Risk assessment of an industrial wastewater treatment and reclamation plant using the bow-tie method

At present, wastewater reuse and recycling in water-stressed countries such as Iran has become a vital option for better management of water scarcity. However, despite the benefits of wastewater reuse, there is a probability of incomplete treatment of wastewater in accordance with the standards. Risk assessment of a wastewater treatment plant is required in order to determine the causes and consequences of failure in the treatment system. Among various methods used for risk assessment, the bow-tie (BT) approach is an efficient technique since it represents a failure event from causes to effects. In this method, for a wastewater treatment plant (WWTP), causes of an adverse event, including the violation of the effluent water quality from the standard limit is studied using fault tree analysis (FTA). Then, the impacts of these adverse events are classified in different scenarios by the use of event tree analysis (ETA). In this study, the BT technique was applied to assess the risk of the WWTP of the Moorchekhort industrial complex (MIC), located in the central part of Iran. The plant consists of two parts, including activated sludge and advanced treatment processes to provide reclaimed water for different industrial uses. Results showed a 41% risk of violation from the effluent standard limit in the MIC WWTP. In addition, analyzing the risk factors revealed that the human error had the largest contribution to the risk calculation of the WWTP failure. In this regard, a number of mitigation measures were proposed to improve the reliability of the WWTP.