STRUCTURAL ANALYSIS OF A BIOFILM THAT ENHANCES OR INHIBITS CARBON STEEL CORROSION IN NUTRITIONALLY POOR AQUATIC ENVIRONMENTS

摘要

Carbon steel coupons were exposed to nutritionally-poor synthetic wastewater inoculated with activated sludge from a municipal waste water plant. Mass loss of the coupons was proportional to the incubation time, and reached 70.4 (mg/cm~2) after incubation for 140 d. The observed mass loss was 5 times as much as that under sterile conditions. Heterogeneous distribution of the dissolved oxygen (DO) concentration on the surface of the steel plate was observed. The average roughness of the metal surface observed after 112 d of incubation was 4.27 mu m. Carbon steel coupons covered with artificial biofilm, which consisted of 0.6 percent agarose and diluted activated sludge (150 mg/l), were exposed to synthetic wastewater. When only one side of the coupon was covered with the artificial biofilm, mass loss of the steel coupon reached 0.46 mg/cm~2/day. On the other hand, complete insulation of both sides with the artificial biofilm resulted in carbon steel corrosion of 0.16 mg/cm~2/day. Complete consumption of the oxygen from the biofilm delayed of the steel oxidation. On the other hand, pH decrease and sluggish decrease of DO in the film were observed when only one side of the steel coupon was covered with the artificial biofilm. These observations indicated that complete polarization due to one side covering by biofilm on the steel surface enhances the microbiologically influenced corrosion (MIC) of carbon steel.