[Show abstract][Hide abstract] ABSTRACT: The evaluation of energy efficiency in water supply systems should account for both actual energy consumed and how efficiently such energy is spent. This work proposes the new concept of Unavoidable Minimum Energy, as the reference for defining an energy efficiency indicator. The aim is to search for possible optimal network configurations that minimize energy consumption and maximize the energy efficiency, acting on the main structural parameters of the system (pipe diameters, leakage rate) and considering the pump efficiency as well. The optimization process is carried out by coupling the heuristic algorithm GHEST with the EPANET solver and applied to a literature synthetic case study.
Full-text · Article · Dec 2014 · Procedia Engineering
[Show abstract][Hide abstract] ABSTRACT: Identifying the main connections between water production, processing and distribution sites can give a clearer comprehension of their structure, importance and criticality. We present a graph-theory based approach which is able to dramatically reduce the complexity of a network to allow a better comprehension of its main flow models. As a starting point, some nodes in the network are marked as primary;A skeletonization procedure then reduces the graph excluding all the pipes which are not essential to connect the primary nodes. The network is further analysed to define a single path between couples of primary nodes. An efficient implementation (in Python+IGraph) is discussed, along with performance improvements. The results can be employed to understand the flow model of a previously unknown network or as a first step to determine its most vulnerable or important elements.
Full-text · Article · Dec 2014 · Procedia Engineering
[Show abstract][Hide abstract] ABSTRACT: The collection and distribution of drinking water resources generally require large quantities of energy, that vary according to factors related to the characteristics of the served area, as well as to design and management choices. Energy intensity indicators (energy per unit of volume) are insufficient to assess the weight of different factors that affect the energy consumption and appear not suitable for the comparison of different water supply systems. The key step of this work is to define a methodology for assessing the energy efficiency of water supply systems. In particular, water losses in water distribution systems, generally assessed in relation to the quantity of high quality water dispersed in the environment, are herein considered in relation to their energy content. In addition to the evaluation of energy balance using the approach proposed by Enrique Cabrera et al. in 'Energy audit of water networks' (see J. Water Res. Plan. Manage. 136 (6), 669-677) an overall efficiency indicator WSEE (Water Supply Energy Efficiency) is then proposed. Its decomposition finally leads to the definition of further indicators, which may help to assess how the structure of the network, leakage rate and/or pumps affect the energy efficiency of the water system. Such indicators can be used to compare different water supply systems and to identify the impact of individual interventions. The proposed energy analysis was applied to two case studies in Northern Italy.
No preview · Article · Aug 2013 · Water Science & Technology Water Supply
[Show abstract][Hide abstract] ABSTRACT: Urban drainage appurtenances separate particulate matter (PM) and detritus unintentionally and by design. Such PM separation impacts conveyance, treatment, and maintenance practices. This study examines two common appurtenances: Gully pots (or catch basins) and screened hydrodynamic separators (HS). Under steady and controlled physical model testing, PM separation was measured for influent granulometry [particle size distributions (PSDs), PM specific gravity]. Catch basin separation ranged from 40 to 99% for a monodisperse (well-graded sand, SW) PSD and 60 to 83% for a hetero-disperse PSD. With similar testing, a clean HS (to avoid scour dominating PM separation), the HS was also loaded with a heterodisperse sandy silt (ML) and tested as a function of flow, with separation of 40 to 65%, as compared to 70 to 99% for the SW, similar to the catch basin. Physical model results were compared to the surface overflow rate (SOR) model, illustrating that the SOR overestimated PM separation by 3–13%. The SOR was extended to unsteady runoff events. For unsteady loading of an HS with complex hydrodynamics and short residence times, the SOR overpredicted measured PM separation by 3–22% on the basis of PM granulometry. For maintenance and coarse PM load inventories, the SOR can reasonably predict the fate of coarse PM, subject to Type I settling in an HS and catch basin units with similar PM separation behavior. If suspended PM mass dominates the particle size distribution (PSD), is the focus of treatment, or for units with long residence times, the continuous phase hydrodynamics must be coupled with a discrete phase model, requiring analytical or numerical models such as computational fluid dynamics (CFD). For conditions illustrated herein, the SOR is reasonably robust.
Read More: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EE.1943-7870.0000512
[Show abstract][Hide abstract] ABSTRACT: Optimization of water distribution network is a NP-hard problem that researchers have tried to deal with using different formulations and algorithmic approaches. Among these, multi-objective heuristic algorithms are interesting because of their capacity for dealing with separate objectives that allow us to choose a posteriori the best compromise, but one of their main drawbacks is the long time required to obtain good solutions. Parallel processing is the most promising way to reduce the computing time and can make the convergence to adequate solutions faster. This paper intends to investigate the possibility of improving the efficacy and efficiency of an NSGA-II algorithm by parallelization of the optimization process at the same time. Results of different parallel implementations of NSGA-II applied to optimal design of small- and medium-size water distribution networks are presented. Good speed-up can be reached with a global model, hence improving the algorithm efficiency. Unlike the global model, the island model (or the hierarchical parallelization) can also improve its efficacy because it introduces fundamental changes in the algorithm exploration method. Possibilities offered by parallel island models have been investigated showing that some parameter configurations can find better solutions compared with the serial version of the algorithm.
