Treatment Reliability When Reusing Reclaimed Water for Irrigation: A Risk Assessment, Ranking and Management Methodology

Water reuse may pose risks to the environment and human health due to pathogens or chemical pollutants (hazards) in reclaimed water arising from treatment or distribution system failures (hazardous events). In this context, the European Regulation EU 2020/741 requires the development of a Risk Management Plan (RMP) from the source to the irrigated fields. This study proposes a methodology to assess and manage the risk to guarantee a reliable treatment able to produce an effluent adequate for reuse. It combines Failure Mode and Effect Analysis (FMEA) with a Risk Priority Number (RPN) approach. FMEA identifies failure modes for the treatment components (hazardous events), their consequences for the system, and the hazards for environment and human health. The RPN measures the failure risk by the product of the likelihood of occurrence L, magnitude of effects M and ease of detection D for each failure. Due to a lack of data, L, M and D are estimated through scores. Failure risks are classified as low, medium, high and very high. The last step is the revision of existing corrective actions or the adoption of new ones to reduce the risk of critical failures (highest RPN). This methodology is applied to a large wastewater treatment plant (Class A technology, according to EU 2020/741). Out of the 303 failure modes identified for the 86 components, 12 are the most critical (very high risk) and the suggested additional corrective actions reduce L and/or D and thus M. This methodology supports an RMP for similar or more complex treatment plants.