The Experts below are selected from a list of 52857 Experts worldwide ranked by ideXlab platform
De Kreuk M.k. - One of the best experts on this subject based on the ideXlab platform.
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Reconsidering hydrolysis kinetics for anaerobic digestion of waste activated sludge applying cascade reactors with ultra-short residence times
'Elsevier BV', 2021Co-Authors: Guo H., Oosterkamp M.j., Tonin F., Hendriks Alexander, Nair Revathy, Van Lier J.b., De Kreuk M.k.Abstract:Hydrolysis is considered to be the rate-limiting step in anaerobic digestion of waste activated sludge (WAS). In this study, an innovative 4 stages cascade anaerobic digestion system was researched to (1) comprehensively clarify whether cascading configuration enhances WAS hydrolysis, and to (2) better understand the governing hydrolysis kinetics in this system. The cascade system consisted of three 2.2 L ultra-short Solids retention times (SRT) continuous stirred tank reactors (CSTRs) and one 15.4 L CSTR. The cascade system was compared with a reference conventional CSTR digester (22 L) in terms of process performance, hydrolytic enzyme activities and microbial community dynamics under mesophilic conditions (35 °C). The results showed that the cascade system achieved a high and stable total chemical oxygen demand (tCOD) reduction efficiency of 40–42%, even at 12 days total SRT that corresponded to only 1.2 days SRT each in the first three reactors of the cascade. The reference-CSTR converted only 31% tCOD into biogas and suffered process deterioration at the applied low SRTs. Calculated specific hydrolysis rates in the first reactors of the cascade system were significantly higher compared to the reference-CSTR, especially at the lowest applied SRTs. The activities of several hydrolytic enzymes produced in the different stages revealed that protease, cellulase, amino peptidases, and most of the tested glycosyl-hydrolases had significantly higher activities in the first three small digesters of the cascade system, compared to the reference-CSTR. This increase in hydrolytic enzyme production by far exceeded the increase in specific hydrolysis rate, indicating that hydrolysis was limited by Solids-Surface availability for enzymatic attack. Correspondingly, high relative abundances of hydrolytic-fermentative bacteria and hydrogenotrophic methanogens as well as the presence of syntrophic bacteria were found in the first three digesters of the cascade system. However, in the fourth reactor, acetoclastic methanogens dominated, similarly as in the reference-CSTR. Overall, the results concluded that using multiple CSTRs that are operated at low SRTs in a cascade mode of operation significantly improved the enzymatic hydrolysis rate and extend in anaerobic WAS digestion. Moreover, the governing hydrolysis kinetics in the cascading reactors were far more complex than the generally assumed simplified first-order kinetics.
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Reconsidering hydrolysis kinetics for anaerobic digestion of waste activated sludge applying cascade reactors with ultra-short residence times
'Elsevier BV', 2021Co-Authors: Guo H., Oosterkamp M.j., Tonin F., Hendriks Alexander, Nair Revathy, Van Lier J.b., De Kreuk M.k.Abstract:Hydrolysis is considered to be the rate-limiting step in anaerobic digestion of waste activated sludge (WAS). In this study, an innovative 4 stages cascade anaerobic digestion system was researched to (1) comprehensively clarify whether cascading configuration enhances WAS hydrolysis, and to (2) better understand the governing hydrolysis kinetics in this system. The cascade system consisted of three 2.2 L ultra-short Solids retention times (SRT) continuous stirred tank reactors (CSTRs) and one 15.4 L CSTR. The cascade system was compared with a reference conventional CSTR digester (22 L) in terms of process performance, hydrolytic enzyme activities and microbial community dynamics under mesophilic conditions (35 °C). The results showed that the cascade system achieved a high and stable total chemical oxygen demand (tCOD) reduction efficiency of 40–42%, even at 12 days total SRT that corresponded to only 1.2 days SRT each in the first three reactors of the cascade. The reference-CSTR converted only 31% tCOD into biogas and suffered process deterioration at the applied low SRTs. Calculated specific hydrolysis rates in the first reactors of the cascade system were significantly higher compared to the reference-CSTR, especially at the lowest applied SRTs. The activities of several hydrolytic enzymes produced in the different stages revealed that protease, cellulase, amino peptidases, and most of the tested glycosyl-hydrolases had significantly higher activities in the first three small digesters of the cascade system, compared to the reference-CSTR. This increase in hydrolytic enzyme production by far exceeded the increase in specific hydrolysis rate, indicating that hydrolysis was limited by Solids-Surface availability for enzymatic attack. Correspondingly, high relative abundances of hydrolytic-fermentative bacteria and hydrogenotrophic methanogens as well as the presence of syntrophic bacteria were found in the first three digesters of the cascade system. However, in the fourth reactor, acetoclastic methanogens dominated, similarly as in the reference-CSTR. Overall, the results concluded that using multiple CSTRs that are operated at low SRTs in a cascade mode of operation significantly improved the enzymatic hydrolysis rate and extend in anaerobic WAS digestion. Moreover, the governing hydrolysis kinetics in the cascading reactors were far more complex than the generally assumed simplified first-order kinetics.Sanitary EngineeringBT/Biocatalysi
D Mcglinchey - One of the best experts on this subject based on the ideXlab platform.
