ABSTRACT
Physical, biological and chemical process take place during wastewater treatment. Any, even the smallest, disruption of any process may pose a risk in operation of the treatment plant. For each type of wastewater, an appropriate method for their purification is established. It depends on the type of sewage, the population equivalent and the type of receiver The paper compares the threats that may pose a risk in municipal sewage treatment plants. Selected, for risk analysis, sewage treatment plants are located in the same city. They were designed in the same technological chain due to similar Population Equivalent (PE) and comparable conditions of discharge purified wastewater to the receiver. Previous risk analyses have shown the importance of the human factor, in the form of management, work organization, documentation and databases, technical knowledge and staff training. Employees of sewage treatment plants in their daily work can prevent negative events or cause them to occur. The location of the selected wastewater treatment plant in the same city area causes that they are managed by the same person and operating in the same way. This ensures a similar response to the same events, similar risk elimination during the operation and quality of databases. These condition allow for the unification of the human factor when comparing the treats at the municipal sewage treatment plants.
