Akif Hocalar - Academia.edu (original) (raw)

Papers by Akif Hocalar

Research paper thumbnail of Nonlinear control of large-scale fed-batch yeast fermentation: control of the specific growth rate

TURKISH JOURNAL OF ENGINEERING AND ENVIRONMENTAL SCIENCES, 2014

Model-based feedback linearizing control is studied for the control of fed-batch yeast fermentati... more Model-based feedback linearizing control is studied for the control of fed-batch yeast fermentation. For this purpose, the specific growth rate of fed-batch baker's yeast fermentation is controlled with a state feedback linearizing control approach. All control algorithms are constructed on reliable primary measurements, data reconciliation, and state estimations developed previously. The obtained biomass concentrations and specific growth rates are used in the control algorithms. Initially, the results of open-loop specific growth rate controlled fed-batch baker's yeast fermentation are given to show the shortcomings of the existing control method in practice. The state feedback linearizing control of the specific growth rate is then applied to the fed-batch baker's yeast fermentation. Different specific growth rate profiles are investigated and results are presented. The successful implementation of the control of the specific growth rate is shown under the critical specific growth rate value and other limiting factors.

Research paper thumbnail of Model Based Control of Large Scale Fed-Batch Baker's Yeast Fermentation

IFAC Proceedings Volumes, 2009

Two different control methods are applied to the technical scale (25 m 3) fed-batch baker's yeast... more Two different control methods are applied to the technical scale (25 m 3) fed-batch baker's yeast fermentation. Feedback linearizing control design is used to manipulate the substrate feeding rate in order to maximize the biomass yield and minimizing the production of ethanol. Firstly, the specific growth rate controller is developed and applied to maintain the specific growth rate at specified trajectory. Secondly, the minimal ethanol controller is developed to maximize biomass productivity, by controlling specific growth rate just above the maximum oxidative growth rate by controlling ethanol concentration. The both controllers worked successfully and can be combined to follow required specific growth rate trajectory and respond successfully to disturbances in overflow fermentations such as Saccharomyces cerevisiae.

Research paper thumbnail of Biogas desulphurization at technical scale by lithotrophic denitrification: Integration of sulphide and nitrogen removal

Process Biochemistry, 2011

Biogas desulphurization was carried out in a continuous bioscrubber with a volume of 5 m 3 using ... more Biogas desulphurization was carried out in a continuous bioscrubber with a volume of 5 m 3 using aerobically treated wastewater containing activated sludge and mixture of nitrate (NO 3 −) and nitrite (NO 2 −) as electron acceptors in industrial relevant conditions. Both nitrate and nitrite were provided from full-scale activated sludge treatment plant operated and controlled using dissolved oxygen and redox sensors to make sure nitrification performed and biogas was provided from anaerobic digester. The biogas flowrate changed from 5 to 25 m 3 /h and wastewater flowrate from 2.5 to 15 m 3 /h. The volumetric sulphide loading rates ranged between 2 and 22 kg S 2− m −3 d −1. The optimum wastewater/biogas ratio observed for maximum H 2 S removal rates was in the range of 2-3 m 3 /m 3 and minimum empty bed residence time (EBRT) determined was around 10 min. Nitrogen removal in the form of nitrate and nitrite was found to be proportional to sulphide removal. The redox potential of the effluent was also monitored and related to the wastewater/biogas ratio. More than 95% of H 2 S has been removed from biogas in this study when the volumetric sulphide loading rates were between 2 and 4 kg S 2− m −3 d −1. This work reveals that sulphide removal can successfully be integrated to biological nitrogen removal (BNR) in industrial wastewater treatment systems.

Research paper thumbnail of State estimation and nonlinear control of industrial fed batch yeast fermentation

Journal of Biotechnology, 2007

Research paper thumbnail of On-line evolutionary optimization of an industrial fed-batch yeast fermentation process

ISA Transactions, 2009

This paper presents two genetic algorithms based on optimization methods to maximize biomass conc... more This paper presents two genetic algorithms based on optimization methods to maximize biomass concentration, and to minimize ethanol formation. The objective function is maximized according to the values of feed flow rate, using genetic search approaches. Five case studies were carried out for different initial conditions, which strongly influence the optimal profiles of feed flow rate for the fermentation process. The ethanol and glucose disturbance effects were examined to stress the effectiveness of proposed approaches. The proposed genetic approaches were implemented for an industrial scale baker's yeast fermentor which produces Saccharomyces cerevisiae known as baker's yeast. The results show that optimal feed flow rate was obtained in a satisfactory and successful way for fed-batch fermentation process.

