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

罗森9704935 当水面以下厌氧膜中的微生物产生硫化氢时，废水收集系统中的混凝土就会发生硫化物腐蚀。 硫化物蒸发到大气中，并重新溶解在冷凝在废水上方管道部分的水分中。 在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，导致混凝土腐蚀。 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（弱解、强解、局部解、整体解的存在性、唯一性、正则性等）的角度分析模型方程（其形式为具有移动或自由边界的耦合偏微分方程系统）。以及解对参数的敏感性。 它还包括用于数值模拟，参数估计和控制的高效，收敛和鲁棒的数值积分方案的开发，分析和测试。 除了使用现有的现场数据来验证模型，一个实验室试验台，提供额外的数据模型验证和参数估计的设计和制造。 电化学技术应用于仪表混凝土样品用于（i）表征混凝土结构，使用电化学阻抗谱（EIS），和（ii）感测腐蚀性物质的扩散分布。 这两项研究的结果的相关性允许混凝土微观结构和扩散过程之间的关系的调查。 计算方案的开发，使用现场和实验室数据，以确定不可测量的参数，出现在模型中，并测试腐蚀减缓控制方案的基础上的模型。 硫化物腐蚀每年在美国造成数百万美元的损失。 已经尝试控制下水道中的硫化物腐蚀。 大多数试图防止硫化氢释放到管道大气中。 强碱被用来杀死生物膜，清洗被用来去除它。添加微量金属沉淀硫化物，防止其释放到大气中。 然而，生物膜是坚韧的，并且快速生长，需要额外的处理。 任何抗生物膜处理都受到限制，因为它必须不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。 任何涉及添加化学品的努力都必须与流经废水收集系统的大量水作斗争：无论化学品多么便宜，必须购买并投入系统的大量水都是昂贵的。 因此，首先需要努力了解并随后中断（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。 研究结果应产生腐蚀过程的更深入的了解，并提供了一个强大的工具，工程师使用的混凝土废水系统的设计和腐蚀减缓程序的制定，测试，调整和评估。 该模型和结果应指导保护技术的改进，硫化物腐蚀是一个问题，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。 它们还可以潜在地降低维护成本。 作为本项目的一部分，开发的建模思想应可转移到其他腐蚀问题，分析和计算技术，结果应使用在移动边界问题，其分析，数值解，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.