title: Importance of reduced sulfur for the equilibrium chemistry and kinetics of Fe(II), Co(II) and Ni(II) supplemented to semi-continuous stirred tank biogas reactors fed with stillage.
abstract: The objective of the present study was to assess major chemical reactions and chemical forms contributing to solubility and speciation of Fe(II), Co(II), and Ni(II) during anaerobic digestion of sulfur (S)-rich stillage in semi-continuous stirred tank biogas reactors (SCSTR). These metals are essential supplements for efficient and stable performance of stillage-fed SCSTR. In particular, the influence of reduced inorganic and organic S species on kinetics and thermodynamics of the metals and their partitioning between aqueous and solid phases were investigated. Solid phase S speciation was determined by use of S K-edge X-ray absorption near-edge spectroscopy. Results demonstrated that the solubility and speciation of supplemented Fe were controlled by precipitation of FeS(s) and formation of the aqueous complexes of Fe-sulfide and Fe-thiol. The relatively high solubility of Co (∼ 20% of total Co content) was attributed to the formation of compounds other than Co-sulfide and Co-thiol, presumably of microbial origin. Nickel had lower solubility than Co and its speciation was regulated by interactions with FeS(s) (e.g. co-precipitation, adsorption, and ion substitution) in addition to precipitation/dissolution of discrete NiS(s) phase and formation of aqueous Ni-sulfide complexes.
authors.affiliation: Department of Thematic Studies - Water and Environmental Studies, Linköping University, SE-581 83 Linköping, Sweden. Electronic address: sepehr.shakeri.yekta@liu.se.
authors.forename: Sepehr
authors.initials: S
authors.lastname: Shakeri Yekta
authors.affiliation: Department of Thematic Studies - Water and Environmental Studies, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Amanda
authors.initials: A
authors.lastname: Lindmark
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Skyllberg
authors.affiliation: Department of Thematic Studies - Water and Environmental Studies, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Asa
authors.initials: A
authors.lastname: Danielsson
authors.affiliation: Department of Thematic Studies - Water and Environmental Studies, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Bo H
authors.initials: BH
authors.lastname: Svensson
mesh_terms: D015502:Absorptiometry, Photon; D019149:Bioreactors; D003035:Cobalt / Q000737:chemistry*; D005583:Fourier Analysis; D005740:Gases; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D021241:Spectrometry, Mass, Electrospray Ionization; D013455:Sulfur / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D005740:Gases; D003035:Cobalt; D013455:Sulfur; D009532:Nickel; D007501:Iron
keywords: Biogas; Kinetics; Stillage; Sulfur; Thermodynamics; Trace metals