Modeling of Dissolved Oxygen Profile in a Slurry Reactor

Activated sludge process (ASP), which is a suspended growth system, is used on a large scale for biological treatment of wastewater. ASP requires air supply. The aeration facilities are designed to meet the oxygen demand of the process while maintaining in the aeration tank minimum desirable dissolved oxygen (DO) concentration. The presence of DO in wastewater is desirable because it prevents the formation of bad odors and toxic gases. The last two form under anaerobic conditions in which anaerobic microorganisms produce hydrogen sulfide and methane. The operation of aeration facilities is continuous which increases the operational cost of the treatment plants. However, the intermittent aeration ASP is now widely attractive both for reducing power requirements of aeration facilities and for upgrading existing biological treatment plants for nitrogen removal. In Iraq, nearly, all sewage treatment plants imply ASP with continuous aeration scheme. But, due to the present state of electrical power supply in Iraq, the stop of aeration process due to power shut down cannot be avoided, i.e., mostly all sewage treatment plants in Iraq are under the condition of forced intermittent aeration system. In designing an ASP, the volume of aeration tank is calculated using a set of design criteria. The designer based on his engineering judgment usually, specifies the tank dimensions. So there is a need of knowing how tank dimensions are specified. Also, in deciding the power required for a mechanical aeration system, a value is randomly chosen based on accepted range for power per unit volume values. The requirements highlighted in the above paragraph can be accomplished using a mathematical model. The Activated Sludge Model No. 1 (ASM1) is usually considered as the reference model, which was primarily developed for municipal ASPs to describe the removal of organic carbon substances and nitrogen. However, with respect to DO dynamics, the model does not include all factors affecting the rate of DO supply. In this study, A model was developed for simulating the DO supply in ASP. The model is a modified version of ASM1 that incorporates all the factors affecting the rate of oxygen supply, such as type of aeration system, tank geometry, and the physical characteristics of treated sewage including the total dissolved solids (TDS) and temperature. The developed model, which is labeled as ASP-DO include nine state variables and eight reaction processes. It solves nine simultaneous nonlinear ordinary differential equation using the 4th order Rung Kutta method. ASP-DO program was written in Maple13 language. It was used as a tool for; studying how aeration tank dimensions affect the concentrations of dissolved oxygen and other interesting components of sewage, determining the power input per aeration basin volume for an ASP equipped with mechanical aeration system, investigating the effects of aeration cut in Hamdan Sewage Treatment Plant (HSTP) on dissolved oxygen level in ASP and the performance of ASP, and determining the best intermittent aeration condition, that will maintain the desirable minimum level of dissolved oxygen in the aeration tanks. The most important conclusions of this study are; as water depth in the aeration tank of ASP increases, the concentration of DO increases, as L/W ratio of the aeration tank increases, the DO concentration increases, ASP-DO model can be used for determining the power input per unit volume of aeration tanks equipped with surface aeration system and it is not recommended to chose a random value based on known values range given in scientific resources, ASPDO model can be, successfully, used to track the variations in DO concentration under different design and operation conditions, the current state of electrical power supply in Basrah may lower the percent of soluble substrate removal to about 47% when air on/off is 3hr/3hr, and the intermittent aeration system can be applied in HSTP with 1.5hr/0.5 hr air on/off.

Biotechnology and Bioengineering, 1992

To check for possible mass transfer limitations of oxygen and/or carbon dioxide in kinetic experiments on microbial desulphurization of coal, it is important to properly measure the volumetric mass transfer coefficient (kLa) especially at high slurry densities. Volumetric mass transfer coefficients of oxygen, at different solid hold-up values (eS = 0 to 0.28) of coal slurries (dpar < 100 * m), were measured in a lab scale fermentor and in a lab scale pachuca tank, using the dynamic gas-liquid absorption method. It was shown that serious errors could occur due to oxygen adsorption at the coal surface. Using the data of an independently measured adsorption isotherm, the real kLa could be calculated from the measured apparent kLa. The results show a kLa decrease of 40% to 50% at a volumetric solid hold-up of 28%.

