Elsevier

Water Research

Volume 206, 1 November 2021, 117673
Water Research

Importance of thermodynamics dependent kinetic parameters in nitrate-based souring mitigation studies

https://doi.org/10.1016/j.watres.2021.117673Get rights and content
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Highlights

  • Ignoring thermodynamic limitation can cause 60% overestimation of souring

  • Effect of pH on souring can be modeled better by incorporating thermodynamics

  • Growth yield (Y) can be used to predict dominant nitrate reduction pathways

  • Elemental sulfur (S0) accumulation occurs due to low solubility of sulfur

  • S0 accumulation during nitrate reduction can be alleviated by increasing temperature

Abstract

Souring is the unwanted formation of hydrogen sulfide (H2S) by sulfate-reducing microorganisms (SRM) in sewer systems and seawater flooded oil reservoirs. Nitrate treatment (NT) is one of the major methods to alleviate souring: The mechanism of souring remediation by NT is stimulation of nitrate reducing microorganisms (NRM) that depending on the nitrate reduction pathway can outcompete SRM for common electron donors, or oxidize sulfide to sulfate. However, some nitrate reduction pathways may challenge the efficacy of NT. Therefore, a precise understanding of souring rate, nitrate reduction rate and pathways is crucial for efficient souring management. Here, we investigate the necessity of incorporating two thermodynamic dependent kinetic parameters, namely, the growth yield (Y), and FT, a parameter related to the minimum catabolic energy production required by cells to utilize a given catabolic reaction. We first show that depending on physiochemical conditions, Y and FT for SRM change significantly in the range of [0-0.4] mole biomass per mole electron donor and [0.0006-0.5], respectively, suggesting that these parameters should not be considered constant and that it is important to couple souring models with thermodynamic models. Then, we highlight this further by showing an experimental dataset that can be modeled very well by considering variable FT. Next, we show that nitrate based lithotrophic sulfide oxidation to sulfate (lNRM3) is the dominant nitrate reduction pathway. Then, arguing that thermodynamics would suggest that S° consumption should proceed faster than S0 production, we infer that the reason for frequently observed S0 accumulation is its low solubility. Last, we suggest that nitrate based souring treatment will suffer less from S0 accumulation if we (i) act early, (ii) increase temperature and (iii) supplement stoichiometrically sufficient nitrate.

Keywords

Modeling
souring
nitrate treatment
thermodynamics
Gibbs energy

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