Analysis of risks affecting the operation and maintenance of wastewater treatment plant systems

The wastewater sector faces significant challenges due to the lack of a comprehensive assessment of operation and maintenance (O&M) risks in treatment plants. This study addresses this gap by integrating expert judgment with quantitative analysis to identify, categorize, and evaluate major risk factors influencing the performance of wastewater treatment plants (WWTPs). Based on semi-structured interviews and survey responses from 50 experts out of 75 invited, fifty-seven risk factors were identified and classified into two main categories: O&M stage-related risks and general risks. Each factor was analyzed according to its probability of occurrence and potential impact on operational efficiency, sustainability, and cost. The findings revealed that "inflation and unexpected price changes", "selection of unqualified contractors based on lowest cost", and "corrosion and deterioration of equipment" were the most critical risks that pose high threats to O&M of WWTPs. The financial risk group was assessed as the most important group for operational efficiency, sustainability, and cost goals. Quantitative results indicated that the occurrence of these risk factors can reduce operational efficiency by 40–54% across most groups, while financial risks specifically cause a 26% efficiency decrease and a 58% cost increase.. This study provides a structured framework for risk management in WWTPs, offering the first quantitative analysis of O&M risks in this context to support decision-makers in enhancing operational resilience, sustainability, and cost control. In addition, a practical O&M risk management checklist was developed based on the study findings to assist WWTP managers and policymakers in applying the research outcomes to real-world O&M practices.