Preparation of biochar from litter biomass and microorganism-loaded biochar for Cd2+ removal from aqueous solutions.

This study explores the potential of biochar derived from freely available litter biomass and microorganism-loaded biochar as an effective method for removing Cd2+ from aqueous solutions. Five different types of litter biomasses (Platanus acerifolia, Cortaderia selloana, Bambusa multiplex, Eucalyptus globulus, Camphora officinarum) were used to prepare biochar through pyrolysis at a fixed pyrolysis temperature of 600 °C and residence time of 3 h. Among these, Eucalyptus globulus biochar (EG-biochar) exhibited the highest adsorption capacity for Cd2+, with a removal efficiency of 83.57% and the highest yield of 32.76%. The pyrolysis conditions were subsequently optimized and the optimal operational parameters were determined as pH 7, biochar dose 1.5 g/L, adsorption temperature 25 °C, contact time 180 min, and ionic strength of 0 M NaNO3. The adsorption behavior was evaluated using Langmuir and Freundlich isotherm models and pseudo-first-order and pseudo-second-order kinetic models. The fitting results indicated that Cd2+ removal involves multiple interactions, including surface complexation, ion exchange, and binding to heterogeneous adsorption sites, rather than a single adsorption mechanism. Additionally, the biochar was enhanced by immobilizing B. subtilis, which improved the adsorption capacity to 124 mg/g and the removal efficiency to 95%. The EG-biochar and B. subtilis-loaded biochar were characterized by Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA) and Brunauer-Emmett-Teller (BET). The results suggest that EG-biochar and microorganism-loaded biochar are viable, sustainable, and environmentally friendly solutions for Cd2+ removal from aqueous solution. This study demonstrates the potential of EG-biochar and B. subtilis-loaded biochar as promising and effective adsorbents for the removal of Cd2+ from aqueous solutions, though further research using real or simulated wastewaters is necessary to validate their performance under more complex conditions.