Jesús Zambrano - Academia.edu (original) (raw)

Papers by Jesús Zambrano

Autothermal Thermophilic Aerobic Digestion (ATAD) is becoming an alternative to conventional dige... more Autothermal Thermophilic Aerobic Digestion (ATAD) is becoming an alternative to conventional digestion systems. Aeration is crucial for the good performance of this process. Nowadays, there is so much to do in the development of new automatic control in ATADs since the existing controls strategies are based just on the empirical knowledge of the process. This paper evaluates a linear robust feedback controller designed according to Quantitative Feedback Theory (QFT) principles, assuring stability and performance in the achievement of optimal operating points non-linearly determined. A previous work, focused on a benchmark adapted to ATAD, was used to validate this approach and to compare with previous control strategies.

This work deals with fault detection of DO sensors under possible clogging condition. The detecti... more This work deals with fault detection of DO sensors under possible clogging condition. The detection of the clogging condition is performed using two fault detection (FD) methods. Method 1 detects changes in the distance between signal spectra and method 2 detects changes in the signal standard deviation. Both FD algorithms are based on the likelihood ratio test implemented in a recursive decision rule. Real data from a dissolved oxygen (DO) sensor located in an aerated basin of an activated sludge process is used as case study. The sensor is used in a closed loop control. Results show that both methods give a quite similar detection results. Hence, in this case study, it seems sufficient to just monitor the standard deviation of the sensor signal. Before making any confirmative conclusions more experiments are, however, needed.

In this paper, an optimization study of simple bioreactors in series is presented. For a given to... more In this paper, an optimization study of simple bioreactors in series is presented. For a given total reactor volume, the zone volumes are optimized with respect to the effluent substrate. Also simple activated sludge models are considered. Both Monod and Contois functions are used for describing the growth kinetics. It is shown that the optimal zone volumes are very different depending on the choice of growth kinetics. In particular, it is studied how the influent steady state substrate concentration influence the optimal configuration.

In this paper, simple activated sludge process (ASP) models with Monod and Contois biomass growth... more In this paper, simple activated sludge process (ASP) models with Monod and Contois biomass growth kinetics are compared. In particular, the cases of an ASP with one or two bioreactors are studied. Of particular concern in this study is to investigate how the effluent substrate concentration depends on the influent substrate concentration. It is shown that the results are very different depending on the number of bioreactors and on the growth kinetics assumed.

In this study, a sensitivity analysis and a calibration were applied to a recent published model ... more In this study, a sensitivity analysis and a calibration were applied to a recent published model (Lindblom et al., 2015) used to replicate nitrous oxide (N 2 O) emissions in an one-stage nitritation-Anammox process using a moving-bed biofilm reactor (MBBR) at Hammarby-Sjstad pilot plant (Stockholm, Sweden), which treats anaerobic digestion liquor. Results indicate that the biofilm porosity, biofilm density, maximum biofilm thickness and boundary layer thickness were the most sensitive parameters of the model.

Linköping Electronic Conference Proceedings, 2017

This work deals with steady-state simulation study of a process formed by a microalgae-bacteria p... more This work deals with steady-state simulation study of a process formed by a microalgae-bacteria photobioreactor (PBR) in an activated sludge configuration. In particular, the process behavior in terms of variations in the sludge retention time and carbon dioxide (CO 2) injected is presented. The optimization is done by considering the total PBR volume as two volumes in series, and aiming for the minimal substrate concentration in the effluent, for a given external light and CO 2 injected. Results suggest that it is possible to obtain an optimum volume distribution of the process that gives a lower effluent substrate concentration compared to the same process using a single volume.

Linköping Electronic Conference Proceedings, 2018

This paper presents a method for monitoring the sludge profiles of a secondary settler using a Ga... more This paper presents a method for monitoring the sludge profiles of a secondary settler using a Gaussian Mixture Model (GMM). A GMM is a parametric probability density function represented as a weighted sum of Gaussian components densities. To illustrate this method, the current approach is applied using real data from a sensor measuring the sludge concentration as a function of the settler level at a wastewater treatment plant (WWTP) in Bromma, Sweden. Results suggest that the GMM approach is a feasible method for monitoring and detecting possible disturbances of the process and fault situations such as sensor clogging. This approach can be a valuable tool for monitoring processes with a repetitive profile.

