I. Takács - Academia.edu (original) (raw)
Papers by I. Takács
Water Science and Technology, 2001
A mathematical model, named A3DX, based on ASM3(A3) for C and N removal, on the bio-P metabolic m... more A mathematical model, named A3DX, based on ASM3(A3) for C and N removal, on the bio-P metabolic model of the Technological University of Delft (D), and on extra processes (X) for chemical and biological phosphorus removal, was developed and used to simulate the treatment of a fermented cheese factory effluent by a sequencing batch reactor (SBR). Experimental data obtained from a pilot-scale SBR were used to calibrate the model. The model calibration was performed by changing a minimal number (four) of default values for parameters, and by introducing a Monod function to account for magnesium limitation. This study suggests that the value of stoichiometric and kinetic model parameters determined with municipal effluents or enriched bio-P cultures can be reasonably used with some agro-industrial effluents with minimal parameter adjustment for calibration.
Water Research, 1985
Abstract Integrated biological systems such as activated sludge-powdered activated carbon [PAC] c... more Abstract Integrated biological systems such as activated sludge-powdered activated carbon [PAC] combinations are used in ever increasing numbers. For conventional activated sludge systems excellent models existed which presumably were also suitable for application to a PAC-fed system. PAC addition enhances bacterial activity, adsorption of dissolved organics and settleability of activated sludge flocs in the final clarifier. Simple laboratory experiments can demonstrate the degree of improvement in a PAC-fed system over the conventional activated sludge one. When using the present model the evaluation of several kinetic constants stemming from simple experiments may help to predict the performance of large scale operation even under unsteady state conditions.
Water Science and Technology, 2018
The wastewater industry is currently facing dramatic changes, shifting away from energy-intensive... more The wastewater industry is currently facing dramatic changes, shifting away from energy-intensive wastewater treatment towards low-energy, sustainable technologies capable of achieving energy positive operation and resource recovery. The latter will shift the focus of the wastewater industry to how one could manage and extract resources from the wastewater, as opposed to the conventional paradigm of treatment. Debatable questions arise: can the more complex models be calibrated, or will additional unknowns be introduced? After almost 30 years using well-known International Water Association (IWA) models, should the community move to other components, processes, or model structures like ‘black box’ models, computational fluid dynamics techniques, etc.? Can new data sources – e.g. on-line sensor data, chemical and molecular analyses, new analytical techniques, off-gas analysis – keep up with the increasing process complexity? Are different methods for data management, data reconciliat...
Proceedings of the Water Environment Federation, 2010
Many unit process models are available in the field of wastewater treatment. All of these models ... more Many unit process models are available in the field of wastewater treatment. All of these models use their own notation, causing problems for documentation, implementation and connection of different models (using different sets of state variables). The main goal of this paper is to propose a new notational framework which allows unique and systematic naming of state variables and parameters of biokinetic models in the wastewater treatment field. The symbols are based on one main letter that gives a general description of the state variable or parameter and several subscript levels that provide greater specification. Only those levels that make the name unique within the model context are needed in creating the symbol. The paper describes specific problems encountered with the currently used notation, presents the proposed framework and provides additional practical examples. The overall result is a framework that can be used in whole plant modelling, which consists of different fields such as activated sludge, anaerobic digestion, sidestream treatment, membrane bioreactors, metabolic approaches, fate of micropollutants and biofilm processes. The main objective of this consensus building paper is to establish a consistent set of rules that can be applied to existing and most importantly, future models. Applying the proposed notation should make it easier for everyone active in the wastewater treatment field to read, write and review documents describing modelling projects.
