Bio-electrochemical system for recovery of silver coupled with power generation and wastewater treatment from silver(I) diammine complex

Abstract

In this study, a bio-electrochemical system was used to investigate the recovery of silver from diammine complex [Ag(NH3)2]+, coupled with power generation and wastewater treatment, measured in terms of chemical oxygen demand (COD) removal. Acetate was oxidized by anodic microorganisms to produce electrons, which were transported to the cathode for the reduction of [Ag(NH3)2]+ complex. After 48 h of operation at different initial [Ag(NH3)2]+ concentrations (1000–3000 mg Ag/L), a Ag removal of over 96%, along with a COD removal of 60–76.80%, and a columbic efficiency of 8.55–14.69%, were achieved. Maximum power density slightly increased by 4.66%, from 3618 to 3795 mW/m3, when 10 mM NaNO3 was added to the catholyte containing 2000 mg Ag/L. The diffusion of [Ag(NH3)2]+ ions through the membrane affected the performance, as the inorganic fouling at the membrane surface increased the internal resistance. This transport was confirmed by the accumulation of silver in anodic biomass (0.853 mg Ag/g biomass) after 58 days. Scanning electron microscope (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analysis demonstrated Ag deposits with a dendritic structure formed at the cathode surface. A deeper understanding on bio-electrochemical technology used for Ag recovery and electricity production from [Ag(NH3)2]+ complex was achieved in this study.