[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.
[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
Journal of Environmental Engineering 07/2012; 138(7):723-733. · 1.40 Impact Factor
[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.
Journal of Hydroinformatics 01/2012; 14(2):310-323. · 1.15 Impact Factor
[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.
Water Science & Technology 01/2011; 65(1):15-21. · 1.10 Impact Factor
[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.
Advances in Engineering Software 05/2010; 41(5):792-801. · 1.22 Impact Factor
[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.
Water Science & Technology 01/2010; 61(1):207-15. · 1.10 Impact Factor
[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.
Environmental Modelling and Software 08/2007; 22(8):1221-1228. · 3.48 Impact Factor
[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.
Water Science & Technology 02/2005; 51(2):109-18. · 1.10 Impact Factor
[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.
8th International Conference on Urban Storm Drainage, Sydney, Australia; 01/1999