Although biochemical systems in wastewater treatment plants are sensitive to construction deviations and operational disturbances, existing risk assessments often lack a multidimensional and quantitative approach. In line with realism, this study proposes a quantitative risk evaluation model based on the 4M1E (Manpower, Machine, Material, Method, Environment) management framework. By integrating expert survey data, a dual-layer hierarchical weighting system is constructed to calculate local weights (LW), total weights (TW), and impact factors (IF). Also, the calculated results are subsequently combined with occurrence probabilities using a risk matrix (R = LS) for multidimensional visualization. The results indicate that the comprehensive risk levels across the five dimensions follow the order: Machine > Environment > Material > Manpower > Method. The findings in this study indicate that mechanical equipment (e.g., core sewage pumps) and external environmental factors (e.g., influent flow and temperature variations) pose the highest risk levels and the largest fluctuation ranges, identifying these items as the core priorities for risk control. Conversely, the operational method dimension exhibits the lowest risk due to the inherent stability of mature treatment processes under normal conditions. In conclusion, this study extends the 4M1E into wastewater treatment engineering, providing an objective, reproducible method for critical risk identification, differentiated hierarchical on-site management, and the optimization of lifecycle maintenance resources.
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