Water Science and Technology, 1986
Full-scale experiments were conducted to study the wastewater treatment plant of a chemical facto... more Full-scale experiments were conducted to study the wastewater treatment plant of a chemical factory. The objective of the study was to upgrade the overloaded biological activated sludge system by powdered activated carbon addition. Improvement of the organic micropollutant removal characteristics was also expected on the basis of previous experiments. During the three months experimental period the applicability and benefits of the process were proved, even under unfavourable conditions. Operation of the plant became stable, the quality of effluent improved about 30% in organic content and in several micropollutants. The upgraded unit could be overloaded by about 20% without any decrease in efficiency.
Proceedings of the Water Environment Federation, 2011
Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion... more Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion at very large utilities and can substantially reduce required digester volumes in space constrained large cities while also allowing for development of regionalized sludge receiving centers. In 2014, DC Water will begin operating a new solids processing train at the Blue Plains Advanced Wastewater Treatment Plant consisting of the CAMBI thermal hydrolysis process for solids pretreatment prior to mesophilic anaerobic digestion. A complete evaluation picture needs to take all impacts on downstream processes into account. The digestion performance at various solids loadings (collection of full-scale data); dewatering performance (full-scale belt-filter-press tests); sludge liquor treatment (DEMON-pilot); pathogen removal, odour issues and land application are discussed in the paper.
Water science and technology : a journal of the International Association on Water Pollution Research, 2015
This study describes the development of a modified activated sludge model No.1 framework to descr... more This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to pa...
Water Environment Research, 2008
Batch and continuous experiments using model and real wastewaters were conducted to investigate t... more Batch and continuous experiments using model and real wastewaters were conducted to investigate the effect of metal salt (ferric and alum) addition in wastewater treatment and the corresponding phosphate removal from a design and operational perspective. Key factors expected to influence the phosphorus removal efficiency, such as pH, alkalinity, metal dose, metal type, initial and residual phosphate concentration, mixing, reaction time, age of flocs, and organic content of wastewater, were investigated. The lowest achievable concentration of orthophosphate under optimal conditions (0.01 to 0.05 mg/L) was similar for both aluminum and iron salts, with a broad optimum pH range of 5.0 to 7.0. Thus, in the typical operating range of wastewater treatment plants, pH is not a sensitive indicator of phosphorus removal efficiency. The most significant effect for engineering practice, apart from the metal dose, is that of mixing intensity and slow kinetic removal of phosphorus in contact with the chemical sludge formed. Experiments show that significant savings in chemical cost could be achieved by vigorously mixing the added chemical at the point of dosage and, if conditions allow, providing a longer contact time between the metal hydroxide flocs and the phosphate content of the wastewater. These conditions promoted the achievement of less than 0.1 mg/L residual orthophosphate content, even at lower metal-to-phosphorus molar ratios. These observations are consistent with the surface complexation model presented in a companion paper (
Water Environment Research, 2008
A phosphate complexation model is developed, in an attempt to understand the mechanistic basis of... more A phosphate complexation model is developed, in an attempt to understand the mechanistic basis of chemically mediated phosphate removal. The model presented here is based on geochemical reaction modeling techniques and uses known surface reactions possible on hydrous ferric oxide (HFO). The types of surface reactions and their reaction stoichiometry and binding energies (logK values) are taken from literature models of phosphate interactions with iron oxides. The most important modeling parameter is the proportionality of converting moles of precipitated HFO to reactive site density. For well-mixed systems and phosphate exposed to ferric chloride during HFO precipitation, there is a phosphate capacity of 1.18 phosphate ions per iron atom. In poorly mixed systems with phosphate exposed to iron after HFO formation, the capacity decreased to 25% of the well-mixed value. The same surface complexation model can describe multiple data sets, by varying only a single parameter proportional to the availability of reactive oxygen functional groups. This reflects the unavailability of reactive oxygen groups to bind phosphate. Electron microscope images and dye adsorption experiments demonstrate changes in reactive surface area with aging of HFO particles. Engineering implications of the model/mechanism are highlighted. Water Environ. Res., 80, 428 (2008).
