## 1 Introduction
### Microalgae Cultivation Systems  
The two main categories of microalgae cultures are the external type (open tanks) and the indoor type (photobioreactors). In both cultivation systems, the light source and its intensity play a key regulatory role. In external systems, microalgae receive sun light, while in internal systems they receive it from various types of artificial sources, such as LEDs and optical fibers. However, in both cropping systems, photosynthetically active solar radiation (PAR), when over the saturation threshold, can be a factor limiting growth and reducing biomass productivity. As a result, cultivation systems that are outdoor cannot be effectively controlled, unlike indoor ones that are monitored [8]. These are outdoor cultivation systems in ponds, reservoirs, and elongated basins, as the name implies. This system is the earliest and most fundamental technique for mass-cultivating microalgae. To achieve high biomass productivity at low cost for industrial-scale microalgae cultivation, the open basin system was developed. This is a straightforward technology that works well in many different nations, including those in Asia, Mexico, the United States, Italy, Spain, and the Netherlands. Species of _Chorella_ and _Spirulina_ are mostly grown in open lake systems across the world. An elongated basin with vertical walls and a flat bottom that is no larger than 0.5 hectares and has a depth of 0.25 to 0.30 m is the typical configuration for microalgae farming. The parameters that must be considered for the construction of these basins are successful mixing of the growing medium, facilities for planting and harvesting food, the entry of carbon dioxide, drainage, flooding, and cleaning. For cultivating microalgae in open systems, a low-cost medium is used, such as various wastes, which provide the necessary nutrients, phosphorus, potassium and nitrogen, and atmospheric CO\({}_{2}\). Consequently, this technology offers the dual advantage of wastewater treatment and microalgae growth at low cost [9]. Outdoor systems can be divided into two categories: natural containers, such as lakes, dams, and lagoons, and artificial lakes or basins. The most commonly used systems include shallow large lakes, reservoirs, circular ponds, and elongated basins, mostly oval in shape [10]. Indoor culture systems are also called closed-type cultures or laboratory systems. Microalgae culture systems are strictly controlled and monitored and are carried out in special reactors, photobioreactors (PBRs). In these reactors, continuous monitoring of important light and temperature parameters is ensured, as well as of possible contamination by parasites and competing species of other microalgae. Oxygen management is the primary drawback of photobioreactors because a proper degassing system is needed. In microalgae culture, photobioreactors are a commonly used system, independent of climate. Polyethylene, solenoid, tubular, vertical, or horizontal column systems, and flat photobioreactors are among the various varieties [11]. In comparison to elongated basins, flat and tubular bioreactors are the most effective and productive system for achieving a higher biomass yield because they shield microalgae from pathogens, infections, predators, and other competing species. Photobioreactors, depending on the method applied, can be discontinuous, continuous, and semi-intermittent [9]. Stirred tanks are another type of photobioreactor, where stirring is performed mechanically using blades. The mixing efficiency is significantly higher compared to the other types, resulting in satisfactory heat and mass transfer. The disadvantage, though, is that mechanical stirring leads to high shear stress in microalgae cells, which is harmful to cells and an expensive method for their operation and maintenance due to the creation of heat by stirring. The biggest disadvantage of photobioreactors of all types is the difficulty in scaling up installations to achieve production for commercial purposes [12]. Escalation is an area that faces problems in general.