Factors influencing silver recovery and power generation in bio-electrochemical reactors.

Abstract

The recovery of silver from Ag+ solution coupled with power generation was investigated in bio-electrochemical system (BES). In this system, chemical energy existing in the organic matter in the anode chamber can be converted biologically to electrical energy which can be used for the reduction of Ag+ ions in the cathode chamber. Results showed that type of substrate influenced the metabolic pathway and affected the cell voltage progression, and columbic efficiency. Silver recovery was not affected by increasing initial pH (2.0 to 7.0) and Ag+ concentration (100 to 1000mg/L) in the catholyte, whereas power generation was improved. A maximum power density of 8258mW/m3 and a columbic efficiency of 21.61% could be achieved with 1000mg/L of Ag+. Ag+ ions were reduced to form metallic deposits as Ag0 crystals on the cathode surface, which were then confirmed by scanning electron microscope (SEM) image and energy dispersive X-ray (EDX) spectrum. The BES reactor had high silver removal (i.e., >96%) after 24h of operation. When considering the crossover of Ag+ ions through the cation exchange membrane, the removal was in the range of 83.73-92.51%. This crossover was not considerable as compared to the Ag+ initial concentration. At higher initial Ag+ concentration (2000mg/L), the silver removal decreased to 88.61% and the maximum power density decreased to 5396mW/m3. This study clearly showed that BES can be employed for silver recovery, wastewater treatment, and also electricity generation.