Properties of Biochars Prepared from Local Biomass in the Mekong Delta, Vietnam

Abstract

Wood- (bamboo and melaleuca) and herbaceous-based (rice husk and water hyacinth) biochars, produced from local biomass by slow pyrolysis at 500°C, 700°C, and 900°C, were examined for their physical and chemical properties. The wood-based biomass produced biochars with lower ash contents (dbash) and higher fixed carbon contents (> 54 wt.%db), greater higher heating value (>23 MJ/kg), higher degree of aromaticity (with O/C, H/C, and volatile matter/fixed carbon ratios were less than 0.08, 0.51, and 0.61, respectively), and smaller amount of salt nutrients (db) compared with those of the herbaceous-based biochars. Their unique properties have generated more interest in using them as a solid fuel, for carbon sequestration, and for soil amendment. The rice husk biochars contained more than 300 g/kgdb silica, which is potential for silicophilic plants. The water hyacinth biochars with the greatest volatile matter/fixed carbon (ranging from 0.72 to 2.35), and highest O/C ratios (0.11 to 0.18), indicating the lowest aromaticity among studied biochars and thus maybe least suitability for carbon sequestration. They also possessed a highest soluble salts content (>240 g/kgdb), highest electrical conductivity (>6489 mS/cm), and greatest liming potential (>6.56 %CaCO₃–eq), which may not be suitable for salt-sensitive plants or low-buffer capacity soils.