Testing antimicrobials against biofilm bacteria

Abstract

A continuous flow reactor system was developed to evaluate the efficacy of antimicrobial treatments against sulfate-reducing bacterial biofilms. An annular reactor operating at a nominal dilution rate of 0.5 h-1 was fed one-tenth strength Postgate C medium diluted in 1.5% NaCl and was inoculated with a mixed culture enriched from oilfield-produced water on the same medium. Thin biofilms developed in this reactor after 2 days of operation. The activity of these biofilms resulted in approximately 50 mg S l-1 of sulfide at steady state prior to biocide treatment. Biocide efficacy was quantified by recording the time required for sulfide production to recover following an antimicrobial treatment. In a control experiment in which pure water was applied, the time required to reach 10 mg S l-1 sulfide after the treatment was 1.7±1.2 h, whereas the time to reach this level of sulfide after a pulse dose of 500 mg l-1 glutaraldehyde was delayed to 61±11 h. Nitrite treatment suppressed sulfide production as long as the nitrite concentration remained above 15 mg N l-1. Sulfide production recovered more rapidly after nitrite treatment than it did after glutaraldehyde treatment.