La presente investigacion tuvo como objetivo analizar el sistema medular del mercado del pollo be... more La presente investigacion tuvo como objetivo analizar el sistema medular del mercado del pollo beneficiado en la RegionCapital, durante el segundo semestre de 2010, partiendo del estudio teorico de las variables macroambientales, lasvariables de “marketing mix” y las variables microambientales que lo afectan. Este trabajo se enmarca en los postulados dela investigacion no experimental, de nivel exploratorio y descriptivo, bajo diseno mixto, bibliografico y de campo. Seutilizo como tecnica de investigacion la entrevista, la encuesta, el estudio bibliografico y la observacion, y comoinstrumentos de recoleccion de datos, el cuestionario, el guion estructurado y la matriz FODA. La poblacion objeto deestudio estuvo representada por la Federacion Nacional de Avicultura de Venezuela (FENAVI), por el Ministerio delPoder Popular para la Alimentacion, el Ministerio del Poder Popular para la Agricultura y Tierras y por la Cadena deDistribucion del Mercado de Pollo Beneficiado en la Region Capi...

International Journal of Productivity and Quality Management, 2020

Water, 2021

This paper proposes a methodology for the layout selection of an urban drainage system as an exte... more This paper proposes a methodology for the layout selection of an urban drainage system as an extension to the methodology for an optimal sewer network design proposed by Duque, Duque, Aguilar, & Saldarriaga. The layout selection approach proposed in this paper uses an objective function that takes into account all input data in the problem, such as: land topography, street network topology, and inflow to each manhole. Once the layout is selected, the network is optimally designed using dynamic programming. The problem of layout selection is solved as a mixed-integer programming problem and is divided into two steps. The first step tries to define an initial layout using the network topology and land topography as a criterion. This allows for an initial hydraulic design and an approximation of the sewer network’s construction costs. The second step uses the data obtained in the previous process to establish an approximation of the construction costs of each arc that can be part of th...

Proceedings of The 59th Conference on imulation and Modelling (SIMS 59), 26-28 September 2018, Oslo Metropolitan University, Norway, Nov 19, 2018

Output-Error (OE) System Identification is used to estimate the nonlinear behavior of an activate... more Output-Error (OE) System Identification is used to estimate the nonlinear behavior of an activated sludge process (ASP) in a Wastewater Treatment Plant (WWTP). The aim is to identify dynamic models to reproduce the effect of different plant dynamics. How the dissolved oxygen concentration of the aerobic tank affect the effluent ammonia concentration and how the internal recirculation affect the nitrate concentration of the anoxic tank is studied. The best fit of the model is estimated by varying the model order through a trial-and-error approach. Three different scenarios are investigated: one Single-Input-Single-Output (SISO) and two Multiple-Input-Multiple-Output (MIMO) structures. In the SISO scenario only the oxygen to the effluent ammonia dynamics is investigated. Then for both the MIMO scenarios the internal recirculation to nitrate concentration dynamics in the anoxic tank is included and in the last scenario the influent flow rate is also included. The approach is evaluated using the Benchmark Simulation Model no.1 (BSM1).

Proceedings of The 9th EUROSIM Congress on Modelling and Simulation, EUROSIM 2016, The 57th SIMS Conference on Simulation and Modelling SIMS 2016, Dec 19, 2018

The analysis of a simplified activated sludge process (ASP) with one main dissolved substrate and... more The analysis of a simplified activated sludge process (ASP) with one main dissolved substrate and one main particulate biomass has been conducted in steady-state conditions. The ASP is formed by a plug-flow reactor and a settler tank. The biomass growth rate is described by a Monod function. For this process, it is not possible to get an explicit expression for the effluent substrate concentration when the process is subject to a fixed sludge age. However, when the substrate concentration of the influent is much greater than that of the effluent, an approximate and explicit relation between them is obtained. Numerical examples with two models for the settler are presented. One model is the ideal settler, which assumes a complete thickening of the sludge. The other model includes hindered settling and sludge compression. Numerical results show the effectiveness and the limitations of the proposed solution under these scenarios.

