Synthesis of Biochar From Agricultural Waste With Alkaline Hydrothermal Method for Soil Remediation

ABSTRACT The utilization of biomass as a value‐added material has gained widespread attention due to the abundance of agricultural waste that remains underutilized. This waste is readily available at an affordable or no cost, yet when left unaddressed, it can contribute to environmental issues, such as the release of methane gas, which pollutes the air and poses risks to human health. The direct burning of agricultural waste further intensifies these problems. Along with a large amount of agricultural waste, critical land problems also arise due to the excessive use of inorganic fertilizers. This study addresses the issues by synthesizing biochar from agricultural waste (rice husks, sawdust, and bagasse) using the hydrothermal method at 180°C with NaOH as a solvent to enhance functional groups and increase adsorption capacity to be applied as a soil remediation agent. Biochar characterization was performed using Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH) methods, and carbon, hydrogen, nitrogen, sulfur (CHNS), and total plate count (TPC) analysis. The result shows, based on the functional group of the biochar of rice husks treated at different NaOH concentrations, the best results were obtained with a 5 M concentration, that applied for the synthesis condition for sawdust and bagasse‐based biochar. A large number of functional groups were exhibited by rice husk‐based biochar, yet they have the smallest surface area. The large number of functional groups, however, supports the ability of biochar in soil remediation. Proven by rice husk‐derived biochar demonstrated excellent performance, promoting leaf growth by 25%, root growth by 31%, and overall plant growth by 41%. Moreover, microorganisms observed in the soil after plantation increased tenfold with the addition of biochar compared to soil without biochar, highlighting the excellent potential of biochar in soil remediation.