Effect of Antimicrobial Silver Nanoparticles on Electrochemically Active Biofilm

The increasing use of silver nanoparticles (AgNPs) in consumer products is of great concern to biological wastewater treatment systems due to their potential antimicrobial activity. The effects of AgNPs on biological wastewater treatment and anaerobic digestion processes have been extensively studied. Microbial electrochemical technologies are emerging bioprocesses for organic waste and wastewater treatment. However, to date, there are no published studies explored the potential effects of AgNPs on electrochemically active biofilms in microbial electrochemical systems. In this work, we first studied the impact of AgNPs (50 mg/L, 30 nm) on electrochemically active biofilm in a dual chamber microbial electrolysis cell (MEC). We confirmed the antibacterial effect of AgNPs against gram-negative E. coli using colony forming units (CFU) method. However, there was no adverse effect of AgNPs on current density and anode kinetics, although 42±4% of influent AgNPs was accumulated within the biofilm anode during each fed-batch cycle (26 h hydraulic residence time) operation of MEC. The characterization of anode biofilm with transmission electron microscopy (TEM) showed that AgNPs were closely networked with extracellular polymeric substances (EPSs) and attached to the surface of electrochemically active bacterial cells. The results represent the experimental evidence that electrochemically active biofilms can be resilient to 50 mg/L of antimicrobial silver nanoparticles.