Mathematical Modeling of Sulfide Corrosion of Concrete in Wastewater Collection Systems - Analysis, Experimental Validation, Parameter Estimation and Control

污水收集系统中混凝土的硫化物腐蚀发生在水面以下厌氧膜中的微生物产生硫化氢时。硫化物蒸发到大气中，并重新溶解在废水上方管道部分凝结的水分中。这种环境中的微生物将硫化物转化为硫酸。酸与水泥中的氢氧化钙和碳酸钙反应，产生硫酸盐矿物，使混凝土腐蚀。研究人员开发了一个腐蚀过程的数学模型，通过现场数据和实验室实验进行调整、测试、识别和验证。工作包括从适定性（存在性、唯一性、弱解、强解、局部解、全局解等的正则性）和解相对于参数的敏感性的角度分析模型方程（采用带有移动边界或自由边界的耦合偏微分方程系统的形式）。它还包括开发、分析和测试高效、收敛和鲁棒的数值积分方案，用于数值模拟、参数估计和控制。除了使用现有的现场数据来验证模型外，还设计和制作了一个实验室试验台，为模型验证和参数估计提供额外的数据。应用于仪表混凝土样品的电化学技术用于(i)使用电化学阻抗谱（EIS）表征混凝土结构，以及（ii）感知腐蚀物质的扩散曲线。这两项研究结果的相关性使得研究混凝土微观结构和扩散过程之间的关系成为可能。开发了计算方案，使用现场和实验室数据来识别模型中出现的不可测量参数，并根据模型测试腐蚀减缓控制方案。在美国，硫化物腐蚀每年造成数百万美元的损失。人们已经尝试控制下水道中的硫化物腐蚀。大多数都试图防止硫化氢释放到管道大气中。用强碱杀死生物膜，用清洗去除生物膜。微量金属的加入使硫化物沉淀，防止其释放到大气中。然而，生物膜是顽强的，并迅速生长，需要额外的治疗。任何抗生物膜处理都受到限制，因为它不能损害作为废水处理系统基础的类似微生物。化学沉淀需要连续处理。任何涉及添加化学物质的努力都必须与流经废水收集系统的大量水相抗衡：无论化学物质多么便宜，必须购买并输入系统的大量水都是昂贵的。因此，需要首先努力了解然后中断（即控制）腐蚀过程，并且可能为某些情况提供唯一可能的补救措施。研究结果将使我们对腐蚀过程有更深入的了解，并为工程师在混凝土废水系统的设计以及腐蚀消减程序的制定、测试、调整和评估中提供有力的工具。模型和结果应该指导在硫化物腐蚀是一个问题的保护技术的改进，并提供洞察其他混凝土结构的腐蚀过程和造成的实质性损害。它们还可能降低维护成本。作为该项目一部分的建模思想应可转移到其他腐蚀问题，由此产生的分析和计算技术应用于移动边界问题，其分析，数值解决，识别和控制领域。

Rosen 9704935 Sulfide corrosion of concrete in wastewater collection systems occurs when microorganisms in anaerobic films below the water surface produce hydrogen sulfide. The sulfide evaporates into the atmosphere and redissolves in moisture that has condensed on the portions of the pipe above the wastewater. Microorganisms in this environment convert the sulfide to sulfuric acid. The acid reacts with calcium hydroxide and calcium carbonate in the cement, producing sulfate minerals and causing the concrete to corrode. The investigators develop a mathematical model of the corrosion process that is tuned, tested, identified and validated via field data and laboratory experiment. The effort includes the analysis of the model equations (which take the form of a system of coupled partial differential equations with moving or free boundaries) from the point of view of well-posedness (existence, uniqueness, regularity of weak, strong, local, global solutions, etc.) and the sensitivity of solutions with respect to parameters. It also includes the development, analysis and testing of efficient, convergent and robust numerical integration schemes for numerical simulation, parameter estimation and control. In addition to using available field data to verify the model, a laboratory test-bed to provide additional data for model verification and parameter estimation is designed and fabricated. Electrochemical techniques applied to instrumented concrete samples are used to (i) characterize the concrete structures using electrochemical impedance spectroscopy (EIS), and (ii) sense the diffusion profiles of corrosive species. Correlation of the results of these two studies allows investigation of relationships between concrete microstructure and diffusion processes. Computational schemes are developed to use the field and laboratory data to identify unmeasurable parameters that appear in the model, and to test corrosion slowing control schemes based upon the model. Sulfide corrosion causes millions of dollars in damage in the U.S. each year. Attempts have been made to control sulfide corrosion in sewers. Most try to prevent the release of hydrogen sulfide into the pipe atmosphere. Strong base has been used to kill the biofilm, and cleaning has been used to remove it. The addition of trace metals precipitates the sulfide, preventing its release to the atmosphere. However, the biofilms are tenacious, and grow back rapidly, requiring additional treatment. Any anti-biofilm treatment is constrained because it must not damage the similar microorganisms that are the basis of the wastewater treatment system. Chemical precipitation requires continuous treatment. Any effort involving chemical addition must contend with the very large volumes of water flowing through wastewater collection systems: no matter how cheap the chemical, the colossal amounts that must be purchased and fed into the system are expensive. Thus an effort to first understand and to then interrupt (i.e. control) the corrosion process is needed, and may provide the only possible remedy for some cases. The results of the study should yield a deeper understanding of the corrosion process, and provide a powerful tool for engineers to use in the design of concrete wastewater systems and in the formulation, testing, tuning and evaluation of corrosion abatement procedures. The model and results should guide improvements in protection techniques where sulfide corrosion is a problem, and provide insight into the corrosion processes of other concrete structures and the substantial damage caused. They could also potentially reduce maintenance costs. The modeling ideas developed as a part of this project should be transferable to other corrosion problems, and the analytical and computational techniques that result should be of use in the area of moving boundary problems, their analysis, numerical solution, identification and control.