DESASS: A software tool for designing, simulating and optimising WWTPs
Environmental Modelling & Software, 2008
This paper presents a very useful software tool to design, simulate and optimise wastewater treat... more This paper presents a very useful software tool to design, simulate and optimise wastewater treatment plants. The program is called DESASS (DEsign and Simulation of Activated Sludge Systems) and has been developed by CALAGUA research group. The mathematical model implemented is the Biological Nutrient Removal Model No.1 (BNRM1) which allows simulating the most important physical, chemical and biological processes taking
A Semi-Industrial Anmbr Plant for Urban Wastewater Treatment at Ambient Temperature: Analysis of the Filtration Process, Energy Balance and Quantification of GHG Emissions
The aim of this study was to evaluate the effect of light intensity and temperature on nutrient r... more The aim of this study was to evaluate the effect of light intensity and temperature on nutrient removal and biomass productivity in a microalgae-bacteria culture and their effects on the microalgae-bacteria competition. Three experiments were carried out at constant temperature and various light intensities: 40, 85 and 125 µE•m-2 •s-1. Other two experiments were carried out at variable temperatures: 23 ± 2 and 28 ± 2 ºC at light intensity of 85 and 125 µE•m-2 •s-1 , respectively. The photobioreactor was fed by the effluent from an anaerobic membrane bioreactor. High nitrogen and phosphorus removal efficiencies (about 99%) were achieved under the following operating 2 conditions: 85-125 µE•m-2 •s-1 and 22 ± 1 ºC. In the microalgae-bacteria culture studied, increasing light intensity favoured microalgae growth and limited the nitrification process. However, a non-graduated temperature increase (up to 32ºC) under the light intensities studied caused the proliferation of nitrifying bacteria and the nitrite and nitrate accumulation. Hence, light intensity and temperature are key parameters in the control of the microalgae-bacteria competition. Biomass productivity significantly increased with light intensity, reaching 50.5 ± 9.6, 80.3 ± 6.5 and 94.3 ± 7.9 mgVSS•L-1 •d-1 for a light intensity of 40, 85 and 125 µE•m-2 •s-1 , respectively.
Evaluation of Activated Sludge Model No.2 at High Phosphorus Concentrations
Environmental Technology, 2001
This paper presents laboratory scale experimentation carried out to study enhanced biological pho... more This paper presents laboratory scale experimentation carried out to study enhanced biological phosphorus removal at high phosphorus concentrations in a sequencing batch reactor. Four series of data obtained in a sequencing batch reactor are examined in light of the Activated Sludge Model No. 2. This model was calibrated using data from the first and second series working at low phosphorus concentrations. The Activated Sludge Model No. 2 successfully characterised the enhanced biological phosphorus removal performance of the sequencing batch reactor at low phosphorus concentrations. The calibrated model was then used to adjust experimental results of the other series working at high phosphorus concentration. Differences between model predictions and experimental data could be explained by redissolution in the anaerobic phase and precipitation in the aerobic phase of calcium phosphates not taken into account by the model. This hypothesis can be justified by the conditions of pH and phosphorus concentration prevailing in the experiments and it was confirmed by the results of another experiment in which precipitated phosphorus profile was measured during the cycle.
In this paper, a revised version of the Morris approach, which includes an improved sampling stra... more In this paper, a revised version of the Morris approach, which includes an improved sampling strategy based on trajectory design, has been adapted to the screening of the most influential parameters of a fuzzy controller applied to WWTPs. Due to the high number of parameters, a systematic approach has been proposed to apply this improved sampling strategy with low computational demand. In order to find out the proper repetition number of elementary effects of each input factor on model output (EE i) calculations, an iterative and automatic procedure has been applied. The results show that the sampling strategy has a significant effect on the parameter significance ranking and that random sampling could lead to a non-proper coverage of the parameter space.
