Removal of Cadmium from Wastewater Using Immobilized <i>Bacillus subtilis</i> with a Biochar–Sodium Alginate Composite Carrier

In order to solve the problems of the long treatment period and easy loss of microorganisms in the biological treatment of wastewater containing Cd(II), immobilized bacteria pellets were prepared by the embedding method with biochar–sodium alginate composite as the carrier and Bacillus subtilis as the target bacteria to achieve efficient removal of Cd(II) in wastewater. Through single-factor and response surface optimization tests, the conditions of treating Cd(II)-containing wastewater by immobilized bacteria pellets were optimized. The results showed that the optimal conditions were as follows: the dosage of immobilized bacteria pellets was 2.02 g/L, the wastewater pH was 6.56, and the Cd(II) initial concentration was 98.7 mg/L. Under these conditions, the ideal removal efficiency of Cd(II) was 91.7%. In addition, the adsorption of Cd(II) by the immobilized pellets conformed to the pseudo-second-order kinetic model and Langmuir equilibrium equation. This study provides a new idea and method for the biological treatment of Cd(II)-containing wastewater.