VULNERABILITY AND RESILIENCE OF THE SEWAGE-WWTP SYSTEM
The purpose of the research project is to characterise the sewage collection system and the wastewater treatment plant, which must not be considered separately, but rather in an integrated and synergic way: the urban drainage systems have been designed with the objectives of both reducing the risk of flooding civil and industrial settlements and limiting the environmental pollution by avoiding creating imbalances in the receiving surface water system.
The problem concerning wastewater disposal can be studied through knowledge of the response of the sewer – WWTP system to a meteoric event. For this purpose, it is possible to use specific software programs that allows to accurately model the network of interest and to analyse the behaviour of the sewage collection system and the wastewater treatment plant, simulating events of various duration and intensity. Numerical modelling makes it possible to characterise a sewer network both from a quantitative point of view, with reference to the flow rates and volumes of water received from the sewage, and from a qualitative point of view, concerning the pollutants present in the wastewater and the treatment processes that they will be subjected at the time of purification.
The integrated modelling of the sewage – treatment plant system makes it possible to promote a sustainable management of the Integrated Water Cycle, enhancing and reusing less noble waters where high quality characteristics are not required, in order to reuse the treated wastewater in the field of fertigation, for the cultivation of plants useful for landscape restoration that can be placed in the whole Integrated Water Cycle or aiming to give value to the resource in relation to the potential linked to the territorial peculiarities.
Moreover, the objective of the research project is to obtain energy recovery from wastewater treatment and from sludge line, which represents the main by-products of the sewage plant. In fact, the application of an anaerobic biological process makes it possible to attack and degrade the organic substance, producing a gas mainly consisting of carbon dioxide and methane (named biogas). The methane generated in this way can be used both to heat the wastewater or sludge from the reactor and to produce energy (for example electricity through reciprocating engines or turbines), but it can also be converted to bio-methane, which has qualitative characteristics entirely comparable with the natural gas of fossil origin. A systematic control and simulation of the sludge line also make it possible to enrich the possibilities of recovering material and energy from the Integrated Water Cycle, giving completeness to the methods and concepts of the sustainability of the integrated sewer and wastewater treatment plant system.
The first step is to identify a small urban reality (about 6000 inhabitants), which can be considered as the neighbourhood of a big city. The choice fell on Caneva, located in the western part of Friuli Venezia-Giulia. Caneva is interesting because the sewerage system is separated, and this peculiarity would increase the possibility of wastewater recovery and reuse in other sectors (for example in agriculture and in the local landscape enhancement).
The main problem of Caneva sewerage system is the water inflow and infiltration into the collectors, which damages the network itself and overloads the downstream treatment plant from a hydraulic point of view. Therefore, it is necessary to carry out an extensive measurement campaign in order to identify the source of these infiltrations.
At the same time, the sewerage system of Caneva was modelled using the EPA-SWMM calculation code, which made it possible to observe the wastewater propagation inside the collectors.