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a model for stresses in a circular silo with an off centre circular core using the concept of a principal stress cap solution for a completely filled silo and comparison with janssen and dem data
Chemical Engineering Research & Design, 2015Co-Authors: A J Matchett, Paul Langston, D McglincheyAbstract:Abstract A steady state, continuum model for stresses in a circular silo with an off-centre circular core has been developed. The model proposes a geometry for the principal stress cap, resulting in the definition of local and general 3-dimensional co-ordinate systems. Three steady state, orthogonal force balances were conducted which gave partial differential equations in terms of the three principal stresses. Initial solutions were limited to completely filled systems in order to test the model and compare to existing data and models. Solutions to systems with finite, off-centre cores will be considered in a subsequent paper. Numerical solutions of the three equations were implemented. The solutions were tailored to give outputs consistent with the Janssen equation for symmetrical stress systems in completely filled silos. The solutions required assumptions about the nature of internal stress distributions. There are few data on internal stress distributions in hoppers and silos, and so the assumptions were necessary to facilitate the solutions. Other solutions to the fundamental force balance equations could be implemented as more information becomes available. The models were then applied to systems with eccentric stress distributions, and a simple model of surcharge was proposed. Two types of stress eccentricity were identified: • surcharge eccentricity, where an underlying symmetrical stress system is surmounted by an eccentric surcharge. • inherent eccentricity, where the underlying stress distribution is eccentric with an eccentric centre of stress. The two types of system have different properties and it is not possible to identify the underlying stress distribution by the shape of the Solids Surface within the hopper. The model gave a discontinuity in principal stress, σ 3 , at the centre of stress, leading to the concept of a virtual core. This presents theoretical and practical issues. The model was then compared to an extensive set of DEM data generated for an eccentrically loaded silo. The outputs, in terms of wall shear stresses, compared reasonably well with the DEM data, but it was possible to get reasonable agreement over a range of model parameters, including underlying symmetrical stress. The inability to identify underlying stress distribution from Surface profiles, plus the fact that a given wall stress distribution can be modelled by a range of internal parameters, make the identification of internal stress systems from Surface and external measurement extremely challenging.
Guo H. - One of the best experts on this subject based on the ideXlab platform.
