**5. Conclusions**

Microalgae are renowned as a powerful biotechnology platform for the production of a wide range of value-added products. These include biofuels, animal and aquaculture feeds, and highvalue commercial products, such as pigments, polysaccharides, bioplastics, and other organic compounds. Microalgae have also been proposed for a biorefinery model where multiple compounds can be produced simultaneously from harvested microalgal biomass grown in wastewaters and in anaerobic digestion digestates. The growth of the biomass in industrial wastewater and/ or anaerobic digestates has been proven to be a feasible alternative to synthetic mediums.

Regarding the anaerobic digestion of microalgae and cyanobacteria biomass, co-digestion allows to improve the low C/N ratio of microalgae and cyanobacteria, balance the nutrients, and avoid the possible inhibitions in many cases. Furthermore, the produced digestate after the anaerobic digestion process presented better stability when a high-carbon biomass is codigested with microalgae or cyanobacteria biomass.

However, the wide variety of microalgae and cyanobacteria and the different types of highcarbon biomass make it difficult to ascertain a general assessment about the enhancement of methane production when these two biomasses are co-digested. In this respect, it seems that the use of microalgae/bacteria consortium could reduce drawbacks from working with pure species by favoring positive synergetic effects. Further studies will be needed in order to obtain a proper mixture culture.
