STRUCTURAL ANALYSIS OF A BIOFILM THAT ENHANCES OR INHIBITSCARBON STEEL CORROSION IN NUTRITIONALLY POORAQUATIC ENVIRONMENTS

摘要

Carbon steel coupons were exposed to nutritionally-poor synthetic wastewater inoculatedrnwith activated sludge from a municipal waste water plant. Mass loss of the coupons wasrnproportional to the incubation time, and reached 70.4 (mg/cm 2) after incubation for 140 d. Thernobserved mass loss was 5 times as much as that under sterile conditions. Heterogeneousrndistribution of the dissolved oxygen (DO) concentration on the surface of the steel plate wasrnobserved. The average roughness of the metal surface observed after 112 d of incubation wasrn4.27 μm.rnCarbon steel coupons covered with artificial biofilm, which consisted of 0.6% agarose andrndiluted activated sludge (150 mg/1), were exposed to synthetic wastewater. When only one sidernof the coupon was covered with the artificial biofilm, mass loss of the steel coupon reachedrn0.46 mg/cm2/day. On the other hand, complete insulation of both sides with the artificialrnbiofilm resulted in carbon steel corrosion of 0.16 mg/cm2/day. Complete consumption of thernoxygen from the biofilm delayed of the steel oxidation. On the other hand, pH decrease andrnsluggish decrease of DO in the film were observed when only one side of the steel coupon wasrncovered with the artificial biofilm. These observations indicated that complete polarization duernto one side covering by biofilm on the steel surface enhances the microbiologically influencedrncorrosion (MIC) of carbon steel.