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Reconsidering hydrolysis kinetics for anaerobic digestion of waste activated sludge applying cascade reactors with ultra-short residence times
'Elsevier BV', 2021Co-Authors: Guo H., Oosterkamp M.j., Tonin F., Hendriks Alexander, Nair Revathy, Van Lier J.b., De Kreuk M.k.Abstract:Hydrolysis is considered to be the rate-limiting step in anaerobic digestion of waste activated sludge (WAS). In this study, an innovative 4 stages cascade anaerobic digestion system was researched to (1) comprehensively clarify whether cascading configuration enhances WAS hydrolysis, and to (2) better understand the governing hydrolysis kinetics in this system. The cascade system consisted of three 2.2 L ultra-short Solids retention times (SRT) continuous stirred tank reactors (CSTRs) and one 15.4 L CSTR. The cascade system was compared with a reference conventional CSTR digester (22 L) in terms of process performance, hydrolytic enzyme activities and microbial community dynamics under mesophilic conditions (35 °C). The results showed that the cascade system achieved a high and stable total chemical oxygen demand (tCOD) reduction efficiency of 40–42%, even at 12 days total SRT that corresponded to only 1.2 days SRT each in the first three reactors of the cascade. The reference-CSTR converted only 31% tCOD into biogas and suffered process deterioration at the applied low SRTs. Calculated specific hydrolysis rates in the first reactors of the cascade system were significantly higher compared to the reference-CSTR, especially at the lowest applied SRTs. The activities of several hydrolytic enzymes produced in the different stages revealed that protease, cellulase, amino peptidases, and most of the tested glycosyl-hydrolases had significantly higher activities in the first three small digesters of the cascade system, compared to the reference-CSTR. This increase in hydrolytic enzyme production by far exceeded the increase in specific hydrolysis rate, indicating that hydrolysis was limited by Solids-Surface availability for enzymatic attack. Correspondingly, high relative abundances of hydrolytic-fermentative bacteria and hydrogenotrophic methanogens as well as the presence of syntrophic bacteria were found in the first three digesters of the cascade system. However, in the fourth reactor, acetoclastic methanogens dominated, similarly as in the reference-CSTR. Overall, the results concluded that using multiple CSTRs that are operated at low SRTs in a cascade mode of operation significantly improved the enzymatic hydrolysis rate and extend in anaerobic WAS digestion. Moreover, the governing hydrolysis kinetics in the cascading reactors were far more complex than the generally assumed simplified first-order kinetics.
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Reconsidering hydrolysis kinetics for anaerobic digestion of waste activated sludge applying cascade reactors with ultra-short residence times
'Elsevier BV', 2021Co-Authors: Guo H., Oosterkamp M.j., Tonin F., Hendriks Alexander, Nair Revathy, Van Lier J.b., De Kreuk M.k.Abstract:Hydrolysis is considered to be the rate-limiting step in anaerobic digestion of waste activated sludge (WAS). In this study, an innovative 4 stages cascade anaerobic digestion system was researched to (1) comprehensively clarify whether cascading configuration enhances WAS hydrolysis, and to (2) better understand the governing hydrolysis kinetics in this system. The cascade system consisted of three 2.2 L ultra-short Solids retention times (SRT) continuous stirred tank reactors (CSTRs) and one 15.4 L CSTR. The cascade system was compared with a reference conventional CSTR digester (22 L) in terms of process performance, hydrolytic enzyme activities and microbial community dynamics under mesophilic conditions (35 °C). The results showed that the cascade system achieved a high and stable total chemical oxygen demand (tCOD) reduction efficiency of 40–42%, even at 12 days total SRT that corresponded to only 1.2 days SRT each in the first three reactors of the cascade. The reference-CSTR converted only 31% tCOD into biogas and suffered process deterioration at the applied low SRTs. Calculated specific hydrolysis rates in the first reactors of the cascade system were significantly higher compared to the reference-CSTR, especially at the lowest applied SRTs. The activities of several hydrolytic enzymes produced in the different stages revealed that protease, cellulase, amino peptidases, and most of the tested glycosyl-hydrolases had significantly higher activities in the first three small digesters of the cascade system, compared to the reference-CSTR. This increase in hydrolytic enzyme production by far exceeded the increase in specific hydrolysis rate, indicating that hydrolysis was limited by Solids-Surface availability for enzymatic attack. Correspondingly, high relative abundances of hydrolytic-fermentative bacteria and hydrogenotrophic methanogens as well as the presence of syntrophic bacteria were found in the first three digesters of the cascade system. However, in the fourth reactor, acetoclastic methanogens dominated, similarly as in the reference-CSTR. Overall, the results concluded that using multiple CSTRs that are operated at low SRTs in a cascade mode of operation significantly improved the enzymatic hydrolysis rate and extend in anaerobic WAS digestion. Moreover, the governing hydrolysis kinetics in the cascading reactors were far more complex than the generally assumed simplified first-order kinetics.Sanitary EngineeringBT/Biocatalysi
John R. Grace - One of the best experts on this subject based on the ideXlab platform.
