Taheriyoun Masoud, Moradinejad Saber
Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran,
Environ Monit Assess. 2015 Jan;187(1):4186. doi: 10.1007/s10661-014-4186-7. Epub 2014 Dec 10.
The reliability of a wastewater treatment plant is a critical issue when the effluent is reused or discharged to water resources. Main factors affecting the performance of the wastewater treatment plant are the variation of the influent, inherent variability in the treatment processes, deficiencies in design, mechanical equipment, and operational failures. Thus, meeting the established reuse/discharge criteria requires assessment of plant reliability. Among many techniques developed in system reliability analysis, fault tree analysis (FTA) is one of the popular and efficient methods. FTA is a top down, deductive failure analysis in which an undesired state of a system is analyzed. In this study, the problem of reliability was studied on Tehran West Town wastewater treatment plant. This plant is a conventional activated sludge process, and the effluent is reused in landscape irrigation. The fault tree diagram was established with the violation of allowable effluent BOD as the top event in the diagram, and the deficiencies of the system were identified based on the developed model. Some basic events are operator's mistake, physical damage, and design problems. The analytical method is minimal cut sets (based on numerical probability) and Monte Carlo simulation. Basic event probabilities were calculated according to available data and experts' opinions. The results showed that human factors, especially human error had a great effect on top event occurrence. The mechanical, climate, and sewer system factors were in subsequent tier. Literature shows applying FTA has been seldom used in the past wastewater treatment plant (WWTP) risk analysis studies. Thus, the developed FTA model in this study considerably improves the insight into causal failure analysis of a WWTP. It provides an efficient tool for WWTP operators and decision makers to achieve the standard limits in wastewater reuse and discharge to the environment.
当废水处理厂的出水被回用或排放到水资源中时，其可靠性是一个关键问题。影响废水处理厂性能的主要因素包括进水的变化、处理过程中固有的变异性、设计缺陷、机械设备问题以及运行故障。因此，要满足既定的回用/排放标准，就需要评估工厂的可靠性。在系统可靠性分析中开发的众多技术中，故障树分析（FTA）是一种常用且有效的方法。FTA是一种自上而下的演绎式故障分析方法，用于分析系统的不良状态。在本研究中，对德黑兰西部城镇污水处理厂的可靠性问题进行了研究。该厂采用传统活性污泥法，出水用于景观灌溉。以违反出水BOD允许值作为故障树图中的顶事件建立了故障树图，并基于所开发的模型识别了系统的缺陷。一些基本事件包括操作人员失误、物理损坏和设计问题。分析方法是最小割集（基于数值概率）和蒙特卡罗模拟。根据现有数据和专家意见计算基本事件概率。结果表明，人为因素，尤其是人为错误对顶事件的发生有很大影响。机械、气候和下水道系统因素排在其后。文献表明，过去在污水处理厂（WWTP）风险分析研究中很少应用FTA。因此，本研究中开发的FTA模型大大提高了对污水处理厂因果故障分析的洞察力。它为污水处理厂操作人员和决策者提供了一个有效的工具，以实现废水回用和排放到环境中的标准限值。
