Prevention and Control of Microbiologically Influenced Concrete Deterioration in Wastewater Concrete Structures Using Escherichia coli Biofilm

One of the most important deterioration mechanisms in wastewater infrastructure is microbial influenced concrete deterioration (MICD). MICD is a process in which microbial organisms accelerate the concrete deterioration by producing sulphuric acid on the surface of concrete. Sulphur oxidizing bacteria (SOB) are aerobic bacteria that convert the sulphur compounds into sulphuric acid on the concrete surface which results in biogenic sulphuric acid deterioration.;Comparing the mechanism of chemical sulphuric acid deterioration with the biogenic sulphuric acid deterioration illustrated that the chemical acidification changes the structure of the mortar by dissolution of C-S-H; however, biogenic acidification causes cracking, spalling, loss of coherence and expansion due to gypsum formation. It was also revealed that the biogenic acidification at an elevated temperature (i.e., 37±1° C) leads to a more severe deterioration comparing with the room temperature biogenic acidification. As shown by the XRD analysis, the biogenic acidification at elevated temperatures resulted in the formation of gypsum in the biofilm-covered mortar which was not a case for the room temperature experiment.;This study was proposed to investigate the use of E.coli DH5α bacterial biofilm as an environmentally friendly alternative to inhibit MICD. MICD was simulated with sulphuric acid solution as well as biogenic acidification using two species of SOB. E.coli biofilm with high amount of extracellular polymeric substance coverage was successfully grown on the mortar surface. All evidence from calcium leach-out concentration, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses suggests that the presence of biofilm prevented or controlled the chemically and biologically induced mortar deterioration. SEM and XRD analysis of mortar specimens under biogenic acidification showed the presence of gypsum crystals on the control mortar without biofilm, which is one of the indicators of concrete deterioration due to sulphate attack; however, there was no sign of gypsum crystals on the biofilm-covered mortar surface. The confocal laser scanning microscopy and volatile suspended solid analyses indicated that the biofilm sustained and was growing during both acidification processes.