Proceedings of the Water Environment Federation
Chemical phosphorus removal using metal (iron and aluminium) salts is frequently used to control ... more Chemical phosphorus removal using metal (iron and aluminium) salts is frequently used to control effluent soluble phosphorus levels in wastewater treatment plants. In the Washington DC area effluent phosphorus requirements are extremely stringent to protect the Chesapeake Bay. Full-scale data from two plants in the area were analysed to establish phosphate behaviour in the presence of iron. Titration experiments and mathematical modelling were performed to determine the role of ferric phosphate and hydroxide precipitation and other mechanisms that may potentially be involved in phosphorus removal. Iron addition is described in the model using a chemical equilibrium approach extended with surface charges and adsorption. The model verifies key observations from full-scale data: (a) extremely low orthophosphate levels can be achieved over a wide range of pH values, (b) a mixture of ferric phosphate and ferric hydroxide precipitate is forming with the hydroxide acting as sorbent, (c) mo...
Current anaerobic digestion models cannot properly simulate processes that are operated under hig... more Current anaerobic digestion models cannot properly simulate processes that are operated under high solids concentrations or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these systems without artificially recalibrating the model parameters. Specifically, we implemented the alternate acetate oxidizing mechanism that is more tolerant to ammonia than the standard aceticlastic pathway. Inhibition values were estimated and an empirical function has been used to apply ammonia inhibition. The model also relates metabolic activity to un-ionised species such as undissociated acetic acid as substrate (although not obligatory for all organisms) and unionised ammonia as inhibitor. The model relies on an equilibrium chemistry module (e.g. including the phosphate buffer), resulting in more accurate pH predictions, which is crucial for proper modeling of CO2 and NH3 stripping. Calibration results from thre...
Process models used for activated sludge, anaerobic digestion and in general wastewater treatment... more Process models used for activated sludge, anaerobic digestion and in general wastewater treatment plant process design and optimization have traditionally focused on important biokinetic conversions. There is a growing realization that abiotic processes occurring in the wastewater (i.e. 'solvent') have a fundamental effect on plant performance. These processes include weak acid-base reactions (ionization), spontaneous or chemical dose-induced precipitate formation and chemical redox conversions, which influence pH, gas transfer, and directly or indirectly the biokinetic processes themselves. There is a large amount of fundamental information available (from chemical and other disciplines), which, due to its complexity and its diverse sources (originating from many different water and process environments), cannot be readily used in wastewater process design as yet. This position paper outlines the need, the methods, available knowledge and the fundamental approaches that would help to focus the effort of research groups to develop a physicochemical framework specifically in support of whole-plant process modeling. The findings are that, in general, existing models such as produced by the International Water Association for biological processes are limited by omission of key corrections such as non-ideal acid-base behavior, as well as major processes (e.g., ion precipitation). While the underlying chemistry is well understood, its applicability to wastewater applications is less well known. This justifies important further research, with both experimental and model development activities to clarify an approach to modeling of physicochemical processes.
The 1st IWA/WEF wastewater treatment modelling seminar (WWTmod2008) took place earlier this year ... more The 1st IWA/WEF wastewater treatment modelling seminar (WWTmod2008) took place earlier this year in Mont-Sainte-Anne, Quebec, Canada, organised in order to allow for debate and the presentation of ideas on this subject. Leiv Rieger, Peter A Vanrolleghem, Imre Takacs and Bruce R Johnson discuss the areas covered at the event.
Water Science and Technology, 1999
Proceedings of the Water Environment Federation, 2008
ABSTRACT Parametric models used in simulation software for the design of wastewater treatment pla... more ABSTRACT Parametric models used in simulation software for the design of wastewater treatment plants involve a number of processes and state variables that can be best represented in a matrix format (e.g. ASM1, ASM2D, ASM3, General ASDM). These models often use different symbols for identical variables and some models are becoming increasingly complex making it difficult to visualize the relationships between the various processes. A standardized notation is first proposed for the major current parametric models which is then used to draw schematic representations of these models. These schematics should constitute useful learning tools, that should facilitate comparisons between various models and provide a better appreciation of the potential and limitations of each model to ensure a better use of activated sludge models by design engineers.
