Monitoring of carbamazepine concentrations in wastewater and groundwater to quantify sewer leakage.

Monitoring of carbamazepine concentrations in wastewater and groundwater enables us to identify and quantify sewer exfiltration. The antiepileptic drug carbamazepine is hardly removed in wastewater treatment plants and not or just slightly attenuated during bank infiltration and subsoil flow. Concentrations in wastewater are generally 1000 times higher than the limit of quantification. In contrast to . many other wastewater tracers carbamazepine is discharged to the environment only via domestic wastewater. The results from this study carried out in Linz, Austria indicate an average exfiltration rate of 1%, expressed as percentage of the dry weather flow that is lost to the groundwater on the city-wide scale. This rate is lower than sewage losses reported in most other studies which attempted to quantify exfiltration on the basis of groundwater pollution. However, it was also possible to identify one area with significantly higher sewage losses. This method seems to be very suitable for the verification of leakage models used to assess sewer exfiltration on a regional scale.     

Quantification of sewer exfiltration using the anti-epileptic drug carbamazepine as marker species for wastewater.

The anti-epileptic drug carbamazepine was used as marker species in wastewater to identify and quantify sewer exfiltration. In several studies carbamazepine turned out to be hardly removed in wastewater treatment and not or just slightly attenuated during bank infiltration. Concentrations in wastewater are generally 1000 times higher than the limit of quantification. In contrast to many other marker species a "young" drug as carbamazepine is discharged to the environment only by wastewater. The results from this study carried out in Linz, Austria indicate an average exfiltration rate, expressed as percentage of the dry weather flow that is lost on the city-wide scale, of 1%. This rate is lower than sewage losses reported in most other studies which attempted to quantify exfiltration on the basis of groundwater pollution. However, it was also possible to identify one area with significant higher sewage losses.     

Groundwater infiltration, surface water inflow and sewerage exfiltration considering hydrodynamic conditions in sewer systems

Sewer systems are closely interlinked with groundwater and surface water. Due to leaks and regular openings in the sewer system (e.g. combined sewer overflow structures with sometimes reverse pressure conditions), groundwater infiltration and surface water inflow as well as exfiltration of sewage take place and cannot be avoided. In the paper a new hydrodynamic sewer network modelling approach will be presented, which includes--besides precipitation--hydrographs of groundwater and surface water as essential boundary conditions. The concept of the modelling approach and the models to describe the infiltration, inflow and exfiltration fluxes are described. The model application to the sewerage system of the City of Dresden during a flood event with complex conditions shows that the processes of infiltration, exfiltration and surface water inflows can be described with a higher reliability and accuracy, showing that surface water inflow causes a pronounced system reaction. Further, according to the simulation results, a high sensitivity of exfiltration rates on the in-sewer water levels and a relatively low influence of the dynamic conditions on the infiltration rates were found.     

The effectiveness of selected microbial and chemical indicators to detect sewer leakage impacts on urban groundwater quality.

Sewer and stormwater pipe leakage can lead to the degradation of urban groundwater quality. This groundwater may be subsequently used for public water supply and so the resulting water treatment and public health consequences can be serious. To understand the impact of sewer exfiltration on groundwater quality, suitable indicators need to be sampled and analysed for. This study examined potential sewer-derived inorganic and microbial parameters in the U.K. city of Doncaster. Sulphite reducing clostridia, faecal streptococci and boron were all detected in groundwater with reductions compared with sewer values ranging from 1 to 6 orders of magnitude for the former two, to 1 to 2 orders of magnitude decrease for boron. The correlation between these two different indicator types suggests that groundwater quality is being adversely affected by sewer leakage in the study area. The employment of several and varied indicators can better demonstrate the effect than use of single parameters.     

A new sewage exfiltration model--parameters and calibration

Exfiltration of waste water from sewer systems represents a potential danger for the soil and the aquifer. Common models, which are used to describe the exfiltration process, are based on the law of Darcy, extended by a more or less detailed consideration of the expansion of leaks, the characteristics of the soil and the colmation layer. But, due to the complexity of the exfiltration process, the calibration of these models includes a significant uncertainty. In this paper, a new exfiltration approach is introduced, which implements the dynamics of the clogging process and the structural conditions near sewer leaks. The calibration is realised according to experimental studies and analysis of groundwater infiltration to sewers. Furthermore, exfiltration rates and the sensitivity of the approach are estimated and evaluated, respectively, by Monte-Carlo simulations.     

