The Biological Inhibition To SRB And Its Electrochemical Evaluation

Sulfate reducing bacteria (SRB) are well recognized as one of the major group of microorganisms involved in biocorrosion. Sulfide produced from the metabolic activities of SRB is of concern due its detrimental effects on the environment. The metabolic activities of nitrate reducing bacteria (NRB) play an important role in the inhibition of SRB activities and removal of sulfide.In this thesis, a sulfate-reducer (strain SRB-1) and a nitrate-reducer (strain NRB-1) were isolated on selective culture media inoculated with production fluids from two distinct oilfields. Based on 16S rRNA gene sequences, strain SRB-1 shared 98% similarities with Desulfovibrio sp. strain LZK1 and NRB-1 was at 99% closely related to Pseudomonas sp. strain ZZ-5.Co-cultivation of the isolated strains was established in order to evaluate the inhibitory effect of NRB-1 on SRB-1 activities. The activity of the co-culture was assessed via chemical analyses of metabolic product(s) and consumption of electron acceptors. Results showed that sulfide was quantitatively reduced by 38% in the co-culture in comparison to control incubation inoculated only with SRB-1, thus indicating that NRB-1 is able to inhibit the activities of SRB-1 to a certain extent. Besides, the effect of NRB-1 on the corrosion behavior of SRB-1 on carbon steel 20# was investigated by electrochemical and microscopy techniques. Results showed that, after 7d of incubation, the corrosion current decreased from 3.86μA-cm-2 in control incubation inoculated only with SRB-1 to 1.01μA·cm-2 in the mixed culture. Drop of the corrosion current implies that the corrosive activities of SRB-1 on carbon steel 20# were influenced by the presence of NRB-1. Analysis of electrochemical impedance spectra (EIS) and scanning electron micrographs (SEM) indicated that the presence of NRB-1 affected the formation of SBR-1 bio film on metal surface, resulting in the increase of the passive film resistance thus reducing the corrosive activities of SRB-1.