Feedstock and pyrolysis conditions affect suitability of biochar for various sustainable energy and environmental applications

Currently, the substitution of continuously depleting coal, a predominant source of global energy, and the treatment of contaminated soil and water bodies with sustainable means are the major concerns. Accordingly, biochars derived from slow pyrolysis of wood and rice residues (400-1000 degrees C) were observed to improve their properties over related feedstocks, among noticeable characteristic variations depending on the biomass type and pyrolysis temperature. Low-temperature pyrolysis produced high-yield biochars, and high-temperature pyrolysis produced low-yield, higher-C, and higher-HHV biochars. Wood residue biochars had higher HHV (21.25-24.05 MJ/kg) and lower H/C and O/C atomic ratios (0.643-0.201 and 0.326-0.084) than rice residue biochars (16.61-18.60 MJ/kg) and (1.22-0.259 and 0.720-0.558), respectively. Thus wood residue biochar, because of its substantially higher HHV than the threshold for an adequate solid fuel, have the potential for energy applica-tions. The wood residue biochars (600-1000 degrees C) have higher C (>85%) than expected for pulverized coal in-jection (PCI, 75%C); and for coke, coke breeze, and recarburiser (85%C), together with much less ash and S content than required for blast furnace (BF). It can be utilized as PCI in BF (100%); as sintering solid fuel and BF nut-coke (50-100%); as BF carbon/ore briquette and steelmaking recarburiser (0-100%); and as a coal blend (2-10%) for coke-making, together with reduced onsite emissions. Wood residue biochars from 400 degrees C have the characteristic potential to replace 22.8% PCI and as a blend with lignite in existing coal-fired power plants. Wood residue biochars (600-1000 degrees C), with less H/C and O/C atomic ratios and a similar polarity index to pulverized fuel combustion coal, can be well applied in power-generating systems. Rice residue biochars (400-1000 degrees C), with poor persistence (O/Corg ratio, 1.228-0.799), higher alkali and alkaline earth metals content, and less HHV than the threshold for an adequate solid fuel, have weak prudence for fuel applications. But with other adaptable properties viz., higher pH, ash, (O/C and N/C) atomic ratios, polarity index, surface functional groups, plant nutrients, and moderate surface areas, can be selectively and judiciously utilized for soil amendment, soil-remediation, C-sequestration, wastewater treatment, and other pollutant abatements. Decision tree ap-proaches, based on the characteristic pertinence of these biochars with literature values, have been developed for their various sustainable energy and environmental usages; and associated environmental concerns and needs to promote them to industrial-level applications have been discussed.