*1.3.1. Open microalgal systems*

[20]. Purple non-sulfur bacteria derive hydrogen from diverse substrates, while green sulfur

Exploring new organisms for hydrogen production, optimization of growth conditions and use of biotechnological techniques can open new doors in making hydrogen a viable fuel for

Biosyngas is produced by the biomass gasification in presence of oxygen, water vapor or air, produces carbon monoxide, hydrogen, methane, water, other hydrocarbons and ashes. For gasification, high temperature (800–1200°C) is essential, and the feedstock needs to have not more than 20% water content in the biomass [23]. Electricity can be produced by burning in boilers and turbines and subsequently, kerosene, wax, naphtha and gasoline can

Ethanol production from or by microalgae has very interesting prospects, but is currently only in the preliminary phase of research. Bioethanol can be used as a biofuel, which can replace part of the fossil-derived petrol. More development is needed to analyze a full-scale production system. Currently, bioethanol is produced by fermenting sugars, which in the case of corn are derived from hydrolyzing starch. Microalgae species with starch content of over 50% have been reported. With new technologies, cellulose and hemicellulose can be hydrolyzed to sugars [25]; thereby, facilitating formation of ethanol from major part of dry algal biomass. Compared to the traditional use of woody biomass, microalgae hold better options some of

• The microalgal cellular composition is very simple and biomass can be utilized readily.

• Microalgal cells consist of copious amounts of polysaccharides, which can be converted to

Ethanol production from or by microalgae has very interesting prospects, but is currently only in the preliminary phase of research. More development is needed to analyze a full-scale production system. **Table 1** highlights the biofuels produced from different species of micro-

The development of dedicated culture systems for microalgae started in the 1950s when algae were investigated as an alternative protein source for the increasing world population. Subsequently, the diverse products and the bioremediation of wastewater potential of algae

directly from sunlight and water, although only in the complete absence of oxygen.

S). Other microalgae can make hydrogen

bacteria get hydrogen gas from hydrogen sulfide (H<sup>2</sup>

future [21, 22].

244 Advances in Biofuels and Bioenergy

*1.2.5. Biosyngas*

be obtained [24].

which are enlisted below [26]:

• Microalgae lack lignin, so the processing becomes easier.

• Microalgae can be genetically engineered to produce ethanol.

**1.3. Cultivation of microalgae for biofuel production**

*1.2.6. Ethanol*

sugar.

algae round the globe.

The open microalgal pond systems are commonly used for cultivation of microalgae as they have good opportunity to utilize the atmospheric carbon dioxide readily available in the atmosphere. There are several configurations of microalgae cultivation systems for biomass production and enhanced phycoremediation of industrial, domestic and agricultural wastewaters. The most commonly used systems for research and industrial microalgal cultivation are as follows:


For open systems, location is an important criterion keeping in mind, the sufficient sunlight availability and the requirement of the algae to be cultivated. The open ponds can be natural or artificial in nature and usually include natural lagoons, circular ponds, tanks and raceway ponds. Cultivation of *Chlorella* sp. was traditionally done in circular ponds, which are usually made up of concrete. They are also equipped with rotating arm to ensure mixing of the culture and prevention of sedimentation of algal biomass. Generally, the raceway ponds comprise race track or oval channel made up of concrete, and they are meant to circulate nutrients and carbon dioxide regularly to the algal cultures [30].

#### *1.3.2. Closed algal systems*

The closed systems (photobioreactors (PBRs)) have well-controlled growth conditions. Generally, these reactors are designed to increase the light accessibility. They also allow perfect mixing to permit the light to be within an optimum value for cell growth and to improve gas exchange. Since photobioreactors solve many problems of the open cultivation, researchers have focused on designing photobioreactors for large microalgal biomass production [30]. There is a wide variation in the design of the photobioreactor depending upon their geometry and construction. Photobioreactors can be built as bags tanks, and towers. Photobioreactors can be plates or tubular and made up of plastic or glass. Tubular photobioreactors seem to be the most suitable. Bubble columns and airlift photobioreactors can also be considered since they produce a relatively high concentration of microalgal biomass product [31]. An auxiliary tank is used to separate the oxygen produced from the photosynthesis. This is important considering that excessive oxygen can negatively affect the microalgae growth [32]. Despite the advancements in the design of photobioreactors for enhancing biofuel productivity in algae cultivation, bottlenecks are yet to be addressed efficiently considering the cost economics of biofuels and their productivity.

**Author details**

Archana Tiwari<sup>1</sup>

**References**

sjbs.2017.05.011 (in Press)

\* and Thomas Kiran<sup>2</sup>

\*Address all correspondence to: panarchana@gmail.com

1 Amity Institute of Biotechnology, Amity University, Noida, India

Water Science & Technology. 2017;**75**(12):2777-2783

large natural water bodies and its impact on CO<sup>2</sup>

of Algal Biomass Utilization. 2015;**6**(2):22-27

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2 International Crops Research Institute for Semi-arid Tropics (ICRISAT), Hyderabad, India

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Biofuels from Microalgae

247

http://dx.doi.org/10.5772/intechopen.73012

#### *1.3.3. Hybrid algal systems*

The hybrid systems are cost-effective and can be used for large algae cultivation [33]. Hybrid systems overcome the limitations of open systems and the high initial and operating cost associated with closed systems. In the hybrid system, the microalgae are initially cultured in closed and controlled photobioreactor system and then shifted to open system in order to enhance the biomass yield [34]. This system offers promising options for algal cultivation toward biofuel production.
