## 1 Introduction
Other compounds of interest are amino acids (leucine, asparagine, glutamine, cysteine, arginine, aspartate, alanine, glycine, lysine, and valine), carbohydrates (\(\beta\)1-3-glucan, amylose, starch, cellulose, and alginates), and vitamins and minerals (vitamin B1, B2, B6, B12, C, E, biotin, folic acid, magnesium, calcium, phosphate, iodine) that are widely used in food additives, health supplements and medicine [23]. The production of biomass from microalgae requires several stages: cultivation, harvesting, and drying. The cultivation stage generates most of the process costs due to its high energy demand caused by the need to maintain a stable medium (temperature, pH, low O\({}_{2}\) concentration) and provide the necessary nutrients for growth including light [24]. Culture systems can be classified as open and closed. Open systems can be circular or raceway pond. Open pond systems are mainly used on an industrial scale, due to their lower cost of operation and easy construction [25]. However, water losses due to evaporation cause limited control over light conditions, temperature and CO\({}_{2}\) diffusion, directly affecting biomass production resulting in low yield [11; 26]. Biomass can be easily contaminated by external agents, limiting its application and preventing its use to obtain high-value products for the pharmaceutical and cosmetic industry [10; 12]. On the other hand, closed microalgae culture systems such as photobioreactors (PBRs) have several advantages over open culture systems. Some of the advantages of PBRs are a better control of the cultivation conditions, to obtain a biomass with homogeneous characteristics, and to minimize contamination by other microorganisms that can affect the quality of the biomass [11; 16; 27]. PBRs allow greater control in growing conditions than in open systems, and, consequently, a higher biomass production per growing area is achieved, as well as greater CO2 and nutrient absorption efficiency [28; 29]. Unlike production in open ponds, PBRs allow the cultivation of a single species of microalgae for prolonged periods with less risk of contamination increasing the potential of use for biomass [16; 27]. In terms of operating costs, PBRs are more expensive than open culture systems. This is mainly due to the energy consumption necessary to maintain the operating conditions of the PBRs such as pumping the culture medium, supplying the adequate concentration of CO2 (carbon source) to carry out the photosynthetic process and removing the excess O2 produced. As an alternative to reduce this consumption, the use of renewable energies could be implemented. Another advantage of PBRs technology over open cultivation systems is the requirement of a smaller cultivation area to obtain a higher biomass production and a better control of the operating conditions to produce biomass with homogeneous characteristics [27]. The biomass obtained in the PBRs has homogeneous characteristics, and can serve as feed to biorefinery processes, reducing fluctuations in the process while preserving the quality of the final products. Besides, PBRs can guarantee the characteristics of the by-products generated by microalgae which can improve economic profitability. The selection of the cultivation system depends on the quality of final products [30]. For example, if a high-quality product with few contaminants is required, closed cultures should be selected, while if an open system is chosen, a microalgae strain capable of inhibiting the growth of other contaminating species in the culture system must be selected to guarantee a high biomass production. Natural climatic conditions and the cost of land availability also play an important role in determining the cropping system [10]. After cultivation, microalgal biomass must be collected. Several methods can be applied at this stage. However, the application of some of them depends on the characteristics of microalgae such as size, cell density, the final product to be obtained, and whether the culture medium is to be reused [8].