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Bioavailability and chemical forms of Co and Ni in the biogasprocess: an evaluation based on sequential and acid volatile sulfide extractions
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, The Institute of Technology.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-90183 Umeå, Sweden.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Several previous studies report stimulatory effects on biogas process performance after trace element 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 the chemical speciation and bioavailability of Co and Ni in lab-scale semi-continuously fed biogas tank reactors, digesting grain stillage. The chemical forms and potential bioavailability of Co and Ni in the reactors were determined by sequential extraction (SE), and analysis of acid volatile sulfide (AVS) together with simultaneously extracted metals (AVS-Me). The results for metal speciation analysis demonstrated that Ni was completely associated to the organic  matter/sulfide fraction and AVS, suggesting low potential Ni-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 performance 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 as determined by SE, AVS and AVS-Me analysis, the complete association of Ni with organic matter/sulfides and AVS shows that Ni was taken up despite its expected low bioavailability. Thus, the results of the present study imply that Ni-sulfide precipitation does not prevent microbial uptake in the studied biogas reactors.

National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-73111OAI: oai:DiVA.org:liu-73111DiVA: diva2:466535
Available from: 2011-12-16 Created: 2011-12-16 Last updated: 2011-12-16Bibliographically approved
In thesis
1. Cobalt and Nickel Bioavailability for Biogas Formation
Open this publication in new window or tab >>Cobalt and Nickel Bioavailability for Biogas Formation
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Supplementation of trace metals such as Co and Ni may improve anaerobic digestion of organic material for biogas formation. Which trace metals that are needed and the quantity to apply are, at least partly, related to metal speciation and bioavailability. According to the common perception, metals have to be dissolved to be available for microbial uptake. However, the impact of trace metal speciation on bioavailability is still unclear. The purpose of the present study was to investigate the effect of Fe-, Co- and Ni-addition on the biogas process performance of stillage-fed lab-scale biogas tank reactors. Metal speciation was determined by sequential extraction (SE), extraction of acid volatile sulfides (AVS) and continuously extracted metals (AVS-Me). Sulfur forms, which may be associated to metal speciation, were studied with S XANES (sulfur X-ray absorption near edge structure). The effect of different Co- and Ni-concentrations on process microflora composition was examined with quantitative PCR (qPCR) and 454-pyrosequencing.

The results showed that Co- and Ni-supplementation stimulated and stabilized the biogas process performance by increasing methane production and substrate utilization and by establishing low concentrations of volatile fatty acids. 10-20% of the total Co-amount was found in the dissolved phase, which shows that Co was relatively available for microbial uptake. Nickel was entirely associated to organic matter/sulfides and AVS, and was therefore considered to be non-bioavailable. Nevertheless, Ni-supplementation had stimulatory effects on the biogas process performance. This implies that Ni was available for microbial uptake despite its extensive association to sulfides and that other mechanisms than solubility govern the availability of this trace metal. The microbial analyzes revealed that it was primarily the methane producers which were affected by the concentration of Co and Ni. At stimulatory Co- and Ni-concentrations, the archaeal methanogenic community was dominated by aceticlastic Methanosarcinales. At lower Co- or Ni-levels, when biogas process performance was poor, an increase in hydrogenotrophic Methanomicrobiales was observed. This indicates a shift in the methanogenic flora, from being dominated by acetate utilizers to increased importance of hydrogen utilizers, and that the former was more dependent on Co and Ni.

Abstract [sv]

Tillsats av spårmetaller kan förbättra rötning av organiskt material till biogas. Typ och mängd av respektive spårmetall som behöver tillsättas för att uppnå stimulerande effekter, varierar mellan processer. Detta är delvis kopplat till specieringen och biotillgängligheten av metallerna. Endast fria metalljoner och vissa metallkomplex antas vara tillgängliga för mikrobiellt upptag. Det är dock i många fall oklart hur metallernas speciering påverkar biotillgängligheten. Syftet med föreliggande studie var därför att undersöka effekten av tillsats av Fe, Co och Ni för biogasproduktion från drank, en restprodukt i produktion av bioetanol från spannmål, samt att undersöka hur dessa metallers speciering påverkar deras biotillgänglighet. Effekten av tillsatserna av Fe, Co och Ni undersöktes på biogasreaktorer i lab-skala. Metallernas speciering bestämdes genom sekventiell extraktion (SE), extraktion av AVS (acid volatile sulfide) och kontinuerligt extraherade metaller (AVS-Me). Svavelformer med betydelse för metallspeciering studerades med S XANES (sulfur X-ray absorption near edge structure). Effekten av olika Co- och Ni-koncentrationer på processens mikroflora undersöktes molekylärbiologiskt med kvantitativ PCR (qPCR) och 454-pyrosekvensering.

Resultaten visade att Co och Ni stimulerade och stabiliserade biogasprocessen genom ökad metanproduktion, ökad utrötningsgrad samt låga halter av flyktiga fettsyror i det studerade systemet. 10-20% av totala mängden Co återfanns i löst fas, vilket visar att Co var relativt lättillgängligt för mikroorganismerna. Nickel var däremot enbart bundet till organiskt material/sulfider och AVS och kunde alltså betraktas som otillgängligt. Trots detta hade även tillsatsen av Ni stimulerande effekter på biogasprocessen. Det innebär att mikroorganismerna har förmåga att komma åt Ni bundet i svårlösliga sulfidföreningar och att andra mekanismer än löslighet reglerar tillgängligheten av denna spårmetall. De molekylärbiologiska analyserna visade att framför allt de metanbildande mikroorganismerna påverkades av halten av Co och Ni. De halter, som gav välfungerande processer, dominerades helt av acetiklastiska Methanosarcinales. Vid lägre halter av Co eller Ni, då processerna gick sämre, tillkom vätgasutnyttjande metanogener. Det tyder på ett skift i bildningen av metan från att ha dominerats av acetatklyvning till att vätgasutnyttjarna fått större betydelse och att de förra är mer beroende av Co och Ni.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 49 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 549
Keyword
Biogas production, bioavailability, cobalt, nickel, sequential extraction, S XANES, 454-pyrosequencing., Biogasproduktion, biotillgänglighet, kobolt, nickel, sekventiell extraktion, S XANES, 454-pyrosekvensering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-73113 (URN)978-91-7519-989-4 (ISBN)
Public defence
2012-01-19, Vallfarten, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
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Supervisors
Available from: 2011-12-16 Created: 2011-12-16 Last updated: 2012-01-31Bibliographically approved

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Gustavsson, JennyShakeri Yekta, SepehrKarlsson, AnnaSvensson, Bo H.

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