... 1136 J. Dudley The comparison between measured and predicted masstransfer coefficients is ...... more ... 1136 J. Dudley The comparison between measured and predicted masstransfer coefficients is ... JH (1984) Correction factors for the dynamic measurement of the volumetric mass transfercoefficient. ... APPENDIX A The calculation procedure adopted was, given the air flowrate: I ...
The conventional way to estimate the performance of an operational aerator is onerous. The proces... more The conventional way to estimate the performance of an operational aerator is onerous. The process involves isolating the aerator from incoming flow; switching the aerator off briefly to allow the dissolved oxygen levels to fall; restarting the aerator; and, monitoring the rate of dissolved oxygen increase to then estimate the mass transfer rate of the aerator, and from that the aeration efficiency. A Kalman filter is a technique for estimating the aerator performance in-situ, without the need for isolating the tank or changing operational settings. The filter provides estimates of the respiration rate and oxygen transfer rate. If there are additional power measurements then the aeration efficiency can also be estimated. The technique was evaluated at four wastewater treatment plants, with the results compared against conventional reaeration tests. The direct measurement of bubble sizes provides additional information on performance that the filter approach can miss. A new measuring...
Sedran et al. (2006) determined the required aerobic reactor volume to achieve 1 mgN/L effluent a... more Sedran et al. (2006) determined the required aerobic reactor volume to achieve 1 mgN/L effluent ammonia in a nitrifying plant, using three commercial simulators (BioWin, GPS-X and Plan-It-Stoat). The paper reports significant differences between the required reactor volumes calculated by different packages using several activated sludge models in each. The authors were unable to find an explanation for these differences. In one scenario of their investigation, Sedran et al. (2006) aimed to ensure that the same models were used, with the same parameters and the same influent data, and still obtained different results from the three packages. This result implies that modeling is an unreliable tool to support wastewater treatment design. The aim of this paper is to clarify some of the questions raised, and provide advice to users of simulation packages to obtain sound process predictions using their simulators. Three simulation companies participated in this study, and all three simula...
Discussion of the reaction models and rate equations commonly used to describe the in situ combus... more Discussion of the reaction models and rate equations commonly used to describe the in situ combustion process, along with the effects of using only a few pseudo-components to represent the many components in crude oil. The theoretical advantages of using combustion tubes to determine kinetic parameters for the in situ combustion process are outlined. Existing approaches to using combustion tubes for this purpose are reviewed and a unification of the methods of Adewusi and Thomas et al. is presented. The results of this method are given, along with a short critique of the role of rate equations in numerical simulation work
The common view of chemical phosphorus removal is an equilibrium reaction between phosphate and i... more The common view of chemical phosphorus removal is an equilibrium reaction between phosphate and iron or aluminium, resulting in the precipitation of a metal phosphate complex. A comprehensive model based on this was developed by Jenkins and Hermanowicz (1993). This view has been replaced by an alternative interpretation (surface complexation modelling), where the dominant mechanism at typical wastewater pH values is the precipitation of iron or aluminium hydroxide, with subsequent phosphate adsorption onto the hydroxide surface (Takács et al., 2006, 2011; Smith et al., 2008a, 2008b, 2011; Szabó et al. 2008) and has been accorded the status of the current best understanding of chemical phosphorus removal (WERF, 2008; WEF, 2008). The Smith model has been extended to include the effects of alkalinity and sulphide on precipitation, competition for hydroxide surface by COD, the inclusion of temperature sensitivity, and the inclusion of pH as a calculated output. WRc, supported by UK wate...
Factorial experimental designs can be used when investigating the effects of more than one factor... more Factorial experimental designs can be used when investigating the effects of more than one factor on the in situ combustion process. The factorial design readily permits investigation of interactions between the factors, and allows some compensation for the effect of experimental error. This is illustrated inter alia by an analysis of twelve combustion tube experiments. A factorial design on oxygen partial pressure, mole fraction and flowrate, and the subsequent statistical analysis, demonstrated that the oxygen partial pressure had no statistically significant effect on any reaction parameter for the limited range and modest pressures employed. The combustion time was dominated by the oxygen flowrate, as were the global reaction rates. Fuel and oxygen consumption depended mainly on the oxygen mole fraction
EXTENDED ABSTRACT Catchment-level modelling has been regarded, since at least the middle 1980s, a... more EXTENDED ABSTRACT Catchment-level modelling has been regarded, since at least the middle 1980s, as a necessary part of providing integrated solutions for improving water quality in receiving waters. However, the tools that have been available to support this level of modelling have not made such modelling convenient. Typically there has been no support for data exchange between different vendors, and different classes of model (e.g., rivers, sewers and sewage works) have used different water quality parameters in their assessment. The purpose of the OpenMI has been to provide a first level of greater ease of data exchange between different programs, by removing the barrier of exchanging data between different programs. The OpenMI has also provided mechanisms to simplify exchanging quantities between different programs – for example, should one program expect flow in US units, and another in cumecs, simple transformations can be defined to ensure that each program can convert the dat...
