Corncob biochar combined with Bacillus subtilis to reduce Cd availability in low Cd-contaminated soil

Yilin Yang; Xiaojun Hu; Huifeng Wang; Xinling Zhong; Kaishan Chen; Biao Huang; Chunxiang Qian

doi:10.1039/d2ra04643a

Corncob biochar combined with Bacillus subtilis to reduce Cd availability in low Cd-contaminated soil

RSC Adv. 2022 Oct 24;12(47):30253-30261. doi: 10.1039/d2ra04643a.

Authors

Yilin Yang¹, Xiaojun Hu¹, Huifeng Wang¹, Xinling Zhong¹, Kaishan Chen¹, Biao Huang², Chunxiang Qian³

Affiliations

¹ School of Chemical and Environmental Engineering, Shanghai Institute of Technology Shanghai 201418 China hu-xj@sit.edu.cn hfwang@sit.edu.cn.
² Institute of Soil Science, Chinese Academy of Sciences Nanjing Jiangsu 210008 China.
³ School of Materials Science and Engineering, Southeast University Nanjing Jiangsu 211189 China.

Abstract

Soil contamination by heavy metals such as Cd can pose a risk to the environment and human health. However, Cd is difficult to immobilize at low concentration levels in soil. Individually, Bacillus subtilis and biochar have been shown to be inefficient at immobilizing Cd in soil. In this study, corncob biochar was generated at different pyrolysis temperatures (300 °C-550 °C), and the Cd immobilization efficiency and performance of corncob biochar loaded with B. subtilis (CB@B) and corncob biochar alone (CB) were evaluated in solutions and in soil. The characterization (SEM and FTIR) of CB generated at different pyrolysis temperatures and CB generated at different pyrolysis temperatures in CB@B (300 °C-550 °C) indicated that a superior pore structure and abundant O-functional groups were obtained at a pyrolysis temperature of 400 °C for both CB@B and CB. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that the formation of Cd compounds was associated with the positive combined biosorption effect of the bacteria and biochar, electronic adsorption, activity of the O-functional groups (C[double bond, length as m-dash]O, COOH, OH, and Si-O-Si), and complexation between extracellular substances and Cd²⁺. Adsorption experiments were conducted in a solution to assess the effects of various operating parameters such as the time, pH, and adsorbent dose. The 400 °C-CB@B and 400 °C-CB samples achieved the largest reductions in the Cd concentration at 81.21% and 5.70%, respectively. Then, CaCl₂ extraction experiments were conducted in soil, and using 0.25%-CB@B, a 55.21% decrease was realized in the Cd concentration after 56 days and a 16.71% increase was realized in soil pH to 8.38. No significant difference was observed in the CB-treated groups, among which 1.0%-CB achieved the largest reduction of 26.08% after 56 days and a 3.20% increase in the soil pH to 7.41. The Tessier sequential extraction method obtained similar trends. Overall, 400 °C-CB@B demonstrated outstanding immobilization efficiency and durability, indicating that it provided a safe and nutrient-rich habitat for B. subtilis to realize a synergistic effect for Cd immobilization.