Capuozzo, Antonella (2025) Mathematical modeling of microbially induced corrosion in concrete sewer systems. [Tesi di dottorato]

Documento PDF Capuozzo_Antonella_38.pdf Visibile a [TBR] Amministratori dell'archivio Download (6MB) | Richiedi una copia

Abstract

Mathematical modeling plays a pivotal role in contemporary scientific research, offering a valuable and cost-effective approach for investigating complex systems across various disciplines. By enabling the simulation and prediction of dynamic behaviors, mathematical models allow for a deeper understanding of underlying mechanisms, thereby reducing the reliance on costly and time-consuming experimental campaigns. In this context, the present doctoral thesis is devoted to the study of microbially induced corrosion (MIC) of concrete in sewer systems through the development and analysis of mathematical models. Specifically, this thesis presents three mathematical models based on ordinary differential equations (ODEs) and partial differential equations (PDEs), each addressing different aspects of the MIC process and microbial ecology in concrete sewers. The first model introduces a two-phase double free boundary model to describe the growth of sulfur-oxidizing bacteria (SOB) biofilms on concrete surfaces, along with the related acid production responsible for the corrosion process. The mathematical model simulates the growth of a single-species biofilm, the resulting sulfuric acid production due to bacterial metabolism, and the advancement of the corrosion front, where concrete is progressively transformed into gypsum. A system of diffusion-reaction PDEs accounts for the key biological, chemical, and physical processes occurring during the oxidation of soluble biodegradable substrates and the transport and conversion of acid with the solid matrix, and is coupled with a moving boundary formulation that describes the progressive advancement of the corrosion front where sound concrete is transformed into gypsum. Numerical simulations, performed to study the model's behavior, reveal how variations in substrate availability and environmental conditions influence biofilm thickness, acid concentration, and the progression of the corrosion front, highlighting the interplay between microbial growth and material degradation. The second model is based on a system of ODEs which describes all main biogeochemical and ecological pathways governing MIC in wastewater pipelines, including the dynamics of key microbial populations -- neutrophilic and acidophilic SOBs -- and their pH-dependent growth, succession, and contribution to acid production. The model incorporates gas–liquid mass transfer, acid–base equilibria, dissolution and precipitation of solid phases, and ionic charge balance, to simulate the evolution of critical chemical variables such as pH, calcium ion concentration, and the formation of corrosion products like gypsum and calcite. Numerical simulations explore the effects of microbial activity and gaseous hydrogen sulfide concentration on the corrosion process, under both carbonated and unaltered concrete conditions. The results provide insight into the mechanisms governing microbial ecology and physicochemical dynamics, offering a predictive framework for understanding and potentially mitigating MIC in wastewater infrastructure. The third model builds upon the initial two-phase double free boundary framework by incorporating a multispecies biofilm component. It couples a system of hyperbolic equations, which governs the transport and growth of various microbial species, with the existing diffusion-reaction system. This integrated approach enables an extended investigation of submerged biofilms within sewer environments, capturing the complex dynamics of a large number of microbial species. Numerical simulations reveal distinct evolutions of microbial population and substrate distributions under submerged and unsubmerged conditions, where the former leads to biocorrosion phenomena and the latter promotes the formation of hazardous gaseous compounds. Overall, this thesis highlights the potential of mathematical modeling as a valuable tool for elucidating the mechanisms underlying MIC, and as a foundation for the development of predictive frameworks to support effective monitoring and mitigation strategies in the context of wastewater infrastructure degradation.

Downloads

Actions (login required)

Modifica documento