Synergistic enhancement of cadmium remediation by cadmium-resistant microorganisms immobilized on biochar

Under culture conditions, the biosorption of cadmium (Cd) from aqueous solutions by viable bacteria immobilized on biochar was investigated, and the underlying biosorption mechanisms were elucidated. To prepare the biosorbent materials, Bacillus cereus (BC) or Enterobacter cloacae (ET) was immobilized on biochar derived from pyrolyzed peanut-corn stover (HY). Batch experiments evaluated the effects of pH (3-8), biosorbent dosage (0.1-5 g L^-1), contact time, and initial Cd(ii) concentration (1-15 mg L^-1). The adsorption kinetics followed a pseudo-second-order model, and the isotherm data fit the Langmuir model, indicating chemisorption and monolayer-type adsorption dominated the adsorption processes of HY, BC, and ET. The fundamental characteristics of the materials were investigated using SEM, XPS, and FTIR. The maximum Langmuir adsorption capacity was 6.075 mg g^-1 for ET-HY, representing an 81.45% increase over pristine biochar (3.348 mg g^-1). Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses confirmed that oxygen-containing functional groups (C-C, C-O, O-C[double bond, length as m-dash]O and -OH) were primarily responsible for Cd(ii) complexation. The primary mechanisms employed by HY, BC, and ET for Cd(ii) removal were precipitation and surface adsorption. This study further deepens the understanding of the biosorption process for Cd(ii) removal by microorganisms immobilized on biochar.