Seismic Vulnerability of Wastewater Treatment Plants

Wastewater treatment systems are complex networks composed by several interconnected elements, each of them characterized by specific seismic vulnerability. In the aftermath of an earthquake it is essential that such systems are fully or at least partially operating for the correct operation. Furthermore, the system failure can result in the deterioration of the environment by leakage of untreated wastewater on soil and/or its discharge into superficial water bodies. This paper deals with the assessment of seismic vulnerability of wastewater treatment plants by analyzing the effects of past earthquakes and taking into account the following factors: (i) plant size (small, medium and large); (ii) typology of wastewaters treated (municipal and industrial); (iii) treatment level performed (primary, secondary and tertiary); (iv) main causes of damages (soil/structure dynamic interaction and inertial overload); (v) elements damaged (structural, e.g. tank walls and bottom, and non-structural, e.g sludge scrapers, baffles, aerators, mechanical mixers). Historical seismic data for each combination of the previously listed factors will be given when available, in order to highlight common features and differences. The final aim of this work is to provide fragility curves and threshold values with respect to the main seismic intensity parameters and considering either the loss of control or the leak of wastewater in the ground from containment system. Once validated such curves could be successfully and easily used implemented into existing or new Quantitative Risk Analysis (QRA) tools or for land-use planning methodologies.