Characterization, bioenergy value, and thermal stability of biochars derived from diverse agriculture and forestry lignocellulosic wastes

In the present study, seven diverse biomasses of Indian origin were characterized and pyrolyzed at 450 °C to produce biochars. The biochars were thoroughly characterized using a variety of techniques to assure their potential energy and environmental and agricultural applications. Biochars derived from crop wastes with low lignin content, viz., rice husk biochar (RHB), rice straw biochar (RSB), maize stover biochar (MSB), and sugarcane biochar (SCB), possessed high ash content, high pH, and low fixed carbon making them suitable for soil amelioration. RSB, RHB, and MSB recorded high cation exchange capacity, making their potential utilization as liming material and removal of heavy metal contaminants. Elemental O/C ratios for all biochars, except maize stover biochar, were in the range of 0.27–0.32, which showed better stability and half-life period. Thermogravimetric analysis (TGA) was carried out to evaluate the thermal stability of biochars up to 900 °C, and the overall mass loss varied in the range of 16–27 wt%. Biochars from eucalyptus (EB), lantana (LB), and pine needle (PNB) were found to have high higher heating values (HHVs) (23–28 MJ/kg), higher fixed carbon, and lower ash content. Correlations were constructed between HHV of biochars and their volatile matter, ash, and fixed carbon content with high but negative correlation with ash content. Rice straw, rice husk, maize stover, and sugarcane trash were poor substrates, as the resultant biochars contained ≤ 60 wt% fixed carbon, high ash, and a relatively low HHV. It is shown that RHB, RSB, MSB, and SCB can be potential materials for soil amendment and plant nutrient, while PNB, LB, and EB are suitable for renewable solid fuel purpose.