Acetate Production from Oil under Sulfate-Reducing Conditions in Bioreactors Injected with Sulfate and Nitrate

Abstract

Oil production by water injection can cause souring in which sulfate in the injection water is reduced to sulfide by resident sulfate-reducing bacteria (SRB). Sulfate (2 mM) in medium injected at a rate of 1 pore volume per day into upflow bioreactors containing residual heavy oil from the Medicine Hat Glauconitic C field was nearly completely reduced to sulfide, and this was associated with the generation of 3 to 4 mM acetate. Inclusion of 4 mM nitrate inhibited souring for 60 days, after which complete sulfate reduction and associated acetate production were once again observed. Sulfate reduction was permanently inhibited when 100 mM nitrate was injected by the nitrite formed under these conditions. Pulsed injection of 4 or 100 mM nitrate inhibited sulfate reduction temporarily. Sulfate reduction resumed once nitrate injection was stopped and was associated with the production of acetate in all cases. The stoichiometry of acetate formation (3 to 4 mM formed per 2 mM sulfate reduced) is consistent with a mechanism in which oil alkanes and water are metabolized to acetate and hydrogen by fermentative and syntrophic bacteria (K. Zengler et al., Nature 401:266 -269, 1999), with the hydrogen being used by SRB to reduce sulfate to sulfide. In support of this model, microbial community analyses by pyrosequencing indicated SRB of the genus Desulfovibrio, which use hydrogen but not acetate as an electron donor for sulfate reduction, to be a major community component. The model explains the high concentrations of acetate that are sometimes found in waters produced from water-injected oil fields.

Identification of toluene degraders in a methanogenic enrichment culture

“…Members of Desulfovibrio sp. are commonly found in a variety of strictly anaerobic oil-impacted environments such as oil reservoirs and enrichment cultures derived from contaminated sites and oil production waters (Grabowski et al, 2005;Fowler et al, 2012;Mbadinga et al, 2012;Callbeck et al, 2013). Though they seem to be ubiquitous in these environments, their specific role has not been elucidated although they have never been associated with hydrocarbon degradation directly.…”

A Post-Genomic View of the Ecophysiology, Catabolism and Biotechnological Relevance of Sulphate-Reducing Prokaryotes

“…These may collaborate with syntrophs (e.g. Deltaproteobacteria of the genera Syntrophus and Smithella), as well as with acetate-and propionate-oxidizing SRB of the genera Desulfobacter and Desulfobulbus, respectively, in the degradation of oil under sulphate-reducing conditions in a manner comparable to that by consortia of these same syntrophs and hydrogenotrophic and acetotrophic methanogens in the absence of sulphate (Callbeck, Agrawal, & Voordouw, 2013;Zengler et al, 1999). The mechanism of oil degradation under sulphate-reducing conditions, which is responsible for oil field souring, remains largely unknown, because this putative oil-degrading consortium of syntrophs and hydrogenotrophic and acetotrophic SRB has not yet been studied in any detail.…”

Implications of Limited Thermophilicity of Nitrite Reduction for Control of Sulfide Production in Oil Reservoirs

“…Coleville synthetic brine medium K (CSBK) (22) with sodium nitrate (10 mM) as the electron acceptor, 3 mM VFA (3 mM [each] acetate, propionate, and butyrate) as the electron donor, and an N 2 -CO 2 headspace was used for cultivation of mNRB and tNRB. For cultivation of tNRB, water samples (20 ml) were concentrated up to 20-fold by centrifugation at 15,000 ϫ g for 20 min in an Avanti JE centrifuge (Beckman Coulter).…”