Thermochemical characterization of post-phytoremediated vetiver (Vetiveria zizanioides (L.) Nash) root and shoot for their prospective bioenergy potential

Abstract

Critical information as regards the thermochemical characterization of biomass is imperative for the design of efficient biomass thermochemical systems. Present study deals with comprehensive characterization of vetiver root (VR) and vetiver shoot (VS) after being employed for phytoremediation of heavy metal-contaminated alluvial soil. Physico-chemical properties, thermal degradation behavior, functional groups, and surface morphology were determined and compared through proximate, ultimate, HHV, TGA, XRD, FTIR, and FESEM analyses. The cellulose and hemicellulose content put together was found to be significantly high in VR (87.73 wt%) and VS (87.65 wt%). VR was found to contain about twofold inorganic matter than VS. Amorphous nature of VS suggested its potential to produce more pyro-gas and biochar vis-a-vis VR. Volatile matter content of VR (80.25 wt%) and VS (79.42 wt%) was significantly higher as compared to other grass biomasses. Porous structures of VR and VS examined via FESEM micrographs, revealed a large surface area for the reactions to occur. The weight loss for VR and VS in the active zone was found to be 56.06% and 45.74%, respectively as per the thermogravimetric experiments. The average activation energy for pyrolysis of VS was found to be 129.76 and 131.93 kJ/mol and that for VR was found to be 162.15 and 162.19 kJ/mol from KAS and FWO methods, respectively. The thermal decomposition of VR and VS was found to follow reaction-order mechanism (specifically R1, R2, and R3 models) and diffusion mechanism (specifically D4 model proposed by Ginstling-Brounshtein) at lower and higher conversions, respectively. • Volatile matter content of VR (80.25%) and VS (79.42%) was significantly higher than some other biomasses. • TG curves revealed that VR released more volatiles (56.06%) vis-a-vis VS (45.74%) in stage-II. • E a for pyrolysis of VS was found to be lower than VR by both KAS and FWO methods. • Average pore size of VS and VR was found to be 51.53 µm and 19.97 µm, respectively. • Amorphous nature of VS suggested its potential to produce engineered biochar.