Synergy of Sodium Nitroprusside and Nitrate in Inhibiting the Activity of Sulfate Reducing Bacteria in Oil-Containing Bioreactors

Abstract

Sodium nitroprusside (SNP) disrupts microbial biofilms through the release of nitric oxide (NO). The actions of SNP on bacteria have been mostly limited to the genera Pseudomonas, Clostridium, and Bacillus. There are no reports of its biocidal action on sulfate-reducing bacteria (SRB), which couple the reduction of sulfate to sulfide with the oxidation of organic electron donors. Here, we report the inhibition and kill of SRB by low SNP concentrations [0.05 mM (15 ppm)] depending on biomass concentration. Chemical reaction of SNP with sulfide did not compromise its efficacy. SNP was more effective than five biocides commonly used to control SRB. Souring, the SRB activity in oil reservoirs, is often controlled by injection of nitrate. Control of SRB-mediated souring in oil-containing bioreactors was inhibited by 4 mM (340 ppm) of sodium nitrate, but required only 0.05 mM (15 ppm) of SNP. Interestingly, nitrate and SNP were found to be highly synergistic with 0.003 mM (1 ppm) of SNP and 1 mM (85 ppm) of sodium nitrate being sufficient in inhibiting souring. Hence, using SNP as an additive may greatly increase the efficacy of nitrate injection in oil reservoirs.

Keywords: biocide; hydrogen sulfide; sodium nitroprusside; souring control; sulfate reduction.

FIGURE 1

Sulfate consumption (A) and sulfide production (B) by batch cultures of mSRB in CSBK medium containing 2 mM sulfate and 3 mM VFA at 30°C in the presence of different concentrations of SNP added at the start of cultivation (t = 0 days); 50 μM SNP is 15 ppm.

FIGURE 2

Sulfate consumption and sulfide production by mSRB and tSRB consortia grown at 30 and 60°C, respectively, in the presence of SNP. Sulfate consumption by mSRB (A), sulfide production by mSRB (B), sulfate consumption by tSRB (C), and sulfide production by tSRB (D) of consortia grown in minimal medium in the presence of different concentrations of SNP added to the culture at the mid-log phase of growth (↓).

FIGURE 3

The effect of nitrate and/or SNP on sulfide production in oil-containing bioreactors. Sulfate, sulfide, nitrate, and nitrite concentrations in the effluents of oil-containing bioreactors are shown as indicated. Bioreactors were treated with nitrate (A), with SNP (B) or with nitrate and SNP (C). Shaded regions indicate the duration of treatment for injection of 2 PV (240 mL).

FIGURE 4

Effect of SNP on the MPNs for SRB and APB in an anaerobic consortium. The MPNs of SRB (A) and of APB (B) after 10 min, 1 h, and 24 h of exposure of an actively growing consortium to 0.5 mM SNP (black bars) are compared with the MPNs for the same consortium not exposed to SNP (gray bars).

FIGURE 5

Heat map of D. vulgaris proteins of which the expression changed significantly between SNP treated (NP) and non-treated control (Ctr) incubations. The values were from log₂ transformed and range from low (blue) to high (orange) abundances.