# Sustainable Microalgae and Cyanobacteria Biotechnology
## 6 Concluding Remarks  
Some microalgae have been cultivated successfully as large-scale or commercially available products: Chlorella vulgaris and _Chlamydomonas reinhardtii_ for bioethanol production [167], \(\beta\)-carotene and coenzyme Q produced by _Isochrysis galhana_[168, 169], _Tetraselmis_ sp. produce skincare substances that reduce the size of melanocytes and the amount of hyperpigmentation [170], halotolerant marine microalgae, such as _Chaotecros mulleri_ and _Tisochrysis lutea_, produce sterols used in the pharmaceutical industry [171], the pigment Astaxanthin successfully commercialized produced by _Heamatococcus pluvialis_[172], and _Chlorococcus_ sp. produce carotenoids and phytoene [173]. Although there are some successful samples of microalgal cultures, some technologies can help to improve biomass are high-valuable compounds production, revalorize waste material by microalgal metabolism, and integrate a downstream process to obtain several products in one cultivation.  
Microalgae and cyanobacteria have numerous biotechnological applications in a variety of industries (Figure 3). Microalgal processes can be divided into two main systems based on their technological application: closed and open The closed system can be used for high valuable compounds, such as the production of food additives, nutraceuticalals, pharmaceutical, and recombinant protein; these types of photobioreactors can be assembled with a full control equipment of pH, temperature, CO2 supply, light supply, medium supply, broth recovery, oxygen control, and sterile conditions, and all are susceptible for high purity compound production. Close photobioreactors can be used to develop recombinant therapeutic protein production, which can be a cost-effective production system compared with mammalian cell culture. Open systems in the other part of applications are useful to produce large amounts of biomass without the need for sterility. The focus in the latter system is a biorefinery process, in which the main product can be biofuels--biodiesel, and biohydrogen--but other compounds such as glycerin, biosurfactants, health products, and feed protein can also be obtained. Microalgal growth has been used in wastewater treatment and phycoremediation processes, clean water recycling in aquaculture, and sustainable fish and vegetable production, such as aquaponics technology. For extremely valuable compounds, OMICS technologies in microalgae require the discovery of new genetically modified microalgae capable of producing pharmaceuticals for human health applications; these systems may have technical advantages as well as cost-effective processes.  
**Author Contributions:** Conceptualization, F.-J.M.-R.; subject 2, J.-F.L.-H., T.K.-M. and M.A.-K.; subject 3, T.K.-M., M.A.-K., C.-A.-A.-G., G.-G.-A.-A. and F.-J.M.-R.; subject 4, J.-F.L.-H., G.-G.-A.-A. and C.-A.-G.; subject 5, J.-F.L.-H. and F.-J.M.-R.; resources, F.-J.M.-R.; writing--review and editing, ALL. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research has received funding from the Consejo de Ciencia y Tecnologia del Estado de Tabasco, Grant No. PRODECTI-2020-01/052.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author.  
**Acknowledgments:** The authors thank CONACYT, Mexico for a PhD grant, No. 334031.  
**Conflicts of Interest:** The authors declare no conflict of interest.