Properties of biochar derived from spent mushroom substrates

Abstract

Spent mushroom substrates, Tremella fuciformis (Tf), Flammulina velutipes (Fv), and Lentinula edodes (Le), were used to produce biochar at different temperatures (300 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Elemental compositions and surface properties of derived biochar were determined. The yield and volatile matter (VM) of the biochars decreased as the pyrolysis temperature increased with Le300 having the highest yield (47.4%). The highest VM was obtained in Tf300 (79.6%). The biochars were alkaline, with Fv700 having the highest pH (11.6). Pyrolysis temperature and feedstock influenced nutrient composition of biochars and highest values were obtained in: Tf300 (N=2.07%), Fv700 (P=12.0 g/kg), Le700 (K=21.9 g/kg), Fv600 (CEC=32.3 cmol/kg), Fv700 (Ash=33.4%) and Le700 (C=58.6%). Heavy metals in the Fv biochar were highest but within their tolerable limits. Fourier transform infrared spectra showed various functional groups on the biochar surfaces with C-O being dominant (except on Le biochar). X-ray diffraction revealed that SiO2 and CaCO3 were present on biochar surfaces. The Fv biochars had the largest surface area with Fv400 having the highest value (210.6 m2g-1) while Le400 had the highest average pore diameter (159.7 Å). These properties render the biochars suitable as soil amendment and in environmental remediation.