Energies, 2019

Building energy performance modeling is essential for energy planning, management, and efficiency... more Building energy performance modeling is essential for energy planning, management, and efficiency. This paper presents a space heating model suitable for auto-generating baseline models of existing multifamily buildings. Required data and parameter input are kept within such a level of detail that baseline models can be auto-generated from, and calibrated by, publicly accessible data sources. The proposed modeling framework consists of a thermal network, a typical hydronic radiator heating system, a simulation procedure, and data handling procedures. The thermal network is a lumped and simplified version of the ISO 52016-1:2017 standard. The data handling consists of procedures to acquire and make use of satellite-based solar radiation data, meteorological reanalysis data (air temperature, ground temperature, wind, albedo, and thermal radiation), and pre-processing procedures of boundary conditions to account for impact from shading objects, window blinds, wind- and stack-driven air...

Applied Water Science, 2019

The aim of this paper is to evaluate and compare the performance of two machine learning methods,... more The aim of this paper is to evaluate and compare the performance of two machine learning methods, Gaussian process regression (GPR) and Gaussian mixture models (GMMs), as two possible methods for monitoring the sludge profile in a secondary settler tank (SST). In GPR, the prediction of the response variable is given as a Gaussian probability density function, whereas in the GMM the probability density function is built as a weighted sum of Gaussian distributions. In both approaches, a residual is calculated and a fault detection criterion is implemented via a recursive decision rule. As case study, GMM and GPR were tested using real data from a sensor measuring the suspended solids concentration as a function of the SST level in a wastewater treatment plant in Bromma, Sweden. Results suggest that GMM gives a faster response but is also more sensitive than GPR to changes during normal conditions.

Energy Procedia, 2019

Phosphorus (P) is one of the essential nutrients for production of food. In modern agriculture, a... more Phosphorus (P) is one of the essential nutrients for production of food. In modern agriculture, a large part of P comes from finite sources. There are several suggested processes for reuse of P from wastewater. In this paper, the energy use of direct reuse of sludge in agriculture is compared to the energy demand connected to use of mineral P and to reuse of P after thermal processing of sludge. The study is based on literature data from life cycle analysis (LCA). In the case of direct sludge reuse the sludge stabilization processes applied and the system boundaries of the LCA has a large impact on the calculated energy demand. The results though indicate that direct reuse of sludge in agriculture is the reuse scenario that potentially has the lowest energy demand (3-71 kWh/kg P), compared to incineration and extraction of P from sludge ashes (45-70 kWh/kg P) or pyrolysis of sludge (46-235 kWh/kg P). The competitiveness compared to mineral P (-4-22 kWh/kg P) depends on the mineral P source and production. For thermal processing, the energy demand derives mainly from energy needed to dry sludge and supplement fuel used during sludge incineration together with chemicals required to extract P. Local conditions, such as available waste heat for drying, can make one of these scenarios preferable.

Energy Procedia, 2019

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Chemical Engineering Science, 2018

The hindered-settling velocity function for the modelling, simulation and control of secondary se... more The hindered-settling velocity function for the modelling, simulation and control of secondary settling tanks can be determined from batch tests. The conventional method is to measure the velocity of the descending sludge-supernatant interface (sludge blanket) as the change in height over time in a vessel with constant cross-sectional area. Each such experiment provides one point on the flux curve since, under idealizing assumptions (monodisperse suspension, no wall-effects), the concentration of sludge remains constant just below the sludge blanket until some wave from the bottom reaches it. A newly developed method of estimation, based on the theory of nonlinear hyperbolic partial differential equations, is applied to both synthetic and experimental data. The method demonstrates that a substantial portion of the flux function may be estimated from a single batch test in a conical vessel. The new method takes into consideration that during an ideal settling experiment in a cone, the concentration just below the sludge blanket increases with time since the mass of suspended solids occupy a reduced volume over time.

