## 4 Conclusions  
It was found that the dry biomass production routes considered in this study are of high energy demand (12.09-12.51 kWh/kg) and with high operating costs (US $210.05-214.59/kg), when compared to other similar studies. This is mainly due to the contribution of the use of tubular photobioreactors as a biomass culture system. However, although PBRs have industrial application for the production of protein, pigments, animal feed, fatty acids and antioxidants [43], and the significant reduction in the consumption of fresh water (compared to open systems for cultivation), there are few studies that analyze and evaluate the implementation of these systems for biomass production. The cultivation stage contributes 96% to 98% of the total energy consumption in the dry biomass production scenarios and 99% of the total production costs, the rest is included in the harvesting and drying stages of the biomass. These results suggest the need to research engineering alternatives to the biomass cultivation system, in order to reduce the operating cost, in addition to biological alternatives that aim to increase biomass productivity.  
The scenarios that use NaOH are the scenarios with the highest energy consumption (12.28 kWh/kg to 12.51 kWh/kg) and production cost per kg of dry biomass produced (US $213.54/kg to US $214.59/kg). The scenarios that consider FeCl3 as flocculant have energy consumption similar to those that use Chitosan (12.09 kWh/kg to 12.32 kWh/kg). Regarding the cost of production, it only increases by a minimal amount in these latter scenarios. However, the use of Chitosan as flocculant guarantees the production of higher quality biomass compared to the scenarios with the other flocculants. This offers the option of being able to reuse the growing medium after the secondary harvest and thus reduce production costs. This is favorable for the production of high-quality biomass, which may well be used in the food, cosmetic or pharmaceutical industries. On the other hand, analyzing the individual impact of the technologies involved in secondary harvesting, centrifugation and vacuum filtering are the ones with the highest energy consumption; regarding the cost of production, centrifugation and belt filter press technologies are the ones with the highest cost, mainly due to the high cost of equipment and associated maintenance. In the drying stage, spray drying is the technology with the highest energy consumption and the highest production cost. This causes a direct impact on the scenarios with these technologies. Additionally, this study estimates a capacity to capture up to 148 tons/ha/year of CO2 by cultivating microalgae in a tubular photobioreactor. This amount depends mainly on the cultivation conditions of the microalgae, that is, the biomass productivity achieved and the spatial configuration of the tubular photobioreactors. Under the same biomass productivity, if some other configuration is implemented to accommodate the tubular photobioreactors on the surface destined for cultivation, ensuring that the amount of light to the photobioreactors is not affected, biomass production and CO2 capture on this surface could be increased. Fresh water consumption is lower for biomass culture in a photobioreactor compared to open culture systems; even so, the consumption of fresh water could be further reduced, using wastewater or recirculating the culture medium after harvest (primary and secondary) towards the culture in the photobioreactor, and additionally the consumption of fresh nutrients would also be reduced. However, to consider this proposal, the type of wastewater and the type of flocculant must be taken into account, as this can cause contamination in the biomass or limit the growth of the biomass.