Laboratory-scale batch experiments (semicontinuously fed) were conducted using a two-level factorial experimental design to investigate principal factors and interactions affecting microbiologically influenced corrosion (MIC) of carbon (C) steel. Factors considered included the C source as chemical oxygen demand (COD), sulfate (SO 4 2-) concentration, calcium carbonate (CaCO 3 ) precipitation, and bacteria inoculation at 20°C. Yates' algorithm was applied to calculate main and interaction effects, and an empirical model indicating major trends was obtained. Experimental results showed CaCO 3 precipitation played a significant role in influencing the biocorrosion tendency of steel. In the supersaturated condition, SO 4 2concentration and bacterial inoculation had no appreciable effects on corrosion. In the undersaturated condition, the corrosion rate was affected significantly by SO 4 2concentration and bacterial inoculation. The effect of each factor on corrosion rate was explored.

No abstract

No abstract

A laboratory experiment was conducted to investigate the corrosion influenced by sulfate‐reducing bacteria (SRB). A mathematical model was developed and fitted to the pitting depths measured at 0.1 and 0.5 mM sulfate concentrations. The model was successful in predicting the pitting depth at two different sulfate concentrations when the kinetic variables reported in the literature were used. The deepest pitting depths were observed to be approximately 0.19 and 0.39 mm for bulk sulfate concentrations of 0.1 and 0.5 mM after 150 days of exposure, respectively. The pitting depths were predicted to be 0.17 and 0.36 mm for bulk sulfate concentrations of 0.1 and 0.5 mM after 150 days of simulation, respectively. The steady‐state pitting depth was predicted to be 0.48 mm for a bulk sulfate concentration of 0.5 mM after 400 days of simulation. The model was most sensitive to the sulfate diffusion coefficient (DSO42−), closely followed by the maximum sulfate utilization rate (q), and the biomass concentration (Xc), but it was less sensitive to the half‐velocity coefficient (Km). At the initial stage, the pitting depth was affected only by q and Xc. As the pitting depth increased, however, the diffusion of sulfate in the reaction zone became one of the dominant limiting factors. The decrease in the q or Xc value by 20% resulted in the increase in the pitting depth by 19%.

Data from this study indicate that fluoridation with natural fluorspar could be practical if the raw water is of an appropriate quality. There has been concern about the availability of commercial fluoride chemicals for publicly fluoridated water, coupled with potential problems of overdosing. Fluorspar, a mineral form of CaF2, may provide a more publicly acceptable approach with many advantages over other widely used fluoridation chemicals. This article describes work aimed at gaining insight into the dissolution equilibrium behavior of fluorspar under various conditions for its use in water fluoridation. By treating fluorspar as a blend of CaF2 and CaCO3, the dissolution equilibria were accurately predicted by a theoretical model that accounted for the effects of temperature, background calcium ion concentration, and initial pH. Experimental results and calculations both showed that the ultimate fluoride concentration was approximately 6.0 mg/L at room temperature. Effects of temperature and background calcium ion concentration were much more significant than initial pH. Fluoridation with natural fluorspar could be a practical process with influents of the appropriate quality.