Biocorrosion of Mild Steel in Drinking Water Conditions and Disinfection

摘要

Corrosion in drinking water distribution systems is a costly phenomenon, mainly due to the replacement of affected pipes. Biocorrosion is also a problem in terms of public health because of the protective environment provided by the corroded surface to potentially harmful microorganisms, especially bacteria. The protection effect of corrosion is particularly relevant in the presence of disinfectants. The conditions leading to microbially induced corrosion are present in drinking water: bacteria and a metal substrata are closely connected as biofilms attached to the distribution system pipe walls. Despite the economic interest of this subject and the need for understanding the phenomenon, the relationships between biofilm and corrosion in drinking water distribution systems are largely unknown. Most of the published studies on biocorrosion and disinfection are empirical from observations made on parts of the pipes of distribution networks. This situation is probably due to the difficulty in distinguishing and controlling the different parameters of this phenomenon, i.e. of the surface area, the fixed and suspended corrosion products, the bacterial populations fixed and suspended, and the relationships existing between these parameters and between each of them and the added oxidant. Our research project therefore focused on the corrosion of steel in conditions relevant to drinking water distribution systems. Using a laboratory reactor, which allowed us to form and to sample biofilms on different surfaces with actual tap water bacterial populations under turbulent flow regime, we studied the biofilm-corrosion relationships and the disinfection of biofilms grown in a corroding environment. This paper presents results obtained on these two aspects following a presentation of the corrosion phenomenon in drinking water distribution systems and the reactor that we used. Corrosion appeared to have an adverse effect on the health of the associated bacterial populations, but the biofilm that developed mainly under or within the corrosion layers was also protected from disinfection because of sheltering by these layers and because of the high chlorine demand.