Electrochemical removal of sulfide on porous carbon-based flow-through electrodes.

Electrochemical oxidation of hydrogen sulfide and its separation from the waste stream in the form of sulfur was studied at low-cost carbon-based porous materials, activated carbon felt (ACF) and graphite felt (GF). Both materials were capable of selective HS oxidation to elemental sulfur in low-conductivity solutions (i.e., <1 mS cm), as well as in raw sewage. The HS removal rate was ten times faster at ACF compared with GF electrode due to the higher surface area and chemisorption of HS. To address the electrode passivation with the electrodeposited sulfur, different electrochemical recovery strategies were tested. GF could be only partially regenerated (i.e., 30% efficiency) using cathodic polarization. Also, both anodic and cathodic polarization improved the sulfide removal in the subsequent working cycle due to the introduction of new redox-active oxygen containing functional groups. Sulfur deposited at the ACF electrode could not be recovered by any of the investigated strategies. Thus, sulfur was incorporated into the carbon matrix and strongly bonded with the carbon functional groups at both GF and ACF electrodes. Although carbon-based electrodes have been widely investigated for electrochemical sulfide removal, this study demonstrates that their application is limited by low regeneration efficiency of the electrodeposited sulfur.