Urban Water最新文献

Detention tanks are frequently used in today's urban stormwater management. It is a recognized fact that these structures are efficient in order to reduce the frequency of flooding. By settling suspended solids and specific particle pollutants, detention tanks also may contribute to reduce pollutant loads discharged into the receiving waters. However, some recent studies report the measured event removal performance of tanks functioning with permanent outflow (online) to be quite low and relatively variable from one site to another. Even if the studies do not refer to it, the measured performance is probably impaired by considerable uncertainty. The aim of this paper is to ascertain to which point uncertainty could explain the weakness and the variability of the measured performance. Initially, the theoretical formulation of relative uncertainty in the pollutant removal performance of any tank is given. Then, this relationship is applied to the case study of an online tank functioning with permanent outflow: the Vénissieux tank. Some original methods are presented in order to assess uncertainty components. Final results obtained show that absolute uncertainty in the measured performance is far from negligible (between 13% and 37% whilst removal rates range between 25% and 73%). In conclusion, a coherent plan of action is proposed that can be used on other sites to reduce uncertainty to a minimum. A critical look is also taken at the general problem of uncertainty assessment.

Rainfall is the most important input for many hydrological and hydraulic design calculations. Ideally, long historical rainfall series should be used and a statistical analysis should be performed on the hydraulic results afterwards. In combination with the detailed models that are commonly used nowadays, this leads to huge calculation times. This research was set up in order to verify which kind of simplifications can be made with respect to the rainfall input. One must find an optimum between accuracy of the modelling results and calculation effort. This optimum can be different for different applications. The different types of rainfall simplifications which are considered here are composite design storms, short selected rainfall series and modified single storm events. In many cases the optimum is more likely a simplified model in combination with continuous long term simulations. Well-calibrated (physically based) simplified models can reach almost the same accuracy as the corresponding detailed models within a fraction of the calculation time. Furthermore, these simplified models are very useful in order to select or compose the proper rainfall input for detailed modelling.

Weekly water consumption data from 48 households in Kuwait were collected over a period of one year. Based on these data, the average per capita water consumption inside a house in Kuwait was estimated to be in the range 182–2018 l/d/person, with an average of 814 l/d/person. Linear regression and neural network models, fitted to the observed data, suggest dependence of the residential water consumption on the number of bathrooms and rooms in the residence, size of the attached garden, income level of the household, atmospheric temperature, relative humidity, and number of people in the residence.

In order to minimise storm water impact on receiving waters, mathematical models to simulate processes occurring in sewer systems are needed. The aim of this study is to propose a simple and reliable conceptual model for simulating suspended solids discharge during storm events. The model has been tested using experimental data acquired in Parco d'Orleans catchment, Palermo, in Fossolo catchment, Bologna, and in Milijakovac catchment, Belgrade. Results obtained show the need to extend the experimental investigations in order to obtain more reliable information about the washoff rate.

This paper provides a review of the numerous factors that have been recognised as influencing the structural stability of rigid sewer pipes in the field. A description of the general process of rigid sewer pipe deterioration and failure is provided and the factors influencing this process considered in three main groups, namely, construction features, local external factors and other factors. Areas of contention and uncertainty are identified, as well as deficiencies in current understanding. General suggestions are made regarding possible directions for future research.

An experimental catchment area was set up in the centre of Paris (France) so as to follow up the quality of wet weather flows from the entry to the exit of a combined sewer network. The distinctive characteristic of this site is its location in a town centre and the extent of the equipment used to monitor the water pollution over the whole length of its course through the catchment area. The results obtained show a change in quality between the runoff entering the sewer network and the combined storm water flow at the sewer's outlet, which cannot be explained only by the mixture with domestic wastewater. In particular, an increase was observed in the concentrations of suspended solids (SS), VSS, COD, BOD and Cu, in the proportion of pollutants linked to particles and in the characteristics of the particles. A calculation of the total masses going in and out of the sewer network during a rainfall event shows that the erosion of in-sewer pollution stocks is the main source of particles and of organic matter in wet weather flows, whereas heavy metals loads originated from roof runoff, due to the corrosion of metallic roofs. Particles eroded from the sewer sediments during rain events were found to be quite different from the particles of type A deposits and organic biofilms. Nevertheless, they have mean organic and metallic loads that are of the same order of magnitude as the particles of the organic layer at water sediment interface. A change in the chemical form of heavy metals was noticed during the transport in the sewer and it is suspected that a fraction of the dissolved metals from the runoff is adsorbed on sewer sediments.

Sustainable development requires sustainable wastewater management (SWM). For this reason, strategies towards SWM have been formulated and discussed in the research literature during the past decade. System analysis has sometimes been used for simulation of different strategies for wastewater management, in order to compare sustainability aspects such as environmental impacts and usage of resources. This paper suggests strategies for SWM based on results from a Swedish environmental system analysis called Organic waste as a plant nutrient resource – system study, and from other studies with similar approaches. As a summary of the study, four strategies for SWM are suggested:

• 1.

  Handle nutrient-rich flows separately from other waste flows.

• 2.

  Recycle nutrients and use energy efficiently.

• 3.

  Avoid contamination of wastewater flows.

• 4.

  Put unavoidable pollution on landfill.

This study investigates the macromixing within a hydrodynamic vortex separator (HDVS). The device is a scale model of a prototype unit and is operated with zero baseflow. The device under investigation is typically used for the removal of settleable and colloidal solids. The macromixing is investigated by conducting tracer experiments from which the residence time distribution (RTD) is obtained and interpreted to characterise the mixing regime within the HDVS. The method of moments and non-linear regression are used to obtain various RTD functions and flow-model parameters to aid in the characterisation of the device's mixing regime and the degree of any non-ideal flow behaviour. The axial dispersion model (ADM) and tanks-in-series model (TISM) are used in this study. The RTD imperfectly approximates a plug-flow distribution but, the device has some amount of dispersion and is equal to approximately 2–3 perfectly stirred tanks in series. The ADM seems to give a closer representation of the experimental curves compared to the TISM. The sludge hopper appears to be acting as a stagnant zone.