Quantification of sewer leakage by a continuous tracer method

Water authorities interested in the evaluation of the structural state of a sewer must quantify leakage to plan strategic intervention. However, the quantification of the exfiltration and the localisation of structural damage are challenging tasks that usually require expensive and time-consuming inspections. Herein, we report one of the first applications of the QUEST-C method to quantify the exfiltration in a continuously operating sewer by dosing two chemical tracers, sodium bromide (NaBr) and lithium chloride (LiCl). The method was applied at the catchment scale in a 14-year-old sewer in Rome, Italy. Preliminary laboratory tests, field measurements, and numerical simulations showed that reliable results require the QUEST-C method to be applied to sewers without lateral inflows, during periods of quasi-steady flow, and that the travel time of the NaBr tracer is minimised. Three sewer reaches were tested and the estimated exfiltration, as a fraction of the dry weather flow (DWF), increased from 0.128 in the agricultural area to 0.208 in the urban area. Although our estimates are at the lower end of the range given in the literature (0.01-0.56 DWF), the exfiltration was not negligible, and interventions should focus on the sewers in urban areas. This illustrates the capability of the QUEST-C method to guide strategic intervention at low cost and without an interruption of sewer operation. However, careful interpretation of the results is recommended for sewers with many lateral inflows, where leakage may be overestimated.     

Quantification of sewer leakage: a review.

One of the goals of the APUSS project (assessing infiltration and exfiltration on the performance of urban sewer systems) is to assess sewer exfiltration, in order to support cities and operators to define problem-oriented rehabilitation strategies. In this paper, we review various methods currently used for the estimation of exfiltration and discuss data needs and applicability for rehabilitation planning. Although each approach has its individual advantages and drawbacks, we identified pressure tests and tracer methods to have the highest potential for decision support in rehabilitation planning. With regard to future challenges (e.g., micropollutants) such methods might play a key role in integrated sewer management.     

Using decision analysis to determine optimal experimental design for monitoring sewer exfiltration with tracers.

The tracer methods developed to assess exfiltration from sewers in the European project APUSS (assessment of the performance of sewer systems) have a high degree of freedom with regard to the choice of tracer and the dosing strategy. These can lead to very different degrees of uncertainty in the measured exfiltration ratio. In this study, we demonstrate how to select an optimal experimental design using decision analysis, which accounts for this uncertainty and its associated costs. Although the results are site-specific, we can conclude generally that, when NaCl is used as the tracer, the accuracy of the exfiltration estimate is most sensitive to the amount of tracer used and the starting time of the experiment.     

Simulation of the wastewater temperature in sewers with TEMPEST.

TEMPEST is a new interactive simulation program for the estimation of the wastewater temperature in sewers. Intuitive graphical user interfaces assist the user in managing data, performing calculations and plotting results. The program calculates the dynamics and longitudinal spatial profiles of the wastewater temperature in sewer lines. Interactions between wastewater, sewer air and surrounding soil are modeled in TEMPEST by mass balance equations, rate expressions found in the literature and a new empirical model of the airflow in the sewer. TEMPEST was developed as a tool which can be applied in practice, i.e., it requires as few input data as possible. These data include the upstream wastewater discharge and temperature, geometric and hydraulic parameters of the sewer, material properties of the sewer pipe and surrounding soil, ambient conditions, and estimates of the capacity of openings for air exchange between sewer and environment. Based on a case study it is shown how TEMPEST can be applied to estimate the decrease of the downstream wastewater temperature caused by heat recovery from the sewer. Because the efficiency of nitrification strongly depends on the wastewater temperature, this application is of practical relevance for situations in which the sewer ends at a nitrifying wastewater treatment plant.     

Evaluation of sewer infiltration/inflow using COD mass flux method: case study in Prague

The combined sewer system of the City of Prague, similar to other relevant locations, is strongly affected by infiltrating waters. The knowledge of their volume is one of the important parameters with respect to sewer system operation, maintenance and reconstruction. The methodology is based on the variation of diurnal chemical oxygen demand (COD) load and continuous water quality monitoring using in-line absorption spectrometry. This approach allows the identification of individual components of the diurnal wastewater hydrograph, in particular the contribution of parasitic water flow to wastewater discharge. The statistical relevance was tested using Monte Carlo simulations on a 7-year data series of flow rate. The results show that application of this methodology provides specific relevant information about individual sub-catchments within an entire sewer system, particularly in terms of absolute and relative values of I/I and structural state indicators. Processing of long-term data series gives clear information about the significance of the monitoring period length for the relevance of obtained results.     

