Shortcomings of individual biochar or microbial technologies often exist in heavy metal removal from wastewater and may be circumvented by coupled use of biochar and microorganisms. In this study, Bacillus subtilis and each of three biochars of different origins (corn stalk, peanut shell, and pine wood) were coupled forming composite systems to treat a cadmium (Cd, 50 mg/l) wastewater formulated with CdCl2 in batch tests. Biochar in composite system enhanced the activity and Cd adsorption of B. subtilis. Compared with single systems with Cd removal up to 33%, the composite system with corn stalk biochar showed up to 62% Cd removal, which was greater than the sum of respective single B. subtilis and biochar systems. Further analysis showed that the removal of Cd by the corn stalk composite system could be considered to consist of three successive stages, that is, the biochar-dominant adsorption stage, the B. subtilis-dominant adsorption stage, and the final biofilm formation stage. The final stage may have provided the composite system with the ability to achieve prolonged steady removal of Cd. The biochar-microorganism composite system shows a promising application for heavy metal wastewater treatment.
Biochar enhanced the activity and cadmium adsorption of Bacillus subtilis.
Corn straw composite system had higher cadmium removal efficiency than peanut shell and pine wood composite systems.
Cadmiun removal in corn straw composite system was higher than the sum of the single biochar and Bacillus subtilis systems.
Cadmium removal in corn straw composite system could be divided into three stages.
These authors contributed equally to this work.