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Chemical Speciation of Sulfur and Metals in Biogas Reactors: Implications for Cobalt and Nickel Bio-uptake Processes
Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Kemisk speciering av svavel och metaller i biogasreaktorer : implikationer för bioupptag av kobolt och nickel (Swedish)
Abstract [en]

A balanced supply of micronutrients, including metals such as iron (Fe), cobalt (Co), and nickel (Ni), is required for the efficient and stable production of biogas. During biogas formation, the uptake of micronutrient metals by microorganisms is controlled by a complex network of biological and chemical reactions, in which reduced sulfur (S) compounds play a central role. This thesis addresses the interrelationship between the overall chemical speciation of S, Fe, Co, and Ni in relation to the metals bio-uptake processes. Laboratory continuous stirred tank biogas reactors (CSTBR) treating S-rich grain stillage, as well as a number full-scale CSTBRs treating sewage sludge and various combinations of organic wastes, termed co-digestion, were considered. Sulfur speciation was evaluated using acid volatile sulfide (AVS) extraction and S X-ray absorption near edge structure (XANES). The chemical speciation of Fe, Co, and Ni was evaluated through the determination of aqueous metals and metal fractions pertaining to solid phases, as well as kinetic and thermodynamic analyses (chemical speciation modelling). The relative Fe to S content in biogas reactors, which in practice is regulated through the addition of Fe for the purpose of sulfide removal or prior to the anaerobic digestion of sewage sludge, is identified as a critical factor for the chemical speciation and bio-uptake of metals. In the reactors treating sewage sludge, the quantity of Fe exceeds that of S, inducing Fe(II)-dominated conditions under anaerobic conditions, while sulfide dominates in the co-digestion and laboratory reactors due to an excess of S over Fe. Under sulfide-dominated conditions, chemical speciation of the metals is regulated by hydrogen sulfide and the formation of metal sulfide precipitates, which in turn restrict the availability of metals for microorganisms. However, despite the limitations set by sulfide, aqueous concentrations of different Co and Ni species were shown to be sufficient to support metal acquisition by the microorganisms under sulfidic conditions. Comparatively, the concentrations of free metal ions and labile metal-phosphate and -carbonate complexes in aqueous phase, which directly participate in bio-uptake processes, are higher under Fe-dominated conditions. This results in an enhanced metal adsorption on cell surfaces and faster bio-uptake rates. It is therefore suggested that the chemical speciation and potential bioavailability of metals may be controlled through adjustments of the influent Fe concentration in relation to S content. The results also indicated that the pool of metal sulfides in the biogas reactors could be regarded as a source of metals for microbial activities. Thus, the recovery and utilisation of this fraction of metals may be considered as a measure with which to minimise the metal dosing concentrations to CSTBRs.

Abstract [sv]