Proceedings of the Water Environment Federation, 2009
ABSTRACT Process models for enhanced biological phosphorus removal systems are shown to predict a... more ABSTRACT Process models for enhanced biological phosphorus removal systems are shown to predict anaerobic behavior better than aerobic behavior. Reasons for this include the use of uncalibrated kinetic parameters as well as difficulties introduced by the choice of model structure. A modeling approach is proposed in which model structure and stoichiometric values for both the anaerobic and aerobic phase are based on accepted metabolic pathways and kinetic parameters are calibrated based on results from a batch experimental system. Based on the results for over 20 experimental continuous-flow systems fed with both acetate and sewage, it is demonstrated that this Proposed Model gives improved predictions of phosphorus removal.
Proceedings of the Water Environment Federation, 2010
ABSTRACT Nutrient assimilation was revisited using a steady state model developed from the activa... more ABSTRACT Nutrient assimilation was revisited using a steady state model developed from the activated sludge modeling concepts. While nitrogen assimilation is only related to organic particulate fractions, the role of inorganic complexes and precipitates was accounted for in phosphorus assimilation. It is shown that the influent aluminum background concentration may contribute significantly to phosphorus assimilation, and that in 3.6% of cases, calcium phosphate may precipitate in activated sludge.A global sensitivity analysis was conducted with the Monte Carlo method to identify the most sensitive model parameters and input variables. The nutrient content of the unbiodegradable mixed liquor fractions emerged as the most sensitive parameters and were calibrated using databases and some assumptions. Most of the remaining variability of nutrient assimilation then comes down to four variables (three influent concentration ratios and SRT), which were used to prepare charts to predict assimilation in design and operation. For an SRT of 20 days, it is proposed to update the typical empirical BOD5:N:P ratio from 100:5:1 to 100:5.7:1.4.
Water Science and Technology, 2001
A mathematical model, named A3DX, based on ASM3(A3) for C and N removal, on the bio-P metabolic m... more A mathematical model, named A3DX, based on ASM3(A3) for C and N removal, on the bio-P metabolic model of the Technological University of Delft (D), and on extra processes (X) for chemical and biological phosphorus removal, was developed and used to simulate the treatment of a fermented cheese factory effluent by a sequencing batch reactor (SBR). Experimental data obtained from a pilot-scale SBR were used to calibrate the model. The model calibration was performed by changing a minimal number (four) of default values for parameters, and by introducing a Monod function to account for magnesium limitation. This study suggests that the value of stoichiometric and kinetic model parameters determined with municipal effluents or enriched bio-P cultures can be reasonably used with some agro-industrial effluents with minimal parameter adjustment for calibration.
Water Research, 1985
Abstract Integrated biological systems such as activated sludge-powdered activated carbon [PAC] c... more Abstract Integrated biological systems such as activated sludge-powdered activated carbon [PAC] combinations are used in ever increasing numbers. For conventional activated sludge systems excellent models existed which presumably were also suitable for application to a PAC-fed system. PAC addition enhances bacterial activity, adsorption of dissolved organics and settleability of activated sludge flocs in the final clarifier. Simple laboratory experiments can demonstrate the degree of improvement in a PAC-fed system over the conventional activated sludge one. When using the present model the evaluation of several kinetic constants stemming from simple experiments may help to predict the performance of large scale operation even under unsteady state conditions.