A fuzzy logic supervisory control system for optimising nitrogen removal and aeration energy cons... more A fuzzy logic supervisory control system for optimising nitrogen removal and aeration energy consumption has been developed. This control system allows optimising and controlling the dissolved oxygen (DO) concentration in the aerobic reactors, the blowers discharge pressure and the effluent ammonia and nitrate concentrations. DO is controlled by adjusting control valve opening and blower discharge pressure is controlled by modifying rotational speed of the blowers. Optimum nitrification/denitrification is achieved by modifying the DO set point in the last aerobic reactor and the internal recirculation. This system has been tested by simulation in a Bardenpho process using the Activated Sludge Model No2. A significant improvement in stability on the activated sludge process is achieved. Moreover, significant energy saving has been achieved with this control strategy.
This paper presents the plant-wide model Biological Nutrient Removal Model Nº 2 (BNRM2). Since ni... more This paper presents the plant-wide model Biological Nutrient Removal Model Nº 2 (BNRM2). Since nitrite was not considered in the BNRM1, and this previous model also failed to accurately simulate the anaerobic digestion because precipitation processes were not considered, an extension of BNRM1 has been developed. This extension comprises all the components and processes required to simulate nitrogen removal via nitrite and the formation of the solids most likely to precipitate in anaerobic digesters. The solids considered in BNRM2 are: struvite, amorphous calcium phosphate, hidroxiapatite, newberite, vivianite, strengite, variscite, and calcium carbonate. With regard to nitrogen removal via nitrite, appart from nitrite oxidising bacteria two groups of ammonium oxidising organisms (AOO) have been considered since different sets of kinetic parameters have been reported for the AOO present in activated sludge systems and SHARON reactors. Due to the new processes considered, BNRM2 allows an accurate prediction of WWTPs performance in wider environmental and operating conditions.
This paper presents a computer tool called DSC (Simulation based Controllers Design) that enables... more This paper presents a computer tool called DSC (Simulation based Controllers Design) that enables an easy design of control systems and strategies applied to wastewater treatment plants. Although the control systems are developed and evaluated by simulation, this tool aims to facilitate the direct implementation of the designed control system to the PC of the full-scale WWTP (wastewater treatment plants). The designed control system can be programmed in a dedicated control application and can be connected to either the simulation software or the SCADA of the plant. To this end, the developed DSC incorporates an OPC server (OLE for process control) which facilitates an open-standard communication protocol for different industrial process applications. The potential capabilities of the DSC tool are illustrated through the example of a fullscale application. An aeration control system applied to a nutrient removing WWTP was designed, tuned and evaluated with the DSC tool before its implementation in the full scale plant. The control parameters obtained by simulation were suitable for the full scale plant with only few modifications to improve the control performance. With the DSC tool, the control systems performance can be easily evaluated by simulation. Once developed and tuned by simulation, the control systems can be directly applied to the full-scale WWTP.
This paper describes a model-based method to optimise filtration in submerged AnMBRs. The method ... more This paper describes a model-based method to optimise filtration in submerged AnMBRs. The method is applied to an advanced knowledge-based control system and considers three statistical methods: (1) sensitivity analysis (Morris screening method) to identify an input subset for the advanced controller; (2) Monte Carlo method (trajectory-based random sampling) to find suitable initial values for the control inputs; and (3) optimisation algorithm (performing as a supervisory controller) to re-calibrate these control inputs in order to minimise plant operating costs. The model-based supervisory controller proposed allowed filtration to be optimised with low computational demands (about 5 minutes). Energy savings of up to 25% were achieved when using gas sparging to scour membranes. Downtime for physical cleaning was about 2.4% of operating time. The operating cost of the AnMBR system after implementing the proposed supervisory controller was about €0.045/m 3 , 53.3% of which were energy costs.
The aim of this study was to develop a model able to correctly reproduce the filtration process o... more The aim of this study was to develop a model able to correctly reproduce the filtration process of submerged anaerobic MBRs (SAnMBRs). The proposed model was calibrated and validated in a SAnMBR demonstration plant fitted with industrial-scale hollow-fibre membranes. Three suspended components were contemplated in the model: total solids concentration; dry mass of cake on the membrane surface; and dry mass of irreversible fouling on the membrane surface. The model addressed the following physical processes: the build-up and compression of the cake layer during filtration; cake layer removal using biogas sparging to scour the membrane; cake layer removal during back-flushing; and the consolidation of irreversible fouling. The short-and long-term validation of the model resulted in correlation coefficients (R 2 ) of 0.962 and 0.929, respectively.
