1,721,655 research outputs found
Data mining application in assessment of weather-based influent scenarios for a WWTP : getting the most out of plant historical data
Full text linkSince the introduction of environmental legislations and directives, the impact of combined sewer overflows (CSO) on receiving water bodies has become a priority concern in water and wastewater treatment industry. Time-consuming and expensive local sampling and monitoring campaigns are usually carried out to estimate the characteristic flow and pollutant concentrations of CSO water. This study focuses on estimating the frequency and duration of wet-weather events and their impacts on influent flow and wastewater characteristics of the largest Italian wastewater treatment plant (WWTP) located in Castiglione Torinese. Eight years (viz. 2009–2016) of historical data in addition to arithmetic mean daily precipitation rates (PI) of the plant catchment area are elaborated. Relationships between PI and volumetric influent flow rate (Qin), chemical oxygen demand (COD), ammonium (N-NH4), and total suspended solids (TSS) are investigated. A time series data mining (TSDM) method is implemented with MATLAB computing package for segmentation of time series by use of a sliding window algorithm (SWA) to partition the available records associated with wet and dry weather events. According to the TSDM results, a case-specific wet-weather definition is proposed for the Castiglione Torinese WWTP. Two significant weather-based influent scenarios are assessed by kernel density estimation. The results confirm that the method suggested within this study based on plant routinely collected data can be used for planning the emergency response and long-term preparedness for extreme climate conditions in a WWTP. Implementing the obtained results in dynamic process simulation models can improve the plant operational efficiency in managing the fluctuating loads
Modelling of methane production and emissions
No full textThis chapter provides a review of the models available for estimating the production and emission of methane from wastewater collection and treatment systems. The details of a number of mechanistic models as well as the simplified empirical models have been summarized. Their limitations have been identified and general methods for calibration and validation have been presented.BT/Environmental Biotechnolog
Different settling regimes in secondary settling tanks : experimental process analysis, model development and calibration
Full text linkNext generation bioreactor models for wastewater treatment systems by means of detailed combined modelling of mixing and biokinetics
Full text linkWastewater treatment plants (WWTP) are needed to treat municipal wastewater to reduce the impact of pollutants on the environment and the ambient nature. The discharge of treated wastewater and the disposal of sludge from treatment plants treating domestic or industrial wastewater are subject to regulations imposed by the authorities. Moreover, during the wastewater treatment process greenhouse gas emissions are produced. These emissions from WWTPs are a matter of growing concern.
The increased importance of wastewater treatment has led to development of mathematical models for optimization and design of wastewater treatment plants. WWTP modelling entails the modelling of the biological reactions (biokinetics) and underlying flow physics of the bioreactors (hydrodynamics). Currently, to model the hydrodynamics of a bioreactor, the tanks-in-series (TIS) modelling approach, which at best can model the flow variations in one direction, is widely used. These models assume a bioreactor as a series of completely mixed tanks and, hence, ignore any variation in the concentrations stemming from the design of a bioreactor or operational conditions. Therefore, these models eventually need rigorous calibration efforts to match measurements. This calibration is generally performed by manipulating kinetic parameters such as half saturation indices (K-values). The calibrated models are then used to assess or formulate different control strategies which includes the determination of an appropriate sensor location and a well-chosen setpoint for the controllers. In addition, the calibrated models are then extrapolated to predict the WWTP performance under different dynamic conditions (diurnal and dry/wet weather conditions) assuming that the flow patterns remain unchanged.
In this thesis, it is hypothesised and confirmed that the bioreactors are not at all completely mixed and, hence, current models wrongfully calibrate the kinetic parameters by correcting for the errors induced by the over-simplified modelling of mixing. Consequently, the need for re-calibration arises at different operational conditions due to the limitation of the current models to incorporate changes in operational conditions.
The thesis comprises of four parts. The first part provides the detailed account of CFD (computational fluid dynamics) modelling of WWTPs. Second part is about integration of CFD hydrodynamic models with the biokinetic models to evaluate the impact of mixing on the process performance. Third part is about model reduction, where detailed knowledge gained from the CFD-biokinetic modelling is used to develop simple but spatially localized compartmental model. The fourth part provides the insight about impact of mixing on the TIS model calibrations.
