## 2 Materials and Methods
### Data Collection for the Design of the Harvest Stage  
As a strategy to reduce costs and energy, microalgae harvesting is usually done through two stages, first the diluted biomass is concentrated from 0.5 to 10-50 g/L approximately, and later, dehydration must be carried out to increase the biomass concentration up to approximately 200 g/L of biomass in dry weight. In the primary harvest, various techniques such as flocculation, bio-floculation, flotation, gravity sedimentation, electroflococulation, among others, can be implemented. In the secondary harvest, centrifugation and filtration techniques are mainly used [31; 32; 40; 49; 50; 51]. Since the biomass has already been concentrated in the primary harvest, energy consumption is lower for this secondary harvest since the amount of water to be removed is less. In this work, the harvest is carried out in two stages. In the primary harvest, the only flocculation is considered, since according to the literature it is considered a promising technology for large-scale harvesting [52]. However, in this primary harvest method, the objective of subsequent processes for the selection of the appropriate coagulant must be considered since this can interfere with the final use of the biomass [53]. In this case, three flocculants were analyzed for the primary harvest, NaOH, FeCl\({}_{3}\), and Chitosan generating three case studies for this stage, C1, C2, and C3, respectively. Each flocculant has a different flocculation mechanism and allows different uses of biomass. This stage is carried out in a clarifier, which is fed with the outflow of the cultivation stage that is mixed with the flocculant. The flocculant used usually depends on the species of algae selected since each species has specific physicochemical characteristics that must be considered [54]. For the design of this stage, it is assumed that the production of microalgae is constant, that the same concentration is always achieved in the culture, 4 g/L, and that the concentration reached after flocculation is 50 g/L for all cases analyzed. Case C1 uses NaOH as flocculant with a concentration of 125 mg/L, achieving a removal efficiency of 94.28%, case C2 with a concentration of 30.52 mg/L of FeCl\({}_{3}\) achieves a removal efficiency of 95.71%, and case C3 with Chitosan in a concentration of 36.36 mg/L, achieves a removal efficiency of 95.71%. These values were taken from what was reported in the study by [PERSON] et al. [52], in which they analyzed flocculation of the _Chlorella_ species with these flocculants. A cost of 350 US $/tons was considered for NaOH, 650 US $/tons for FeCl\({}_{3}\) and 1680 US $/tons for Chitosan. Centrifugation and filtration techniques were considered for the secondary harvest to achieve a higher concentration of biomass from the primary harvest. These two technologies were selected for their ability to be applied on an industrial scale (capacity and speed of processing [11]). At this stage, centrifugation and three types of filtration technologies were considered, generating four study cases D1, D2, D3, and D4. Different filtration technologies are applicable to the microalgal biomass dehydration process; in this study the use of membrane filtration technologies was discarded due to the high cost of operation and consumables required, and that their large-scale application is limited [53]. Vacuum Filter (D2), Belt Filter (D3), and Pressure Filter (D4) were considered as filtering technologies and Decanter Centrifuge (D1) for secondary harvest. The literature has reported removal efficiencies of 99.99% for centrifugation and 90% for filtering the _Chlorella_ species [37; 55]. Considering this information reported in the literature, removal efficiency was set in all technologies for the second harvest of 90% and that concentrations of 200 g/L of biomass are reached in the effluent of this stage (approximately 20% biomass in dry weight) in order to be able to compare them with each other.