Papers by Lorenzo Benedetti
Water Science & Technology, 2013
This project aims at finding cost-efficient sets of measures to meet the Water Framework Directiv... more This project aims at finding cost-efficient sets of measures to meet the Water Framework Directive (WFD) derived goals for the Dommel River (The Netherlands). Within the project, both acute and long-term impacts of the urban wastewater system on the chemical and ecological quality of the river are studied with a monitoring campaign in the urban wastewater system (wastewater treatment plant and sewers) and in the receiving surface water system. An integrated model, which proved to be a powerful tool to analyse the interactions within the integrated urban wastewater system, was first used to evaluate measures in the urban wastewater system using the existing infrastructure and new real-time control strategies. As the latter resulted to be beneficial but not sufficient, this paper investigated the use of additional infrastructural measures to improve the system cost-effectively and have it meet the Directive's goals. Finally, an uncertainty analysis was conducted to investigate the impact of uncertainty in the main model assumptions and model parameters on the performance robustness of the selected set of measures. Apart from some extreme worst-case scenarios, the proposed set of measures turned out to be sufficiently robust. Due to the substantial savings obtained with the results of this project, the pay-back time of the whole monitoring and modelling work proved to be less than 5 months. This illustrates the power of mathematical modelling for decision support in the context of complex urban water systems.
Water Science & Technology, 2012
Application of activated sludge models (ASMs) to full-scale wastewater treatment plants (WWTPs) i... more Application of activated sludge models (ASMs) to full-scale wastewater treatment plants (WWTPs) is still hampered by the problem of model calibration of these over-parameterised models. This either requires expert knowledge or global methods that explore a large parameter space. However, a better balance in structure between the submodels (ASM, hydraulic, aeration, etc.) and improved quality of influent data result in much smaller calibration efforts. In this contribution, a methodology is proposed that links data frequency and model structure to calibration quality and output uncertainty. It is composed of defining the model structure, the input data, an automated calibration, confidence interval computation and uncertainty propagation to the model output. Apart from the last step, the methodology is applied to an existing WWTP using three models differing only in the aeration submodel. A sensitivity analysis was performed on all models, allowing the ranking of the most important parameters to select in the subsequent calibration step. The aeration submodel proved very important to get good NH(4) predictions. Finally, the impact of data frequency was explored. Lowering the frequency resulted in larger deviations of parameter estimates from their default values and larger confidence intervals. Autocorrelation due to high frequency calibration data has an opposite effect on the confidence intervals. The proposed methodology opens doors to facilitate and improve calibration efforts and to design measurement campaigns.
Proceedings of the Water Environment Federation, 2012
ABSTRACT Design guideline safety factors (SF) are based on the accumulated experience of the indu... more ABSTRACT Design guideline safety factors (SF) are based on the accumulated experience of the industry and account for the uncertainty and variability inherent in the wastewater treatment process. Models on the other hand, as implemented in most commercial simulators, do not explicitly account for uncertainty. This paper discusses how to deal with variability and uncertainty in an explicit way when using a dynamic model combined with uncertainty analysis to perform a post-project evaluation. Through the use of time series, the response of the design to the variability of key inputs can be captured in the dynamic model. In order to incorporate uncertainty, selected model parameters can be described with probability density functions (PDF). Scenario analysis can be used to simulate discreet operational conditions or events. Uncertainty can then be propagated to the dynamic model outputs with the use of Monte Carlo simulations. To test this approach, the upgrade of the Eindhoven WWTP (Waterboard De Dommel, The Netherlands) was selected as a case study. The project focused on how variability and uncertainty are incorporated in design guidelines and highlighted key issues linked to the inclusion of the sources of uncertainty in the calibrated model.
Water Science & Technology, 2013
Modeling of integrated urban water systems (IUWS) has seen a rapid development in recent years. M... more Modeling of integrated urban water systems (IUWS) has seen a rapid development in recent years. Models and software are available that describe the process dynamics in sewers, wastewater treatment plants (WWTPs), receiving water systems as well as at the interfaces between the submodels. Successful applications of integrated modeling are, however, relatively scarce. One of the reasons for this is the lack of high-quality monitoring data with the required spatial and temporal resolution and accuracy to calibrate and validate the integrated models, even though the state of the art of monitoring itself is no longer the limiting factor. This paper discusses the efforts to be able to meet the data requirements associated with integrated modeling and describes the methods applied to validate the monitoring data and to use submodels as software sensor to provide the necessary input for other submodels. The main conclusion of the paper is that state of the art monitoring is in principle sufficient to provide the data necessary to calibrate integrated models, but practical limitations resulting in incomplete data-sets hamper widespread application. In order to overcome these difficulties, redundancy of future monitoring networks should be increased and, at the same time, data handling (including data validation, mining and assimilation) should receive much more attention.