Aerobic transformations in sewer systems: are they relevant?

In-sewer transformation processes affect wastewater quality. Especially during dwf the transformation processes can exert a significant influence on wastewater quality. The transformation rates under aerobic conditions were estimated from an oxygen mass balance over a sewer reach. Oxygen probes were installed at the upstream and downstream end of the sewer reach. Moreover, 14 wastewater samples, taken at the downstream end of the sewer reach, were used to measure the oxygen uptake rate and the water quality parameters COD(total), COD(dissolved) and ammonium. The results show that the rate of fluctuations in COD concentrations in sewer systems is an order of magnitude higher than the aerobic transformation rate. Consequently, it is concluded that the aerobic transformations in sewer systems are generally not relevant with respect to the influent fluctuations for Dutch wastewater systems. However, in situations with very long aerobic transport times, the aerobic conversions can be significant. An ASM1 based model concept for transformations in sewer systems was used to study the applicability of the model for Dutch sewer conditions. The difference between the measured and simulated values was rather low for the range of upstream dissolved oxygen and COD(total), COD(dissolved) and COD(suspended) levels. Therefore, it is concluded that the ASM1 based sewer model properly describes the changes in dissolved oxygen level in an aerobic sewer reach.     

An integrated approach for improving the wastewater discharge and treatment systems

Since treatment plants have been built all over Germany during the last decades, the water quality of receiving streams has been improved remarkably. But there are still a lot of quality problems left, which are caused e.g. by combined sewer overflows (CSO), treatment plant effluents or rainwater discharges from separate sewer systems. At present different efforts are undertaken to control sewer systems in order to improve the operation of urban drainage systems or more generally, design processes. The Emschergenossenschaft and Lippeverband (EG/LV) are carrying out research studies, which are focusing on a minimization of total emissions from sewer systems both from wastewater treatment plant (WWTP) effluents and from CSO. They consider dynamic interactions between rainfall, resultant wastewater, combined sewers, WWTP and receiving streams. Therefore, in an advanced wastewater treatment, a model-based improvement of WWTP operation becomes more and more essential, and consequently a highly qualified operational staff is needed. Some aspects of the current research studies are presented in this report. The need and the use of an integrated approach to combine existing model components in order to optimize dynamic management of combined sewer systems (CSS) with a benefit for nature are outlined.     

GIS-based applications of sensitivity analysis for sewer models

Sensitivity analysis (SA) evaluates the impact of changes in model parameters on model predictions. Such an analysis is commonly used when developing or applying environmental models to improve the understanding of underlying system behaviours and the impact and interactions of model parameters. The novelty of this paper is a geo-referenced visualization of sensitivity indices for model parameters in a combined sewer model using geographic information system (GIS) software. The result is a collection of maps for each analysis, where sensitivity indices (calculated for model parameters of interest) are illustrated according to a predefined symbology. In this paper, four types of maps (an uncertainty map, calibration map, vulnerability map, and design map) are created for an example case study. This article highlights the advantages and limitations of GIS-based SA of sewer models. The conclusion shows that for all analyzed applications, GIS-based SA is useful for analyzing, discussing and interpreting the model parameter sensitivity and its spatial dimension. The method can lead to a comprehensive view of the sewer system.     

Hydrogen sulfide emission in sewer networks: a two-phase modeling approach to the sulfur cycle.

Wherever transport of anaerobic wastewater occurs, potential problems associated with hydrogen sulfide in relation to odor nuisance, health risk and corrosion exist. Improved understanding of prediction of hydrogen sulfide emission into the sewer atmosphere is needed for better evaluation of such problems in sewer networks. A two-phase model for emission of hydrogen sulfide along stretches of gravity sewers is presented to estimate the occurrence of both sulfide in the water phase and hydrogen sulfide in the sewer atmosphere. The model takes into account air-water mass transfer of hydrogen sulfide and interactions with other processes in the sulfur cycle. Various emission scenarios are simulated to illustrate the release characteristics of hydrogen sulfide.     

The hydraulic capacity of deteriorating sewer systems.

