A simple two-dimensional mathematical model capable of describing the interactions taking place in the bulk fl uid and biofi lm between sulfate reducing bacteria (SRB), substrates and biocide agents was used for the numerical evaluation of biocide treatment against SRB. The characteristics inherent to thick biofi lms formed in large diameter oilfi eld pipelines were taken into account by assuming that the biocide treatment will remove little of the biofi lm and not kill the SRB present in the biofi lm. The evaluation model considered SRB disinfection/proliferation, and biocide deactivation within the bulk fl uid, as well as many features of biofi lm interactions with the bulk fl uid such as mass transfer, live SRB detachment and biocide agent deactivation. These interactions are represented by simple coeffi cients as far as possible. Simulation results, using reported kinetic parameters for SRB, acetate and biocide agents such as chlorine and glutaraldehyde, showed that biocide treatments in oilfi eld water pipelines are sensitive to the disinfection rate coefficient and the biocide agent concentration as well as to the decay rate coeffi cient of the biocide agent in the bulk fl uid, but are not sensitive to the biocide deactivation rate on the biofi lm surface, nor to the SRB concentration in the biofi lm. Various extreme conditions of biocide treatments were simulated using the proposed discretization method, which was adapted to take into account the biofi lm interactions with the bulk fl uid, to investigate the sensitivity of the numerical method and the suitability of the model developed to determine minimum effective biocide concentrations.

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