Physicochemical Properties of Biochar Derived from Agricultural Biomass Using a Developed Farmer Friendly Biochar Kiln

Abstract

Agricultural biomass residues represent a substantial underutilized resource, and their conversion into biochar offers a practical approach for sustainable waste management, renewable energy production, and carbon sequestration. The present study was conducted to evaluate the physicochemical properties of biochar produced from four locally available agricultural biomass feedstocks, namely cotton waste, pigeon pea, rice husk, and pruned wood, using the developed farmer-friendly natural draft biochar kiln. The selected biomass feedstocks were initially characterised for their physicochemical properties and were then carbonised under three air opening conditions (100% closed, 100% opened, and 50% opened). The produced biochar was subsequently analysed for proximate composition, ultimate composition, calorific value, and pH. A two-factor Completely Randomised Design (CRD) was used to evaluate the effects of biomass type and air opening treatment. Among the biomass feedstocks, pigeon pea recorded the highest volatile matter (82.58%) and carbon content (67.50%), whereas rice husk exhibited the highest ash content (15.48%) and fixed carbon content (16.47%). The physicochemical characteristics of the produced biochar varied significantly with biomass type. Rice husk biochar recorded the highest fixed carbon content (72.80%) and carbon content (77.19%), while pruned wood biochar recorded the highest calorific value (28.72 MJ kg⁻¹). The pH of the biochars ranged from 8.44 to 10.11, indicating their alkaline nature and suitability for soil amendment applications. Statistical analysis revealed that biomass type significantly influenced all evaluated physicochemical properties, whereas air opening treatment had a significant effect only on biomass moisture content and showed limited influence on the quality of the produced biochar. Overall, the developed farmer-friendly biochar kiln successfully converted locally available agricultural biomass into quality biochar suitable for renewable energy, carbon sequestration, and sustainable agricultural applications. The findings further indicate that biomass selection plays a more important role than air opening conditions in determining biochar quality.