Water science and technology : a journal of the International Association on Water Pollution Research, 2018

Biofilm fouling is known to impact the data quality of sensors, but little is known about the exa... more Biofilm fouling is known to impact the data quality of sensors, but little is known about the exact effects. We studied the effects of artificial and real biofilm fouling on dissolved oxygen (DO) sensors in full-scale water resource recovery facilities, and how this can automatically be detected. Biofilm fouling resulted in different drift direction and bias magnitudes for optical (OPT) and electrochemical (MEC) DO sensors. The OPT-sensor was more affected by biofilm fouling compared to the MEC-sensor, especially during summer conditions. A bias of 1 mg/L was detected by analysing the impulse response (IR) of the automatic air cleaning system in the DO sensor. The IR is an effect of a temporal increase in DO concentration during the automatic air cleaning. The IRs received distinct pattern changes that were matched with faults including: biofilm fouling, disturbances in the air supply to the cleaning system, and damaged sensor membrane, which can be used for fault diagnosis. The res...

Journal of Environmental Chemical Engineering, 2017

Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analy... more Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analyzed in steady-state operation using a reduced model consisting of one soluble substrate and one particulate biomass component modelling the dominating biological process. Monod biomass growth rate is assumed. Two settler models are studied. One is the commonly used ideal settler, or point settler, which is assumed to never be overloaded and to have unlimited flux capacity. The other recently published steady-state settler model includes hindered and compressive settling, and models a realistic limiting flux capacity. Generally, the steady-state concentration profiles within the PFR and the settler are governed by nonlinear ordinary differential equations. It is shown that the steady-state behaviour of the ASP can, however, be captured by equations without derivatives. New theoretical results are given, such as conditions by means of inequalities on input variables and parameters for a steady-state solution to exist. Another novel finding is that, if the incoming substrate concentration is increased from a low or moderate stationary value and the solids residence time is kept fixed, then this results in a lower effluent concentration in the new steady state. The steady-state equations are solved numerically for different operating conditions. For common parameter values, numerical solutions reveal that an ASP having a PFR, instead of a continuously stirred tank reactor, is far more efficient in reducing the effluent substrate concentration and this can be obtained for much lower recycle ratios, which reduces the pumping energy considerably.

Autothermal Thermophilic Aerobic Digestion (ATAD) is becoming an alternative to conventional dige... more Autothermal Thermophilic Aerobic Digestion (ATAD) is becoming an alternative to conventional digestion systems. Aeration is crucial for the good performance of this process. Nowadays, there is so much to do in the development of new automatic control in ATADs since the existing controls strategies are based just on the empirical knowledge of the process. This paper evaluates a linear robust feedback controller designed according to Quantitative Feedback Theory (QFT) principles, assuring stability and performance in the achievement of optimal operating points non-linearly determined. A previous work, focused on a benchmark adapted to ATAD, was used to validate this approach and to compare with previous control strategies.

This work deals with fault detection of DO sensors under possible clogging condition. The detecti... more This work deals with fault detection of DO sensors under possible clogging condition. The detection of the clogging condition is performed using two fault detection (FD) methods. Method 1 detects changes in the distance between signal spectra and method 2 detects changes in the signal standard deviation. Both FD algorithms are based on the likelihood ratio test implemented in a recursive decision rule. Real data from a dissolved oxygen (DO) sensor located in an aerated basin of an activated sludge process is used as case study. The sensor is used in a closed loop control. Results show that both methods give a quite similar detection results. Hence, in this case study, it seems sufficient to just monitor the standard deviation of the sensor signal. Before making any confirmative conclusions more experiments are, however, needed.

In this paper, an optimization study of simple bioreactors in series is presented. For a given to... more In this paper, an optimization study of simple bioreactors in series is presented. For a given total reactor volume, the zone volumes are optimized with respect to the effluent substrate. Also simple activated sludge models are considered. Both Monod and Contois functions are used for describing the growth kinetics. It is shown that the optimal zone volumes are very different depending on the choice of growth kinetics. In particular, it is studied how the influent steady state substrate concentration influence the optimal configuration.

