Metabolic stress induced by nitrite enhances biocide kill of sulfate reducing bacteria in oilfield enrichments

Abstract

Biocides are commonly employed in oilfield settings to mitigate the activity of sulfate reducing bacteria (SRB) that cause biofouling, reservoir souring and microbiologically influenced corrosion. Key challenges of applying biocides in the oilfield include their environmental toxicity and the need to apply high concentrations to overcome their deactivation and degradation by chemical and physical conditions. One strategy to reduce biocide dosages and ecotoxicity is to apply chemicals that enhance their activity. Nitrite, a known metabolic inhibitor of SRB, was previously found to be synergistic in inhibiting sulfate reduction when used in combination with glutaraldehyde. In the present study, pre-treatment of an SRB enrichment with 2.0 mM nitrite to lower cellular ATP was found to enhance the biocidal activity of glutaraldehyde. These results revealed a linear relationship exists between the decrease in adenylate energy charge of an SRB enrichment and a 10,000-fold increase in planktonic SRB kill, supporting a mechanism that metabolic stress imposed by nitrite enhances the biocidal activity of glutaraldehyde. Furthermore, the results showed increasing nitrite pre-treatment times support lower doses of glutaraldehyde needed to achieve enhanced SRB kill while a nitrite concentration of less than 0.04 mM was effective suggesting nitrite is a very efficient biocide enhancer.