Understanding the early-stage spatially distributed behaviors of microbially induced concrete corrosion in the sewer system

Microbial-induced concrete corrosion (MICC) has been recognized as one of the main factors causing damage to urban sewer pipelines. However, little is known about the neutralization and degradation of the concrete pipe during the early-stage MICC, which is a key point for the trenchless protection of sewer pipelines. In the present study, the corrosion behaviors of concrete pipe were simulated in a pilot-scale sewer system for 180 days and correlated to the change of microbial communities. The results revealed the post-corrosion characteristics in different spatial locations of the sewer during the early-stage MICC. Apart from the biogenic sulfuric acid attack and gypsum formation at the upper part (UP), the bottom part (BP) of the concrete pipe suffered severe degradation due to volatile fatty acids (VFAs) generated. Under the action of microbial metabolism, the decomposition of hydrates and pore coarsening occurred, resulting in decreased mechanical strength. In terms of microbiology, the dominating functional bacteria were fermentation bacteria (FB), such as Macellibacteroides, Trichococcus, Longilinea, etc. FB played a major role in the production of VFAs, which would create suitable conditions for the subsequent development of microorganisms. The early fermentation processes were key factors contributing to concrete pipe corrosion, especially at BP. The relative abundance of sulfate-reducing bacteria (Desulfovibrio) and methanogenic archaea increased with exposure to age. The findings can provide a theoretical basis for the protection of urban concrete sewer pipelines.