The presence of nitrate- and sulfate-reducing bacteria contributes to ineffectiveness souring control by nitrate injection

Nitrate injection has been widely used to minimize the production of biological hydrogen sulfide in oil and gas field industry, by controlling the growth of sulfate-reducing bacteria (SRB) chemically and biologically. This study aimed to investigate the changes in the bacterial community in response to nitrate addition used to control biological souring. Specifically, we examined the effect of nitrate addition in an artificial souring experiment, using diluted crude oil as substrate and electron donor. Desulfotignum sp. was the predominant SRB under all conditions tested. Addition of nitrate at the beginning (No) repressed the growth of SRB, as revealed by chemical and bacterial community analysis, concomitant with significant growth of the nitrate-reducing bacteria (NRB) Thalassospira sp. Nitrate addition after SRB growth (at day 28, N-28) successfully remediated the sulfide produced by SRB, but no significant reduction in sulfate was observed subsequently; moreover, the bacterial communities before and after nitrate addition remained identical. Isolation of Desulfotignum YB01 (D. YB01) proved the resistance of this predominant SRB in high nitrate environment. Simultaneous reduction of sulfate and nitrate by D. YB01 was also observed in this study. Therefore, the phenomenon in the N28 experiment might be the result of the role of Arcobacter sp. which are nitrate-reducing sulfide-oxidizing bacteria, and/or the ability of Desulfotignum sp. to reduce nitrate and/or nitrite as a stress response. Thus, SRB might persist after nitrate addition, potentially causing subsequent SRB outbreaks.