Characterization and pyrolysis behavior of the green microalga Micractinium conductrix grown in lab-scale tubular photobioreactor using Py-GC/MS and TGA/MS

Abstract

Nowadays, microalgae are widely discussed as a promising feedstock for biofuel production. For higher crude bio-oil yield with good quality, microalgal biomass productivity and bio-oil characteristics are essential parameters. However, the same microalgal species has different chemical compositions at different growth phases. Therefore, the present study aimed to identify the best growth phase for high biomass productivity and optimal bio-oil production from the green microalga Micractinium conductrix via Py-GC/MS and TGA/MS analysis. M. conductrix was grown in a tubular photobioreactor and harvested at early exponential phase (EEP), middle exponential phase (MEP), late exponential phase (LEP) and stationary phase (STP). LEP showed the maximum significant (P ≤ 0.05) biomass productivity of 0.058 ± 0.004 g L−1 d-1, with maximum significant lipid and carbohydrate contents (28.7 ± 1.1 and 42.9 ± 1.2%dw, respectively). TGA/MS results confirmed that biomass harvested at MEP and LEP showed higher extent of conversion or mass loss reaction via thermal degradation with the lowest residual solid products. In addition, the hydrocarbon fragments in gaseous products (H2, C2H6, CH4, C2H4) from TGA/MS analysis were found to be released more abundantly at LEP. Moreover, Py-GC/MS results revealed that thermal decomposition of biomass harvested at LEP resulted in the highest significant relative contents of aliphatic hydrocarbons (41.2%) with lowest nitrogen-containing compounds (6.3%). The present study showed the significant impact of harvest time of microalgae on products characteristics of thermal decomposition and nominated LEP as the optimum growth phase to harvest M. conductrix for upgraded bio-oil production.