Water Science and Technology, 2018
The wastewater industry is currently facing dramatic changes, shifting away from energy-intensive... more The wastewater industry is currently facing dramatic changes, shifting away from energy-intensive wastewater treatment towards low-energy, sustainable technologies capable of achieving energy positive operation and resource recovery. The latter will shift the focus of the wastewater industry to how one could manage and extract resources from the wastewater, as opposed to the conventional paradigm of treatment. Debatable questions arise: can the more complex models be calibrated, or will additional unknowns be introduced? After almost 30 years using well-known International Water Association (IWA) models, should the community move to other components, processes, or model structures like ‘black box’ models, computational fluid dynamics techniques, etc.? Can new data sources – e.g. on-line sensor data, chemical and molecular analyses, new analytical techniques, off-gas analysis – keep up with the increasing process complexity? Are different methods for data management, data reconciliat...
Proceedings of the Water Environment Federation, 2010
Many unit process models are available in the field of wastewater treatment. All of these models ... more Many unit process models are available in the field of wastewater treatment. All of these models use their own notation, causing problems for documentation, implementation and connection of different models (using different sets of state variables). The main goal of this paper is to propose a new notational framework which allows unique and systematic naming of state variables and parameters of biokinetic models in the wastewater treatment field. The symbols are based on one main letter that gives a general description of the state variable or parameter and several subscript levels that provide greater specification. Only those levels that make the name unique within the model context are needed in creating the symbol. The paper describes specific problems encountered with the currently used notation, presents the proposed framework and provides additional practical examples. The overall result is a framework that can be used in whole plant modelling, which consists of different fields such as activated sludge, anaerobic digestion, sidestream treatment, membrane bioreactors, metabolic approaches, fate of micropollutants and biofilm processes. The main objective of this consensus building paper is to establish a consistent set of rules that can be applied to existing and most importantly, future models. Applying the proposed notation should make it easier for everyone active in the wastewater treatment field to read, write and review documents describing modelling projects.
Water Science and Technology, 1986
Full-scale experiments were conducted to study the wastewater treatment plant of a chemical facto... more Full-scale experiments were conducted to study the wastewater treatment plant of a chemical factory. The objective of the study was to upgrade the overloaded biological activated sludge system by powdered activated carbon addition. Improvement of the organic micropollutant removal characteristics was also expected on the basis of previous experiments. During the three months experimental period the applicability and benefits of the process were proved, even under unfavourable conditions. Operation of the plant became stable, the quality of effluent improved about 30% in organic content and in several micropollutants. The upgraded unit could be overloaded by about 20% without any decrease in efficiency.
Proceedings of the Water Environment Federation, 2011
Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion... more Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion at very large utilities and can substantially reduce required digester volumes in space constrained large cities while also allowing for development of regionalized sludge receiving centers. In 2014, DC Water will begin operating a new solids processing train at the Blue Plains Advanced Wastewater Treatment Plant consisting of the CAMBI thermal hydrolysis process for solids pretreatment prior to mesophilic anaerobic digestion. A complete evaluation picture needs to take all impacts on downstream processes into account. The digestion performance at various solids loadings (collection of full-scale data); dewatering performance (full-scale belt-filter-press tests); sludge liquor treatment (DEMON-pilot); pathogen removal, odour issues and land application are discussed in the paper.
Water science and technology : a journal of the International Association on Water Pollution Research, 2015
This study describes the development of a modified activated sludge model No.1 framework to descr... more This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to pa...
