The Effects of slow Pyrolysis on the Microbial, Nutritional and Elemental properties of Biochar Produced from Rice husk

Abstract

Wastes from rice systems, such as rice husks, are burnt openly, polluting the environment and affecting human health. This study was conducted to valorize rice husk, a rice system waste, by converting it into biochar. Rice husk was slowly pyrolyzed to biochar at a temperature of 350 ℃ to assess the changes in proximate (volatile matter, ash, dry matter and organic matter), elemental (fixed carbon, Nitrogen, Phosphorus, potassium, calcium, C/N ratio and electrical conductivity) and microbial count (Total aerobic, Total yeast, E. coli, S. aureus (MacConkey agar), Salmonella typhi, Pseudomonas spp. and Bile tolerant bacteria). Results from proximate analysis of biochar indicated negligible levels of ether extract, crude protein and crude fibre. Volatile matter, ash and organic matter contents of biochar were 56.37%, 43.40% and 56.60%. Elemental composition of rice husk and biochar showed a significant reduction in EC (down from 1.15 to 0.91 mS/cm), C/N ratio (43.32 to 30.94) and sodium (0.40 to 0.1 mg/kg) content of biochar and significantly increased the pH (5.83 to 7.42), fixed carbon (27.03 to 38.3%), Nitrogen (0.63 to1.24%), phosphorus (0.19 to 0.51 mg/kg), potassium (0.65 to 1.29 mg/kg), calcium (0.3 to 0.42 mg/kg) and magnesium (0.11 to 0.21 mg/kg) contents after pyrolyzing rice husk into biochar. Microbial analysis indicated that E. coli, Salmonella typhi, and Pseudomonas spp were not detected on both rice husk and rice husk biochar. Pyrolysis, however, significantly reduced total aerobic count, total yeast/mould and S. aureus and eliminated bile-tolerant bacteria. Microbial, elemental and proximate properties of biochar indicate the potential of biochar as a feed additive for the growth and reduction in the environmental footprints of livestock.