Catalytic microwave torrefaction of microalga Chlorella vulgaris FSP-E with magnesium oxide optimized via taguchi approach: A thermo-energetic analysis

Biochar is a promising material and fuel for environmental sustainability. Microalgal biochar is produced using catalytic microwave torrefaction of Chlorella vulgaris FSP-E residue with magnesium oxide as a microwave absorber to enhance heating. Using Taguchi experimental design (TED) and Analysis of Variance (ANOVA), the effects of microwave power, catalyst concentration, and duration on energy yield are investigated. Both TED and ANOVA confirm the significant effects of microwave power and catalyst concentration, while only a slight effect from duration. The calorific values of produced biochar (21.12–26.22 MJ⋅kg⁻¹) are close to coal. The maximum deoxygenation and carbonization extents are 56.69% and 35.23%, respectively. The optimal parameter combination of low microwave power (450 W), low duration (25 min), and high catalyst concentration (10 wt% MgO) poses the highest upgrading energy index (UEI) value. This confirms that better energy efficiency leans towards light torrefaction conditions with maximized catalyst concentration to produce the maximum energy yield while consuming the least electricity input.