In this paper, simple activated sludge process (ASP) models with Monod and Contois biomass growth... more In this paper, simple activated sludge process (ASP) models with Monod and Contois biomass growth kinetics are compared. In particular, the cases of an ASP with one or two bioreactors are studied. Of particular concern in this study is to investigate how the effluent substrate concentration depends on the influent substrate concentration. It is shown that the results are very different depending on the number of bioreactors and on the growth kinetics assumed.

In this study, a sensitivity analysis and a calibration were applied to a recent published model ... more In this study, a sensitivity analysis and a calibration were applied to a recent published model (Lindblom et al., 2015) used to replicate nitrous oxide (N 2 O) emissions in an one-stage nitritation-Anammox process using a moving-bed biofilm reactor (MBBR) at Hammarby-Sjstad pilot plant (Stockholm, Sweden), which treats anaerobic digestion liquor. Results indicate that the biofilm porosity, biofilm density, maximum biofilm thickness and boundary layer thickness were the most sensitive parameters of the model.

Linköping Electronic Conference Proceedings, 2017

This work deals with steady-state simulation study of a process formed by a microalgae-bacteria p... more This work deals with steady-state simulation study of a process formed by a microalgae-bacteria photobioreactor (PBR) in an activated sludge configuration. In particular, the process behavior in terms of variations in the sludge retention time and carbon dioxide (CO 2) injected is presented. The optimization is done by considering the total PBR volume as two volumes in series, and aiming for the minimal substrate concentration in the effluent, for a given external light and CO 2 injected. Results suggest that it is possible to obtain an optimum volume distribution of the process that gives a lower effluent substrate concentration compared to the same process using a single volume.

Linköping Electronic Conference Proceedings, 2018

This paper presents a method for monitoring the sludge profiles of a secondary settler using a Ga... more This paper presents a method for monitoring the sludge profiles of a secondary settler using a Gaussian Mixture Model (GMM). A GMM is a parametric probability density function represented as a weighted sum of Gaussian components densities. To illustrate this method, the current approach is applied using real data from a sensor measuring the sludge concentration as a function of the settler level at a wastewater treatment plant (WWTP) in Bromma, Sweden. Results suggest that the GMM approach is a feasible method for monitoring and detecting possible disturbances of the process and fault situations such as sensor clogging. This approach can be a valuable tool for monitoring processes with a repetitive profile.

La presente investigacion tuvo como objetivo analizar el sistema medular del mercado del pollo be... more La presente investigacion tuvo como objetivo analizar el sistema medular del mercado del pollo beneficiado en la RegionCapital, durante el segundo semestre de 2010, partiendo del estudio teorico de las variables macroambientales, lasvariables de “marketing mix” y las variables microambientales que lo afectan. Este trabajo se enmarca en los postulados dela investigacion no experimental, de nivel exploratorio y descriptivo, bajo diseno mixto, bibliografico y de campo. Seutilizo como tecnica de investigacion la entrevista, la encuesta, el estudio bibliografico y la observacion, y comoinstrumentos de recoleccion de datos, el cuestionario, el guion estructurado y la matriz FODA. La poblacion objeto deestudio estuvo representada por la Federacion Nacional de Avicultura de Venezuela (FENAVI), por el Ministerio delPoder Popular para la Alimentacion, el Ministerio del Poder Popular para la Agricultura y Tierras y por la Cadena deDistribucion del Mercado de Pollo Beneficiado en la Region Capi...

International Journal of Productivity and Quality Management, 2020

Water, 2021

This paper proposes a methodology for the layout selection of an urban drainage system as an exte... more This paper proposes a methodology for the layout selection of an urban drainage system as an extension to the methodology for an optimal sewer network design proposed by Duque, Duque, Aguilar, & Saldarriaga. The layout selection approach proposed in this paper uses an objective function that takes into account all input data in the problem, such as: land topography, street network topology, and inflow to each manhole. Once the layout is selected, the network is optimally designed using dynamic programming. The problem of layout selection is solved as a mixed-integer programming problem and is divided into two steps. The first step tries to define an initial layout using the network topology and land topography as a criterion. This allows for an initial hydraulic design and an approximation of the sewer network’s construction costs. The second step uses the data obtained in the previous process to establish an approximation of the construction costs of each arc that can be part of th...

