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20 Application of Sustainable Micro-Algal Species in the Production of Bioenergy

to remove contaminating microorganisms like bacteria. Autoclavable and single-use

filtration systems are also available.

20.2.2.2

Autoclaving

Autoclaving is done to sterilize the equipment and media using high-pressure sat-

urated steam at a higher temperature of 121 ^∘C. Commercial autoclaves that are

generally used are both large and small, for small quantities, cookers may be used.

For liquids’ autoclaving, maintain the liquid level in the containers in such a way to

prevent excess buildup of pressure. Precipitate formation should be avoided in the

liquid because they may aggregate the nutrients, organics, and metals in the form of

particulates. Fewer scientists have also considered it as a positive attribute because

the precipitates may slowly release the nutrients. Autoclaving can be done in Teflon

bottles to reduce the development of precipitates in the saltwater. Distilled water can

also be added to avoid precipitation. Autoclaving glass/plastic wares at higher pres-

sure and temperatures may cause the release of certain substances from the walls of

the vessels. Pyrex bottles will release metals that are used for its manufacture. Poly-

carbonate bottles will release plastic stabilizers during the process of autoclaving. It

is advised to use a small quantity of deionized water in plastic containers to confine

the dissolved plasticizers.

20.2.2.3

Dry Heat

Dry heat is also used for sterilizing glassware like tubes, beakers, and glass pipettes,

etc. This glassware has to be cleaned and dried. The vessel openings should be lay-

ered with aluminum foil to protect the sterility. The glass vessels are placed in an

oven at a temperature approximately equal to 160 ^∘C at least for two hours.

20.2.2.4

Pasteurization

It is the most effective method of sterilizing seawater and the growth media. The

process of sterilization by this method is time-consuming. This is applicable for ster-

ilizing liquids that cannot be autoclaved to temperatures greater than 100 ^∘C. The

process includes heating of liquid to a certain temperature for a particular time inter-

val and then cooling it immediately to remove it from the heating source. The entire

process is carried out in a water bath, fitted with provisions for temperature regu-

lation. The major disadvantage associated with this process is that it is carried out

for a longer duration. Other methods of sterilization are microwaving and using of

UV radiations. For the UV treatment to be effective, the water must be placed in a

quartz glass tube.

20.2.3

Culture Conditions

20.2.3.1

Temperature

Temperature reflects the conditions from which the microalgae are isolated. Tem-

perature should not be above 30 ^∘C because high temperatures are fatal for marine

algae. Following are the isolation temperatures that need to be implemented:

●Polar isolates: <10 ^∘C

●Temperate isolates: 10–25 ^∘C

●Tropical isolates: >20 ^∘C