Remediation of Arsenic and Heavy Metals and Soil Stabilization by Waste Chitosan based Biochar

Objectives : This study aims to evaluate the feasibility of converting waste chitosan adsorbents, laden with microalgae, into biochar for application as a stabilizing agent to remediate heavy metal-contaminated soil and improve soil quality.Methods : Waste chitosan adsorbents were converted into biochar through two processes: dry thermal carbonization at 400°C to produce pyrochar and hydrothermal carbonization at 200°C to produce hydrochar. The elemental compositions, surface functional groups, morphologies of the biochars were evaluated by elemental analyzer, FT-IR spectrometer, and SEM analysis. The arsenic and heavy metal adsorption characteristics of the produced biochars were assessed. Additionally, the produced biochars were applied as stabilizing agents to arsenic and heavy metal-contaminated soil with varying mixing ratios of 2, 5 and 10 wt%. After a one-week soil stabilization experiment, soil properties and TCLP(Toxicity Characteristic Leaching Procedure) leaching tests were conducted.Results and Discussion : The pyrochar produced from waste chitosan exhibited a porous structure with high pH (pH 10) and minimal surface functional groups. The hydrochar consisted of spherical particles with functional groups such as hydroxyl and amine groups on the surface, exhibiting a slightly acidic pH of 5.8. Pyrochar has a higher adsorption capacity for cationic heavy metals compared to hydrochar due to its porous structure and high pH. On the other hand, when applied to soil, hydrochar demonstrated superior stabilization efficiency for arsenic and heavy metals. This is attributed to the diverse surface functional groups containing oxygen on the hydrochar. The stabilization efficiency was influenced by the biochar mixing ratio, with a 5% hydrochar application resulting in 10-64% stabilization efficiency for all elements.Conclusion : This study confirmed that biochar produced from waste chitosan effectively stabilizes arsenic and heavy metals in soils. Additionally, the quantity of biochar used can impact its effectiveness in stabilization.