Proceedings of The 59th Conference on imulation and Modelling (SIMS 59), 26-28 September 2018, Oslo Metropolitan University, Norway, Nov 19, 2018

Output-Error (OE) System Identification is used to estimate the nonlinear behavior of an activate... more Output-Error (OE) System Identification is used to estimate the nonlinear behavior of an activated sludge process (ASP) in a Wastewater Treatment Plant (WWTP). The aim is to identify dynamic models to reproduce the effect of different plant dynamics. How the dissolved oxygen concentration of the aerobic tank affect the effluent ammonia concentration and how the internal recirculation affect the nitrate concentration of the anoxic tank is studied. The best fit of the model is estimated by varying the model order through a trial-and-error approach. Three different scenarios are investigated: one Single-Input-Single-Output (SISO) and two Multiple-Input-Multiple-Output (MIMO) structures. In the SISO scenario only the oxygen to the effluent ammonia dynamics is investigated. Then for both the MIMO scenarios the internal recirculation to nitrate concentration dynamics in the anoxic tank is included and in the last scenario the influent flow rate is also included. The approach is evaluated using the Benchmark Simulation Model no.1 (BSM1).

Proceedings of The 9th EUROSIM Congress on Modelling and Simulation, EUROSIM 2016, The 57th SIMS Conference on Simulation and Modelling SIMS 2016, Dec 19, 2018

The analysis of a simplified activated sludge process (ASP) with one main dissolved substrate and... more The analysis of a simplified activated sludge process (ASP) with one main dissolved substrate and one main particulate biomass has been conducted in steady-state conditions. The ASP is formed by a plug-flow reactor and a settler tank. The biomass growth rate is described by a Monod function. For this process, it is not possible to get an explicit expression for the effluent substrate concentration when the process is subject to a fixed sludge age. However, when the substrate concentration of the influent is much greater than that of the effluent, an approximate and explicit relation between them is obtained. Numerical examples with two models for the settler are presented. One model is the ideal settler, which assumes a complete thickening of the sludge. The other model includes hindered settling and sludge compression. Numerical results show the effectiveness and the limitations of the proposed solution under these scenarios.

Energies, 2019

Building energy performance modeling is essential for energy planning, management, and efficiency... more Building energy performance modeling is essential for energy planning, management, and efficiency. This paper presents a space heating model suitable for auto-generating baseline models of existing multifamily buildings. Required data and parameter input are kept within such a level of detail that baseline models can be auto-generated from, and calibrated by, publicly accessible data sources. The proposed modeling framework consists of a thermal network, a typical hydronic radiator heating system, a simulation procedure, and data handling procedures. The thermal network is a lumped and simplified version of the ISO 52016-1:2017 standard. The data handling consists of procedures to acquire and make use of satellite-based solar radiation data, meteorological reanalysis data (air temperature, ground temperature, wind, albedo, and thermal radiation), and pre-processing procedures of boundary conditions to account for impact from shading objects, window blinds, wind- and stack-driven air...

Applied Water Science, 2019

The aim of this paper is to evaluate and compare the performance of two machine learning methods,... more The aim of this paper is to evaluate and compare the performance of two machine learning methods, Gaussian process regression (GPR) and Gaussian mixture models (GMMs), as two possible methods for monitoring the sludge profile in a secondary settler tank (SST). In GPR, the prediction of the response variable is given as a Gaussian probability density function, whereas in the GMM the probability density function is built as a weighted sum of Gaussian distributions. In both approaches, a residual is calculated and a fault detection criterion is implemented via a recursive decision rule. As case study, GMM and GPR were tested using real data from a sensor measuring the suspended solids concentration as a function of the SST level in a wastewater treatment plant in Bromma, Sweden. Results suggest that GMM gives a faster response but is also more sensitive than GPR to changes during normal conditions.

