20.2 Cultivation and Processing of Microalgae

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20.2.3.2

Lighting

Cell cultures are placed in an area with a huge window along with supplementary

lighting. Natural lighting may also be provided. The most commonly used system

involves usage of the white fluorescent bulb which can give the required flux density

needed for the cell growth. Recently, light-emitting diodes (LEDs) are also being

used. Continuous lighting may also damage the algal cells and it even kills some

algae. The light and dark regimes may be varied between 12 : 12 and 16 : 8. It is strictly

recommended to avoid direct sunlight.

20.2.3.3

Culture Media

There are two different culture media, defined and undefined. In the case of defined

media, high-quality deionized water is used along with the nutrients which are

needed to make the formulation. Undefined media is of seawater base, which can

be natural or artificial and is added with nutrients. It is very important to prepare

the media with good quality seawater. The quality of seawater can be improved by

aging to allow for bacterial degradation. Sometimes, brands of synthetic seawater

may also be utilized. Pre-filtering of seawater may also be done to remove larger

particles. Nitrogen (N2) and phosphorous (P) are the major nutrients of all culture

media. Nitrate or ammonium may also be used. Organic nutrients are also added.

Amino acids and inorganic orthophosphate may be used for additional nitrogen and

phosphorous, respectively. Certain algal groups such as diatoms and chrysophytes

require silica. Certain metals such as iron, copper, zinc, cobalt, manganese, and

nickel are also added in trace amounts. Vitamins consisting of thiamin (B1), biotin

(H), and cyanocobalamin (B12) are also used. Historically, the soil enrichment

extract was also used for the growth of many algal cultures. Sieved sandy loam

soil is most commonly used. There are many variations in different culture media

preparation.

20.2.3.4

pH

The control of pH in culture is very significant because some algae will grow merely

with certain pH values. Seawater has a pH of 8. Seawater has its own buffering capac-

ity and hence it is easy to keep the pH of such media. The pH of seawater can be

decreased before autoclaving in order to compensate the subsequent increase in pH.

20.2.3.5

Aeration

Aeration is not suggested for many processes, as it may become a physical distur-

bance for the growing cells. In certain situations involving heterotrophic dinoflagel-

lates, aeration is very much essential.

20.2.4

Culture Methods

20.2.4.1

Batch Culture

In a complete culture medium, algal inoculums are placed in a fixed amount and

are incubated in an appropriate environment for promoting its growth. When algal

cultures are grown in limited volumes, resources are finite and are used up com-

pletely. The pattern of growth involves lag phase, exponential phase, and stationary

phase.