title: Chemical speciation of sulfur and metals in biogas reactors - Implications for cobalt and nickel bio-uptake processes.
abstract: This article deals with the interrelationship between overall chemical speciation of S, Fe, Co, and Ni in relation to metals bio-uptake processes in continuous stirred tank biogas reactors (CSTBR). To address this topic, laboratory CSTBRs digesting sulfur(S)-rich stillage, as well as full-scale CSTBRs treating sewage sludge and various combinations of organic wastes, termed co-digestion, were targeted. Sulfur speciation was evaluated using acid volatile sulfide extraction and X-ray absorption spectroscopy. Metal speciation was evaluated by chemical fractionation, kinetic and thermodynamic analyses. Relative Fe to S content is identified as a critical factor for chemical speciation and bio-uptake of metals. In reactors treating sewage sludge, quantity of Fe exceeds that of S, inducing Fe-dominated conditions, while sulfide dominates in laboratory and co-digestion reactors due to an excess of S over Fe. Under sulfide-dominated conditions, metals availability for microorganisms is restricted due to formation of metal-sulfide precipitates. However, aqueous concentrations of different Co and Ni species were shown to be sufficient to support metal acquisition by microorganisms under sulfidic conditions. Concentrations of free metal ions and labile metal complexes in aqueous phase, which directly participate in bio-uptake processes, are higher under Fe-dominated conditions. This in turn enhances metal adsorption on cell surfaces and bio-uptake rates.
authors.affiliation: Department of Thematic Studies-Environmental Change, Linköping University, SE-581 83 Linköping, Sweden. Electronic address: sepehr.shakeri.yekta@liu.se.
authors.forename: Sepehr Shakeri
authors.initials: SS
authors.lastname: Yekta
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-Environmental Change, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Danielsson
authors.affiliation: Department of Thematic Studies-Environmental Change, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Annika
authors.initials: A
authors.lastname: Björn
authors.affiliation: Department of Thematic Studies-Environmental Change, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Bo H
authors.initials: BH
authors.lastname: Svensson
mesh_terms: D000693:Anaerobiosis; D056804:Biofuels; D019149:Bioreactors; D003035:Cobalt / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D012722:Sewage / Q000032:analysis; D013457:Sulfur Compounds / Q000737:chemistry*; D014865:Waste Disposal, Fluid
chemical_list: D056804:Biofuels; D008670:Metals; D012722:Sewage; D013457:Sulfur Compounds; D003035:Cobalt; D009532:Nickel; D007501:Iron
keywords: Bio-uptake; Biogas; Chemical speciation; Cobalt; Iron; Nickel; Sulfur