Journal of Cleaner Production, 2019

The aim of the present study was to compare the oxygen transfer efficiency in a conventional activated sludge and a membrane bioreactor system. The oxygen transfer was evaluated by means of the oxygen transfer coefficient (kLa)20 and α-factor calculation, under different total suspended solids concentration, extracellular polymeric substances, sludge viscosity and size of the flocs. The (kLa)20 and α-factor showed an exponential decreasing trend with total suspended solid, with a stronger (kLa)20 dependence in the conventional activated sludge than the membrane bioreactor. It was noted that the (kLa)20 in the conventional activated sludge become comparable to that in membrane bioreactor when the TSS concentration in the conventional activated sludge was higher than 5 gTSS L-1. Operating under high carbon to nitrogen ratio, the (kLa)20 increased in both conventional activated sludge and membrane bioreactor because of the sludge deflocculation and a weaker dependence of (kLa)20 with total suspended solid was noted. The results indicated that the most important parameters on the oxygen transfer efficiency were in order: the total suspended solid concentration, flocs size, sludge viscosity, the protein to polysaccharides ratio and extracellular polymeric substances content. Based on the influence of the main biomass features affecting the (kLa)20 and considering the typical operating conditions in both systems, those of membrane bioreactor appeared to be more favorable to oxygen transfer efficiency compared to conventional activated sludge process.

Environmental Engineering and Management Journal, 2009

The study on the distribution of oxygen transfer rate in a stirred bioreactor for Propionibacterium shermanii broths underlined the major influence of the presence and concentration of biomass on the interphasic transfer of oxygen. Owing to the bubbles surface blockage by the bacterial cells, the accumulation of biomass from 30.5 to 120.5 g/l d.w. led to the decreasing of k l a for about 1.3-2.4 times. Compared with the simulated broths without biomass having similar apparent viscosity, the oxygen transfer rate became for about 1.22-4.54 times lower in the bacterial broths. The intensification of aeration promoted the acceleration of oxygen transfer for about 1.2-1.9 times, due to the intensification of turbulence and of the extent of free interfacial area needed for the oxygen transfer, this influence being similar to that recorded for the mixing efficiency. Moreover, the increase of aeration rate led to the increase of oxygen transfer efficiency. Indifferent of the operating parameters of the bioreactor, k l a increased from the inferior region to the superior one, being nonuniformly distributed inside the broths.

Revista De Chimie Bucharest Original Edition, 2014

Various strategies for improving the mass transfer rate of oxygen have been used in order to obtain a good efficiency of aerobic fermentation processes. The paper focuses on studies concerning the influence of solid carrier addition in the liquid phase on oxygen volumetric mass transfer coefficient in a stirred and aerated tank bioreactor. The selected oxygen carriers (vectors) can be easily separated and they have no harmful effect on the microbial population implied in bioprocesses. Fine particle of activated carbon, silicon oil impregnated activated carbon, bacterial cellulose, magnetite, and bacterial cellulose-magnetite composite were used as oxygen-vectors. An enhancement of oxygen transfer was indicated by an increase in volumetric mass transfer coefficient, k l a, which was determined by a dynamic method. A significant improvement of oxygen mass transfer in the presence of magnetite and bacterial cellulose-magnetite composite was highlighted.

1999

The aim of this research was to show the impact of the flow conditions and variations in the aeration intensity on changes in the predicted dissolved oxygen (DO) concentrations in a full-scale activated sludge reactor. The Activated Sludge Model No. 1 was used to describe the biochemical processes. The studies were performed at the Rock Creek wastewater treatment plant in Hillsboro, OR (USA). The simulation results were compared with data originating from two 24-hour experiments. The model that best reflected the spatial and diurnal distributions of the DO concentrations was the one-dimensional advection-dispersion equation with a variable overall oxygen mass transfer coefficient in the source term for dissolved oxygen.

Journal of Physics: Conference Series, 2020

Wastewater systems are high-energy consuming processes that discharge considerable amounts of pollutants into aquatic ecosystems, thus requiring appropriate optimization. Therefore, a full-scale activated sludge process was studied in this work through mathematical modeling of heterotrophic and nitrifying microorganisms. The airflow rate was introduced as the controlling parameter to accomplish the degradation of pollutants. Moreover, a sensitivity analysis was performed to determine the most sensible parameters that should be evaluated through further experiments, aiming to improve the model. The obtained results indicated that readily biological oxygen demand degradation and the oxidation of ammonia to nitrite could be achieved with an airflow rate of 35 m 3 air d-1. The sensitivity analysis showed that heterotrophic kinetic parameters and oxygen mass transfer coefficient through diffusers are the most sensitive to the system. These results also proved that the air-diffusing systems can work at 0.3% of their maximum capacity to accomplish degradation. Future studies should consider other oxygen-consuming variables.