No preview · Article · Apr 2012 · Journal of Hydroinformatics
[Show abstract][Hide abstract] ABSTRACT: Roadside gully pots are the connecting points between surface runoff and the underground drainage network; therefore they can be considered as the most superficial component of urban drainage systems. Gully pots are supposed to trap particulate matter washed off the catchment surface, but also to collect and convey stormwater into the network. The continuous accumulation of particulate matter results in a progressive loss of the gully pot hydraulic conveyance, thereby increasing the probability of urban flooding during rainstorm events. This study has therefore the objective to determine which variables influence the gully pot capability of retaining solids (efficiency), both experimentally and analytically. Several laboratory tests have been performed on a simple plastic gully pot, with different inflow rates and using both mono and hetero-disperse particle samples. Particular attention has been given to the influence exerted by the way particle settling velocity is expressed: efficiency has been analytically determined by means of multiple settling velocity formulas proposed by various authors and eventually compared to experimental data. Results deriving from the adoption of each single settling velocity formula have been extensively analysed, showing fairly different outcomes.
No preview · Article · Dec 2011 · Water Science & Technology
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a new model named GHEST, a multi-population evolutionary-strategy-like algorithm
applied to the optimal design of water distribution networks (WDN). GHEST hunts for the optimal solution
by means of two different complementary processes. The first one, synthesizes and transmits the
genetic patrimony (heritage) of the parent solutions using their statistical indicators. The second one,
called ‘‘shuffle”, avoids the search to get stuck in local minima whenever the evolutionary potential of
the population appears to be exhausted. GHEST makes use of hydraulic network solver EPANET 2. Tests
carried out on classical WDN optimal design problems are shown for three small and well-known networks
and for a large-size one. Performances exhibited, in terms of minimum cost, are equal or better
than those found in previous works (where directly comparable). The algorithm has been tested with different
setups, achieving good results for almost all of them. Its performance can be particularly appreciated
in large-size optimization problems as evidenced by results on Balerma network, where a new
minimum cost has been set and the evaluation number to reach the former minimum has been decreased
by about 35 times. Results are supported by an extensive comparison with previous works on the benchmark
networks here tested.
Full-text · Article · May 2010 · Advances in Engineering Software
[Show abstract][Hide abstract] ABSTRACT: The Navile Channel (Bologna, Italy) is an ancient artificial water course derived from the Reno river. It is the main receiving water body for the urban catchment of Bologna sewer systems and also for the Waste Water Treatment Plant (WWTP) main outlet. The aim of this work is to evaluate the Combined Sewer Overflows (CSOs) impact on Navile Channel's water quality. In order to collect Navile flow and water quality data in both dry and wet weather conditions, two measuring and sampling stations were installed, right upstream and downstream the WWTP outflow. The study shows that even in case of low intensity rain events, CSOs have a significant effect on both water quantity and quality, spilling a considerable amount of pollutants into the Navile Channel and presenting also acute toxicity effects. The collected data shown a good correlations between the concentrations of TSS and of chemical compounds analyzed, suggesting that the most part of such substances is attached to suspended solids. Resulting toxicity values are fairly high in both measuring points and seem to confirm synergistic interactions between heavy metals.
Preview · Article · Jan 2010 · Water Science & Technology
[Show abstract][Hide abstract] ABSTRACT: Navile Channel (Bologna, Italy) is artificial, derives from the Reno river, and receives water also from the urban catchment and from the WWTP main outlet. Discharges usually range from few cubic meters per second, especially during dry periods in summer times, up to several cubic meters per second during wet weather. The WWTP outflow increases the Navile Channel's flow by up to 1800 liters per second, during dry weather period. During storms the urban catchment contributes mainly through CSOs, whose harmful effect was object of previous studies (Artina et al., 2004a). To collect flow and water quality data in both dry and wet weather conditions, on the Navile Channel two measuring and sampling stations were set, upstream and downstream the WWTP main outlet. The study shows that CSOs activate even with slight events, spilling a huge amount of pollutants into the Navile Channel, with concentrations of orders of magnitude higher than in dry weather flow, showing also an acute toxicity behaviour.