A fuzzy logic-based control system that uses low-cost sensors for controlling and optimizing the ... more A fuzzy logic-based control system that uses low-cost sensors for controlling and optimizing the biological nitrogen removal in continuous systems has been developed. The novelty of this control system is the use of several pH, ORP, and dissolved oxygen (DO) sensors instead of on-line nitrogen sensors/analyzers. The nitrogen control system was developed and implemented in a UCT pilot plant fed with wastewater from a full-scale plant. The developed nitrification controller allows the effluent ammonium concentration to be maintained below the effluent criteria discharge with the minimum energy consumption. The denitrification process controller allows the energy consumption derived from pumping to be minimized, as the control system only increases the internal recycle flow rate when the anoxic reactor reveals further capacity for denitrification. This advanced control strategy offers an attractive alternative to on-line, nitrogen analyzer-based control systems since it involves lower investment, maintenance, and operational costs that are derived from the instrumentation.
An anaerobic aerobic laboratory scale sequencing batch reactor (SBR) was operated to study the ef... more An anaerobic aerobic laboratory scale sequencing batch reactor (SBR) was operated to study the effect of pH on enhanced biological phosphorus removal. Seven steady states were achieved under different operating conditions. In all of them, a slight variation in the pH value was observed during anaerobic phase. However, pH rose significantly during aerobic phase. The increase observed was due to phosphorus uptake and carbon dioxide stripping. When pH was higher than 8.2-8.25 the phosphorus uptake rate clearly decreased. The capability of Activated Sludge Model No. 2d (ASM2d) and Biological Nutrient Removal Model No. 1 (BNRM1) to simulate experimental results was evaluated. Both models successfully characterized the enhanced biological phosphorus removal performance of the SBR. Furthermore, BNRM1 also reproduced the pH variations observed and the decrease in the phosphorus uptake rate. This model includes a switch function in the kinetic expressions to represent the pH inhibition in biological processes. The pH inhibition constants related to polyphosphate storage process were obtained by adjusting model predictions to measured phosphorus concentrations. On the other hand, pH inhibition should be included in ASM2d to accurately simulate experimental phosphorus evolution observed in an A/O SBR.
The results of a sensitivity analysis of a filtration model for submerged anaerobic MBRs (AnMBRs)... more The results of a sensitivity analysis of a filtration model for submerged anaerobic MBRs (AnMBRs) are assessed in this paper. This study aimed to (1) identify the less-(or non-) influential factors of the model in order to facilitate model calibration and (2) validate the modelling approach (i.e. to determine the need for each of the proposed factors to be included in the model). The sensitivity analysis was conducted using a revised version of the Morris screening method. The dynamic simulations were conducted using long-term data obtained from an AnMBR plant fitted with industrial-scale hollow-fibre membranes. Of the 14 factors in the model, six were identified as influential, i.e. those calibrated using off-line protocols. A dynamic calibration (based on optimisation algorithms) of these influential factors was conducted. The resulting estimated model factors accurately predicted membrane performance.
Currently, the two most developed techniques for recovering phosphorus from wastewater consist of... more Currently, the two most developed techniques for recovering phosphorus from wastewater consist of the formation of calcium phosphates and struvite (MgNH 4 PO 4 Á6H 2 O). In this work the influence of the operational conditions on the struvite precipitation process (pH in the reactor, hydraulic retention time, and magnesium:phosphorus, nitrogen:phosphorus, and calcium:magnesium molar ratios) have been studied. Twenty-three experiments with artificial wastewater were performed in a stirred reactor. In order to obtain the pH value maintenance during the crystallization process, a fuzzy logic control has been developed. High phosphorus removal efficiencies were reliably achieved precipitating the struvite as easily dried crystals or as pellets made up of agglomerated crystals.
