Department of Hydrobiology
Cultivation

Sunlight or light as energy source, water and inorganic nutrients are the basic needs for growth of algae; temperature and pH are also crucial parameters. There are two common methods to grow algal cells:
1. Open-pond system: It is a good and cheap possibility to grow algae in tropical climate, where the variance of temperature, fall, humidity and radiation are small. The advantage of this method is the cheapness because it is not needed to use complex laboratory system to ensure light and temperature for growing.
2. Photobioreactor: In continental climate, where the temperature, fall and radiation variability is large; it is not possible to grow algal cells in open-pond system. Photobioreactors help to grow algae in laboratory under constant temperature and radiation.

To enlarge the cell number in photobioreactor it is necessary to determine and observe some kind of biological, chemical and physical parameters.

Biological parameters:

1. Predators & Parasites: One of the most important things to grow algal cells in photobioreactors is the so called "axenic-culture-growing". Only the chosen algal species should be in the photobioreactor, other species can change the growth rate of the used algal strain, especially predators (they feed upon the used algae) and parasites (they disease the used algal strain).
2. Biological toxins: Not only predators and parasites can cause enormous problems during cultivation but biological toxins as well. This problem based on the infection of other, toxin producer algal species. This problem can not arise if the used culture, the used algal strain is axenic.

Chemical parameters:

1. Nutrients: One of the most important non-biological parameters are the nutrients. The availability and balance of nutrients dramatically affect productivity of algae populations. The types and amounts of nutrients in the medium depend on the algal species, because different species could need different compounds especially trace elements.
2. Salts: Algae occur in seawater and freshwater as well. The addition of extra salt in medium depends on the algal species: the seawater-living algae species need extra amount of salts, especially sodium-chloride; but in contrast, the increase of salinity in freshwater cause the death of algal cells. This points to the fact that it is important to control salinity of the medium in the photobioreactor.

Physical parameters:

1. Temperature: Specific temperatures must be maintained for specific algal strains. In photobioreactor living algal strain needs constant temperature to thrive. It is important to determine the best temperature for the used strains.
2. Light: Like to temperature, light intensity depends on the used algal strains as well. The too much or too less light can cause decreasing or death of algal cells.
3. pH (pondus Hidrogenii): Most of the freshwater algal species prefer the neutral pH (~ 7). The alkaline or acid water does not suited for growing algae.
4. Pumping: To circulate the medium in the photobioreactor is crucial for maintaining algal growth rate. It is possible to pump sterile air or carbon-dioxide enriched air throughout the bioreactor.

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