Inlet Concentration Changes Research Articles

Thermophilic waste air treatment of an airborne ethyl acetate/toluene mixture in a bubble column reactor: Stability towards temperature changes

Thermophilic waste air treatment in a lab-scale bubble column reactor (BCR) was used to remove an ethyl acetate/toluene mixture under both mesophilic and thermophilic conditions, at 30–50 °C. Additional tests, e.g., toluene mass transfer measurement and monitoring of microbial population development, explained the observed bioreactor response to the conducted loading tests and temperature changes. The maximum overall elimination capacity at thermophilic conditions (50 °C) was 136.9 g·m−3 h-1, however hysteresis in elimination capacity was observed in response to ascending/descending temperature and inlet concentration changes. Representatives of genera Cupriavidus, Variovorax and order Rhodospirillales were found to be predominant in the degrading microbial population, depending on the operating temperature. Thermobacillus and Blastocatella were abundant at high (50 °C) and low (30 °C) temperatures, respectively. The observed gradual shift in microbial population caused a small yet significant gradual change in developing a preference for toluene at the expense of ethyl acetate, which explains the observed hysteresis. Yet, the whole bioreactor removal efficiency remained similar at the same temperature, thus demonstrating the advantages of using thermophiles in bioreactors with temperature variation, such as robustness and flexibility.

Determination of competitive adsorption isotherms applying the nonlinear frequency response method: Part I. Theoretical analysis

In this work adsorption equilibria of binary mixtures are quantified analyzing the nonlinear frequency response of a chromatographic column. Local partial derivatives of an isotherm model can be estimated for certain steady-states from the low frequency asymptotes of the corresponding frequency response functions (FRFs). The required FRFs correspond to two different compounds and the type of the imposed inlet concentration changes, e.g. periodical inlet concentration changes of only one compound or of both of them. For an accurate determination of isotherm parameters, it is necessary to approach as close as possible the low frequency asymptotic behaviour of these functions. Based on principles valid for the FRFs corresponding to the adsorption of a single solute, frequencies needed to reach the low frequency asymptotes of the functions of interest for estimating competitive isotherms are defined in this paper. The relation between the accuracy of the isotherm parameters determined and numbers and types of periodical inlet concentration changes and steady-states analyzed is also evaluated.

Determination of competitive adsorption isotherms applying the nonlinear frequency response method: Part II. Experimental demonstration

This paper demonstrates an experimental application of the nonlinear frequency response (FR) method extension to determine adsorption isotherms of binary mixtures. This method, based on the analysis of the response of a chromatographic column subjected to the sinusoidal inlet concentration changes, is shown to be an alternative for isotherm determination. The critical issue related to the successful application of the method is to reach experimentally the low frequency asymptotic behaviour of the corresponding frequency response functions (FRFs). Although, there are different possibilities to perform periodical inlet concentration changes, in this paper only simultaneous changes for both components were considered. The adsorption of phenol and 2-phenylethanol on octadecyl silica was analyzed experimentally using a mixture of methanol and water as a solvent. Parameters of competitive isotherms were also estimated for comparison using the classical perturbation method. Despite certain differences between competitive isotherms estimated with the two methods that were found, the obtained results show the potential of the nonlinear FR method for measuring competitive isotherms.

Theoretical investigation of the adsorption of a binary mixture in a chromatographic column using the nonlinear frequency response technique

The nonlinear frequency response of a chromatographic column for the adsorption of two dissolved components is analyzed using the concept of higher order frequency response functions (FRFs) which is based on the Volterra series and generalized Fourier transform. By applying this concept a nonlinear model of a system is replaced by an infinite series of the FRFs of the first, second, etc. order. The FRFs up to the third order are derived theoretically starting from the equilibrium-dispersive model, which is used for description of a chromatographic column, and applying the harmonic probing method. The functions that relate outlet concentration changes of each component to the corresponding inlet concentration changes are derived. At the inlet of a chromatographic column, it is considered: (a) the concentration change of one of the components keeping the concentration of the other component constant and (b) the concentration change of both components keeping their ratio constant. The FRFs are calculated numerically for different steady-state concentrations and relative mixture compositions. It has been found that, despite certain differences in initial conditions, the FRFs exhibit similar behavior. For higher frequencies, the amplitudes of the FRFs tend to zero and phases to −∞. In the low frequency range, which is of interest for investigation of equilibrium parameters, these functions have similar behavior, but tend to different asymptotic values. Correlations between coefficients of competitive adsorption isotherms, i.e. partial isotherm derivatives, and the derived FRFs are established. This theoretical result offers the potential to use the analysis of the nonlinear frequency response of a chromatographic column for estimation of competitive adsorption isotherms.

Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part II

The aim of this paper is to investigate the possibility of applying a nonlinear frequency response (FR) method described by Ilić et al. [2007b. Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part I. Theoretical basis and simulations, this volume, doi: 10.1016/j.ces.2007.05.004] to determine single solute adsorption isotherms. The method is based on the analysis of the nonlinear FR of a chromatographic column to a periodical change of the inlet concentration around several steady-state concentrations. The first, second and third local derivatives of single solute isotherms are estimated from the low-frequency asymptotic behaviour of the corresponding FR functions. The adsorption of 4- tert-butylphenol and ethyl benzoate as single solutes is studied on octadecyl silica ( C 18 ) from methanol–water mixture (60:40). Experiments are performed using a standard gradient HPLC unit capable to realize inlet concentration changes in a nearly sine waveform. Small injections of compounds into the not preloaded column, as well as conventional frontal analysis experiments are performed for rough estimation of the adsorption isotherm coefficients and comparison with the results obtained using the nonlinear FR method.

Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part I. Theoretical basis and simulations

A method for determination of single solute adsorption isotherms based on the analysis of the nonlinear frequency response (FR) of a chromatographic column is developed theoretically. In order to demonstrate this method, the FR of a chromatographic column is simulated for the periodical inlet concentration changes (sine waveform) around several steady-state concentrations. The frequency response functions (FRFs) up to the third order are calculated from the inlet and outlet concentration changes, which are analysed using the fast Fourier transform. Afterwards the coefficients of an adsorption isotherm are estimated from the low-frequency asymptotes of the FRFs and their derivatives. The obtained coefficients compare well with those used for simulations. Also discussed are some aspects that might affect the accuracy of the suggested method when it is applied to the analysis of experimental data, e.g. influence of velocity fluctuations, noise and size of the analysed data set.

Removal of hydrogen sulfide, benzene and toluene by a fluidized bed bioreactor

The dominant off gases from publicly owned treatment works include hydrogen sulfide, benzene, and toluene. In this research, hydrogen sulfide oxidized byBacillus cereus, and benzene with toluene were removed by VOC-degrading microbial consortium. The optimum operating condition of the fluidized bed bioreactor including both microorganisms was 30 ‡C, pH 6–8, and 150 cm of liquid bed height. The critical loading rate of hydrogen sulfide, benzene and toluene in the bioreactor was about 15 g/m3h, 10 g/m3h and 12 g/m3h, respectively. The fluidized bed bioreactor showed an excellent elimination capacity for 580 hours of continuous operation, and maintained stable removal efficiency at sudden inlet concentration changes.

Design and testing of a control system for reverse‐flow catalytic afterburners

AbstractThe design and testing of a control system for reverse‐flow catalytic afterburners based on a two‐variable bifurcation map is focused on. The combustion of lean methane–air mixtures is considered as the test reaction and a bench‐scale apparatus, with a special temperature‐control system based on dynamic compensation of the thermal losses to achieve adiabatic operation, is used for validation purposes. The aim of the control system is to avoid both catalyst overheating and reaction extinction when the adiabatic temperature increases and the flow rate of the feed changes. Stability maps of the reactor are obtained by means of numerical simulations, showing the values of the operating parameters (switching time), which allows fulfillment of the operating constraints (catalyst maximum temperature and methane conversion) when the inlet concentration and flow rate change. This system was realized and tested experimentally, mainly for inlet concentration changes, proving to be effective in all cases investigated. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Adsorption Effect on the Dynamic Response of a Biochemical Reaction in a Biofilm Reactor for Wastewater Treatment

AbstractThe dynamic behavior of a completely mixed, three‐phase, fluidized bed biofilm reactor treating simulated domestic wastewater was studied with step changes in inlet concentration. It was found that the response curves showed second order characteristics, i.e., as the inlet concentration was increased, the outlet concentration also increased, reached a peak value and then decreased until it leveled to a new steady‐state value corresponding to the new inlet concentration level. Nonlinear regression analysis was performed using Monod‐type rate equations with and without an adsorption term. As a result, the theoretical curve of the kinetic model that incorporates the adsorption term has best fit to the actual response in most cases. Thus, it was concluded that the adsorption of a substrate onto the biofilm and carrier particles has a significant effect on the dynamic response in biofilm processes.

