The USEPA's distribution system water quality modelling program: a historical perspective

Hydraulic and water quality models have become widely used to understand both the hydraulic behaviour, and the fate and transport of contaminants in drinking water distribution systems. Research conducted by the United States (US) Environmental Protection Agency (EPA) played a major role in the development and application of hydraulic/water quality modelling in the United States and throughout the world. Eventually this research led to the development of EPANET, an integrated hydraulic/water quality model, and had a major influence on the implementation of the United States Safe Drinking Water Act (SDWA). The modelling research conducted by the US EPA has helped many drinking water utilities throughout the world alleviate public health threats due to the deterioration of water quality in drinking water networks. The US EPA has provided over 100 000 downloads of the EPANET software over the last 2 years.     

Towards quantification of uncertainty in predicting water quality failures in integrated catchment model studies

This paper describes the development and application of a method for estimating uncertainty in the prediction of sewer flow quantity and quality and how this may impact on the prediction of water quality failures in integrated catchment modelling (ICM) studies. The method is generic and readily adaptable for use with different flow quality prediction models that are used in ICM studies. Use is made of the elicitation concept, whereby expert knowledge combined with a limited amount of data are translated into probability distributions describing the level of uncertainty of various input and model variables. This type of approach can be used even if little or no site specific data is available. Integrated catchment modelling studies often use complex deterministic models. To apply the results of elicitation in a case study, a computational reduction method has been developed in order to determine levels of uncertainty in model outputs with a reasonably practical level of computational effort. This approach was applied to determine the level of uncertainty in the number of water quality failures predicted by an ICM study, due to uncertainty associated with input and model parameters of the urban drainage model component of the ICM. For a small case study catchment in the UK, it was shown that the predicted number of water quality failures in the receiving water could vary by around 45% of the number predicted without consideration of model uncertainty for dissolved oxygen and around 32% for unionised ammonia. It was concluded that the potential overall levels of uncertainty in the ICM outputs could be significant. Any solutions designed using modelling approaches that do not consider uncertainty associated with model input and model parameters may be significantly over-dimensioned or under-dimensioned. With changing external inputs, such as rainfall and river flows due to climate change, better accounting for uncertainty is required.     

Applying global sensitivity analysis to the modelling of flow and water quality in sewers

While several approaches for global sensitivity analysis (GSA) have been proposed in literature, only few applications exist in urban drainage modelling. This contribution discusses two GSA methods applied to a sewer flow and sewer water quality model: Standardised Regression Coefficients (SRCs) using Monte-Carlo simulation as well as the Morris Screening method. For selected model variables we evaluate how the sensitivities are influenced by the choice of the rainfall event. The aims are to i) compare both methods concerning the similarity of results and their applicability, ii) discuss the implications for factor fixing (identifying non-influential parameters) and factor prioritisation (identifying important parameters) and iii) rank the important parameters for the investigated model. It was shown that both methods lead to similar results for the hydraulic model. Parameter interactions and non-linearity were identified for the water quality model and the parameter ranking differs between the methods. For the investigated model the results allow a sound choice of output variables and rainfall events in view of detailed uncertainty analysis or model calibration. We advocate the simultaneous use of both methods for a first model assessment as they allow answering both factor fixing and factor prioritisation at low computational cost.     

Assessment of the integrated urban water quality model complexity through identifiability analysis

Urban sources of water pollution have often been cited as the primary cause of poor water quality in receiving water bodies (RWB), and recently many studies have been conducted to investigate both continuous sources, such as wastewater-treatment plant (WWTP) effluents, and intermittent sources, such as combined sewer overflows (CSOs). An urban drainage system must be considered jointly, i.e., by means of an integrated approach. However, although the benefits of an integrated approach have been widely demonstrated, several aspects have prevented its wide application, such as the scarcity of field data for not only the input and output variables but also parameters that govern intermediate stages of the system, which are useful for robust calibration. These factors, along with the high complexity level of the currently adopted approaches, introduce uncertainties in the modelling process that are not always identifiable. In this study, the identifiability analysis was applied to a complex integrated catchment: the Nocella basin (Italy). This system is characterised by two main urban areas served by two WWTPs and has a small river as the RWB. The system was simulated by employing an integrated model developed in previous studies. The main goal of the study was to assess the right number of parameters that can be estimated on the basis of data-source availability. A preliminary sensitivity analysis was undertaken to reduce the model parameters to the most sensitive ones. Subsequently, the identifiability analysis was carried out by progressively considering new data sources and assessing the added value provided by each of them. In the process, several identifiability methods were compared and some new techniques were proposed for reducing subjectivity of the analysis. The study showed the potential of the identifiability analysis for selecting the most relevant parameters in the model, thus allowing for model simplification, and in assessing the impact of data sources for model reliability, thus guiding the analyst in the design of future monitoring campaigns. Further, the analysis showed some critical points in integrated urban drainage modelling, such as the interaction between water quality processes on the catchment and in the sewer, that can prevent the identifiability of some of the related parameters.     

