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

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 man-agement. Here, we investigate the necessity of incorporating two thermodynamic dependent kinetic parameters, namely, the growth yield (Y), and F-T, 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 F-T 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 F-T. Next, we show that nitrate based lithotrophic sulfide oxidation to sulfate (lNRM(3)) is the dominant nitrate reduction pathway. Then, arguing that thermody-namics would suggest that S degrees consumption should proceed faster than S-0 production, we infer that the reason for frequently observed S-0 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 stoi-chiometrically sufficient nitrate.

Automated summary

The study highlights the importance of understanding souring rate, nitrate reduction rate, and pathways for efficient souring management. Incorporating thermodynamic dependent kinetic parameters such as growth yield and F-T significantly affects sulfate-reducing microorganisms. Experimental data shows that considering variable F-T can lead to better modeling in nitrate-based souring treatment.