**Comparative Thermogravimetric Assessment on the Combustion of Coal, Microalgae Biomass and Their Blend**

#### **Ricardo N. Coimbra 1, Carla Escapa 2 and Marta Otero 1,3,\***


Received: 5 July 2019; Accepted: 29 July 2019; Published: 1 August 2019

**Abstract:** In this work, thermogravimetric analysis (TGA), differential thermogravimetry (DTG), and differential scanning calorimetric (DSC) were used to assess the combustion of microalgae biomass, a bituminous coal, and their blend. Furthermore, different correlations were tested for estimating the high heating value of microalgae biomass and coal, with both materials possessing similar values. TGA evidenced differences between the combustion of the studied fuels, but no relevant interaction occurred during their co-combustion, as shown by the DTG and DSC curves. These curves also indicated that the combustion of the blend mostly resembled that of coal in terms of weight loss and heat release. Moreover, non-isothermal kinetic analysis revealed that the apparent activation energies corresponding to the combustion of the blend and coal were quite close. Overall, the obtained results indicated that co-combustion with coal might be a feasible waste to energy managemen<sup>t</sup> option for the valorization of microalgae biomass resulting from wastewater treatment.

**Keywords:** sustainable energy; thermal valorization; kinetic modelling; iso-conversional methods; zero-waste water treatment; *Chlorella sorokiniana*