Water Environment Research, 2008
Batch and continuous experiments using model and real wastewaters were conducted to investigate t... more Batch and continuous experiments using model and real wastewaters were conducted to investigate the effect of metal salt (ferric and alum) addition in wastewater treatment and the corresponding phosphate removal from a design and operational perspective. Key factors expected to influence the phosphorus removal efficiency, such as pH, alkalinity, metal dose, metal type, initial and residual phosphate concentration, mixing, reaction time, age of flocs, and organic content of wastewater, were investigated. The lowest achievable concentration of orthophosphate under optimal conditions (0.01 to 0.05 mg/L) was similar for both aluminum and iron salts, with a broad optimum pH range of 5.0 to 7.0. Thus, in the typical operating range of wastewater treatment plants, pH is not a sensitive indicator of phosphorus removal efficiency. The most significant effect for engineering practice, apart from the metal dose, is that of mixing intensity and slow kinetic removal of phosphorus in contact with the chemical sludge formed. Experiments show that significant savings in chemical cost could be achieved by vigorously mixing the added chemical at the point of dosage and, if conditions allow, providing a longer contact time between the metal hydroxide flocs and the phosphate content of the wastewater. These conditions promoted the achievement of less than 0.1 mg/L residual orthophosphate content, even at lower metal-to-phosphorus molar ratios. These observations are consistent with the surface complexation model presented in a companion paper (
Water Environment Research, 2008
A phosphate complexation model is developed, in an attempt to understand the mechanistic basis of... more A phosphate complexation model is developed, in an attempt to understand the mechanistic basis of chemically mediated phosphate removal. The model presented here is based on geochemical reaction modeling techniques and uses known surface reactions possible on hydrous ferric oxide (HFO). The types of surface reactions and their reaction stoichiometry and binding energies (logK values) are taken from literature models of phosphate interactions with iron oxides. The most important modeling parameter is the proportionality of converting moles of precipitated HFO to reactive site density. For well-mixed systems and phosphate exposed to ferric chloride during HFO precipitation, there is a phosphate capacity of 1.18 phosphate ions per iron atom. In poorly mixed systems with phosphate exposed to iron after HFO formation, the capacity decreased to 25% of the well-mixed value. The same surface complexation model can describe multiple data sets, by varying only a single parameter proportional to the availability of reactive oxygen functional groups. This reflects the unavailability of reactive oxygen groups to bind phosphate. Electron microscope images and dye adsorption experiments demonstrate changes in reactive surface area with aging of HFO particles. Engineering implications of the model/mechanism are highlighted. Water Environ. Res., 80, 428 (2008).
Proceedings of the Water Environment Federation
Chemical phosphorus removal using metal (iron and aluminium) salts is frequently used to control ... more Chemical phosphorus removal using metal (iron and aluminium) salts is frequently used to control effluent soluble phosphorus levels in wastewater treatment plants. In the Washington DC area effluent phosphorus requirements are extremely stringent to protect the Chesapeake Bay. Full-scale data from two plants in the area were analysed to establish phosphate behaviour in the presence of iron. Titration experiments and mathematical modelling were performed to determine the role of ferric phosphate and hydroxide precipitation and other mechanisms that may potentially be involved in phosphorus removal. Iron addition is described in the model using a chemical equilibrium approach extended with surface charges and adsorption. The model verifies key observations from full-scale data: (a) extremely low orthophosphate levels can be achieved over a wide range of pH values, (b) a mixture of ferric phosphate and ferric hydroxide precipitate is forming with the hydroxide acting as sorbent, (c) mo...
Current anaerobic digestion models cannot properly simulate processes that are operated under hig... more Current anaerobic digestion models cannot properly simulate processes that are operated under high solids concentrations or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these systems without artificially recalibrating the model parameters. Specifically, we implemented the alternate acetate oxidizing mechanism that is more tolerant to ammonia than the standard aceticlastic pathway. Inhibition values were estimated and an empirical function has been used to apply ammonia inhibition. The model also relates metabolic activity to un-ionised species such as undissociated acetic acid as substrate (although not obligatory for all organisms) and unionised ammonia as inhibitor. The model relies on an equilibrium chemistry module (e.g. including the phosphate buffer), resulting in more accurate pH predictions, which is crucial for proper modeling of CO2 and NH3 stripping. Calibration results from thre...
