Hydrogen sulfide (H2S) is formed by the biological reduction of sulfates and the decomposition of organic material. In spite of being present at relatively low concentrations in wastewater (i.e., 10-20 mg/L), sulfide represents a major problem for municipal wastewater systems as it is toxic, corrosive, and odorous. Sulfide is often formed in high concentrations during anaerobic digestion processes, where sulfate-reducing bacteria compete with methanogens and decrease the yield and quality of the produced biogas.
Currently applied methods for the control of sulfide production in sewers are based on the addition of large amounts of chemicals. Minimization of sulfide production in anaerobic digestion is also a challenge, as it is difficult to separate sulfide from wastewater without removing the organic matter, which is necessary for the growth of methanogens.
Here, we have developed material capable of complete and 100% selective oxidation of sulfide to elemental and colloidal sulfur. This material is based on the coating of manganese oxide, which is known to have high affinity towards sulfide oxidation in natural processes (e.g., sediments). We have exploited for the first time this affinity of Mn for water and wastewater treatment applications. One of the major challengues was achieving complete stability of the material coating under both anodic and cathodic polarization. The ongoing work is focused on the development of stable Mn-oxide coatings on conductive metal supports. We are adapting our system to streams containing low concentration of sulfide (e.g., municipal wastewater), as well as to highly concentrated, hydrogen sulfide - rich streams (e.g., alkaline streams from H2S scrubbers).
Watintech project is a coordinated by Prof Ignasi Rodríguez-Roda, from the Technologies and Evaluation research area of ICRA. The project proposes the combination of different decentralised treatment approaches for sewage and urban run-off. The objective is to recover “on-demand” valuable products from these aqueous flows in a decentralized manner. The products to be recovered include water, energy (methane) and the generation of caustic and oxygen to avoid sewer corrosion and odours, all to be used locally.
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