1992

Area Head * The colleagues who helped me with the spelling and gramma of this thesis Mr. Mike Smith Miss. Lindsay Dawes Mr. Radleigh Hartford * Professor R.c. Everson, who acted as Mentor for his motivation and encouragement. *Mr. Andre Steynberg, as my supervisor and project leader guided me in this stage of the development of my carreer. *My wife Janni and my son John for their patience and support during the preparation of this work. 1 * My parents who taught me the first steps in Chemistry * Last but not least, God, without His help this thesis would not have been possible III ABSTRACT BYDRODYNAMIC STUD~ES AND REACTOR MODELLING OF A THREE PHASE SLURRY REACTOR ~N TISCHER TROPSCH APPLICATION In this .study the hydrodynamic characteristics of the slurry bed .reactor was investigated. This study was aimed to the under-"standing of the important parameters that describe the hydrodynamic regime and their quantification • In order to determine the relevant parameters the use of a theoretical model was necessary. This model should include all the hydrodynamic parameters in form of correlations. A sensitivity study was done and the parameters which have great impact,.were determined. An extensive literature review was done in order to gather the experience of previous investigations. Unfortunately all the experience was obtained in a different hydrodynamic regime and therefore the published results could not be used directly in our study. Hydrodynamic test were performed in the works pilot plant at the operating conditions. Unlike a laboratory, the instrumentation used was the one use in commercial reactors with the commercially aceptable range of accuracy. A mass balance was done around the reactor to ensure that the data was sound. Heat balance was also performed and the study of the heat transfer coefficient was performed. Although this was beyond the scope of this study was here included due to its importance in the design of slurry bed reactors. An existing computer model was adapted for the churn-turbulent regime and the hydrodynamic parameters were implemented. This reactor model was coupled with flashes subroutines in order to have a complete reactor train. This computedrmodel was used for the design of the Slurry Bed Commercial Reactor to be c'ommisioned on 1993 at Sasol One. IV

This research covers the modeling of the velocity profile of a bioreactor with recycle; the concept of biochemical process. The biochemical process adopted is fermentation and a plug-flow fermenter (PFF) was taken as a case study. The derivation of workable model equations for monitoring and predicting the velocity profile of a PFF were obtained, together with obtaining the model equations for investigating the effect of microbial and substrate concentrations on the discharge coefficient, bioreactor's volume. Constant data were sourced from literatures, together with hypothetical values to simulate the derived model equations using Mathlab. The substrate concentration decreases with time as biomass population increases with time. Effect of biomass concentration on discharge coefficient, shows that increase in biomass concentration brings a corresponding increase in the discharge coefficient as well as the bioreactor's volume revealed that substrate concentration is depleting alongside with bioreactor's volume follows the same trend of change when substrate concentration is decreasing irrespective of whether the length or area of the bioreactor is varied. The effect of microbial concentration on bioreactor volume when area and length of bioreactor are varied reveals that the process followed same trend only that there is a presence of lag phase upon the influence of inhibitors. The inverse substrate concentration increases, the space velocity also increases, and there is a linear trend of change on the inverse substrate concentration with respect to space velocity.

Water Research, 2000

AbstractÐA general dynamic model of the activated sludge reactor, including biological processes, hydraulics, oxygen transfer and temperature, was veri®ed against both steady-state and dynamic ®eld data. These data originated from the Rock Creek wastewater treatment plant located in Hillsboro, Oregon (USA). During simulations only one set of the model parameters was used. The model was capable of predicting dissolved oxygen concentrations and consumption, ammonia concentrations, and nitrate+nitrite concentrations with time and distance along the activated sludge reactor. Uncertainty analysis enabled the classi®cation of model parameters (kinetic and stoichiometric coecients, and wastewater components) according to model sensitivity. The maximum growth rate of nitri®ers, m A,max , and the ammonia concentration, S NH , were the most sensitive coecient and wastewater component, respectively, when the sum of ammonia, nitrate+nitrite, dissolved oxygen concentrations and total oxygen uptake rate was taken into account. Application of the model was demonstrated by analyzing the impact of changing the operational mode (from A/O process to 4-stage Bardenpho) on dissolved oxygen conditions and nitrogen removal. 7