Process models used for activated sludge, anaerobic digestion and in general wastewater treatment... more Process models used for activated sludge, anaerobic digestion and in general wastewater treatment plant process design and optimization have traditionally focused on important biokinetic conversions. There is a growing realization that abiotic processes occurring in the wastewater (i.e. 'solvent') have a fundamental effect on plant performance. These processes include weak acid-base reactions (ionization), spontaneous or chemical dose-induced precipitate formation and chemical redox conversions, which influence pH, gas transfer, and directly or indirectly the biokinetic processes themselves. There is a large amount of fundamental information available (from chemical and other disciplines), which, due to its complexity and its diverse sources (originating from many different water and process environments), cannot be readily used in wastewater process design as yet. This position paper outlines the need, the methods, available knowledge and the fundamental approaches that would help to focus the effort of research groups to develop a physicochemical framework specifically in support of whole-plant process modeling. The findings are that, in general, existing models such as produced by the International Water Association for biological processes are limited by omission of key corrections such as non-ideal acid-base behavior, as well as major processes (e.g., ion precipitation). While the underlying chemistry is well understood, its applicability to wastewater applications is less well known. This justifies important further research, with both experimental and model development activities to clarify an approach to modeling of physicochemical processes.
The 1st IWA/WEF wastewater treatment modelling seminar (WWTmod2008) took place earlier this year ... more The 1st IWA/WEF wastewater treatment modelling seminar (WWTmod2008) took place earlier this year in Mont-Sainte-Anne, Quebec, Canada, organised in order to allow for debate and the presentation of ideas on this subject. Leiv Rieger, Peter A Vanrolleghem, Imre Takacs and Bruce R Johnson discuss the areas covered at the event.
Water Science and Technology, 1999
Proceedings of the Water Environment Federation, 2008
ABSTRACT Parametric models used in simulation software for the design of wastewater treatment pla... more ABSTRACT Parametric models used in simulation software for the design of wastewater treatment plants involve a number of processes and state variables that can be best represented in a matrix format (e.g. ASM1, ASM2D, ASM3, General ASDM). These models often use different symbols for identical variables and some models are becoming increasingly complex making it difficult to visualize the relationships between the various processes. A standardized notation is first proposed for the major current parametric models which is then used to draw schematic representations of these models. These schematics should constitute useful learning tools, that should facilitate comparisons between various models and provide a better appreciation of the potential and limitations of each model to ensure a better use of activated sludge models by design engineers.
Proceedings of the Water Environment Federation, 2009
ABSTRACT Process models for enhanced biological phosphorus removal systems are shown to predict a... more ABSTRACT Process models for enhanced biological phosphorus removal systems are shown to predict anaerobic behavior better than aerobic behavior. Reasons for this include the use of uncalibrated kinetic parameters as well as difficulties introduced by the choice of model structure. A modeling approach is proposed in which model structure and stoichiometric values for both the anaerobic and aerobic phase are based on accepted metabolic pathways and kinetic parameters are calibrated based on results from a batch experimental system. Based on the results for over 20 experimental continuous-flow systems fed with both acetate and sewage, it is demonstrated that this Proposed Model gives improved predictions of phosphorus removal.
Proceedings of the Water Environment Federation, 2010
ABSTRACT Nutrient assimilation was revisited using a steady state model developed from the activa... more ABSTRACT Nutrient assimilation was revisited using a steady state model developed from the activated sludge modeling concepts. While nitrogen assimilation is only related to organic particulate fractions, the role of inorganic complexes and precipitates was accounted for in phosphorus assimilation. It is shown that the influent aluminum background concentration may contribute significantly to phosphorus assimilation, and that in 3.6% of cases, calcium phosphate may precipitate in activated sludge.A global sensitivity analysis was conducted with the Monte Carlo method to identify the most sensitive model parameters and input variables. The nutrient content of the unbiodegradable mixed liquor fractions emerged as the most sensitive parameters and were calibrated using databases and some assumptions. Most of the remaining variability of nutrient assimilation then comes down to four variables (three influent concentration ratios and SRT), which were used to prepare charts to predict assimilation in design and operation. For an SRT of 20 days, it is proposed to update the typical empirical BOD5:N:P ratio from 100:5:1 to 100:5.7:1.4.