Laboratory Evaluation of H₂S Bioscavenging in Produced Water at 60°C

Nitrate can control biogenic souring by lowering sulfate reducing bacteria (SRB) metabolic activity and shifting the microbial community such that nitrate-reducing bacteria (NRB) out-compete SRB for nutrients. Nitrate was applied in a laboratory study using a 20-cc packed bed upflow reactor to determine kinetic rate of H₂S removal. The objectives of the testing were to (1) enrich for nitrate-reducing, sulfide-oxidizing microorganisms derived from produced water and (2) determine the kinetic rate of H₂S removal at 60^˚C in a synthetic medium with an H₂S:nitrate molar ratio of 2, and (3) describe the microbial community involved in nitrate-mediated souring control in this system. Sulfide was measured at the face and at the discharge of the column to determine the sulfide oxidation rate. Residence time in the reactor was varied by changing flow rate but a removal rate of nearly 50% H₂S was achieved across the column in one hour residence time. This paper provides a description of the microbial community cultivated at high temperature using 16S rRNA to profile the population dynamics resulting from nitrate treatment. Phospholipid fatty acid analysis was also used for taxonomic evaluation and quantifying physiological changes in the biomass due to nitrate treatment.