In the first part, detailed CFD hydrodynamic modelling of a bioreactor of Eindhoven WWTP is performed. The impact of reactor configuration and process conditions on gas dispersion is observed. Potential regions of poor mixing are identified. The different flow patterns are discussed in detail. Similarly, hydrodynamic modelling of an oxidation ditch (OD) of La Bisbal d’Empordà WWTP is performed. The OD is equipped with four surface aerators (rotors). The impact of 2-rotor and 4-rotor strategy on the flow patterns is observed and discussed in detail.
In the second part, the CFD hydrodynamic model of Eindhoven WWTP is extended by integrating it with bio-kinetic models, firstly with ASM1 and secondly with ASMG1. The impact of local mixing conditions on the dissolved oxygen (DO) and ammonium concentrations is observed and described. Regions of poor mixing are observed and hence their impact on overall process heterogeneity is discussed. The impact of DO variations on the nitrous oxide concentrations is also observed and it is shown that low DO concentrations tend to increase the nitrous oxide production. Similarly, the OD is also extended with a bio-kinetic model i.e. the ASM1 model. It is observed that the surface aerators have an inherent operational limitation and the DO concentrations at the bottom are very low (nearly anoxic).
In the third part, the compartmental modelling (CM) was setup based on the DO concentrations using CFD-biokinetic model. A novel idea of cumulative species distribution (CSDs) to quantify the variations is introduced here as well. The CSDs serve as a decision support tool for the CM. A detailed stepwise procedure for the compartmentalisation is provided. Based on the procedure, the CMs are developed for both case studies. The CMs are also developed for different conditions and it is found that the CM network is different under varying conditions. Therefore, an idea of dynamic compartmental model is suggested at the end. Furthermore, this part also illustrates the impact of sensor location on the controller performance using a compartmental model. It is found that the controller’s performance highly depends on the sensor location and setpoint. An optimal sensor location can improve the effluent quality at reduced cost.
In the last part, the impact of mixing on a CSTR based model calibration is shown. It is shown that the TIS models predict different estimated values under different mixing conditions. Therefore, it is important to take into account the mixing conditions before performing calibrations. The impact of sensor locations on the TIS model calibrations is also shown. The TIS model calibrations vary significantly if the sensor location for data collection are changed.
It is concluded that this thesis has demonstrated the ability of CFD-biokinetic modelling to evaluate the process more accurately. Tthe derivation of a compartmental model has also provided the solution of high computational demands, commonly attributed to CFD modelling
Understanding hydrodynamics in membrane bioreactor systems for wastewater treatment: two-phase empirical and numerical modelling and experimental validation
Full text linkDevelopment and application of a framework for model structure evaluation in environmental modelling
Full text linkIn a fast developing world with an ever rising population, the pressures on our natural environment are continuously increasing, causing problems such as floods, water- and air pollution, droughts,... Insight in the driving mechanisms causing these threats is essential in order to properly mitigate these problems. During the last decades, mathematical models became an essential part of scientific research to better understand and predict natural phenomena.
Notwithstanding the diversity of currently existing models and modelling frameworks, the identification of the most appropriate model structure for a given problem remains a research challenge. The latter is the main focus of this dissertation, which aims to improve current practices of model structure comparison and evaluation. This is done by making individual model decisions more transparent and explicitly testable.