This paper describes a numerical procedure for estimating differential mass and energy profiles a... more This paper describes a numerical procedure for estimating differential mass and energy profiles along a combustion tube. The technique solves the governing differential equations using a simple finite-difference procedure. The predicted combustion front location shows good agreement with that estimated from experimental temperature profiles.
Al~tract-The standard equations for aerator testing assume that the entire test tank is aerated. ... more Al~tract-The standard equations for aerator testing assume that the entire test tank is aerated. In a typical oxidation ditch the direct aerated volume is a small part of the entire tank, invalidating the assumptions behind these equations. A simple modification is proposed to correctly model the hydraulics and aeration configuration of an oxidation ditch.
This paper reviews the developments in process modelling, and outlines the benefits of dynamic mo... more This paper reviews the developments in process modelling, and outlines the benefits of dynamic modelling compared to steady-state modelling. The alternative uses of modelling, for design, operation and training, are included. The models covered are the COD-based models from the IAWQmodels #1 and #2 and WRc's BOD-based model. The relevance of BOD modelling for practitioners, rather than academics, is discussed, and likely routes for the future development are presented. The authors' practical experience using these models, principally under WRc's STOAT software, is also presented in the form of case studieshighlighting the experience of sampling programmes, calibration, validation and the continuing importance of the engineer's role.
The Halifax process was first proposed as a means of minimising the bulking of activated sludge. ... more The Halifax process was first proposed as a means of minimising the bulking of activated sludge. In one system using this process, bulking continued to OCCUI: An analysis of the process, using dynamic modelling fools, predicted that the process contains the potential for effluent quali@ to become worse as the hydraulic loading to the process is reducedcontrary to common experience with more conventional layouts.
Journal of Water Supply: Research and Technology—AQUA, 2008
The EU-funded project, TECHNEAU, is intended (among other tasks) to develop a new water treatment... more The EU-funded project, TECHNEAU, is intended (among other tasks) to develop a new water treatment simulator, in part to implement new process models to be developed within TECHNEAU. Before beginning any software development there has been a review of existing water treatment simulators, to identify what would be needed for a new system. This review has identified that there has been little usage of water treatment modelling, with the two main objections being the quantity of data required to calibrate the models, and the fragility of the models when applied outside the calibration region.
... 1136 J. Dudley The comparison between measured and predicted masstransfer coefficients is ...... more ... 1136 J. Dudley The comparison between measured and predicted masstransfer coefficients is ... JH (1984) Correction factors for the dynamic measurement of the volumetric mass transfercoefficient. ... APPENDIX A The calculation procedure adopted was, given the air flowrate: I ...
The conventional way to estimate the performance of an operational aerator is onerous. The proces... more The conventional way to estimate the performance of an operational aerator is onerous. The process involves isolating the aerator from incoming flow; switching the aerator off briefly to allow the dissolved oxygen levels to fall; restarting the aerator; and, monitoring the rate of dissolved oxygen increase to then estimate the mass transfer rate of the aerator, and from that the aeration efficiency. A Kalman filter is a technique for estimating the aerator performance in-situ, without the need for isolating the tank or changing operational settings. The filter provides estimates of the respiration rate and oxygen transfer rate. If there are additional power measurements then the aeration efficiency can also be estimated. The technique was evaluated at four wastewater treatment plants, with the results compared against conventional reaeration tests. The direct measurement of bubble sizes provides additional information on performance that the filter approach can miss. A new measuring...
Sedran et al. (2006) determined the required aerobic reactor volume to achieve 1 mgN/L effluent a... more Sedran et al. (2006) determined the required aerobic reactor volume to achieve 1 mgN/L effluent ammonia in a nitrifying plant, using three commercial simulators (BioWin, GPS-X and Plan-It-Stoat). The paper reports significant differences between the required reactor volumes calculated by different packages using several activated sludge models in each. The authors were unable to find an explanation for these differences. In one scenario of their investigation, Sedran et al. (2006) aimed to ensure that the same models were used, with the same parameters and the same influent data, and still obtained different results from the three packages. This result implies that modeling is an unreliable tool to support wastewater treatment design. The aim of this paper is to clarify some of the questions raised, and provide advice to users of simulation packages to obtain sound process predictions using their simulators. Three simulation companies participated in this study, and all three simula...