Diyala Journal of Engineering Sciences, 2020

This work was devoted to study the influence of wellknown catalyst carriers (activated utilized in catalytic reactions carbon and silica) on the hydrodynamic parameters and mass transfer rate in a slurry reactor. The influence of silica and activated carbon particles concentration up to 20% v/v on regime transition, average gas holdup, mass transfer coefficient, and CO 2 removal was studied in a semi-batch slurry bubble column reactor (SBC) with a porous gas sparger. The effects of hydrophobicity and surfactant were also investigated. It was concluded the gas holdup is reduced and the point of transition from laminar to turbulent regime is shifted to less gas velocity when the hydrophobic and hydrophilic particles concentration was larger than 3% (v/v). The Particle hydrophobicity, gas velocity, and electrolyte concentration have positive impacts on gas holdup while slurry concentration gave a different trend. Experimental results show that the optical fiber probe is valid to use in a slurry bubble column and can also generate useful data such as bubble rise velocity and bubble distribution. The optical fiber probe was proved to be good technique for estimation of volumetric mass transfer coefficient within an error of ±18%. Mass transfer experiments with gaseous CO 2 showed a behavior of removal in the same trend of increasing gas holdup with gas velocity. A noticeable removal of gaseous pollutants was observed for non-wettable particles at solid loading of 3%v/v. Mathematical correlations were formulated for CO 2 removal as function of studied operating variables with correlation factors of 0.95-0.98. The present study depicts the effect of catalyst carrier on the hydrodynamic characteristics and mass transfer in a slurry reactor.

Chemical Engineering & Technology, 2001

Animal cell line culture is difficult in the existing conventional bioreactors. A substantial amount of animal cells are destroyed by the impinging fan blades or entrapment inside the bubbles. An endeavor has been made to design and develop a new type of bioreactor suitable for animal cell culture. The bioreactor is named a see-saw' bioreactor from its underlying principle of operation. In this paper, the oxygen transfer characteristics of the see-saw' bioreactor are modeled and tried to be verified.

Chemical Engineering & Technology, 2013

Oxygen mass transfer from air to the liquid phase in bioreactors with aerobic cultures has long been a serious impairment to the productivity of various bioprocesses. An increase of the oxygen mass transfer rate (OTR) can be the key to overcome oxygen limitation. The influence of higher air pressure on OTR was measured and a significantly enhanced OTR could be obtained. The oxygen volumetric mass transfer coefficient (k L a) was described by a function of the air pressure in a stirred lab-scale pressurized bioreactor. The correlation obtained proved that k L a slightly decreased with higher air pressure, following a power function.

Water Research, 2000

AbstractÐA general dynamic model of the activated sludge reactor, including biological processes, hydraulics, oxygen transfer and temperature, was veri®ed against both steady-state and dynamic ®eld data. These data originated from the Rock Creek wastewater treatment plant located in Hillsboro, Oregon (USA). During simulations only one set of the model parameters was used. The model was capable of predicting dissolved oxygen concentrations and consumption, ammonia concentrations, and nitrate+nitrite concentrations with time and distance along the activated sludge reactor. Uncertainty analysis enabled the classi®cation of model parameters (kinetic and stoichiometric coecients, and wastewater components) according to model sensitivity. The maximum growth rate of nitri®ers, m A,max , and the ammonia concentration, S NH , were the most sensitive coecient and wastewater component, respectively, when the sum of ammonia, nitrate+nitrite, dissolved oxygen concentrations and total oxygen uptake rate was taken into account. Application of the model was demonstrated by analyzing the impact of changing the operational mode (from A/O process to 4-stage Bardenpho) on dissolved oxygen conditions and nitrogen removal. 7

Iranian journal of environmental health science & engineering, 2013

In this study, a miniature stirred tank bioreactor was designed for treatment of waste gas containing benzene, toluene and xylene. Oxygen mass transfer characteristics for various twin and single-impeller systems were investigated for 6 configurations in a vessel with 10 cm of inner diameter and working volume of 1.77L. Three types of impellers, namely, Rushton turbine, Pitched 4blades and Pitched 2blades impellers with downward pumping have been used. Deionized water was used as a liquid phase. With respect to other independent variables such as agitation speed, aeration rate, type of sparger, number of impellers, the relative performance of these impellers was assessed by comparing the values of (KLa) as a key parameter. Based on the experimental data, empirical correlations as a function of the operational conditions have been proposed, to study the oxygen transfer rates from air bubbles generated in the bioreactor. It was shown that twin Rushton turbine configuration demonstrate...