This work studied the influence of the characteristics of the supernatants on the struvite precip... more This work studied the influence of the characteristics of the supernatants on the struvite precipitation process. Eighteen experiments with the supernatants generated in an anaerobic digestion pilot plant were performed in a stirred reactor. In order to obtain the pH control during the crystallization process, a Fuzzy Logic based controller was used. High phosphorus precipitation and recovery efficiencies were obtained. The composition of the supernatants was analyzed in order to study its influence on the solids formed from those solutions. The presence of calcium reduced the percentage of phosphorus precipitated as struvite leading to the formation of amorphous calcium phosphate (ACP), which tended to be lost with the effluent of the reactor. Calcite was also formed when supernatants with high magnesium:phosphorus (Mg/P) and calcium:phosphorus (Ca/P) molar ratios were employed. Some ammonium volatilization by conversion to NH 3 occurred in all the experiments. The use of air to increase the pH to an adequate value showed to be feasible. Aeration cleaned struvite crystals from suspended solids, which makes aeration interesting for struvite separation. However, aeration slightly increased the loss of phosphorus with the effluent of the reactor and promoted ammonium volatilization.
The aim of this study was the long-term validation of a model capable of reproducing the filtrati... more The aim of this study was the long-term validation of a model capable of reproducing the filtration process occurring in a submerged anaerobic membrane bioreactor (SAnMBR) system. The proposed model was validated using data obtained from a SAnMBR demonstration plant fitted with industrial-scale hollowfibre membranes. The validation was carried out using both lightly and heavily fouled membranes operating at different bulk concentrations, gas sparging intensities and transmembrane fluxes. Across a broad spectrum of operating conditions, the model correctly forecast the respective experimental data in the long term. The simulation results revealed the importance of controlling irreversible fouling in order to ensure sustainable long-term membrane performance. Industrial-scale hollow fibre modules; long-term validation; resistance in series; filtration model; submerged anaerobic membrane bioreactor A filtration model for SAnMBRs has been validated using long-term data. The model was validated for lightly and heavily fouled full-scale HF membranes. Different MLTS levels, gas sparging intensities and permeate fluxes were applied. The model reproduced the experimental data accurately.
DESASS: A software tool for designing, simulating and optimising WWTPs
Environmental Modelling & Software, 2008
This paper presents a very useful software tool to design, simulate and optimise wastewater treat... more This paper presents a very useful software tool to design, simulate and optimise wastewater treatment plants. The program is called DESASS (DEsign and Simulation of Activated Sludge Systems) and has been developed by CALAGUA research group. The mathematical model implemented is the Biological Nutrient Removal Model No.1 (BNRM1) which allows simulating the most important physical, chemical and biological processes taking
A Semi-Industrial Anmbr Plant for Urban Wastewater Treatment at Ambient Temperature: Analysis of the Filtration Process, Energy Balance and Quantification of GHG Emissions
The aim of this study was to evaluate the effect of light intensity and temperature on nutrient r... more The aim of this study was to evaluate the effect of light intensity and temperature on nutrient removal and biomass productivity in a microalgae-bacteria culture and their effects on the microalgae-bacteria competition. Three experiments were carried out at constant temperature and various light intensities: 40, 85 and 125 µE•m-2 •s-1. Other two experiments were carried out at variable temperatures: 23 ± 2 and 28 ± 2 ºC at light intensity of 85 and 125 µE•m-2 •s-1 , respectively. The photobioreactor was fed by the effluent from an anaerobic membrane bioreactor. High nitrogen and phosphorus removal efficiencies (about 99%) were achieved under the following operating 2 conditions: 85-125 µE•m-2 •s-1 and 22 ± 1 ºC. In the microalgae-bacteria culture studied, increasing light intensity favoured microalgae growth and limited the nitrification process. However, a non-graduated temperature increase (up to 32ºC) under the light intensities studied caused the proliferation of nitrifying bacteria and the nitrite and nitrate accumulation. Hence, light intensity and temperature are key parameters in the control of the microalgae-bacteria competition. Biomass productivity significantly increased with light intensity, reaching 50.5 ± 9.6, 80.3 ± 6.5 and 94.3 ± 7.9 mgVSS•L-1 •d-1 for a light intensity of 40, 85 and 125 µE•m-2 •s-1 , respectively.