Research paper thumbnail of State estimation and error diagnosis in industrial fed-batch yeast fermentation

AIChE Journal, 2006

Measurements provide the basis for monitoring and control of industrial processes as well as mode... more Measurements provide the basis for monitoring and control of industrial processes as well as model development and validation. Therefore, systematic approaches are of great value to increase accuracy and reliability of measurements. In bioprocesses, linear conservation relations such as elements and enthalpy can be employed to relate conversion rates. In this work, a systematic approach has been applied to production scale fed-batch yeast fermentations. The six data sets obtained from two industrial size bubble columns, one with 25 m3 volumes and the other with 100 m3 volumes, are analyzed for state estimation and error diagnosis. A statistical test is employed for error diagnosis. The serial elimination method is used to analyze and locate the source of errors. The conversion rates are calculated from primary measurements such as flow rates, temperatures, and concentrations. When available measurements are more than the degrees of freedom of the system, it is said that the system is redundant. The redundancy is, therefore, used for error detection and data reconciliation for the six data sets in this work. In addition to elemental balances, heat balance has been set up for the bubble columns, and metabolic heat production rate is employed as an additional measurement. The redundancy is employed for state estimation, and biomass concentration and specific growth rate have been estimated with great accuracy. The estimations can be further used for process monitoring and control. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Research paper thumbnail of Monitoring and control of biogas desulphurization using oxidation reduction potential under denitrifiying conditions

Journal of Chemical Technology & Biotechnology, 2011

BACKGROUND: Hydrogen sulphide (H 2 S) present in biogas can be oxidized to elemental sulphur (S 0... more BACKGROUND: Hydrogen sulphide (H 2 S) present in biogas can be oxidized to elemental sulphur (S 0) or sulphate (SO 4 2−) using nitrate and nitrite. Both nitrate and nitrite are normally available in most wastewater treatment plants and could be used to oxidize H 2 S depending on the molar loading ratio of wastewater and biogas. A control approach is required in order to minimize the fluctuations in inlet and outlet H 2 S concentrations in biogas, and the oxidation potential of the wastewater used. RESULTS: A control scheme has been developed for biogas desulphurization using oxidation reduction potential under industrial conditions. The redox potential was maintained at about +50 to +100 mV in the activated sludge plant to monitor the performance of the nitrification process. The redox potential in the bioscrubber was related to sulphide removal from biogas. More than 90% of the hydrogen sulphide was removed from the biogas. CONCLUSION: The oxidation reduction potential can be used as a key parameter for monitoring and controlling biogas cleaning. Fluctuations of the inlet H 2 S concentration in biogas can be compensated by manipulating the flowrates of wastewater used in order to achieve consistent and desired H 2 S concentrations in treated biogas.

Research paper thumbnail of Nonlinear control of large-scale fed-batch yeast fermentation: control of the specific growth rate

TURKISH JOURNAL OF ENGINEERING AND ENVIRONMENTAL SCIENCES, 2014

Model-based feedback linearizing control is studied for the control of fed-batch yeast fermentati... more Model-based feedback linearizing control is studied for the control of fed-batch yeast fermentation. For this purpose, the specific growth rate of fed-batch baker's yeast fermentation is controlled with a state feedback linearizing control approach. All control algorithms are constructed on reliable primary measurements, data reconciliation, and state estimations developed previously. The obtained biomass concentrations and specific growth rates are used in the control algorithms. Initially, the results of open-loop specific growth rate controlled fed-batch baker's yeast fermentation are given to show the shortcomings of the existing control method in practice. The state feedback linearizing control of the specific growth rate is then applied to the fed-batch baker's yeast fermentation. Different specific growth rate profiles are investigated and results are presented. The successful implementation of the control of the specific growth rate is shown under the critical specific growth rate value and other limiting factors.

Research paper thumbnail of Model Based Control of Large Scale Fed-Batch Baker's Yeast Fermentation

IFAC Proceedings Volumes, 2009

Two different control methods are applied to the technical scale (25 m 3) fed-batch baker's yeast... more Two different control methods are applied to the technical scale (25 m 3) fed-batch baker's yeast fermentation. Feedback linearizing control design is used to manipulate the substrate feeding rate in order to maximize the biomass yield and minimizing the production of ethanol. Firstly, the specific growth rate controller is developed and applied to maintain the specific growth rate at specified trajectory. Secondly, the minimal ethanol controller is developed to maximize biomass productivity, by controlling specific growth rate just above the maximum oxidative growth rate by controlling ethanol concentration. The both controllers worked successfully and can be combined to follow required specific growth rate trajectory and respond successfully to disturbances in overflow fermentations such as Saccharomyces cerevisiae.

