Effects of sulfide removal by Fe addition on chemical speciation of Co(II) and Ni(II) during anaerobic digestion of stillage: Implications for microbial metal uptake
2014 (English)Manuscript (preprint) (Other academic)
The effects of sulfide removal by addition of Fe on chemical speciation of Co and Ni and how it may affect the microbial metal uptake processes in biogas reactors were assessed. The influent Fe concentration was increased in a semi-continuous stirred tank biogas reactor fed with sulfur-rich stillage. Performance of the reactor, turnover kinetics of volatile carboxylic acids as well as changes in the chemical speciation of Co and Ni were investigated. The results demonstrated that approximately 95% decrease in gaseous hydrogen sulfide content of the biogas, which was caused by addition of Fe, had no apparent effects on methane production and process stability, while it enhanced the short-term turnover time of propionate. Sulfide removal decreased the overall solubility of Co and Ni partially by 1) lowering the formation of the dominant Co- and Ni-sulfide complexes in the aqueous phase and 2) by promoting processes such as adsorption and coprecipitation of Co and Ni with FeS(s). Combination of chemical speciation and bio-uptake models suggested that a higher concentration of free Co and Ni ions is achieved at low sulfide concentrations which favors the active bio-uptake of these metals. However, it was argued that the decrease in soluble metal concentrations, which was induced as a result of the addition of Fe, demotes potential diffusion-driven, passive metal uptake by microorganisms.
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IdentifiersURN: urn:nbn:se:liu:diva-112854OAI: oai:DiVA.org:liu-112854DiVA: diva2:772932