Inhibitory and Bactericidal Properties of a Number of Dihydroxyazo Compounds

Inhibitory and bactericidal properties of a number of dihydroxyazo compounds have been studied in the Postgate medium containing sulfate-reducing bacteria (SRB) in planktonic form. Sulfate-reducing bacterium strain Luk used in this study was phylogenetically closed (99% similarity of 16S rRNA genes) to the type strain Desulfomicrobium apsheronum 1105^T isolated from petroleum reservoir. The number of sulfate-reducing bacteria was counted by a method called the direct microscopic count. Special counting chamber was used. Biogenic H₂S concentration was defined daily by the iodometric titration. Small concentrations (5-20 mg/L) of the compounds under study have been used. These compounds induce a decrease of the bacterial cells quantity and H₂S production by SRB. Dihydroxyazo compounds inhibit carbon steel corrosion and hydrogen permeation through the steel membrane in the presence of SRB. Corrosion tests of the carbon steel samples were carried out by weight-loss method. Most high corrosion rate of steel in the inoculated media is observed in third day of bacteria development when maximum concentration of H₂S is reached (190 mg/L). Its value is equal to 0.28 g/(m²h). Protective effect of the bactericides depends on the structure of their molecules. For estimation of hydrogen permeation into metal, two-chamber cell with a vertical steel membrane similar to the Devanathan cell was used. Entrance side of the membrane contacted with the working solution. The measurements were conducted under corrosion potential, cathodic and anodic polarization of the entrance membrane side. The SEM image of the membrane entrance side after the hydrogen permeation test for 2 h in the inoculated media in the absence and presence of the inhibitors is compared. Effect of dihydroxyazo compounds depends on their molecular structure. A presence of nitro-group or Cl-atom and 1-phenyl-3-methylpirazole group in the molecule increases the bactericidal and inhibitory ability of the substance. At that, a number of SRB cells, production of hydrogen sulfide by them sharply decreases, inhibitory effect essentially increases and hydrogen permeation into metal is retarded by 2.5 times in the stationary phase of bacterial vital cycle.