Enhanced kill of sulfate reducing bacteria using timed sequential addition of oxyanion and biocide

Abstract

A process is provided for the time dependent reduction and kill of cellular bacteria in a fluid by sequential exposure to nitrites and a low concentration of biocide. Oilfield water containing sulfate-reducing bacteria can be supplied with a timed sequential exposure of nitrite and biocide. The timed sequential addition of the biocide following exposure to the nitrite provides enhanced kill of the sulfate-reducing bacteria at concentrations of biocide that are lower than would be possible using simultaneous addition of these materials.

1 . A method of killing sulfate-reducing bacteria in an aqueous medium, the method comprising the steps of:
 contacting the sulfate-reducing bacteria with a first concentration of an oxyanion;   waiting a specific time period; and   contacting the sulfate-reducing bacteria with a second concentration of a biocide.   
     
     
         2 . The method of  claim 1 , wherein the oxyanion is selected from the group consisting of nitrite, molybdate, tungstate, selenate, anthraquinone and combinations of one or more thereof. 
     
     
         3 . The method of  claim 1 , wherein the specific time period comprises between 2 hours and 2 weeks including 2 hours, 4 hours, 8 hours, 10 hours, 15 hours, 20 hours, 24 hours, 30 hours, 40 hours, 48 hours, 60 hours, 3 days, 4 days, 5 days, 1 week, 10 days, or 2 weeks. 
     
     
         4 . The method of  claim 1 , wherein the biocide is selected from the group consisting of formaldehyde, glutaraldehyde, acrolein, quaternary amine compounds, cocodiamine, bronopol, 2-2-dibromo-3-nitrilo-propionamide (DBNPA), isothiazolone, carbamates, metronidazole, and combinations of one or more thereof. 
     
     
         5 . The method of  claim 1 , wherein the oxyanion is a combination of more than one individual oxyanion and wherein the biocide is a combination of more than one individual biocide. 
     
     
         6 . The method of  claim 1 , wherein the oxyanion comprises nitrite. 
     
     
         7 . The method of  claim 1 , wherein the oxyanion consists essentially of nitrite. 
     
     
         8 . The method of  claim 1 , wherein the oxyanion stresses the sulfate-reducing bacteria without directly killing the sulfate-reducing bacteria and the biocide directly kills the sulfate-reducing bacteria. 
     
     
         9 . The method of  claim 1 , wherein the aqueous medium is oilfield water.