Evaluation of Activated Sludge Model No.2 at High Phosphorus Concentrations
Environmental Technology, 2001
This paper presents laboratory scale experimentation carried out to study enhanced biological pho... more This paper presents laboratory scale experimentation carried out to study enhanced biological phosphorus removal at high phosphorus concentrations in a sequencing batch reactor. Four series of data obtained in a sequencing batch reactor are examined in light of the Activated Sludge Model No. 2. This model was calibrated using data from the first and second series working at low phosphorus concentrations. The Activated Sludge Model No. 2 successfully characterised the enhanced biological phosphorus removal performance of the sequencing batch reactor at low phosphorus concentrations. The calibrated model was then used to adjust experimental results of the other series working at high phosphorus concentration. Differences between model predictions and experimental data could be explained by redissolution in the anaerobic phase and precipitation in the aerobic phase of calcium phosphates not taken into account by the model. This hypothesis can be justified by the conditions of pH and phosphorus concentration prevailing in the experiments and it was confirmed by the results of another experiment in which precipitated phosphorus profile was measured during the cycle.
In this paper, a revised version of the Morris approach, which includes an improved sampling stra... more In this paper, a revised version of the Morris approach, which includes an improved sampling strategy based on trajectory design, has been adapted to the screening of the most influential parameters of a fuzzy controller applied to WWTPs. Due to the high number of parameters, a systematic approach has been proposed to apply this improved sampling strategy with low computational demand. In order to find out the proper repetition number of elementary effects of each input factor on model output (EE i) calculations, an iterative and automatic procedure has been applied. The results show that the sampling strategy has a significant effect on the parameter significance ranking and that random sampling could lead to a non-proper coverage of the parameter space.
A fuzzy logic supervisory control system for optimising nitrogen removal and aeration energy cons... more A fuzzy logic supervisory control system for optimising nitrogen removal and aeration energy consumption has been developed. This control system allows optimising and controlling the dissolved oxygen (DO) concentration in the aerobic reactors, the blowers discharge pressure and the effluent ammonia and nitrate concentrations. DO is controlled by adjusting control valve opening and blower discharge pressure is controlled by modifying rotational speed of the blowers. Optimum nitrification/denitrification is achieved by modifying the DO set point in the last aerobic reactor and the internal recirculation. This system has been tested by simulation in a Bardenpho process using the Activated Sludge Model No2. A significant improvement in stability on the activated sludge process is achieved. Moreover, significant energy saving has been achieved with this control strategy.
This paper presents the plant-wide model Biological Nutrient Removal Model Nº 2 (BNRM2). Since ni... more This paper presents the plant-wide model Biological Nutrient Removal Model Nº 2 (BNRM2). Since nitrite was not considered in the BNRM1, and this previous model also failed to accurately simulate the anaerobic digestion because precipitation processes were not considered, an extension of BNRM1 has been developed. This extension comprises all the components and processes required to simulate nitrogen removal via nitrite and the formation of the solids most likely to precipitate in anaerobic digesters. The solids considered in BNRM2 are: struvite, amorphous calcium phosphate, hidroxiapatite, newberite, vivianite, strengite, variscite, and calcium carbonate. With regard to nitrogen removal via nitrite, appart from nitrite oxidising bacteria two groups of ammonium oxidising organisms (AOO) have been considered since different sets of kinetic parameters have been reported for the AOO present in activated sludge systems and SHARON reactors. Due to the new processes considered, BNRM2 allows an accurate prediction of WWTPs performance in wider environmental and operating conditions.