Discussion of the reaction models and rate equations commonly used to describe the in situ combus... more Discussion of the reaction models and rate equations commonly used to describe the in situ combustion process, along with the effects of using only a few pseudo-components to represent the many components in crude oil. The theoretical advantages of using combustion tubes to determine kinetic parameters for the in situ combustion process are outlined. Existing approaches to using combustion tubes for this purpose are reviewed and a unification of the methods of Adewusi and Thomas et al. is presented. The results of this method are given, along with a short critique of the role of rate equations in numerical simulation work
The common view of chemical phosphorus removal is an equilibrium reaction between phosphate and i... more The common view of chemical phosphorus removal is an equilibrium reaction between phosphate and iron or aluminium, resulting in the precipitation of a metal phosphate complex. A comprehensive model based on this was developed by Jenkins and Hermanowicz (1993). This view has been replaced by an alternative interpretation (surface complexation modelling), where the dominant mechanism at typical wastewater pH values is the precipitation of iron or aluminium hydroxide, with subsequent phosphate adsorption onto the hydroxide surface (Takács et al., 2006, 2011; Smith et al., 2008a, 2008b, 2011; Szabó et al. 2008) and has been accorded the status of the current best understanding of chemical phosphorus removal (WERF, 2008; WEF, 2008). The Smith model has been extended to include the effects of alkalinity and sulphide on precipitation, competition for hydroxide surface by COD, the inclusion of temperature sensitivity, and the inclusion of pH as a calculated output. WRc, supported by UK wate...
Factorial experimental designs can be used when investigating the effects of more than one factor... more Factorial experimental designs can be used when investigating the effects of more than one factor on the in situ combustion process. The factorial design readily permits investigation of interactions between the factors, and allows some compensation for the effect of experimental error. This is illustrated inter alia by an analysis of twelve combustion tube experiments. A factorial design on oxygen partial pressure, mole fraction and flowrate, and the subsequent statistical analysis, demonstrated that the oxygen partial pressure had no statistically significant effect on any reaction parameter for the limited range and modest pressures employed. The combustion time was dominated by the oxygen flowrate, as were the global reaction rates. Fuel and oxygen consumption depended mainly on the oxygen mole fraction
EXTENDED ABSTRACT Catchment-level modelling has been regarded, since at least the middle 1980s, a... more EXTENDED ABSTRACT Catchment-level modelling has been regarded, since at least the middle 1980s, as a necessary part of providing integrated solutions for improving water quality in receiving waters. However, the tools that have been available to support this level of modelling have not made such modelling convenient. Typically there has been no support for data exchange between different vendors, and different classes of model (e.g., rivers, sewers and sewage works) have used different water quality parameters in their assessment. The purpose of the OpenMI has been to provide a first level of greater ease of data exchange between different programs, by removing the barrier of exchanging data between different programs. The OpenMI has also provided mechanisms to simplify exchanging quantities between different programs – for example, should one program expect flow in US units, and another in cumecs, simple transformations can be defined to ensure that each program can convert the dat...
This paper describes a numerical procedure for estimating differential mass and energy profiles a... more This paper describes a numerical procedure for estimating differential mass and energy profiles along a combustion tube. The technique solves the governing differential equations using a simple finite-difference procedure. The predicted combustion front location shows good agreement with that estimated from experimental temperature profiles.
Al~tract-The standard equations for aerator testing assume that the entire test tank is aerated. ... more Al~tract-The standard equations for aerator testing assume that the entire test tank is aerated. In a typical oxidation ditch the direct aerated volume is a small part of the entire tank, invalidating the assumptions behind these equations. A simple modification is proposed to correctly model the hydraulics and aeration configuration of an oxidation ditch.
This paper reviews the developments in process modelling, and outlines the benefits of dynamic mo... more This paper reviews the developments in process modelling, and outlines the benefits of dynamic modelling compared to steady-state modelling. The alternative uses of modelling, for design, operation and training, are included. The models covered are the COD-based models from the IAWQmodels #1 and #2 and WRc's BOD-based model. The relevance of BOD modelling for practitioners, rather than academics, is discussed, and likely routes for the future development are presented. The authors' practical experience using these models, principally under WRc's STOAT software, is also presented in the form of case studieshighlighting the experience of sampling programmes, calibration, validation and the continuing importance of the engineer's role.
The Halifax process was first proposed as a means of minimising the bulking of activated sludge. ... more The Halifax process was first proposed as a means of minimising the bulking of activated sludge. In one system using this process, bulking continued to OCCUI: An analysis of the process, using dynamic modelling fools, predicted that the process contains the potential for effluent quali@ to become worse as the hydraulic loading to the process is reducedcontrary to common experience with more conventional layouts.
Journal of Water Supply: Research and Technology—AQUA, 2008
The EU-funded project, TECHNEAU, is intended (among other tasks) to develop a new water treatment... more The EU-funded project, TECHNEAU, is intended (among other tasks) to develop a new water treatment simulator, in part to implement new process models to be developed within TECHNEAU. Before beginning any software development there has been a review of existing water treatment simulators, to identify what would be needed for a new system. This review has identified that there has been little usage of water treatment modelling, with the two main objections being the quantity of data required to calibrate the models, and the fragility of the models when applied outside the calibration region.
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