Energy Procedia, 2019

Phosphorus (P) is one of the essential nutrients for production of food. In modern agriculture, a... more Phosphorus (P) is one of the essential nutrients for production of food. In modern agriculture, a large part of P comes from finite sources. There are several suggested processes for reuse of P from wastewater. In this paper, the energy use of direct reuse of sludge in agriculture is compared to the energy demand connected to use of mineral P and to reuse of P after thermal processing of sludge. The study is based on literature data from life cycle analysis (LCA). In the case of direct sludge reuse the sludge stabilization processes applied and the system boundaries of the LCA has a large impact on the calculated energy demand. The results though indicate that direct reuse of sludge in agriculture is the reuse scenario that potentially has the lowest energy demand (3-71 kWh/kg P), compared to incineration and extraction of P from sludge ashes (45-70 kWh/kg P) or pyrolysis of sludge (46-235 kWh/kg P). The competitiveness compared to mineral P (-4-22 kWh/kg P) depends on the mineral P source and production. For thermal processing, the energy demand derives mainly from energy needed to dry sludge and supplement fuel used during sludge incineration together with chemicals required to extract P. Local conditions, such as available waste heat for drying, can make one of these scenarios preferable.

Energy Procedia, 2019

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Chemical Engineering Science, 2018

The hindered-settling velocity function for the modelling, simulation and control of secondary se... more The hindered-settling velocity function for the modelling, simulation and control of secondary settling tanks can be determined from batch tests. The conventional method is to measure the velocity of the descending sludge-supernatant interface (sludge blanket) as the change in height over time in a vessel with constant cross-sectional area. Each such experiment provides one point on the flux curve since, under idealizing assumptions (monodisperse suspension, no wall-effects), the concentration of sludge remains constant just below the sludge blanket until some wave from the bottom reaches it. A newly developed method of estimation, based on the theory of nonlinear hyperbolic partial differential equations, is applied to both synthetic and experimental data. The method demonstrates that a substantial portion of the flux function may be estimated from a single batch test in a conical vessel. The new method takes into consideration that during an ideal settling experiment in a cone, the concentration just below the sludge blanket increases with time since the mass of suspended solids occupy a reduced volume over time.

Water science and technology : a journal of the International Association on Water Pollution Research, 2018

Biofilm fouling is known to impact the data quality of sensors, but little is known about the exa... more Biofilm fouling is known to impact the data quality of sensors, but little is known about the exact effects. We studied the effects of artificial and real biofilm fouling on dissolved oxygen (DO) sensors in full-scale water resource recovery facilities, and how this can automatically be detected. Biofilm fouling resulted in different drift direction and bias magnitudes for optical (OPT) and electrochemical (MEC) DO sensors. The OPT-sensor was more affected by biofilm fouling compared to the MEC-sensor, especially during summer conditions. A bias of 1 mg/L was detected by analysing the impulse response (IR) of the automatic air cleaning system in the DO sensor. The IR is an effect of a temporal increase in DO concentration during the automatic air cleaning. The IRs received distinct pattern changes that were matched with faults including: biofilm fouling, disturbances in the air supply to the cleaning system, and damaged sensor membrane, which can be used for fault diagnosis. The res...

Journal of Environmental Chemical Engineering, 2017

Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analy... more Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analyzed in steady-state operation using a reduced model consisting of one soluble substrate and one particulate biomass component modelling the dominating biological process. Monod biomass growth rate is assumed. Two settler models are studied. One is the commonly used ideal settler, or point settler, which is assumed to never be overloaded and to have unlimited flux capacity. The other recently published steady-state settler model includes hindered and compressive settling, and models a realistic limiting flux capacity. Generally, the steady-state concentration profiles within the PFR and the settler are governed by nonlinear ordinary differential equations. It is shown that the steady-state behaviour of the ASP can, however, be captured by equations without derivatives. New theoretical results are given, such as conditions by means of inequalities on input variables and parameters for a steady-state solution to exist. Another novel finding is that, if the incoming substrate concentration is increased from a low or moderate stationary value and the solids residence time is kept fixed, then this results in a lower effluent concentration in the new steady state. The steady-state equations are solved numerically for different operating conditions. For common parameter values, numerical solutions reveal that an ASP having a PFR, instead of a continuously stirred tank reactor, is far more efficient in reducing the effluent substrate concentration and this can be obtained for much lower recycle ratios, which reduces the pumping energy considerably.