Influence of water and sediment quality on benthic biota in an acidified river

Water and sediment quality and benthic biota were investigated in all seasons during three years in the River Akagawa that receives the effluent from a mine drainage treatment plant at its upstream site. The upper reaches kept the low pH, the comparatively high concentrations of metals and a large amount of iron deposited on the riverbed. The predominant macroinvertebrates were Protonemura sp., Capnidae, Nemoura sp. and Chironomidae in the upper and middle reaches. In the lowest reaches, the community structure of the macroinvertebrate changed into Chironomidae, Trichoptera (Hydropsychidae) and Ephemeroptera (Baetis sp.) as the pH was increased. From the results of multivariate analyses, it was found that the restoration of pH and attached algae and the increase in the concentrations of nutrients and organic matter promoted the inhabitation of Chironomidae and Hydropsychidae, whereas the dissolved metals in the river water inhibited the inhabitation of these families. Moreover, the sedimentation of metals would cause a severe damage to the inhabitation of Hydropsychidae compared with that of Chironomidae.     

A decision support system for water quality issues in the Manzanares River (Madrid, Spain)

The Manzanares River, located in Madrid (Spain), is the main water supplier of a highly populated region, and it also receives wastewater from the same area. The effluents of eight Waste Water Treatment Plants (WWTPs) downstream of the river, which represent 90% of the flow in the middle and lower parts of the river, are the primary sources of water pollution. Although the situation has improved slightly in the last two years, the water in the river is highly polluted, making it uninhabitable for aquatic life. Water quality modelling is typically used to assess the effect of treatment improvements in water bodies. In this work, the GESCAL module of the Aquatool Decision Support System Shell was used to simulate water quality in the Manzanares River. GESCAL is appropriate for modelling in an integrated way water quality for whole water resources systems, including reservoirs and rivers. A model was built that simulates conductivity, phosphorous, carbonaceous organic matter, dissolved oxygen, organic nitrogen, ammonia, and nitrates. The period from October 2006 to September 2008 was selected for calibration due to the many treatment modifications that occurred during this time. An earlier and longer period, from October 2000 to September 2006, was used for validation. In addition, a daily model was used to analyse the robustness of the GESCAL model. Once the GESCAL model was validated, different scenarios were considered and simulated. First, different combinations of nutrient elimination among the different WWTPs were simulated, leading to the conclusion that investments have to focus on three of the proposed WWTPs. Moreover, these treatments will not be sufficient to maintain fish habitat conditions at all times. Additional measures, such as the increment of the flow in the river or oxygen injection, were simulated. Incrementing the flow of the Manzanares River has been shown to be an efficient means of increasing water quality, but this implies an increment in the risk of water scarcity situations in the Madrid water supply system.     

Adsorptive removal of veterinary antibiotics from water using an integrated photocatalyst (IPCA)

ABSTRACT

The synthesising of a novel catalyst known as the integrated photo-catalysts (IPCA) by impregnating activated carbon (AC) with titanium dioxide (TiO₂) particles by ultra-sonication was used. The kinetics of antibiotics removal using adsorption and photodegradation were monitored and modelled. The effects of photocatalyst concentration and solution pH were investigated. Maximum removal percentages for both AC and IPCA were above 50% for an initial concentration of 100 mg/L. Adsorption using AC and IPCA followed the Langmuir and Freundlich isotherms. Higher coefficients of correlation were obtained for the Langmuir isotherms for four of the antibiotics. With regard to the photodegradation, it was found that photocatalysis attained almost 100% degradation of the target contaminants. Complete degradation was achieved within half-lives of 60 to 102 minutes for all the compounds. Although both photo-catalysts effectively degraded the contaminants, the IPCA had the unique advantages of possessing both adsorptive and photocatalytic properties.     

