**7. Microalgae for biodiesel production**

Microalgae as compared to conventional crops have high photosynthetic efficiency and therefore potentially high productivity per unit area of plantation. The U.S. Department of Energy's Aquatic Species Program (1978- 1996) focused on biodiesel production from micro‐ algae because biodiesel is a promising fuel product in many ways because it is useful to counter "Energy Security" and "Climate Changes". Day by day the energy required in Transportation sector is increasing and petroleum will not be able to fulfill the all requirements, in that case Microalgae is one of the substitutes to petroleum. Through photosynthesis metabolism, microalgae absorb CO2 and release oxygen; it will reduce the global warming effect.

### **7.1. Current biodiesel feedstock**

Biodiesel can be produce from various feedstock's which is soybean oil, rapeseed, Jatropha, mustard, jojoba, sunflower, palm oil, coconut hemp, animal fats, sewage sludge and algae. A comparison of feedstock for biodiesel is as below in table 5.


**Table 5.** Feedstock for biodiesel [93]

### **7.2. Potential of using microalgae as biodiesel feedstock**

The cells are naked or covered by scales, lorica or cell wall. The flagellate cell usually possesses two heterodynamic flagella but posterior (a) flagellum is sometimes reduced. Tubular mastigonemes on anterior (b) flagellum possess lateral filaments. Mixotrophic and heterotro‐ phic species engulf particles (e.g. bacteria) through splitted R2 microtubules. Because major photosynthetic carotenoid is fucoxanthin, chrysophycean chloroplasts are golden-yellow in color. Asexual reproduction by means of binary fission, sporogenesis etc. Sexual reproduction has been reported in some species. The chrysophycean algae produce cysts surrounded by siliceous wall, statospore via sexual or asexual reproduction. Statospores form microfossils to

Microalgae as compared to conventional crops have high photosynthetic efficiency and therefore potentially high productivity per unit area of plantation. The U.S. Department of Energy's Aquatic Species Program (1978- 1996) focused on biodiesel production from micro‐ algae because biodiesel is a promising fuel product in many ways because it is useful to counter "Energy Security" and "Climate Changes". Day by day the energy required in Transportation sector is increasing and petroleum will not be able to fulfill the all requirements, in that case Microalgae is one of the substitutes to petroleum. Through photosynthesis metabolism,

Biodiesel can be produce from various feedstock's which is soybean oil, rapeseed, Jatropha, mustard, jojoba, sunflower, palm oil, coconut hemp, animal fats, sewage sludge and algae. A

> **Land use (sqm/year/L of biodiesel)**

**Productivity of Biodiesel (Liter Biodiesel/Hectare /Year))**

microalgae absorb CO2 and release oxygen; it will reduce the global warming effect.

**Oil content (% dry weight biomass)**

**Maize** 44 56 179 **Soybean** 18 15 661 **Jatropha** 28 13 772 **Rapeseed** 41 10 1014 **Sunflower** 40 9 1113 **Palm oil** 36 2 5585 **Microalgae (Low Oil Content)** 30 0.2 61,091 **Microalgae (medium Oil Content)** 50 0.1 101,782 **Microalgae (high Oil Content)** 70 0.1 142,475

be used for paleoenvironmental reconstruction.

116 Biofuels - Status and Perspective

**7. Microalgae for biodiesel production**

comparison of feedstock for biodiesel is as below in table 5.

**7.1. Current biodiesel feedstock**

**Feedstock**

**Table 5.** Feedstock for biodiesel [93]

Microalgae are emerging as a potential high-volume source of lipids for advanced biofuels. While commercial production of microalgae has been established for human nutritional products like *Spirulina*, *beta carotene*, and *omega-3* fatty acids for at least three decades, the concept of using microalgae as an aquaculture source for energy production on the mega-ton scale meaningful to the petroleum industry has enjoyed a recent resurgence. Over conventional crops, algae can be grown under conditions which are unsuitable for conventional crop production and algae can be grow on the land which is not arable land. Microalgae potential because of the fact that they grow very quickly and live in harsh conditions due to their unicellular structure even Microalgae are able to double their mass within few hours. Micro‐ algae are preferred over Macroalgae because Microalgae have much higher lipid content than Macroalgae.