This paper presents a computer tool called DSC (Simulation based Controllers Design) that enables... more This paper presents a computer tool called DSC (Simulation based Controllers Design) that enables an easy design of control systems and strategies applied to wastewater treatment plants. Although the control systems are developed and evaluated by simulation, this tool aims to facilitate the direct implementation of the designed control system to the PC of the full-scale WWTP (wastewater treatment plants). The designed control system can be programmed in a dedicated control application and can be connected to either the simulation software or the SCADA of the plant. To this end, the developed DSC incorporates an OPC server (OLE for process control) which facilitates an open-standard communication protocol for different industrial process applications. The potential capabilities of the DSC tool are illustrated through the example of a fullscale application. An aeration control system applied to a nutrient removing WWTP was designed, tuned and evaluated with the DSC tool before its implementation in the full scale plant. The control parameters obtained by simulation were suitable for the full scale plant with only few modifications to improve the control performance. With the DSC tool, the control systems performance can be easily evaluated by simulation. Once developed and tuned by simulation, the control systems can be directly applied to the full-scale WWTP.
This paper describes a model-based method to optimise filtration in submerged AnMBRs. The method ... more This paper describes a model-based method to optimise filtration in submerged AnMBRs. The method is applied to an advanced knowledge-based control system and considers three statistical methods: (1) sensitivity analysis (Morris screening method) to identify an input subset for the advanced controller; (2) Monte Carlo method (trajectory-based random sampling) to find suitable initial values for the control inputs; and (3) optimisation algorithm (performing as a supervisory controller) to re-calibrate these control inputs in order to minimise plant operating costs. The model-based supervisory controller proposed allowed filtration to be optimised with low computational demands (about 5 minutes). Energy savings of up to 25% were achieved when using gas sparging to scour membranes. Downtime for physical cleaning was about 2.4% of operating time. The operating cost of the AnMBR system after implementing the proposed supervisory controller was about €0.045/m 3 , 53.3% of which were energy costs.
The aim of this study was to develop a model able to correctly reproduce the filtration process o... more The aim of this study was to develop a model able to correctly reproduce the filtration process of submerged anaerobic MBRs (SAnMBRs). The proposed model was calibrated and validated in a SAnMBR demonstration plant fitted with industrial-scale hollow-fibre membranes. Three suspended components were contemplated in the model: total solids concentration; dry mass of cake on the membrane surface; and dry mass of irreversible fouling on the membrane surface. The model addressed the following physical processes: the build-up and compression of the cake layer during filtration; cake layer removal using biogas sparging to scour the membrane; cake layer removal during back-flushing; and the consolidation of irreversible fouling. The short-and long-term validation of the model resulted in correlation coefficients (R 2 ) of 0.962 and 0.929, respectively.
A fuzzy logic-based control system that uses low-cost sensors for controlling and optimizing the ... more A fuzzy logic-based control system that uses low-cost sensors for controlling and optimizing the biological nitrogen removal in continuous systems has been developed. The novelty of this control system is the use of several pH, ORP, and dissolved oxygen (DO) sensors instead of on-line nitrogen sensors/analyzers. The nitrogen control system was developed and implemented in a UCT pilot plant fed with wastewater from a full-scale plant. The developed nitrification controller allows the effluent ammonium concentration to be maintained below the effluent criteria discharge with the minimum energy consumption. The denitrification process controller allows the energy consumption derived from pumping to be minimized, as the control system only increases the internal recycle flow rate when the anoxic reactor reveals further capacity for denitrification. This advanced control strategy offers an attractive alternative to on-line, nitrogen analyzer-based control systems since it involves lower investment, maintenance, and operational costs that are derived from the instrumentation.
An anaerobic aerobic laboratory scale sequencing batch reactor (SBR) was operated to study the ef... more An anaerobic aerobic laboratory scale sequencing batch reactor (SBR) was operated to study the effect of pH on enhanced biological phosphorus removal. Seven steady states were achieved under different operating conditions. In all of them, a slight variation in the pH value was observed during anaerobic phase. However, pH rose significantly during aerobic phase. The increase observed was due to phosphorus uptake and carbon dioxide stripping. When pH was higher than 8.2-8.25 the phosphorus uptake rate clearly decreased. The capability of Activated Sludge Model No. 2d (ASM2d) and Biological Nutrient Removal Model No. 1 (BNRM1) to simulate experimental results was evaluated. Both models successfully characterized the enhanced biological phosphorus removal performance of the SBR. Furthermore, BNRM1 also reproduced the pH variations observed and the decrease in the phosphorus uptake rate. This model includes a switch function in the kinetic expressions to represent the pH inhibition in biological processes. The pH inhibition constants related to polyphosphate storage process were obtained by adjusting model predictions to measured phosphorus concentrations. On the other hand, pH inhibition should be included in ASM2d to accurately simulate experimental phosphorus evolution observed in an A/O SBR.
