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Water leakages represent a crucial aspect in the management of water distribution networks (WDNs). The pressure control, by means of pressure reducing valves, is an economical and viable strategy to contain water leakages and it has been deeply investigated in literature for many years. However, in the presence of high excess pressure and high discharges, thus high energy potential, it may be more convenient to install an energy production device (e.g., a turbine, a pump as turbine) in order not to dissipate the excess pressure, but rather to convert it into energy by means of an electrical generator. Nevertheless, whenever the pressure containment could ensure large water savings but small energy production, the installation of a pressure reducing valve may be more convenient due to the lower purchase and maintenance costs. In literature, many studies have dealt with the optimal location of such valves within WDNs in order to maximize leakage reduction. In this study, the optimization of both the number and location of pressure reducing valves is performed, with the aim of maximizing water savings and minimizing investment cost. Instead of employing external software to compute flow through links and pressure at nodes, the hydraulic resolution of the case study network is coupled with optimization procedure in one single mathematical model. Due to the strong non-linearities modelling of the hydraulic network, as well as the presence of both continuous and integer optimization variables, the resulting mathematical problem is mixed integer non-linear programming (MINLP). A global optimization solver is employed to solve the problem and the achieved results are presented with reference to a literature case study network. According to the results, the proposed optimization ensures an improvement in leakage reduction of 21%, compared to other studies on the same network. [ABSTRACT FROM AUTHOR]

The energy efficiency of water supply systems is usually very low. They are affected by a high rate of water leakage with a significant loss in terms of the energy that is embedded in the lost water flow. Furthermore, the strategy to reduce the water loss frequently involves pressure reduction with a further decrease in energy efficiency. Several solutions have been proposed in the literature to reduce the pressure in the water distribution networks and recover the hydraulic energy, such as special turbines or pumps as turbines (PATs). Despite the positive aspects related to the use of such devices, the high installation costs, together with the limited hydraulic control capacity and the small power availability, limited the diffusion of such devices among the water utilities. A new device is proposed herein, which consists of two submersible PATs inserted into a booster cylinder. The high control capacity, together with the small production and installation costs, makes this technology very promising. The device has been installed in the Hydro Energy Lab of the CeSMA of the University of Naples and the first experimental results on its behavior are presented herein. A slight difference arises between the performance booster curves and the bare curves provided by the manufacturer due to measurement errors as well as to the presence of head loss within the system. Nevertheless, the energy efficiency of the plant results will be preserved, making this design a promising solution to overcome most of the limitations of the present technologies when low energy is available and large discharge variation occurs. [ABSTRACT FROM AUTHOR]