**Table 6.** Chemical composition of biofuel source microalgae

The majority of companies trying to demonstrate commercial production of microalgae for energy and other markets were found within the past six years. The pace of innovation in systems engineering, cultivation techniques, intracellular productivity improvement techni‐ ques, and business model development has been extremely rapid. Production and productivity levels have jumped by orders of magnitude each year over the past three to four years, for example from less than 100 verifiable gallons of algae oil produced by the entire industry in 2009 to over 20,000 gallons delivered to customers in 2010.

Table 7, shows that Microalgae (low, medium and high Oil Content) have been found to have incredible production level compared to other oil seed crops.


**Table 7.** Oil content in some microalgae


**Table 8.** Chemical composition of some food source microalgae (% of dry matter) [120]

### **7.3. Biodiesel production from microalgae biomass**

Liquid fuel can be obtained by the process of oil extraction from algae. Hexane is an organic solvent which is used for this process. The hexane removes the oil from the algae. The mixture of hexane and oil is distilled leaving pure algae oil. This technique has significance that solvent is reused for each cycle. Algae fiber, which is remain after this process can be used as fertilizer.

The methodology mostly used for biodiesel production is based on the transesterfication reaction, as follows:

**Species Oil content Species, % Oil content, % Botryococcus braunii** 25–75 Isochrysis sp. 25–33 **Chlorella sp.** 28–32 **M. Subterraneus** 39.3 **Chlorella emersonii** 63 **Monallanthus salina** 420 **Chlorella minutissima** 57 **N. laevis** 69.1 **Chlorella protothecoides** 23 **Nannochloris sp.** 20–35 **Chlorella sorokiniana** 22 **Nitzchia sp.** 45–47 **Chlorella vulgaris** 40, 56.6 **P.incisa** 62 **Cylindrotheca** 16–37 **Phaeodactylum tricornutum** 20–30 **Crypthecodinium cohni** 20 **Schizochytrium sp** . 50–77 **Dunaliella primolecta** 23 **Tetraselmis sueica** 15–23

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

**Anabaena cylindrica** 25–30 43–56 4–7 **Chalmydomonas rheinhardii** 17 48 21 **Chlorella vulgaris** 12–17 51–58 14–22 **Dunaliella salina** 32 57 6 **Porphyidium Cruentum** 40–57 28–39 9–14 **Spirulina maxima** 13–16 60–71 6–7 **Baker's yeast** 38 39 1 **Meat** 1 43 34 **Milk** 38 26 28 **Rice** 77 8 2 **Soya bean** 30 37 20

**Table 8.** Chemical composition of some food source microalgae (% of dry matter) [120]

Liquid fuel can be obtained by the process of oil extraction from algae. Hexane is an organic solvent which is used for this process. The hexane removes the oil from the algae. The mixture of hexane and oil is distilled leaving pure algae oil. This technique has significance that solvent is reused for each cycle. Algae fiber, which is remain after this process can be used as fertilizer.

The methodology mostly used for biodiesel production is based on the transesterfication

**7.3. Biodiesel production from microalgae biomass**

reaction, as follows:

**Table 7.** Oil content in some microalgae

118 Biofuels - Status and Perspective

The transesterfication reaction, as above, 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. The biodiesel consists of a biodegradable fuel produced from renewable sources.


**Table 9.** Properties of biodiesel from microalgal oil, biodiesel fuel & ASTM biodiesel standard [120].

The synthesis of this fuel can be accomplished by methodologies such as cracking, esterification or transesterfication using animal fat or vegetable oils. Table 9 shows a comparison of characteristics of biofuels and petro diesel along with ASTM biodiesel standard [118].

### **7.4. Current limitations for algal biodiesel production**

Algae biodiesel is still a new technology because more than 30 years, research and development program was initiated by US Department of Energy but due to lack of funding and comparative low cost of petroleum fuel than algae biodiesel, in 1996 this program was discontinued. Now further research will be required to make algae fuel more viable and efficient then petroleum [120]. Algae biodiesel have also lower stability during regular seasonal temperature because during processing, microalgae differ in polyunsaturated from which is other form of biodiesel and polyunsaturated fats have an ability to retain their fluidity at lower temperature during winter but it will have also lower stability during regular seasonal temperature.


**Table 10.** Chemical composition of biofuel source microalgae
