Electrochemically active biofilms responses to gadolinium stress during wastewater treatment in bioelectrochemical systems

Abstract

Gadolinium-based contrast agents used in magnetic resonance imaging (MRI) contribute to increasing gadolinium(III) [Gd(III)] concentrations in aquatic environments, as conventional wastewater treatment plants lack effective removal mechanisms. This study investigated the potential of single-chamber microbial fuel cells (SCMFCs) for Gd(III) removal, focusing on removal efficiency and the physiological responses of electrochemically active biofilms. SCMFCs demonstrated exceptional Gd(III) removal efficiency exceeding 99.75 ± 0.007% across various initial concentrations (10-60 mg/L). Power output and chemical oxygen demand (COD) removal efficiency showed dose-dependent responses to Gd(III) stress, with maximum power output decreasing from 479.56 mV to 260.43 mV as Gd(III) increased from 0 to 60 mg/L. COD removal efficiency declined from 96.49 ± 1.2% to 90.23 ± 1.6% over the same range. Microbial community analysis revealed selective enrichment of exoelectrogens at lower Gd(III) concentrations, with Geobacter relative abundance decreasing from 11.14% to 1.82%. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) analyses demonstrated that elevated Gd(III) concentrations reduced electrochemically active bacterial colonization in anode biofilms. Fourier-transform infrared spectroscopy (FTIR) identified specific functional groups associated with Gd(III) biosorption, while predictive functional profiling indicated upregulation of metal resistance genes under Gd(III) exposure. These findings demonstrate the effectiveness of SCMFCs in Gd(III) removal from wastewater while elucidating microbial adaptation mechanisms to rare earth element exposure, providing insights for developing sustainable treatment solutions for emerging contaminants.