Sewer and wastewater systems suffer from insufficient capacity, construction flaws and pipe deterioration. Consequences are structural failures, local floods, surface erosion and pollution of receiving waters bodies. European cities spend in the order of five billion Euro per year for wastewater network rehabilitation. This amount is estimated to increase due to network ageing. The project CARE-S (Computer Aided RE-habilitation of Sewer Networks) deals with sewer and storm water networks. The final project goal is to develop integrated software, which provides the most cost-efficient system of maintenance, repair and rehabilitation of sewer networks. Decisions on investments in rehabilitation often have to be made with uncertain information about the structural condition and the hydraulic performance of a sewer system. Because of this, decision-making involves considerable risks. This paper presents the results of research focused on the study of hydraulic effects caused by failures due to temporal decline of sewer systems. Hydraulic simulations are usually carried out by running commercial models that apply, as input, default values of parameters that strongly influence results. Using CCTV inspections information as dataset to catalogue principal types of failures affecting pipes, a 3D model was used to evaluate their hydraulic consequences. The translation of failures effects in parameters values producing the same hydraulic conditions caused by failures was carried out through the comparison of laboratory experiences and 3D simulations results. Those parameters could be the input of 1D commercial models instead of the default values commonly inserted.     

Integrated modelling for the evaluation of infiltration effects.

The objective of the present study is the estimation of the potential benefits of sewer pipe rehabilitation for the performance of the drainage system and the wastewater treatment plant (WWTP) as well as for the receiving water quality. The relation of sewer system status and the infiltration rate is assessed based on statistical analysis of 470 km of CCTV (Closed Circuit Television) inspected sewers of the city of Dresden. The potential reduction of infiltration rates and the consequent performance improvements of the urban wastewater system are simulated as a function of rehabilitation activities in the network. The integrated model is applied to an artificial system with input from a real sewer network. In this paper, the general design of the integrated model and its data requirements are presented. For an exemplary study, the consequences of the simulations are discussed with respect to the prioritisation of rehabilitation activities in the network.     

Factors influencing exfiltration processes in sewers.

Exfiltration from sewers is widespread and emerging legislation may require water service providers to identify, and rectify, its sources in sewerage systems. This paper describes exfiltration test apparatus and a series of experiments undertaken using sewage to gain a better understanding of the influence of sewage solids and sediments on leakage rates. An overview of the results obtained is given, which demonstrates that most previous estimates of exfiltration leakage rates were too high due to a lack of appreciation of the "self-repairing" action of sewage and sewage associated solids. Exfiltration rates of 0.1% of the sewer flow or 0.001 I/s have been recorded for defects up to 6 mm wide.     

Dynamics of rain-induced pollutographs of solubles in sewers.

When looking at acute receiving water impacts due to combined sewer overflows the characteristics of the background diurnal sewage flux variation may influence the peak loads from combined sewer overflows (CSO) and wastewater treatment plant (WWTP) effluent significantly. In this paper, effects on the dynamic compounds transported in the sewer, on CSO discharges and WWTP loading are evaluated by means of hydrodynamic simulations. The simulations are based on different scenarios for diurnal dry-weather flow variations induced by different infiltration rates.     

ArcEGMO-URBAN--hydrological model for point sources in river basins.

The new model ArcEGMO-URBAN aims at deterministic and spatiotemporal modelling of water, nitrogen and phosphorus fluxes from all urbanised areas of a river basin considering all potential sources. Pollution loads are calculated for discrete urban patches and balanced on the level of hydrological subbasins. Modelling results can be defined by the user of any level of spatial and/or temporal aggregation, e.g. matter balances for river basins or river sections and years or months, respectively. To process spatial data, a Geographic Information System is linked to the model. Information on urban land use and general characteristics of river basins is based on digital coverages, partly generated from remote-sensing data. Moreover, statistical data, e.g. on population, sewer systems, wastewater treatment plants etc. are included. Stormwater runoff from impervious surfaces is calculated as one input to the sewer network. Wastewater is considered with its main sewer system, pumping stations and treatment plants. Finally, the discharge is balanced for discrete river sections. Modelling results attest ArcEGMO-URBAN its ability to realistically quantify matter fluxes and major pollution sources as well as their seasonal variation. This makes the model an applicable tool for the analysis of scenarios with e.g. varying population distribution or climatic and technological conditions.