Palm kernel shell biochar production, characteristics and carbon sequestration potential

Abstract

Properties of palm kernel shell (PKS) biochar were studied to identify its potential for soil amendment and carbon sequestration. In this study, slow pyrolysis of PKS was conducted using the Biochar Experimenters Kit at final temperatures 400°C - 600°C and holding times 30 - 90 min with a heating rate of 7.3 ± 0.6°C min-1. Samples were characterised using CHNS/O analyser, Brunauer-Emmet-Teller (BET), leaching column for cation exchange capacity (CEC), energy dispersive X-ray (EDX) and Fourier transform infrared (FTIR) spectrometers. The C content increased from 46 wt.% to 73 wt.% after pyrolysis, while hydrogen (H) and oxygen (O) contents decreased due to dehydration, decarboxylation and demethanation. The molar H/C and O/C ratios of PKS biochar ranged from 0.32-0.54 and 0.08-0.21, respectively, suggesting high stability in soil. PKS biochar at 500°C (90 min) exhibited the greatest carbon sequestration potential of 0.63 kgCO2/ kgPKS. The pH was between 9.3 to 12.0, while CEC increased from 3.00 to 4.44 cmol kg-1 only for biochar at 400°C (60 min). The BET surface area and total pore volume increased from 106 m2 g-1 and 0.01 cm3 g-1 (raw) to 329 m2 g-1 and 0.31 cm3 g-1 (biochar) at 600°C (60 min) whereas water holding capacity increased from 2.23 g(H2O)/10 g to 6.21 g(H2O)/10 g at 500°C (30 min), respectively. Plant nutrients were retained in PKS biochar (400°C and 500°C). PKS biochar can potentially sequester carbon and improve nutrient and water retention in acidic low-fertility soils.