Micro-aeration for sulfide removal in anaerobic treatment of high-solid wastewater: a pilot-scale study
The presence of sulfur compounds (e.g. protein, sulfate, thiosulfate, sulfite, etc.) in the feed stream generates highly corrosive and odorous hydrogen sulfide during anaerobic digestion. The high sulfide level in the biogas stream is not only poisonous to many novel metal catalysts employed in thermo-catalytic processes; but also reduces the quality of methane as a renewable energy. This study used an innovative, low-maintenance, low-cost biological sulfide removal technology to remove sulfides simultaneously from both gas and liquid phase. ORP (Oxidation- Reduction-Potential) was used as controlling parameter to precisely regulate air injection to the sulfide oxidizing unit attached to the digester. The micro-aeration technique provided just enough oxygen to partially oxidize sulfides to elemental sulfur without inhibiting methanogenesis. The integrated system was capable of reducing hydrogen sulfide in biogas from 2,450 to less than 2 ppmV with minimal sulfate production. More than 98% of sulfide removed was recovered as elemental sulfur. This technology will widen the use of biogas as a renewable energy since the maintenance of downstream processes, the biogas purification requirement, and the production of SOx will dramatically be reduced. Importantly, the technology does not require inoculation of special bacteria, addition of nutrients and trace element, or pH control.