## 3 Results and Discussion
### Evaluation of Production Costs by Process Scenarios
The cultivation stage (including preculture) absorbs 99% of the operating costs (US $14,876,000/year), this is mainly due to the cost associated with the maintenance  
Figure 6: Distribution of energy consumption in the harvesting and drying stages of biomass. All scenarios are fed from the PBR effluent.  
of the PBR, which is directly associated with the purchase cost of the equipment, the high energy consumption and the cost of the raw material of the process that is necessary in this stage (99% of the raw material costs are required in this stage). Figure 7 shows the distribution of the production cost in the harvesting and drying stages. Analogously to the results of energy consumption, the primary harvest stage has little variation in production costs for the different scenarios. However, it can be observed in Figure 7 that the scenarios that consider the flocculant FeCl\({}_{3}\) (case C2) are of lower cost (scenarios 9 to 16). Figure 7 shows a group of scenarios that presents a greater difference in the cost of production, these are 1, 2, 5, 6, 9, 10, 13, 14, 17, 18, 21 and 22. This group of scenarios includes centrifugation and belt filter press technologies. These technologies have the highest production cost compared to the other two secondary harvest technologies. The high cost of operation for these two technologies is associated with the high cost of maintenance of the equipment, since they are the ones with the highest equipment purchase cost. It is also observed that spray drying increases operating costs in those scenarios that consider it. On the other hand, in the group of scenarios with the lowest production cost are those that consider vacuum filter and pressure filter for secondary harvest.  
The results allow us to detect the impact of the integration of various technologies in production scenarios. This is relevant in the process design; if we want to implement a biomass production system in which it is necessary for the biomass to meet certain specifications, the first thing that must be taken into account is if the technology does not affect the quality for the purpose wanted. For example: (1) it was already mentioned that the type of flocculant can contaminate the biomass and limit its use for certain applications, (2) if you want to obtain high quality products, for example for the food or pharmaceutical area, centrifugation should be considered over another technology for secondary harvest, (3) or if the purpose is to obtain proteins, when using a drum dryer there is a risk that it reaches a temperature higher than necessary and this causes the denaturation of the proteins. However, taking all this into account has a direct impact on the scenario to be considered, and in turn, on energy consumption and production costs.  
Comparison of Scenarios, Energy and Water Consumption vs. Production Cost per kg of Biomass Produced  
To compare the scenarios under the same basis, the energy consumption, fresh water consumption and the cost of production were determined per scenario to produce 1 kg of dry biomass (Figures 8 and 9). Regarding energy consumption and production cost shown in Figure 8, two groups of scenarios are observed, the first (located in the upper  
Figure 7: Distribution of the production cost in the harvesting and drying stages of the biomass. All scenarios are fed from the PBR effluent.  
right corner) with high energy consumption and production cost (scenarios 1 to 8), and the second (located in the lower left corner) with low energy consumption and low production costs (scenarios 9 to 24). In the first group, they have the characteristic of using NaOH as flocculant. This group of scenarios has the lowest biomass production compared to the rest of the scenarios, this is due to the flocculation efficiency in the primary harvest. In this group, it is observed that scenarios 1 and 2 are those with the highest energy consumption and production cost, they consider the secondary harvest with centrifugation (technology with the highest production cost) and only differ in the drying technology. In the second group are the scenarios that use FeCl\({}_{3}\) and Chitosan. Similar scenarios, that is, they use the same technology for secondary harvest and drying, and that they only differ in the type of flocculant, show the same energy consumption and only differ in the cost of production. The scenarios that consider Chitosan have a slightly higher cost of production than the scenarios that use FeCl\({}_{3}\). In this second group it is clearly observed that scenarios 16 and 24 are the ones with the lowest energy consumption (both 12.10 kWh/kg) and production cost. The production cost for scenarios 16 and 24 are US $210.05/kg and US $210.07/kg, respectively, practically the same. In general, it is observed that the scenarios that consider pressure filter in the secondary harvest (case D4), for example, scenarios 7, 8, 15, 16, 23 and 24, are those with the lowest energy consumption and production cost. On the contrary, those scenarios that consider centrifugation in the secondary harvest (case D1) are those with the highest energy consumption and production cost (scenarios 1, 2, 9, 10, 17 and 18).  
Figure 8: Total energy consumption vs. total production cost per kg biomass produced.  
Estimates of both energy consumption and production cost are high due to the kind of cultivation system considered depending on which other production systems they are compared to. These results allow knowing estimates regarding the energy consumption and production cost of the process (if the purpose is the production of biomass through photobioreactors) considering the operating conditions established for this study. In a similar study reported by [PERSON] et al. [42], it was determined that the energy consumption to produce 1000 kg of dry biomass, grown in PBR, is from 4500 kWh to 8200 kWh approximately (depending on the technologies considered for each process stage). Regarding the costs of biomass production, there is a wide variety of reports in the literature. [PERSON] et al. [63] report that biomass production in open systems (open raceway ponds) can have a value of $510/ton of wet biomass produced, and, although the cost of biomass production can still be increased when considering the biomass drying, this would probably still be much lower than that determined in our study.