Optimized production of invasive animal biochar for arsenic immobilization and methane oxidation in contaminated soils using response surface methodology

The apple snail (Pomacea canaliculata Lamarck) is among the 100 worst invasive alien species worldwide. Apple snail residues discarded during daily management are potential raw materials for biochar production. This study optimized the factors for producing apple snail biochar (ASB) using response surface methodology (RSM) and analyzed the As removal capacity and soil remediation effects of the optimal ASB. The optimal ASB occurred for 348.63 °C pyrolysis temperature, 2.19 h pyrolysis time, and 2.53 Fe3+/Fe2+ molar ratio. For the optimal ASB, the maximum experimental As(III) removal ratio was 98.72%. Temperature and the Fe3+/Fe2+ molar ratio were essential factors affecting the As removal ratio of ASB. The ASB had a rough surface, and As (1.09%) was evident on its surface after adsorption. The As(III) adsorption capacity on ASB was 10.59 mg/g at 288 K, 9.75 mg/g at 298 K, and 11.82 mg/g at 308 K. The As immobilization efficiency in the 3% and 5% ASB treatments exceeded 50% after 15 d. The 5% ASB treatment increased the soil organic matter, total N, available N, total P, and available P content by 120%, 245%, 47%, 62%, and 154%, respectively. Within 15 d, the soil methane oxidation potential peaked at 4.05 μg/g/h in the 5% ASB treatment. The maximum methane oxidation rate occurred after 10 d in the 5% ASB treatment. ASB has multiple benefits for As immobilization, quality improvement, and methane oxidation in soil. This study provides a reference for optimized production and application of invasive animal biochar in contaminated soil.