Mechanisms underlying enhanced bioremediation of sulfamethoxazole and zinc(II) by Bacillus sp. SDB4 immobilized on biochar

Abstract

Microbial remediation is an eco-friendly and promising approach for the decontamination of wastewater containing sulfamethoxazole (SMX) and Zn2+. However, free bacteria are sensitive to environmental variation, limiting the application. In this study, biochar-immobilized Bacillus paramycoides SDB4 (ISDB4) was used to overcome the disadvantages. The results showed that the removal by ISDB4 was significantly increased under different pH conditions and initial combined contaminant concentrations. Notably, at pH 7, SMX (20 mg L−1) and Zn2+ (100 mg L−1) were completely removed by ISDB4, and their levels were 29.28% and 92.34% higher than that of SDB4, respectively. Besides, ISDB4 showed excellent reusability with 43.24% of SMX and 50.34% of Zn2+ removal efficiencies after five continuous cycles. Such improvements might be related to enhanced biotransformation of SMX from 45.81% with SDB4 to 89.98% with ISDB4. Compared with SDB4, the contributions of ion exchange and complexation of ISDB4 with Zn2+ increased by 9.53% and 6.72%, respectively. In case of ISDB4, SEM-EDS and FTIR showed that biochar provided sufficient space for the attachment and proliferation of SDB4, and the removal of combined contaminants was enhanced by SDB4 due to the presence of functional groups and light metals on biochar. This study provides a green and effective strategy for the bioremediation of antibiotic and heavy metal co-contaminated aquaculture wastewater.