Enhanced simultaneous removal of sulfamethoxazole and zinc (II) in the biochar-immobilized bioreactor: Performance, microbial structures and gene functions

Abstract

Biochar-immobilized functional bacteria Bacillus SDB4 was applied for sulfamethoxazole (SMX) and zinc (Zn²⁺) simultaneous removal in the bioreactor. Under the optimal operating conditions of HRT of 10 h, pH of 7.0, SMX concentration of 10 mg L^-1 and Zn²⁺ concentration of 50 mg L^-1, the removal efficiencies of SMX and Zn²⁺ by the immobilized reactor (IR) were 97.42% and 96.14%, respectively, 20.39% and 30.15% higher than those by free bioreactor (FR). SEM-EDS and FTIR results revealed that the functional groups and light metals on the carrier promoted the biosorption and biotransformation of SMX and Zn²⁺ in IR. Moreover, the improvement of SMX and Zn²⁺ removal might be related to the abundance enhancement of functional bacteria and genes. Bacillus SDB4 responsible for SMX and Zn²⁺ removal was the main strain in IR and FR. Biochar increased the relative abundance of Bacillus from 32.12% in FR to 38.73% in IR and improved the abundances of functional genes (such as carbohydrate metabolism, replication and repair and membrane transport) by 1.82%-11.04%. The correlations among the physicochemical properties, microbial communities, functional genes and SMX-Zn²⁺ co-contaminant removal proposed new insights into the mechanisms of biochar enhanced microbial removal of antibiotics and heavy metals in biochar-immobilized bioreactors.

Keywords: Bacillus sp.; Biochar-immobilized bioreactor; Combined contaminants removal; Enhanced microbial remediation; Functional gene; Microbial community structure.