The results of a sensitivity analysis of a filtration model for submerged anaerobic MBRs (AnMBRs)... more The results of a sensitivity analysis of a filtration model for submerged anaerobic MBRs (AnMBRs) are assessed in this paper. This study aimed to (1) identify the less-(or non-) influential factors of the model in order to facilitate model calibration and (2) validate the modelling approach (i.e. to determine the need for each of the proposed factors to be included in the model). The sensitivity analysis was conducted using a revised version of the Morris screening method. The dynamic simulations were conducted using long-term data obtained from an AnMBR plant fitted with industrial-scale hollow-fibre membranes. Of the 14 factors in the model, six were identified as influential, i.e. those calibrated using off-line protocols. A dynamic calibration (based on optimisation algorithms) of these influential factors was conducted. The resulting estimated model factors accurately predicted membrane performance.
Currently, the two most developed techniques for recovering phosphorus from wastewater consist of... more Currently, the two most developed techniques for recovering phosphorus from wastewater consist of the formation of calcium phosphates and struvite (MgNH 4 PO 4 Á6H 2 O). In this work the influence of the operational conditions on the struvite precipitation process (pH in the reactor, hydraulic retention time, and magnesium:phosphorus, nitrogen:phosphorus, and calcium:magnesium molar ratios) have been studied. Twenty-three experiments with artificial wastewater were performed in a stirred reactor. In order to obtain the pH value maintenance during the crystallization process, a fuzzy logic control has been developed. High phosphorus removal efficiencies were reliably achieved precipitating the struvite as easily dried crystals or as pellets made up of agglomerated crystals.
This work studied the influence of the characteristics of the supernatants on the struvite precip... more This work studied the influence of the characteristics of the supernatants on the struvite precipitation process. Eighteen experiments with the supernatants generated in an anaerobic digestion pilot plant were performed in a stirred reactor. In order to obtain the pH control during the crystallization process, a Fuzzy Logic based controller was used. High phosphorus precipitation and recovery efficiencies were obtained. The composition of the supernatants was analyzed in order to study its influence on the solids formed from those solutions. The presence of calcium reduced the percentage of phosphorus precipitated as struvite leading to the formation of amorphous calcium phosphate (ACP), which tended to be lost with the effluent of the reactor. Calcite was also formed when supernatants with high magnesium:phosphorus (Mg/P) and calcium:phosphorus (Ca/P) molar ratios were employed. Some ammonium volatilization by conversion to NH 3 occurred in all the experiments. The use of air to increase the pH to an adequate value showed to be feasible. Aeration cleaned struvite crystals from suspended solids, which makes aeration interesting for struvite separation. However, aeration slightly increased the loss of phosphorus with the effluent of the reactor and promoted ammonium volatilization.
The aim of this study was the long-term validation of a model capable of reproducing the filtrati... more The aim of this study was the long-term validation of a model capable of reproducing the filtration process occurring in a submerged anaerobic membrane bioreactor (SAnMBR) system. The proposed model was validated using data obtained from a SAnMBR demonstration plant fitted with industrial-scale hollowfibre membranes. The validation was carried out using both lightly and heavily fouled membranes operating at different bulk concentrations, gas sparging intensities and transmembrane fluxes. Across a broad spectrum of operating conditions, the model correctly forecast the respective experimental data in the long term. The simulation results revealed the importance of controlling irreversible fouling in order to ensure sustainable long-term membrane performance. Industrial-scale hollow fibre modules; long-term validation; resistance in series; filtration model; submerged anaerobic membrane bioreactor A filtration model for SAnMBRs has been validated using long-term data. The model was validated for lightly and heavily fouled full-scale HF membranes. Different MLTS levels, gas sparging intensities and permeate fluxes were applied. The model reproduced the experimental data accurately.
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