HSE Risk Assessment of Sahand Urban Wastewater Treatment Plant Using Fuzzy FMEA Method.

Abstract

Abstract Background and objective: Sewage should be treated before entering the environment due to the presence of various contaminating materials such as pathogens and organic matter (sugars, proteins, fats, etc.) and unfavorable changes in its quality (color, odor, etc.). The wastewater treatment plants, as one of the most important urban substructures, are responsible for recycling of water and nutrients from the sewage collected from homes and industrial units. An structural failure in treatment plants results in unfavorable outcomes such as untreated sewages containing a variety of chemical and biological contaminations and entering them into urban environments and agricultural land, which can lead to serious health problems like the spread of epidemic diseases. Therefore, identifying and estimating the likelihood of this event and its severity in sewage treatment plants is critical for the design and implementation of risk management plans for managers and decision makers of these infrastructures. Accordingly, this study was designed to evaluate the health, safety, and environmental (HSE) risk of Sahand urban wastewater treatment plant using a fuzzy Failure Mode and Effects Analysis (FMEA) method. Materials and Methods: In order to identify the defects of the existing equipment, a method of occurrence of defects was used for the analysis of its effects. Besides, the FMEA worksheet was completed and severity and probability of occurrence, ad probability of discovery, and finally the risk priority number were obtained. The fuzzy membership functions were determined according to the experts' opinions by the mathematical program, and the severity, probability and probability of the discovery and RPN became fuzzy. Finally, with respect to fuzzy logic outputs, the risks were prioritized and corrective actions were proposed in proportion to the risk type. Results: The results of the traditional FMEA worksheet tables indicated that out of a total of 327 deficiencies in the Sahand urban wastewater treatment plant, 324 defective were low risk and acceptable, and 3 defects were moderate and unacceptable risks. But the results of the fuzzy FMEA showed that there is a high risk of 327 defects in the Sahand urban wastewater treatment plant. Also, 46 defective states were low risk, 256 medium risk, and 22 high risk. The results also showed that the relative importance of the three factors of severity, probability of occurrence and probability of discovery was different. In the present study, the importance of outcome severity was more important than the other two factors, according to experts. Conclusion: The results of the risk assessment using the fuzzy table showed that HSE risk assessment of sewage treatment plant through fuzzy FMEA provides more accurate and better results than traditional FMEA. In this regard, fuzzy FMEA results showed that the involvement of experts in risk assessment and the construction of fuzzy models gives more realistic results, and prioritizes corrective actions. Keywords: FMEA; wastewater treatment plant; risk assessment; fuzzy FMEA; fuzzy table.