An optimization model for water quantity and quality integrated management of an urban lake in a water deficient city

This paper presents an optimization model for water quantity and quality integrated management of an urban lake in a water deficient city. A representative water quantity and quality safeguard system served urban lake, including multi-source water supply facilities, recirculating water purification facilities and surplus water discharge facilities, is widely used in Chinese water deficient cities. Because it is complicated, any mismanagement will result in water quality deterioration, water waste and high operation cost. The presented model attempts to achieve the objectives of controlling water pollution, reducing economic cost and improving water utilization efficiency through an optimized operating water safeguard system. The model is applied to Qingjing Lake in Tianjin, China. Results show that the model plays a more positive role for water quantity and quality integrated management.     

Estimating the effect of water quality on surface water supplies

River quality models derived by regression analysis are often quick and cheap to produce. They can be used as a basis for forecasting river quality and to calculate the effects of water quality constraints on the operation of water supplies drawn from rivers and impoundments. Results for nitrate show that to operate intakes according to river quality is a poor method of controlling quality in impoundments.     

Comparison between a detailed and a simplified integrated model for the assessment of urban drainage environmental impact on an ephemeral river

The benefit of integrated analysis has been demonstrated in technical literature and it is also required by the EU Water Framework Directive 60/2000, which proposes a water-quality-orientated view of the whole urban drainage system and oversees new ways of assessing its performance. Integrated models, such as any complex modelling approach, often have prohibitive data availability requirements that reduce their applicability. Moreover, widely different approaches can be applied, ranging from simple conceptual models to complex physically based ones. In the present paper, two approaches have been compared using data from an experimental catchment in Bologna (Italy), which consists of a part of the Bologna sewer network and a reach of the Savena River. The paper shows how river modelling has the most relevant role in conditioning the overall response of the integrated approach. This behaviour is mainly attributable to the ephemeral characteristics of the river determining quality model parameter values much higher than those presented in literature for permanent rivers.     

Analysis of the QUESTOR water quality model using a Fourier amplitude sensitivity test (FAST) for two UK rivers

This paper presents the sensitivity analysis of a well-known in-stream water quality model, QUESTOR (QUality Evaluation and Simulation TOol for River systems) as applied to two rivers of contrasting land-use in the northeast of England: the 'rural' Ouse and the 'urban' Aire. The analysis employed a version of the Fourier Amplitude Sensitivity Test (FAST) that quantifies the contribution of changes in individual parameters and combination of parameters to the variance of the model output (here the Nash-Sutcliffe) in an efficient way. The quantification of the sensitivity of the model output to the parameters led to the identification of the most influential parameters. Differences between the Aire and the Ouse were found, reflecting their different water quality regime. Results highlighted the importance of interactions between two, or more, parameters on the model output. It led to question the one-at-a-time calibration method currently applied with QUESTOR and underlined the importance of including interactions between parameters in sensitivity analyses. Comparison of the relative influence of parameters versus input data showed contrasting results. In the urban system, the inputs from discharges (sewage treatment works and industrial effluents) were highly influential on model outputs and generally more important than the model parameters. For the rural river, the tributary discharges were most influential, but only at a similar or a lower level than the model parameters.     

Effect of phosphorus stripping on water chemistry and diatom ecology in an eastern lowland river

The effect of nutrient removal at Ashford sewage treatment works on the benthic diatom ecology of the River Stour was studied. This paper describes assemblages above and below the works both before and after phosphorus stripping was installed. Taxa typical of eutrophic conditions dominated all samples, including those upstream of the works, suggesting that the river was already eutrophic before receiving the sewage effluent. Once nutrient removal was installed, phosphorus concentrations measured downstream of the works were similar to those measured upstream; however, there was little change in the diatom flora. Analysis of chemical data collected from the site suggest that the river may be nitrogen-limited for part of the year, and that, even with phosphorus stripping installed, the river still exceeds the Environment Agency's proposed interim targets for phosphorus concentrations in a eutrophic river.     

