## 4 Optimisation of the Microalgae Biomass Cultivation and Valuable Products Synthesis  
In order to achieve the desired technological effect in the cultivation of microalgae and to obtain valuable end products, it is essential to create and maintain suitable incubation conditions for the biomass. This includes modifying the physical and chemical parameters of the culture medium as well as the operating conditions of the production process. These modifications include the regulation of temperature, oxygen and carbon dioxide concentration, illumination type, photoperiod, and radiation intensity [99]. Modern technologies also utilise genetic engineering methods that allow the DNA of microalgae to be modified in order to increase the production efficiency of certain compounds [100].  
Induction methods for the accumulation phase of valuable products in microalgae cells usually involve limiting the availability of essential building blocks such as nitrogen, phosphorus, or silicon (in the case of diatoms), which leads to a halt in cell division and activation of biosynthetic pathways [101]. It is important to maintain a balance between the growth rate of biomass and the efficiency of the accumulation of storage substances, which can be achieved by two-stage cultivation strategies [102].  
Another approach to increase autotrophic biomass growth is the appropriate design of PBRs. For example, automated systems equipped with sensors that orientate the PBR perpendicular to sunlight can increase the proportion of photosynthetically active radiation and improve photosynthetic efficiency [103]. Alternatively, chemical compounds can be added to the microalgae cultures to influence the metabolic pathways of biosynthesis in order to increase the accumulation of valuable products. For example, studies have shown that the addition of myo-inositol to _Dunaliella_ sp. cultures increases cellular lipid content by 33% [104].  
However, challenges to widespread application include the regulatory mechanisms of gene expression and the limited number of microalgae strains suitable for genetic modification. Research to increase the activity of enzymes involved in lipid biosynthesis, such as acetyl-CoA carboxylase, and to stimulate starch storage in mutants is an example of efforts to improve production efficiency [105]. Mathematical models for optimising the cultivation processes of microalgae, such as dynamic flux balance analysis (DFBA), allow the prediction of the effects of changes in illumination and other conditions on the composition of metabolites [106]. These models are validated against experimental data, which increases their accuracy in predicting production yields [107].  
An equally important aspect is the understanding of the interactions between microalgae and other microorganisms, especially bacteria. The reciprocal relationships between microalgae and bacteria can improve the growth of microalgae and increase the production of metabolites, including carbohydrates, pigments, and lipids, which opens up new possibilities for optimising cultivation processes [108]. The methods used and described in the literature to optimise the production of microalgae biomass are summarised in Table 3.  
\begin{table}
\begin{tabular}{c c c} \hline
**Optimisation Approach** & **Species** & **Achieved Outcome** & **References** \\ \hline  & & Increased growth and lipid & \\ Monitoring and maintenance of & _Chlorella vulgaris, Nannochloropsis_ & accumulation efficiency through & \\ proper incubation conditions & sp., _Scenedesmus obliquus_ & optimisation of pH (6.5–8.5), & [109; 110] \\  & & temperature (20–30 \({}^{\circ}\)C), light & intensity, and aeration \\ \hline \end{tabular}
\end{table}
Table 3: Selected optimisation methods used in microalgae biomass cultivation technology.  
\begin{table}
\begin{tabular}{c c c c} \hline