För att en effektiv och stabil biogasproduktion från organiskt avfall skall uppnås, behöver mikroorganismer i biogasreaktorer ha tillgång till näringsämnen inklusive spårmetaller såsom järn (Fe), kobolt (Co), och nickel (Ni). Mikroorganismernas upptag av spårmetaller styrs av biologiska och kemiska reaktioner som påverkar metallernas tillgänglighet, där framför allt interaktioner mellan metaller och reducerat svavel (S) spelar en viktig roll. Avhandlingen analyserar sambandet mellan kemisk speciering av S, Fe, Co, och Ni i relation till metallernas biologiska upptagsprocesser. Omrörda tankreaktorer (CSTBR) i lab.- och fullskala för produktion av biogas från spannmålsdrank, avloppsslam, och olika kombinationer av organiska avfall (samrötning) har utgjort basen för studierna. Svavelspeciering analyserades med hjälp av AVS (acid volatile sulfide) extraktion och S XANES (sulfur X-ray absorption near edge structure). Speciering av Fe, Co, och Ni utvärderades med hjälp av sekventiell extraktion, mätning av metall koncentrationer i löst och fast faser samt genom kinetiska och termodynamiska analyser (kemisk specieringsmodellering). Biogasreaktorers relativa mängder av Fe och S, identifierades som en central faktor för kemisk speciering och bio-upptag av metaller. Järn-mängden regleras bl a genom tillsats av Fe för att rena biogasen från vätesulfid eller vid diverse fällningsreaktioner i reningsverk före rötningsstegen av avloppsslam. Därför är järnhalterna högre än S-halterna i reaktorer, som behandlar avloppsslam. Detta leder till en Fe(II)-dominerande miljö. Däremot dominerade vätesulfid i de samrötnings- och laboratoriereaktorer, som ingick i studien. Under dessa förhållande styrs den kemiska metallspecieringen av sulfid och fr a genom fällning av metallsulfider, som då begränsar tillgängligheten av metaller för mikroorganismerna. Trots begränsningarna via sulfidfällningen var koncentrationen av de lösta Co och Ni formerna tillräckliga för bio-upptag av dessa metaller. Vid de Fe-dominerade förhållandena var koncentrationer av fria metalljoner och labila komplex (t.ex. med fosfat och karbonat), som direkt deltar i bio-upptagsprocesser, relativt höga, vilket medför relativt goda möjligheter för metalladsorption till cellytor och bio-upptag. Resultaten visar att den kemiska specieringen och därmed biotillgängligheten av metaller skulle kunna regleras genom justering av inflödet Fe i förhållande till S. Resultaten visade också att metallsulfider i fast fas sannolikt utnyttjas av mikroorganismer som en källa till metaller. Det innebär att en återanvändning av denna metallfraktion skulle kunna utnyttjas som en del i att minimera metalldoseringskoncentrationer.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 46 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 637
Keyword [en]
Biogas, Anaerobic digestion, Chemical speciation, bio-uptake, Sulfur, Iron, Cobalt, Nickel
Keyword [sv]
Biogas, Anaerob nedbrytning, Kemisk speciering, Bio-upptag, Svavel, Järn, Kobolt, Nickel
National Category
Environmental Sciences Environmental Biotechnology
Identifiers
URN: urn:nbn:se:liu:diva-112855DOI: 10.3384/diss.diva-112855ISBN: 978-91-7519-162-1 (print)OAI: oai:DiVA.org:liu-112855DiVA: diva2:772943
Public defence
2015-01-22, Vallfarten, Hus Vallfarten, Campus Valla, Linköpings universitet, Linköping, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2014-12-17 Created: 2014-12-17 Last updated: 2014-12-19Bibliographically approved
List of papers
1. Sulphur K-edge XANES and acid volatile sulphide analyses of changes in chemical speciation of S and Fe during sequential extraction of trace metals in anoxic sludge from biogas reactors
Open this publication in new window or tab >>Sulphur K-edge XANES and acid volatile sulphide analyses of changes in chemical speciation of S and Fe during sequential extraction of trace metals in anoxic sludge from biogas reactors
2012 (English)In: Talanta: The International Journal of Pure and Applied Analytical Chemistry, ISSN 0039-9140, E-ISSN 1873-3573, Vol. 89, 470-477 p.Article in journal (Refereed) Published
Abstract [en]

The effect of sequential extraction of trace metals on sulphur (S) speciation in anoxic sludge samples from two lab-scale biogas reactors augmented with Fe was investigated. Analyses of sulphur K-edge X-ray absorption near edge structure (S XANES) spectroscopy and acid volatile sulphide (AVS) were conducted on the residues from each step of the sequential extraction. The S speciation in sludge samples after AVS analysis was also determined by S XANES. Sulphur was mainly present as FeS (~60% of total S) and reduced organic S (~30% of total S), such as organic sulphide and thiol groups, in the anoxic solid phase. Sulphur XANES and AVS analyses showed that during first step of the extraction procedure (the. removal of exchangeable cations), a part of the FeS fraction corresponding to 20% of total S was transformed to zero-valent S, whereas Fe was not released into the solution during this transformation. After the last extraction step (organic/sulphide fraction) a secondary Fe phase was formed. The change in chemical speciation of S and Fe occurring during sequential extraction procedure suggests indirect effects on trace metals associated to the FeS fraction that may lead to incorrect results. Furthermore, by S XANES it was verified that the AVS analysis effectively removed the FeS fraction. The present results identified critical limitations for the application of sequential extraction for trace metal speciation analysis outside the framework for which the methods were developed.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Sequential extraction, Biogas, Sulphur speciation, Sulphur K-edge XANES, Acid volatile sulphide, Trace metals
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-73112 (URN)10.1016/j.talanta.2011.12.065 (DOI)000301278000068 ()
Note
funding agencies|Swedish Energy Agency||Available from: 2011-12-16 Created: 2011-12-16 Last updated: 2017-12-08Bibliographically approved
2. Potential bioavailability and chemical forms of Co and Ni in the biogas process-An evaluation based on sequential and acid volatile sulfide extractions
Open this publication in new window or tab >>Potential bioavailability and chemical forms of Co and Ni in the biogas process-An evaluation based on sequential and acid volatile sulfide extractions
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2013 (English)In: Engineering in Life Sciences, ISSN 1618-0240, E-ISSN 1618-2863, Vol. 13, no 6, 572-579 p.Article in journal (Refereed) Published
Abstract [en]

Several previous studies reported stimulatory effects on biogas process performance after trace metal supplementation. However, the regulation of the bioavailability in relation to chemical speciation, e.g. the role of sulfide is not fully understood. The objective of the present study was to determine the effect of sulfide on chemical speciation and bioavailability of Co and Ni in lab-scale semicontinuous stirred biogas tank reactors treating stillage. The chemical forms and potential bioavailability of Co and Ni were studied by sequential extraction, analysis of acid-volatile sulfide (AVS), and simultaneously extracted metals. The results demonstrated that Ni was completely associated to the organic matter/sulfide fraction and AVS, suggesting low potential bioavailability. Cobalt was predominantly associated to organic matter/sulfide and AVS, but also to more soluble fractions, which are considered to be more bioavailable. Process data showed that both Co and Ni were available for microbial uptake. Although the actual bioavailability of Co could be explained by association to more bioavailable chemical fractions, the complete association of Ni with organic matter/sulfides and AVS implies that Ni was taken up despite its expected low bioavailability. It was concluded that extensive Co- and Ni-sulfide precipitation did not inhibit microbial uptake of Co and Ni in the reactors.

