one cell. Microalgae biomass contains compounds like protein, carbohydrates, lipids and nucleic acid. The percentages of compounds vary with the type of algae. Under good condition, biomass of green algae can be double in less than 24 hours [20]. Green algae can have huge lipid contents, continuously over 50% [23]. Oil content found in green algae may be different; a comparison of the oil content in algae is shown in table 2. Microalgae are capable of fixing CO2 in the atmosphere, thus facilitating the reduction of increasing atmospheric CO2 levels


**Table 2.** Oil content of algal species

Many microalgae species can be induced to accumulate substantial quantities of lipids [105] thus contributing to a high oil yield. The average lipid content varies between 1 and 70% but under certain conditions some species can reach 90% of dry weight [20, 74, 75, 109].Table 3 presents both lipid content and lipid and biomass productivities of different marine and freshwater microalgae species, showing significant differences between the various species [74, 95, 96, 109]. As shown in table 2, oil content in microalgae can reach 75% by weight of dry biomass but associated with low productivities (e.g. for Botryococcus braunii). Most common algae (Chlorella, Crypthecodinium, Cylindrotheca, Dunaliella, Isochrysis, Nannochloris, Nannochloropsis, Neochloris, Nitzschia, Phaeodactylum, Porphyridium, Schizochytrium, Tetraselmis) have oil levels between 20 and 50% but higher productivities can be reached.

Chlorella seems to be a good option for biodiesel production. Yet, as other species are so efficient and productive as this one, the selection of the most adequate species needs to take into account other factors, such as for example the ability of microalgae to develop using the nutrients available or under specific environmental conditions. All these parameters should be considered simultaneously in the selection of the most adequate species or strains for biodiesel production.

Also significant is the composition of fatty acids of the different microalgae species, as they can have a significant effect on the characteristics of biodiesel produced. These are composed of saturated and unsaturated fatty acids with 12–22 carbon atoms, some of them of v3 and v6 families. The analysis of seven fresh water microalgae species for the fatty acid compositions shows that all of them synthesized C14:0, C16:0, C18:1, C18:2, and C18:3 fatty acids.

The relative intensity of other individual fatty acids chains is species specific, e.g. C16:4 and C18:4 in *Ankistrodesmus sp*., C18:4 and C22:6 in *Isochrysis sp.,* C16:2, C16:3 and C20:5 in *Nannochloris sp*., C16:2, C16:3, and C20:5 in *Nietzsche sp.* Different nutritional and environmen‐ tal factors, cultivation conditions and growth phases may affect the fatty acid composition. For example, nitrogen deficiency and salt stress induced the accumulation of C18:1 in all treated species and to some extent C20:5 in *B. braunii*.
