## 3 Results and Discussion
### Classification of the Scenarios Depending on the Use of Biomass
On the other hand, the cost of FeCl\({}_{3}\) for one year of operation is the lowest of the three cases analyzed in the primary harvest (flocculation), US $544/year, which causes the scenarios with this flocculant to be economically competitive with those scenarios using Chitosan (more expensive flocculant, case C3, Figure 8). The removal efficiency is higher for the cases that consider FeCl\({}_{3}\) than for those that consider NaOH, and this achieves a higher biomass production for the scenarios that use C2 as a secondary harvest. However, the contamination that the biomass can suffer when using FeCl\({}_{3}\) limits its use, and prevents the recovery of the culture medium after harvest, which causes the options to improve the economy of these production scenarios to be reduced, (scenarios 9 to 16). On the other hand, if biomass is to be used for the production of compounds of commercial interest (metal-free), it would be necessary to integrate biomass purification stages, which would increase production costs.  
The consumption of Chitosan as a flocculant has been reported as effective and does not contaminate the biomass. However, its high cost limits its implementation if its purpose is not to produce higher quality biomass [53; 61]. [PERSON] et al. [65] report that the use of Chitosan as flocculant allows the use of the culture medium after harvest and that it can maintain growth by planting with fresh algae cultures. Furthermore, the harvested cells are intact and alive after flocculation and are capable of reproducing and growing. This is an additional advantage in applications where chemicals and drugs must be recovered from biomass free of undesirable and potentially toxic contaminants. Besides, Chitosan is produced from chitin, a structural element in the exoskeletons of crabs and shrimp, which allows it to be produced in a more sustainable way than other synthetic organic polymers [66]. The results of this study show that the scenarios that consider Chitosan as flocculant (scenarios 17 to 24) are within the group of scenarios with lower energy consumption and production cost per kg of biomass produced (Figure 8). According to the aforementioned bibliographic review, the biomass produced in these scenarios has greater advantages over the biomass produced in the scenarios that consider NaOH and FeCl\({}_{3}\). Additionally, it was mentioned earlier that scenarios using a drum dryer could be considered less appropriate to obtain high-quality biomass to produce proteins, because the protein denaturation temperature is reached in this equipment [41]. Once the bibliography has been analyzed, considering the quality of biomass and production costs, the scenarios with the potential to produce high-quality biomass are 17, 19, 21 and 23 (Figure 10).  
Figure 10: Scenarios for the production of high-quality biomass (harvested with Chitosan).  
Considering the four scenarios with the highest potential to produce higher quality biomass, and considering energy consumption and unit production cost, scenario 23 has the lowest energy consumption and lowest production cost (12.10 kWh/kg and US $210.32/kg) (Figure 8). Scenario 23 considers flocculation with Chitosan, pressure filter and spray dryer. In Figure 8, it is observed that scenario 24 has slightly lower values than scenario 23, for energy consumption and production cost. However, it has to be considered that scenario 24 uses a drum dryer and this can reduce the quality of the biomass if there is not a good control of the drying temperature. Energy consumption in all scenarios is high, mainly caused by high energy consumption in the cultivation system. One option to remedy this consumption could be to consider the use of renewable energy sources, either totally or partially, such as solar or wind energy, and with this, minimize CO2 emissions by generating the energy necessary for the process. Regarding the operating cost, this could be reduced by recycling the growing medium after harvest or by using wastewater as a source of nutrients in the growth stage.