Evaluating bioenergy potential of the Para grass (Brachiaria mutica) biomass produced on a land-free cultivation system while keeping the water-energy-environment nexus sustainable

Abstract

Producing biomass as a renewable bioenergy feedstock is challenging due to scarcity of agricultural lands. In the present study, a land-free cultivation system was employed to produce the Para grass biomass using industrial and urban wastewaters as growth media. The biomass was pyrolyzed at four different heating rates (10 °C min−1, 20 °C min−1, 30 °C min−1, 40 °C min−1) under an inert environment. The pyrolysis data were analyzed using three isoconversional models namely Flynn-Wall-Ozawa (FWO), Kissenger-Akahira-Sunose (KAS), and Starink. The pyrolysis of both samples occurred in three stages, while major pyrolysis occurred during the second stage (200–400 °C) at the corresponding conversion points (α) ranging from 0.20 to 0.65. The high heating values (HHV) of the biomasses produced on wastewaters were shown to be 18.85 MJKg−1 and 18.14 MJKg−1, respectively. The activation energies ranged from 136.45 to 149.18 kJmol−1, 133.35–146.71 kJmol−1, 133.85–147.23 kJmol−1 estimated through for FWO, KAS, and Starink methods, respectively. Pre-exponential factors showed the first order reaction kinetics and a lower difference (<5 KJmol−1) between the enthalpy change and activation energy (Ea) values indicated the favorable reaction thermodynamics. The pyrolytic gases mainly contained hydrocarbons, aromatics, alcohols, phenols, ketones, aldehydes, carboxylic acids, and esters. Interestingly, the wastewater cultivation improved HHV of the biomasses, lowered the Ea-values, and made the pyrolysis more energy efficient, and this improvement was more obvious for industrial wastewater cultivation. Hence, employing a land-free cultivation system could be a novel and promising approach to produce renewable biomass with improved pyrolysis potential to fuel the future while keeping the energy-water-environment nexus sustainable.