[Show abstract][Hide abstract] ABSTRACT: Roadside gully pots are the link between surface runoff and the drainage system, and therefore are to be regarded as relevant component of it. It is a well-established opinion that their main function is to protect downstream drainage, treatment plant as well as receiving waters from excessive sediment loads. Anyway a continuous inflow of solids to a device designed in order to trap them, leads unavoidably to gradual silting and eventually to clogging problems. These factors appear quite relevant in Italian cities, mainly served by combined sewer systems where trapped gullies are required to prevent the exit of bad odour, being then particularly subject to silting and clogging problems. Aim of the present study is to investigate which variables influence the gully pot capability in retaining solids (efficiency). Experimental laboratory tests have been carried out on a simple plastic gully pot (40 x 40 cm), testing different characteristics of the rainfall events (inflow rate) and of the influent solids (diameter, particle size distribution and specific gravity). Tests results fairly well agree with ones obtained in previous researches, and extend their substantial validity also to contexts and conditions where they had not been directly verified.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this article is to test the performance of two commercial models for the simulation of sewer systems (InfoWorks, developed by Wallingford Ltd and Mouse, developed by DHI), basing on the experimental data sampled in a 1.15 ha watershed located near Bologna, Italy.
The experimental catchment is part of a truck transit and parking area, completely asphalt paved and drained into a first flush tank. Hydrologic and water quality data collected for almost 8 months inside the tank have been used to calibrate the models through a trial and error procedure for both quantity and quality aspects. A sensitivity analysis for the most relevant qualityequantity parameters has also been performed, testing therefore the behaviour of these models in a small impervious watershed and their reliability as a support tool in the design phase.
No preview · Article · Aug 2007 · Environmental Modelling and Software
[Show abstract][Hide abstract] ABSTRACT: This paper is about a monitoring study carried out in a commercial-industrial site
near Bologna (Italy). The experimental activity aims to determine a suitable
relationship between single pollutant components and the hydrological response
of catchment related to this specific kind of anthropic activity. The experimental
catchment is part of a stocking area, run over every day by several trucks. The
watershed area is about 1.15 ha, almost completely impermeable, including a
parking area and charge-discharge zone for trucks and also a small part of the
warehouse building roofs. Storm water is collected by a small drainage system
into a first foul flush tank, whose useful volume is about 36 m3. In order to study
both hydraulic and water quality aspects, the site has been equipped with several
instruments, like an automatic sampler, rainfall gauge, submerged level sensor,
turbidity meter and a multiparametric probe. Rainfall data, tank water level and
turbidity have been recorded continuously for 8 months; during that period 57
rainfall events (> 1 mm) have taken place (total rainfall of 451mm). For five of
those events, samples were collected and analyzed obtaining TSS, COD, heavy
metals, toxicity and other parameters concentration. Results obtained from the
acute toxicity tests, carried out with Vibrio Fischeri on water samples collected
have exhibited some particular effects caused by the bio-ecological conditions of
runoff stormwater. An important issue comes from the lack of a clear linear
correlation between organic, inorganic pollutants and the toxicity percentage.
Keywords: experimental catchment, first flush, total suspended solids, toxicity,
[Show abstract][Hide abstract] ABSTRACT: Performance indicators implemented in a decision support system (DSS) for the technical, managerial and economic evaluation of urban drainage systems (UDS), called MOMA FD, are presented. Several kinds of information are collected and processed by MOMA FD to evaluate both present situation and future scenarios of development and enhancement. Particular interest is focused on the evaluation of the environmental impact, which is considered a very relevant factor in the decision making process to identify the priorities for UDS improvements.
No preview · Article · Feb 2005 · Water Science & Technology
[Show abstract][Hide abstract] ABSTRACT: One of the most effective solution for the control of river pollution is to introduce storages (i.e. tanks) in the sewerage system in order to retain at least a part of the storm waters and deliver it later to the treatment plant. However little effort has been spent in the assessment of the efficiency of multiple tanks patterns which may be constituted by gathering several subcatchment-storage systems in parallel, serial or dendritic layouts (fig.1).
The paper refers about situations studied on theoretical and experimental basis (on real urban pilot sites). The effect of water transfer among tanks, in terms of water volumes discharged to the environment, regulated by different local and centralised real time control techniques is also analysed.
The investigation is performed by fully dynamic numerical models for the simulation of hydrodynamic transport and diffusion phenomena in the sewerage system and in the receiving rivers. The models were previously calibrated on the basis of several field surveys. Results are available in terms of overflow volumes and frequencies and are being extended by considering also quality issues. Suspended sediments and other major pollution indicators are being modelled in order to determine directly the effectiveness of the different tank layouts.
To generalise achieved results, the study considers the effects of sewer overflows from the above mentioned system layouts on pollution of river reaches of different characteristics. The simulations cover different distribution of these overflows along the longitudinal axis of the river and provide a wide range of different impact scenarios.