A diagnostic framework, focusing on a flexible and open model structure definition and specifying the requirements for future model developments, is described. Methods for model structure evaluation are documented, implemented, extended and applied on both respirometric and hydrological models. For the specific case of lumped hydrological models, the unity between apparently different models is illustrated. A schematic representation of these model structures provides a more transparent communication tool, while meeting the requirements of the diagnostic approach
Model refinements in view of wastewater treatment plant optimization : improving the balance in sub-model detail
Full text linkWater is a very vulnerable resource and needs to be protected. In order to optimise wastewater treatment technology, we need to better understand the processes taking place in them. Mathematical modelling is a powerful tool to build knowledge about complex processes as it can exploit the power of computation. In this work wastewater treatment plant process optimization was pursued through the development of new models. In order to describe/model a WWTP it is mandatory to describe all of the processes in a sufficiently detailed manner (i.e. not overly complex nor oversimplified). Indeed, it does not make sense to use an overly detailed bio-kinetic model including hundreds of components and to oversimplify hydraulics, chemical reactions, aeration or settling behaviour. At this point WWTP models consist of highly detailed bio-kinetic models but often lack detail of other critical processes (hydraulics, chemical processes, gas-liquid transfers, aeration, energy consumption…). Emphasis is given to sub processes that are known to have a large impact on the overall process performance, i.e. influent characterization, primary sedimentation, aeration and energy consumption. The gathered knowledge is a step forward towards improving the way we design and operate our wastewater treatment infrastructure
Modelling cooling and corrosion aspects of a cooling water cycle
No full textSchoon water en energie zijn uitputbare hulpbronnen die op een optimale manier moeten worden gebruikt. De beschikbaarheid van waterbronnen wordt beïnvloed door grootschalig waterverbruik en de lozing van giftige chemicaliën door de industrie. Daarnaast kan het minimaliseren van het energieverbruik de emissies verminderen die een duidelijke invloed hebben op het klimaat op aarde. Het koelwatersysteem van een productiefabriek verbruikt een grote hoeveelheid water. Het koelwatersysteem is nodig om ongewenste warmte-energie van productieprocessen op te vangen en af te geven aan de omgeving. Open recirculerende koelwatersystemen hergebruiken het koelwater binnen het circuit, in plaats van continu grote hoeveelheden water te onttrekken aan nabijgelegen waterbronnen. Koeltorens zorgen ervoor dat bijna 2% van het koelwater verdampt, waardoor de warmte-energie vrijkomt en de temperatuur daalt, en waardoor het koelmedium wordt geregenereerd. Een makeup waterstroom vult koelwater aan voor het systeem, terwijl een blowdownstroom de ophoping van corrosieve ionen in het systeem voorkomt. Productie-installaties proberen behandeld afvalwater te hergebruiken als makeup water. Dit verhoogt echter het corrosiepotentieel van het koelwater. Corrosieremmers worden toegevoegd om de corrosiesnelheid van metalen onderdelen van het koelwatersysteem te minimaliseren. Het is belangrijk om het gebruik van giftige chemicaliën te verminderen en er tegelijkertijd voor te zorgen dat de corrosiekosten worden geminimaliseerd.
In dit proefschrift worden twee problemen behandeld: 1) Hoe kan de energie-efficiëntie van het koelwatersysteem worden gemaximaliseerd? 2) Hoe kunnen de doseringen van meerdere corrosie-inhibitoren die aan het systeem worden toegevoegd worden geoptimaliseerd, terwijl het totale chemicaliënverbruik en de corrosiesnelheid worden geminimaliseerd?
De koeltoren verbruikt de meeste energie door de werking van pompen en ventilatoren. Er werd een model ontwikkeld om de koelwateruittredetemperatuur en het koelwaterdebiet van een koeltoren te voorspellen. Het model werd gebruikt om de werking van de ventilatoren te optimaliseren zodat de energie-efficiëntie wordt gemaximaliseerd. De modelontwikkeling en -optimalisatie werd uitgevoerd voor twee typen koeltorens: koeltorens met geïnduceerde trek en koeltorens met hybride trek.
Optimalisatie van de dosering van corrosieremmers wordt gewoonlijk uitgevoerd door de efficiëntie van de corrosieremming te meten met electrochemical impedance spectroscopie en potentiodynamische polarisatie. Lineaire polarisatieweerstandsmetingen (LPR) zijn goedkoper en worden regelmatig online gemeten. De corrosiesnelheid is niet zo direct gerelateerd aan de dosering van corrosieremmers als de inhibitie-efficiëntie. De relatie tussen corrosieremmers en de corrosiesnelheid zou verkeerd kunnen worden weergegeven door het model, afhankelijk van de Sobol gevoeligheid van remmers of de (non)lineariteit van het model, zoals aangetoond in deze studie.
Er werden dus twee hybride modellen ontwikkeld voor twee doeleinden. Enerzijds werd een koeltorenmodel dat de temperatuur en het debiet van het koelwater kan voorspellen, gebruikt om de energie-efficiëntie van de koeltoren te maximaliseren. Anderzijds werd een hybride model gebaseerd op een aanpassing van de Butler-Volmer vergelijking ontwikkeld voor het minimaliseren van het totale gebruik van corrosieremmers en het minimaliseren van de corrosiesnelheid
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