Research paper thumbnail of Biogas desulphurization at technical scale by lithotrophic denitrification: Integration of sulphide and nitrogen removal

Process Biochemistry, 2011

Biogas desulphurization was carried out in a continuous bioscrubber with a volume of 5 m 3 using ... more Biogas desulphurization was carried out in a continuous bioscrubber with a volume of 5 m 3 using aerobically treated wastewater containing activated sludge and mixture of nitrate (NO 3 −) and nitrite (NO 2 −) as electron acceptors in industrial relevant conditions. Both nitrate and nitrite were provided from full-scale activated sludge treatment plant operated and controlled using dissolved oxygen and redox sensors to make sure nitrification performed and biogas was provided from anaerobic digester. The biogas flowrate changed from 5 to 25 m 3 /h and wastewater flowrate from 2.5 to 15 m 3 /h. The volumetric sulphide loading rates ranged between 2 and 22 kg S 2− m −3 d −1. The optimum wastewater/biogas ratio observed for maximum H 2 S removal rates was in the range of 2-3 m 3 /m 3 and minimum empty bed residence time (EBRT) determined was around 10 min. Nitrogen removal in the form of nitrate and nitrite was found to be proportional to sulphide removal. The redox potential of the effluent was also monitored and related to the wastewater/biogas ratio. More than 95% of H 2 S has been removed from biogas in this study when the volumetric sulphide loading rates were between 2 and 4 kg S 2− m −3 d −1. This work reveals that sulphide removal can successfully be integrated to biological nitrogen removal (BNR) in industrial wastewater treatment systems.

Research paper thumbnail of State estimation and nonlinear control of industrial fed batch yeast fermentation

Journal of Biotechnology, 2007

Research paper thumbnail of On-line evolutionary optimization of an industrial fed-batch yeast fermentation process

ISA Transactions, 2009

This paper presents two genetic algorithms based on optimization methods to maximize biomass conc... more This paper presents two genetic algorithms based on optimization methods to maximize biomass concentration, and to minimize ethanol formation. The objective function is maximized according to the values of feed flow rate, using genetic search approaches. Five case studies were carried out for different initial conditions, which strongly influence the optimal profiles of feed flow rate for the fermentation process. The ethanol and glucose disturbance effects were examined to stress the effectiveness of proposed approaches. The proposed genetic approaches were implemented for an industrial scale baker's yeast fermentor which produces Saccharomyces cerevisiae known as baker's yeast. The results show that optimal feed flow rate was obtained in a satisfactory and successful way for fed-batch fermentation process.

Research paper thumbnail of State estimation and error diagnosis in industrial fed-batch yeast fermentation

AIChE Journal, 2006

Measurements provide the basis for monitoring and control of industrial processes as well as mode... more Measurements provide the basis for monitoring and control of industrial processes as well as model development and validation. Therefore, systematic approaches are of great value to increase accuracy and reliability of measurements. In bioprocesses, linear conservation relations such as elements and enthalpy can be employed to relate conversion rates. In this work, a systematic approach has been applied to production scale fed-batch yeast fermentations. The six data sets obtained from two industrial size bubble columns, one with 25 m3 volumes and the other with 100 m3 volumes, are analyzed for state estimation and error diagnosis. A statistical test is employed for error diagnosis. The serial elimination method is used to analyze and locate the source of errors. The conversion rates are calculated from primary measurements such as flow rates, temperatures, and concentrations. When available measurements are more than the degrees of freedom of the system, it is said that the system is redundant. The redundancy is, therefore, used for error detection and data reconciliation for the six data sets in this work. In addition to elemental balances, heat balance has been set up for the bubble columns, and metabolic heat production rate is employed as an additional measurement. The redundancy is employed for state estimation, and biomass concentration and specific growth rate have been estimated with great accuracy. The estimations can be further used for process monitoring and control. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Research paper thumbnail of Monitoring and control of biogas desulphurization using oxidation reduction potential under denitrifiying conditions

Journal of Chemical Technology & Biotechnology, 2011

BACKGROUND: Hydrogen sulphide (H 2 S) present in biogas can be oxidized to elemental sulphur (S 0... more BACKGROUND: Hydrogen sulphide (H 2 S) present in biogas can be oxidized to elemental sulphur (S 0) or sulphate (SO 4 2−) using nitrate and nitrite. Both nitrate and nitrite are normally available in most wastewater treatment plants and could be used to oxidize H 2 S depending on the molar loading ratio of wastewater and biogas. A control approach is required in order to minimize the fluctuations in inlet and outlet H 2 S concentrations in biogas, and the oxidation potential of the wastewater used. RESULTS: A control scheme has been developed for biogas desulphurization using oxidation reduction potential under industrial conditions. The redox potential was maintained at about +50 to +100 mV in the activated sludge plant to monitor the performance of the nitrification process. The redox potential in the bioscrubber was related to sulphide removal from biogas. More than 90% of the hydrogen sulphide was removed from the biogas. CONCLUSION: The oxidation reduction potential can be used as a key parameter for monitoring and controlling biogas cleaning. Fluctuations of the inlet H 2 S concentration in biogas can be compensated by manipulating the flowrates of wastewater used in order to achieve consistent and desired H 2 S concentrations in treated biogas.