A Techno-Environmental Assessment of Biochar from Rice Husk, Neem Leaves, and Sludge for Agriculture and Wastewater Remediation

Biochar is a low oxygen pyrolysis product with a high carbon content that is characterized by stability, porosity, and multiple ecological uses. This study is a comparison of rice husk, neem leaves and sludge biochar obtained under slow pyrolysis (400–500°C) to determine nutrient retention, heavy metal adsorption, energy balance and long-term climatic benefits. This study was conducted in 2 phases - (I) remediation performance (II) environmental assessment. Rice husk biochar produced the largest yield and phosphorus retention in soil, neem biochar showed the best heavy metal adsorption (Pb, Cd, Cr, Cu, Zn, Ni), and potassium retention in soil, and sludge biochar showed the most nitrogen retention in soil with good Cd and Cu adsorption. Cradle-to-gate Life cycle assessment (LCA) showed that rice husk biochar and neem biochar were comparable in carbon sequestration (approx.1.27 t CO ₂ e/t feedstock), better than sludge biochar (approx. 1.12 t CO₂e/t feedstock). Energy savings were highest for rice husk (approx. 35 MJ/kg) and neem (approx. 34 MJ/kg), while sludge was lower (approx. 27 MJ/kg) due to higher drying energy demand. Net GHG offset was greatest in the sludge biochar, rice husk biochar and neem biochar respectively, and the neem biochar further helped to offset methane. The sensitivity analysis was also used to analyse the strength of the results based on a ± 10% variation of the initial conditions. Overall, the study shows that biochar can be used to enhance soil, to treat wastewater, and to mitigate climate change in long term, along with providing a future roadmap which aligns with government policies for sustainable development, supporting SDG 6, SDG 12, and SDG 13.