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a state of the art review of gas solid turbulent fluidization
Chemical Engineering Science, 2000Co-Authors: Naoko Ellis, I A Abba, John R. GraceAbstract:Abstract Turbulent fluidization has only been widely recognized as a distinct flow regime for the past two decades, even though it is commonly utilized in industrial fluidized-bed reactors due to vigorous gas–Solids contacting, favourable bed-to-Surface heat transfer, high Solids hold-ups (typically 25–35% by volume), and limited axial mixing of gas. Despite its practical importance, turbulent fluidization has received much less attention than the adjacent flow regimes of bubbling, slugging and fast fluidization, due to the challenges of experimental and theoretical work related to this flow regime. However, recent years have seen an upsurge in interest in turbulent fluidization. Various methods – pressure fluctuations, visual observations, capacitance signals, optical fibre probes and bed expansion – have been used to determine the transition velocity, usually denoted U c , at which turbulent fluidization begins. Different methods tend to give different results. There appear to be as many as three different types of turbulent fluidization, depending on such factors as mean particle size, particle size distribution, column diameter and internal baffles, if any. When turbulent fluidization is preceded by bubbling, U c denotes a change from closed laminar bubble wakes to open turbulent wakes. The upper boundary of turbulent fluidization occurs when a distinct upper bed Surface disappears due to substantial entrainment. Much of the literature regarding the turbulent fluidization flow regime adopts the terminology of the bubbling regime, ascribing such properties as bubble diameter and bubble rising velocity, despite the transitory and distorted nature of the voids. Turbulent beds exhibit non-uniform radial voidage distributions, with lower time-mean voidages near the wall than in the interior of the column. Axial mixing of both gas and Solids is usually characterized by axial dispersion coefficients and Peclet numbers which depend on the column dimensions, as well as the gas and particle properties. Empirical equations are presented for prediction of these quantities for both gas and Solids. Surface-to-bed convective heat transfer coefficients tend to reach a maximum in the turbulent fluidization regime. When turbulent beds are represented by two-phase models, interphase mass exchange is rapid. Reactor models vary widely, some treating the turbulent bed as a single phase homogeneous suspension subject to axial dispersion, while others assume two-phase behaviour. A probabilistic approach that merges these approaches as the gas velocity increases shows promise. While considerable progress has been made, substantial challenges remain in understanding and characterizing the turbulent fluidization flow regime.
A J Matchett - One of the best experts on this subject based on the ideXlab platform.
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a model for stresses in a circular silo with an off centre circular core using the concept of a principal stress cap solution for a completely filled silo and comparison with janssen and dem data
Chemical Engineering Research & Design, 2015Co-Authors: A J Matchett, Paul Langston, D McglincheyAbstract:Abstract A steady state, continuum model for stresses in a circular silo with an off-centre circular core has been developed. The model proposes a geometry for the principal stress cap, resulting in the definition of local and general 3-dimensional co-ordinate systems. Three steady state, orthogonal force balances were conducted which gave partial differential equations in terms of the three principal stresses. Initial solutions were limited to completely filled systems in order to test the model and compare to existing data and models. Solutions to systems with finite, off-centre cores will be considered in a subsequent paper. Numerical solutions of the three equations were implemented. The solutions were tailored to give outputs consistent with the Janssen equation for symmetrical stress systems in completely filled silos. The solutions required assumptions about the nature of internal stress distributions. There are few data on internal stress distributions in hoppers and silos, and so the assumptions were necessary to facilitate the solutions. Other solutions to the fundamental force balance equations could be implemented as more information becomes available. The models were then applied to systems with eccentric stress distributions, and a simple model of surcharge was proposed. Two types of stress eccentricity were identified: • surcharge eccentricity, where an underlying symmetrical stress system is surmounted by an eccentric surcharge. • inherent eccentricity, where the underlying stress distribution is eccentric with an eccentric centre of stress. The two types of system have different properties and it is not possible to identify the underlying stress distribution by the shape of the Solids Surface within the hopper. The model gave a discontinuity in principal stress, σ 3 , at the centre of stress, leading to the concept of a virtual core. This presents theoretical and practical issues. The model was then compared to an extensive set of DEM data generated for an eccentrically loaded silo. The outputs, in terms of wall shear stresses, compared reasonably well with the DEM data, but it was possible to get reasonable agreement over a range of model parameters, including underlying symmetrical stress. The inability to identify underlying stress distribution from Surface profiles, plus the fact that a given wall stress distribution can be modelled by a range of internal parameters, make the identification of internal stress systems from Surface and external measurement extremely challenging.