Proceedings of the Water Environment Federation, 2012
Water Science & Technology, 2013
While the general principles and modelling approaches for integrated management/modelling of urba... more While the general principles and modelling approaches for integrated management/modelling of urban water systems already present a decade ago still hold, in recent years aspects like model interfacing and wastewater treatment plant (WWTP) influent generation as complements to sewer modelling have been investigated and several new or improved systems analysis methods have become available. New/improved software tools coupled with the current high computational capacity have enabled the application of integrated modelling to several practical cases, and advancements in monitoring water quantity and quality have been substantial and now allow the collecting of data in sufficient quality and quantity to permit using integrated models for real-time applications too. Further developments are warranted in the field of data quality assurance and efficient maintenance.
This paper illustrates how a dynamic model can be used to evaluate a plant upgrade on the basis o... more This paper illustrates how a dynamic model can be used to evaluate a plant upgrade on the basis of post-upgrade performance data. The case study is that of the Eindhoven wastewater treatment plant upgrade completed in 2006. As a first step, the design process based on a static model was thoroughly analyzed and the choices regarding variability and uncertainty (i.e. safety factors) were made explicit. This involved the interpretation of the design guidelines and other assumptions made by the engineers. As a second step, a (calibrated) dynamic model of the plant was set up, able to reproduce the anticipated variability (duration and frequency). The third step was to define probability density functions for the parameters assumed to be uncertain, and propagate that uncertainty with the dynamic model by means of Monte Carlo simulations. The last step was the statistical evaluation and interpretation of the simulation results. This work should be regarded as a 'learning exercise' increasing the understanding of how and to what extent variability and uncertainty are currently incorporated in design guidelines used in practice and how model-based post-project appraisals could be performed.
At the WWTP of Oostende, operated by Aquafin, an advanced aeration control is installed, based on... more At the WWTP of Oostende, operated by Aquafin, an advanced aeration control is installed, based on online measurement of oxygen in the carrousel and of both nitrate and ammonium at the effluent of the activated sludge tanks. As the plant meets the discharge limits at all times, a model was set up to evaluate the possibilities to reduce the energy consumption of the plant without giving in on the effluent quality. Taking into account that the plant already has advanced aeration control, none of the scenarios showed an important gain in energy consumption without decreasing the effluent quality.
The present document presents in details the final state of Benchmark Simulation Model no. 1 (BSM... more The present document presents in details the final state of Benchmark Simulation Model no. 1 (BSM1). The model equations to be implemented for the proposed layout, the procedure to test the implementation and the performance criteria to be used are described, as well as the sensors and control handles. Finally open-loop and closed-loop results obtained with a Matlab-Simulink and a FORTRAN implementations are proposed.
Executive summary The availability of a common ground to describe uncertainty-related issues is n... more Executive summary The availability of a common ground to describe uncertainty-related issues is necessary to be able to systematically tackle them. The basic terminology consists of the definition of uncertainty: location (where can uncertainty hide? in model structure? parameters?), level (how bad is the knowledge we have? can we define probability distributions of quantities? do we know that we don't know about something?) and nature (is the phenomenon inherently variable? or can we reduce the uncertainty with more ...
This paper will introduce the CD4WC project and its first results after approximately 1.5 years f... more This paper will introduce the CD4WC project and its first results after approximately 1.5 years from its beginning.
Proceedings of the Water Environment Federation, 2009
Wastewater treatment plant control and monitoring can help to achieve good effluent quality, in a... more Wastewater treatment plant control and monitoring can help to achieve good effluent quality, in a complex, highly non-linear process. The Benchmark Simulation Model no. 2 (BSM2) is a useful tool to competitively evaluate plant-wide control on a long-term basis. A key component to characterise the system for control is outputparameter sensitivity. This paper brings the results of a global sensitivity analysis performed on the BSM2 model in its open loop version, by means of Monte Carlo (MC) experiments and linear regression. This study presents methods that were applied to make computationally demanding MC experiments on such a complex model feasible, by reducing the computation time for a single simulation and by setting low but sufficient number of runs for the MC experiments; it was found that 50 times the number of uncertain parameters was necessary. The most sensitive parameters turned out to be the design and operation parameters, followed by the wastewater treatment model parameters, while the adopted BSM2 evaluation criteria are rather insensitive to variations in sludge treatment models parameters. The results are verified on a closed loop version of BSM2, and allow future uncertainty analysis studies on BSM2 to be conducted on a smaller set of parameters and to focus the attention on the most critical parameters.
Uploads
Papers by Lorenzo Benedetti