The quality of drinking water prepared from bank-filtered river water in the Netherlands

The quality of raw water and drinking water was analysed at 18 sites in the Rhine delta in an integrated program with hydrological,chemical and toxicological parameters. About 600 different organic compounds have been detected,of which about 200 could be identified,and 400 more have been classified on the basis of their mass spectra. Lipophilic compounds with a log P(octanol/water) greater than 3.2 are adsorbed during the first few meters of the bank infiltration. More hydrophilic compounds are often not adsorbed and not removed by the currently used water purification systems,such as aeration and sand filtration.The presence of organohalogens was demonstrated with surrogate parameters,such as extractable and adsorbable organohalogen. All the samples tested were mutagenic in the Ames test with strain TA98 + S9 mix. Only part of the mutagenic activity was related to compounds originating from Rhine water.     

基于安全、生态、景观三要素的城市水系规划——以阜南新区水系整治规划为例

该文提出从城市安全、生态、景观三大格局出发,统一规划城市水系的防洪排涝功能、生态功能与景观功能。并以阜南新区水系整治规划为例,运用这三大规划策略与措施,构建满足安全、生态、景观三方面功能的城市水系格局,从而达到水城相融的效果,营造一个富于淮北水乡地域特色的阜阳城南新区。     

Sensitivity analysis of some critical factors affecting simulated intrusion volumes during a low pressure transient event in a full-scale water distribution system

Intrusion events caused by transient low pressures may result in the contamination of a water distribution system (DS). This work aims at estimating the range of potential intrusion volumes that could result from a real downsurge event caused by a momentary pump shutdown. A model calibrated with transient low pressure recordings was used to simulate total intrusion volumes through leakage orifices and submerged air vacuum valves (AVVs). Four critical factors influencing intrusion volumes were varied: the external head of (untreated) water on leakage orifices, the external head of (untreated) water on submerged air vacuum valves, the leakage rate, and the diameter of AVVs' outlet orifice (represented by a multiplicative factor). Leakage orifices' head and AVVs' orifice head levels were assessed through fieldwork. Two sets of runs were generated as part of two statistically designed experiments. A first set of 81 runs was based on a complete factorial design in which each factor was varied over 3 levels. A second set of 40 runs was based on a latin hypercube design, better suited for experimental runs on a computer model. The simulations were conducted using commercially available transient analysis software. Responses, measured by total intrusion volumes, ranged from 10 to 366 L. A second degree polynomial was used to analyze the total intrusion volumes. Sensitivity analyses of both designs revealed that the relationship between the total intrusion volume and the four contributing factors is not monotonic, with the AVVs' orifice head being the most influential factor. When intrusion through both pathways occurs concurrently, interactions between the intrusion flows through leakage orifices and submerged AVVs influence intrusion volumes. When only intrusion through leakage orifices is considered, the total intrusion volume is more largely influenced by the leakage rate than by the leakage orifices' head. The latter mainly impacts the extent of the area affected by intrusion.     

Monitoring of water quality from roof runoff: Interpretation using multivariate analysis

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Temperature, pH, conductivity, colour, turbidity, anions, cations, alkalinity, total hardness and total organic carbon were screened using standard analytical techniques. Total flora at 22 °C and 36 °C, total coliforms, Escherichia coli and enterococci were analysed. Overall, the collected rainwater had good physicochemical quality but did not meet the requirements for drinking water. The stored rainwater is characterised by low conductivity, hardness and alkalinity compared to mains water. Three widely used bacterial indicators - total coliforms, E. coli and enterococci - were detected in the majority of samples, indicating microbiological contamination of the water. To elucidate factors affecting the rainwater composition, principal component analysis and cluster analysis were applied to the complete data set of 50 observations. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. E. coli and enterococci occurred simultaneously, and their presence was linked to precipitation. Runoff quality is also unpredictable because it is sensitive to the weather. Cluster analysis differentiated three clusters: ionic composition, parameters linked with the microbiological load and indicators of faecal contamination. In future surveys, parameters from these three groups will be simultaneously monitored to more accurately characterise roof-collected rainwater.     

