## 1 Introduction  
Microalgae are photosynthetic unicellular and multicellular microorganisms living in almost all of Earth's ecosystems, as they can be found in oceans, rivers, lakes, and soils [1, 2]. The classification of each specie is based on pigment composition and diversity of structural features. The great interest in these phytoplankton lies in their ability to produce bioactive compounds through photosynthesis. In this process, microalgae convert solar energy into chemical energy by fixing atmospheric CO\({}_{2}\)[3]. Therefore, the photosynthetic process makes microalgae cultivation an excellent option for capturing this air pollutant. Additionally, depending on the microalgal species, they can absorb dissolved inorganic carbon from the aquatic surroundings in the forms of H\({}_{2}\)CO\({}_{3}\), HCO\({}_{3}\)\({}^{-}\) and CO\({}_{2}\)[4]. Microalgal biomass has many potential applications in several industries. In the cosmetic industry, bioactive compounds can be extracted from biomass and incorporated into several products [5]. Microalgal biomass can generate large amounts of lipids, proteins, and carbohydrates in a short time [5]. Microalgal protein can be converted into nutritional and pharmaceutical products, while lipids can be used to produce biodiesel [4]. Another microalgal application is nutrient removal from wastewater, promoting their treatment [6]. The major challenge of microalgal cultivation lies in the harvesting process due to the small cell size of microalgal cells (1-30 \(\upmu\)m diameter) and their colloidal stability in suspension. [PERSON] et al. [7] estimate that the cost involved in the harvesting process accounts for over 30% of the total production cost. Therefore, it is crucial to find an efficient harvesting method, taking into account the microalgal species, the maximum amount of biomass to be recovered, and the operational and energetic costs [8]. According to [PERSON] et el. [8], the selection of harvesting methods depends on the end product requirements, cell size and density, salt concentration, and moisture content. Therefore, two or more techniques can be combined. Technologies for microalgal harvesting involve physical-, chemical-, biological- and electrical-based methods. The most common processes are coagulation/flocculation, gravity sedimentation, dissolved air flotation, electrical processes, centrifugation, membrane filtration, and magnetic separation [9; 10]. However, some of these techniques can be energy-consuming (centrifugation), time-consuming (gravity sedimentation), or toxic to microalgal biomass (chemical coagulation/flocculation) [11]. Coagulation and flocculation are two of the most widely used methods for microalgal harvesting, as they are economical and allow the treatment of large amounts of diluted cultures. Coagulation and flocculation can be achieved in several ways, and various approaches for microalgal aggregation have been studied in recent years [12]. Coagulation consists of destabilizing the negative charge of colloidal particles (such as microalgae), whereas flocculation entails the aggregation of neutralized particles into flocs and their decantation over time [13]. The two methods combined with sedimentation or filtration can increase the overall recovery efficiency, promoting 100% recovered biomass [8]. For many years, chemical coagulants were used to harvest microalgae such as ferric sulfate, aluminum sulfate, and ferric chloride [14]. Due to contamination of the biomass by metallic ions and the degree of toxicity of some chemical coagulants (e.g., aluminum sulfate), which can cause damage to human health (e.g., Alzheimer's disease), biocogagulants have been increasingly used as alternative compounds for microalgae harvesting. Biocoagulants have attracted the attention of researchers because they are natural, biodegradable, inexpensive, non-toxic to algal biomass, and promote high coagulation efficiencies [13].