Place, publisher, year, edition, pages
WILEY-BLACKWELL, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA, 2013
Keyword
Biogas production, Cobalt, Nickel, Potential bioavailability, Speciation
National Category
Social Sciences
Identifiers
urn:nbn:se:liu:diva-102075 (URN)10.1002/elsc.201200162 (DOI)000326458900009 ()
Note

Funding Agencies|Swedish Energy Agency|32928-122263-1|

Available from: 2013-12-03 Created: 2013-11-29 Last updated: 2017-12-06
3. 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
Open this publication in new window or tab >>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
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2014 (English)In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 269, 83-88 p.Article in journal (Refereed) Published
Abstract [en]

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 Kedge 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 (similar to 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.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Biogas; Stillage; Sulfur; Trace metals; Thermodynamics; Kinetics
National Category
Social Sciences
Identifiers
urn:nbn:se:liu:diva-106983 (URN)10.1016/j.jhazmat.2014.01.051 (DOI)000335109100012 ()
Available from: 2014-06-04 Created: 2014-06-02 Last updated: 2017-12-05
4. Thermodynamic modeling of iron and trace metal solubility and speciation under sulfidic and ferruginous conditions in full scale continuous stirred tank biogas reactors
Open this publication in new window or tab >>Thermodynamic modeling of iron and trace metal solubility and speciation under sulfidic and ferruginous conditions in full scale continuous stirred tank biogas reactors
2014 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 47, 61-73 p.Article in journal (Refereed) Published
Abstract [en]

We investigated the equilibrium chemistry and chemical speciation of S, Fe and metals (Co, Ni, Cu, Zn, Cd, and Pb) in eight full scale Continuous Stirred Tank Biogas Reactors (CSTBR). Five reactors were digesting mixtures of different organic wastes (referred to as Co-Digester; CD) and three were digesting Sewage Sludge (SS). Iron was continuously added to the CD reactors to remove sulfide produced during anaerobic digestion and SS was rich in Fe, amended for phosphate removal in wastewater treatment plants prior to anaerobic digestion. As a consequence of different S:Fe molar ratios (0.3–2.8), ferruginous (Fe(II)-dominated) conditions prevailed in SS reactors and sulfidic (S(-II)-dominated) conditions in CD reactors. In all reactors, the chemical speciation of S, as determined by S K-edge X-ray Absorption Near-Edge Structure spectroscopy, was dominated by FeS(s). Reduced organic S forms, consisting of RSH (thiol) and RSR (organic sulfide), were the second most abundant S species. Zero-valent S (elemental S, polysulfides, and possible traces of pyrite) was detected in all reactors, ranging between 6% and 26% of total S, with the highest proportion formed under ferruginous conditions. Thermodynamic modeling suggested that Fe in the aqueous phase was dominated by Fe(II)-thiol complexes under sulfidic conditions (CD reactors) and by Fe(II)-phosphate complexes under ferruginous conditions (SS reactors). Thiols, representing organic functional groups, and sulfide complexes were the major aqueous species of Co(II), Ni(II), Cd(II) and Pb(II) under sulfidic conditions. Under ferruginous conditions thiol complexes were still important, but carbonate and phosphate complexes in particular dominated the aqueous phase speciation of Co(II) and Ni(II). The aqueous phase speciation of Zn and Cu was dominated by Zn(II)-sulfide and Cu(I)-polysulfide complexes, respectively. The results highlights the importance of S:Fe molar ratio as a regulating factor for the chemical speciation of metals in biogas reactors which in turn is important for microbial trace metal uptake and growth as well as potential metal toxicity. Both these aspects are critical for a successful performance of biogas production process.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Environmental Biotechnology
Identifiers
urn:nbn:se:liu:diva-108096 (URN)10.1016/j.apgeochem.2014.05.001 (DOI)000341340200007 ()
Available from: 2014-06-25 Created: 2014-06-25 Last updated: 2017-12-05Bibliographically approved
5. 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
Open this publication in new window or tab >>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
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

National Category
Environmental Biotechnology
Identifiers
urn:nbn:se:liu:diva-112854 (URN)
Available from: 2014-12-17 Created: 2014-12-17 Last updated: 2014-12-17Bibliographically approved

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