*3.1.1 Biomass by open pond cultivation*

*Biotechnological Applications of Biomass*

maximum photosynthetic rate [22].

biotechnological and industrial applications [3].

**3.1 Algaculture (culture of microalgae in hatcheries)**

**3. The microalgae biomass**

*Photosynthesis – Irradiance curve.*

**Figure 9.**

proportional to the functional absorption cross-section of the effective area that PS II presents to an incoming photon. *<sup>B</sup> Pm* is the assimilation number which is the

Microalgae is a promising renewable resource for biofuels, and optimization and control of the biomass growth production have gained economic and commercial interests. Algae do not compete with traditional food crops for space and resources [5]. Microalgae are highly diverse and differences within and between both species and populations lead to significant differences in biogeography and the environment. The macromolecular composition of the microalgae is of interest for understanding nutrient competition within microalgal communities, food web interactions, and developing algal systems for the development of biofuels, nutraceuticals, and mariculture [3]. Production of microalgae-derived metabolites requires processes for culturing the algae, recovery of the biomass, and further downstream processing to purify the metabolite. The cost of producing microalgal bioactive agents has to be weighed as the downstream recovery of the microalgal products can be substantially more expensive than the culturing of the microalgae [5]. Depending on their origin, algae are referred to as terrestrial algae, snow algae, seaweeds, and phytoplankton. Ubiquitous in marine, freshwater, and terrestrial habitats and possessing broad biochemical diversity, which is the basis for many

Hatcheries are used to produce a range of microalgae biomass, which are used in a variety of ways for commercial purposes. Studies have adduced the success of a microalgae hatchery system to the following factors: (i) the dimensions of the container/bioreactor where microalgae are cultured, (ii) exposure to illumination, and (iii) concentration of microalgal cells within the reactor [23, 24]. Photosynthesis is one of the basic biochemical transformations of photosynthetic micro-organisms that convert solar energy into chemical energy. Many microalgae are autotrophs, which use photosynthesis to produce food. Some heterotrophic microalgae can grow in the dark by utilizing organic carbon. Some microalgae grow by combining both autotrophy and heterotrophy into a hybrid cultivation mode called mixotrophy [4, 6]. Diatoms and dinoflagellates are the two types of microalgae. Diatoms can be spheres, triangles,

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There are two main advantages of culturing microalgae using the open pond system. Firstly, an open pond system is easier to build and operate. Secondly, open ponds are cheaper than closed bioreactors because closed bioreactors require parts that are expensive to acquire. However, where the temperature is the growth or lipid accumulation limiting factor, using open pond systems may decrease the productivity of certain commercially important strains such as *Arthrospira sp.* Waste heat and CO2 from industrial sources can be used to compensate for this [24]. Some organizations use the open raceway pond approach, employing foam fractionation to concentrate microalgal cells before they are lysed by the cavitation bubble collapse. Some commercial outdoor raceway ponds are located near power plants where 4–15% CO2 from the flue gas is fed to the raceway ponds. 1.8 units of CO2 are required to produce one unit of algal biomass, and the practical operation of open ponds has shown that dissolved CO2 in water is not enough; therefore, the bubbling of air into water improves CO2 dissolution [25]. Maintaining algae monocultures in open ponds poses serious challenges due to contamination with local algae species and invasion of algae predators. Some strategic operation models adopting higher salinity, pH, or temperature operating conditions have been proposed to provide a selective microenvironment to cultivate some commercial strains. In this regard, therefore, successes have been recorded in open ponds *Spiriluna* monoculture commercial cultivation at high pH values ranging from 9.0 to 11.0. In another operation, β-carotene is produced from *Dulaliella* sp. in open ponds wi high salinity values [25, 26] (**Figure 10**).
