• CAPEX
• centralization
• collecting system
• construction cost
• cost functions
• design
• OPEX
• optimization
• wastewater
• wastewater treatment plant
• WWTP

This thesis focuses on the wastewater treatment plants (WWTPs) located in the Italian municipalities of Coreglia Antelminelli, Bagni di Lucca and Borgo a Mozzano. In these municipalities, the number of the WWTPs in operation is too high compared to the Population Equivalent served (resulting a system which is both expensive and difficult to manage). Therefore, the aim of this thesis is a technical - economic optimization study for the centralization of the wastewater collection and treatment services, in order to achieve a reduction in the operating expense (OPEX) and an improvement in the status of the environment.
The focal point of this study is the realization of the Maximum Centralization Scenario, in which all the WWTPs taken into account are replaced by a single wastewater treatment plant. The Maximum Centralization Scenario represents the starting scenario with all of the necessary parameters from which various scenarios and possible solutions for the centralization, based on economic criteria can be derived. Its realization is subdivided into two phases:
1) Designing on a georeferenced map of a new pipeline system collecting and transporting the wastewater to the only WWTP in operation, and determining the terrain profiles crossed by the pipelines.

2) Computing hydraulic features of the pipelines. This phase consists of two steps:

• The profiles determined in the first phase are imported into a numerical computing program: by an algorithm, the developments of the pipelines are calculated and, consequently, so are the diameters of the pipelines and the geographic coordinates of the critical points showing considerable differences in height to overcome by the use of special devices.

• The geographic coordinates of the critical points are imported in the georeferenced map, which leads to the evaluation of the most suitable devices for overcoming the differences in height, based on the comparison between the position of the critical points and the land morphology.

Once the Maximum Centralization Scenario is complete, using cost functions based on technical parameters, the capital expenditure (CAPEX) and the OPEX are computed.
On the basis of the ratio between the Population Equivalent served and the length of the pipelines, two optimized solutions are obtained from the Maximum Centralization Scenario, gradually considering lower percentages of Population Equivalent served. The process is iterative: the peak flow rates and the diameters of the pipelines are computed again and, consequently, so are the CAPEX and the OPEX of these new configurations, allowing an economic comparison between the created scenarios.