Damköhler number distributions and constituent removal in treatment wetlands

Using hypothetical wetland simulations and data from the literature, Kadlec [Eco. Eng. 15 (2000) 105] recently demonstrated that plug-flow models commonly used to quantify treatment wetland performance fail to describe conditions other than those under which calibration data are collected. Parameters of these models (removal rate constants ( k) and background concentrations ( C*)) demonstrate apparent dependence on inlet concentration and hydraulic loading rate which is not alleviated by including dispersion to address non-ideal flow. The phenomenon can be understood as resulting from an interdependence between k and local flow velocity, due to the functional dependence of each on drag-inducing surfaces (and attached biofilms) associated with submerged vegetation and litter. This paper presents a simple method, based on theoretical considerations, for determining C* using inlet–outlet data, independent of the degree of mixing or the nature of the removal processes. This paper also expands upon the hypothetical multi-channel example to suggest a modeling approach in which a wetland is treated conceptually as an ensemble of parallel, non-interacting stream tubes in plug-flow, characterized by a continuous distribution of Damköhler numbers. The Damköhler number distribution (DND) can be estimated from the residence time distribution (RTD) under the assumption of uniform flow path length. For such a wetland, under steady state conditions and with constant inlet concentration, the fraction of a removable pollutant remaining as a function of normalized distance from inlet to outlet is given by the Laplace transform of the DND. Similarly, the DND can be derived from the inverse Laplace transform of the normalized concentration versus normalized distance curve. Given both an RTD and a DND, it is possible to investigate the relationship between k and residence time, and the mechanistic nature of the removal process. Employing these concepts makes it possible to generate an expression for normalized concentration as a function of fractional distance that is unaffected by changes in inlet concentration, and inherently takes into account changes in hydraulic loading rate.

Kinetic model for dynamic response of three-phase fluidized bed biofilm reactor for wastewater treatment

Step changes in inlet concentration has been introduced into the completely mixed three-phase fluidized bed biofilm reactor treating simulated domestic wastewater to study the dynamic behavior of the system and to establish the suitable kinetic model from the response curve. Three identical reactors having different biomass volumes were operated in parallel. It was found that the response curves showed second-order characteristics, and thus at least two first-order differential equations are necessary to simulate the substrate and biomass response curves. Nonlinear regression analysis was performed using different types of rate equations and their corresponding kinetic parameters were used to simulate the theoretical response curve using the Runge–Kutta numerical integration method. As a result, although various types of conventional biokinetic models such as Monod, Haldane and Andrew types were examined, all the theoretical substrate response curves underestimated time constants compared to the actual substrate response plots. On the other hand, the theoretical curve of the kinetic model that incorporates adsorption term has best fit to the actual response in most of the cases. Thus, it was concluded that adsorption of substrate onto biofilm and carrier particles has significant effect on the dynamic response in biofilm processes.

Evaluation of kinetic parameters of biochemical reaction in three-phase fluidized bed biofilm reactor for wastewater treatment

This study evaluates the kinetic parameters of biochemical reaction in three-phase fluidized bed biofilm reactor from the steady state values of the response of the system to step changes in inlet concentration. It was observed from the outlet biological oxygen demand (BOD 5) plot of the response of the system that as the inlet BOD 5 was increased, the outlet BOD 5 also increased, reached a peak value and then decreased until it leveled to a new steady state value corresponding to the new inlet concentration level. The increase in BOD 5 was attributed to the accumulation of substrate within the reactor as well as the decrease in biofilm substrate consumption rate as the microorganisms adjusted to the new environment. Using the substrate balance at steady state and assuming Monod kinetics, an equation relating the substrate consumption rate to substrate concentration (BOD 5) and total biofilm surface area had been established. Monod kinetic parameters were found to be K=2.20 g/m 2/day, K m=17.41 g/m 3 and K/ K m=0.13 m/day. The ratio K/ K m can be taken as the indicator for biofilm substrate degradation effectiveness at low substrate concentrations.

Development of effective hydrogen sulphide removing equipment using Thiobacillus sp.IW

Hydrogen sulphide is one of the commonest odours emitted by chemical plants. To remove the hydrogen sulphide biologically, a three phase fluidised bed bioreactor was used in which Thiobacillus sp.IW was immobilised on activated carbon. The optimum operating conditions of the bioreactor were 30°C, pH7, aspect ratio (L/D) = 1 and at these conditions, the system removed over 94% of the hydrogen sulphide in the concentration range of 100–200 ppm and flow rate of 1.0–2.0 litre min −1. From the upset and recovery test, the system proved stable within the moderate inlet concentration changes investigated.

Response of composition in biological reactors to changes in inlet concentration

Response of composition in biological reactors to changes in inlet concentration