**4. Conclusions**

The elemental and proximate analysis, DTG and DSC curves showed remarkable differences between MB and BC, which were mainly related to the relative low fixed-carbon and large volatiles, oxygen and nitrogen content of the first. Despite these differences, both the DTG and DSC combustion curves of the blend MB-BC (wt. 10% MB) were equal to those of BC, which was further corroborated by the corresponding characteristic parameters. The small differences between the experimental and the weighted average composition calculated DTG and DSC curves pointed to unremarkable interactions between MB and BC during the combustion of their blend. On the other hand, the HHV of MB (23 MJ/kg) was very close to that of BC (24 MJ/kg), which is favorable for co-combustion applications. The HHV of MB and BC were adequately estimated by correlations that were based on their elemental analysis or on both their elemental and proximate analysis. Furthermore, the *E\** estimated by the iso-conversional models of FWO and KAS for the combustion of MB-BC (103 and 94 kJ/mol, respectively) rather approached those of BC (89 and 79 kJ/mol, respectively) as compared with MB (197 and 196 kJ/mol, respectively). Globally, the results pointed to co-combustion as an encouraging option for the thermal valorization of microalgae biomass resulting from wastewater treatment.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1073/12/15/2962/s1.

**Author Contributions:** Conceptualization and methodology, R.N.C. and M.O.; software and formal analysis, R.N.C.; investigation, R.N.C., C.E. and M.O.; writing—original draft preparation, R.N.C. and M.O.; writing—review and editing, R.N.C., C.E. and M.O.; funding acquisition, M.O.

**Funding:** This research received funding by Fundação para a Ciência e a Tecnologia (FCT, Lisboa, Portugal), gran<sup>t</sup> number IF/00314/2015.

**Acknowledgments:** Thanks are due to FCT/MCTES for the financial support to CESAM (UID/AMB/50017/2019), through national funds.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