Application of an efficient search technique for solving optimal regional water quality management problems

This article presents a simple yet effective search algorithmic method for solving regional water quality management problems. Essentially, the algorithm assigns the amount of wastewater flow to be treated at each treatment plant together with the associated level of treatment. When necessary this set of assigned values is adjusted appropriately (by raising the treatment efficiency of. and/or reduction of wastewater quantity to be treated by the treatment plant concerned), so that all the physical and water quality constraints are satisfied. Optimization is achieved by the use of a Random Polyhedron Search (RPS) algorithm which identifies progressively superior solutions. The paper comprises two parts: the first, in which feasibility is confined to treatment plant/transfer capacities, and the second, in which constraints relating to the in-stream quality of the receiving water are incorporated.     

Evaluating online data of water quality changes in a pilot drinking water distribution system with multivariate data exploration methods

The distribution of drinking water generates soft deposits and biofilms in the pipelines of distribution systems. Disturbances in water distribution can detach these deposits and biofilms and thus deteriorate the water quality. We studied the effects of simulated pressure shocks on the water quality with online analysers. The study was conducted with copper and composite plastic pipelines in a pilot distribution system. The online data gathered during the study was evaluated with Self-Organising Map (SOM) and Sammon's mapping, which are useful methods in exploring large amounts of multivariate data. The objective was to test the usefulness of these methods in pinpointing the abnormal water quality changes in the online data. The pressure shocks increased temporarily the number of particles, turbidity and electrical conductivity. SOM and Sammon's mapping were able to separate these situations from the normal data and thus make those visible. Therefore these methods make it possible to detect abrupt changes in water quality and thus to react rapidly to any disturbances in the system. These methods are useful in developing alert systems and predictive applications connected to online monitoring.     

Impact of urban geometry on outdoor thermal comfort and air quality from field measurements in Curitiba,Brazil

Urban climate can have severe impacts on people who use outdoor spaces within a city. In its essence, urban climate is directly linked to the configuration of street axes, building heights and their attributes. Thus, the role of urban planners can be crucial for guaranteeing outdoor thermal comfort and air quality in open spaces. This paper presents observed and estimated relations between urban morphology and changes in microclimate and air quality within a city center. Two approaches are presented, showing results of field measurements and urban climate simulations using the ENVI-met software suite. From measured microclimatic data and comfort surveys, carried out in downtown Curitiba, Brazil, the impact of street geometry on ambient temperatures and on daytime pedestrian comfort levels was evaluated, using the sky-view factor (SVF) as indicator of the complexity of the urban geometry. The impact of street orientation relative to prevailing winds and the resulting effects of ventilation (air speed and spatial distribution) on the dispersion of traffic-generated air pollutants were additionally analyzed by means of computer simulations. Results show the impact of urban geometry on human thermal comfort in pedestrian streets and on the outcomes of pollutant dispersion scenarios.     

Impacts of rainfall events on runoff water quality in an agricultural environment in temperate areas

Since a rise in dissolved organic carbon (DOC) concentrations has been observed for surface waters at least over the last two decades, a change in weather conditions (temperature and precipitations) has been proposed to partly explain this increase. While the majority of DOC delivery from soils to stream occurs during rainfall events, a better understanding of the rainfall influence on DOC release is needed. This study has been conducted in Brittany, western France, on agricultural experimental plots receiving either cattle manure (CM) or pig slurry (PS) as fertilizers in accordance with local practices. Each plot was instrumented with a flow meter and an auto sampler for runoff measurements. The results show that export of DOC during high intensity events is higher than during lower intensity rainfalls. Fertilization has a noticeable impact on total organic carbon (TOC) fluxes with an increase of five to seven folds for PS and CM respectively. If TOC shock load occurs shortly after the rainfall peak, DOC maximum appears with the first flush of the event. Organic carbon (OC) is mainly under colloidal (41.2%) and soluble (23.9%) forms during the first stage of a rainfall event and a control of rainfall intensity on OC colloidal transport is suggested. These findings highlight the potential risk of receiving water quality degradation due to the increase of heavier rainfall events with climate change in temperate areas.