Completely Mixed Batch Reactor Research Articles

The Development of an Efficient Simplified Technique to Estimate Diffusivity in a Completely Mixed Batch Reactor

Liquid-phase adsorption technology has been widely applied to address environmental problems related to the removal of pollutants from aqueous streams. Simple and effective methods for determining mass transfer parameters, including intra-particle and fluid-to-solid film resistances, are crucial for designing adsorption processes. The efficient simplified diffusion technique (ES technique), based on a completely mixed batch reactor (CMBR), is proposed in this study to address these needs. In this study, we compare three diffusivity (Ds) determination methods: the rigorous diffusion technique (R technique), the simplified diffusion technique (S technique), and the ES technique. Although the simulation results from the R technique are excellent, it is a very complicated and time-consuming approach that is not convenient for practical use. The S technique provides a much simpler approach, but its results are only valid in cases where the contribution of fluid film resistance is negligible (Biot number > 40). The ES technique proposed in this study can overcome those limitations. The estimation errors of the ES technique are significantly smaller than that of the S technique when compared with the R technique. The proposed ES technique would be very useful for field applications to determine diffusivity for aqueous adsorption systems.

Experimental and numerical study of methylparaben decomposition in aqueous solution using the UV/H2O2 process

The present paper aims at presenting a kinetic model that is supposed to result in the decomposition of methylparaben in completely mixed batch reactor (CMBR) using the UV/H2O2 process. The proposed model incorporates photochemical, chemical reactions and their constant rates to formulate the overall kinetic rate expressions which are integrated into MATLAB. Thus, the changes in pH values during the process of oxidation are taken into consideration. In addition, the effects of hydrogen peroxide (HP) dosage, as well as the concentration of hydroxyl radicals, are examined. Accordingly, the pseudo-first-order rate constant, its variation as functions of HP concentration, incident UV-light intensity and the limitations of the adopted approach are discussed. In line with that, the authors provided evidence of the validity of the kinetic model through the exposure of previous experimental studies as reported in the literature review then through the evidence of the present experimental data.

Destruction of Aqueous Phase Organic Pollutants Using Ultraviolet Light-Emitting Diodes and Photocatalysis

The photocatalytic degradation of dyes (Allura Red AC and Brilliant Blue FCF) in water using ultraviolet light-emitting diodes (UV-LED) and an immobilized titanium dioxide (TiO2) as a photocatalyst was investigated using a novel bench-top Teflon® reactor. This reactor has been uniquely designed to contain low-powered UV-LEDs combined with TiO2 immobilized substrates. A sol-gel method was used to anneal TiO2 to three different substrates: standard microscope quartz slides, quartz cylinders, and borosilicate beads. Scanning electron microscopy (SEM), Raman spectroscopy, and mass comparisons techniques were performed for TiO2 characterization. High-resolution images confirmed the presence and morphology of TiO2 on the substrates. These analyses demonstrated the TiO2 coating was uniform and predominantly had the anatase crystalline phase structure. The slide had the largest individual TiO2 surface area of 0.187 mg cm−2. Results indicated the size, shape, packing, and stirring properties were factors that determine overall photocatalytic properties and degradation inside the reactor. The adjusted rate constants for an ideal completely mixed batch reactor (CMBR) were 1.69 * 10−3, 5.39 * 10−3, and 4.46 * 10−3 min−1 for the slides, beads, and cylinders, respectively. Beads were the best-performing substrate as determined by the greatest degradation rate for the model organic compound, Allura Red AC. The beads and cylinders showed 58 and 51% degradation of Allura Red AC, respectively. Actinometry experiments revealed cylinders had the largest fluence rate of 0.0782 J·L−1 s−1. Optimization of the sol-gel application method and reactor operating parameters was performed to maximize the degradation rate and the overall degradation of Allura Red AC. Electric energy per order (EEO) was calculated and optimized at 9.20, 10.5, and 12.7 kWh·m−3 order−1 for the glass beads, cylinders, and slides, respectively.

Modeling the pH effects on nitrogen removal in the anammox-enriched granular sludge.

The aim of the study was to determine the pH effects on nitrogen removal in the anammox-enriched granular sludge. The experimental data were extracted from a 4 L completely-mixed batch reactor with the granular sludge at different initial pH values (6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5) and constant temperature T = 30 °C. Simulations were run in GPS-X 6.4 using a comprehensive mechanistic model Mantis2. Two kinetic parameters, the maximum specific growth rates of ammonia oxidizing bacteria (AOB) and anammox bacteria, were optimized at different pH scenarios. The inhibitory effects of the pH extremes on the anammox-enriched sludge were discussed in terms of the inhibition of free nitrous acid and free ammonia and metabolic mechanisms. Two different pH functions were used to examine the pH effects on the nitrogen removal kinetics. The pH optima for AOB and anammox bacteria were 7.4 and 7.6, respectively. The maximum specific growth rates of AOB and anammox bacteria at the pH optima were 0.81-0.85 d-1 and 0.36-0.38 d-1 (at T = 30 °C). The measured specific anammox activities (SAAs), predicted SAAs by Mantis2 and fitted SAAs by the Michaelis pH function at the pH optima were 0.895, 0.858 and 0.831 gN/(gVSS·d), respectively (VSS: volatile suspended solids).

A simplified technique to determine intraparticle diffusivity of macro-reticular resins

Abstract Both resins and activated carbons are commonly used as adsorbents in water and wastewater treatment. In general, intraparticle diffusion mechanisms within macro reticular resin particles (such as XAD-2000) are different from those in activated carbon particles. Currently, completely mixed batch reactor (CMBR) technique can be used to determine the intraparticle diffusivity for phenolic compounds adsorbed onto activated carbon systems. However, the technology cannot determine the intraparticle diffusivity accurately if the fluid-film resistance is significant, such as synthetic macro-reticular resins. Therefore, this study develops a technique to determine the intraparticle diffusivities of XAD-2000 resin. This paper characterized the concentration decay curves of para-nitrophenol in CMBR to determine effective pore diffusivity (D P ) of the resin. The obtained mean and standard deviation of D P are about 1.1 × 10 −5 and 3.2 × 10 −6 (cm 2 s −1 ), respectively. The technology developed in this study has the advantages of significant chemical saving and easy operation.

Using polypyrrole nanocomposites coated on rice husk ash for the removal of anions, heavy metals, COD from textile wastewater

In this study, a new application of polypyrrole (PPy) synthesized chemically in presence of ferric chloride as an oxidant coated on rice husk ash (RHA) by oxidative chemical polymerization method is used, ferric chloride has been found to be the chemical oxidant and water has been reported the best solvent for chemical polymerization of pyrrole. The removal of anions, heavy metals such as copper, iron and zinc and COD (chemical oxygen demand) from textile wastewater using completely mixed batch reactor (CMBR) technique is investigated when polypyrrole and its blend and nanocomposites with rice husk ash were used. Experiments were done using PPy/RHA during 30min with 5min intervals. It is observed that by increasing the time (5–20min) removal efficiency increased but, after 20min the efficiency did not increase significantly. It can be concluded that RHA in the composites does not play significant role in the anions and COD removal but the role of RHA in the removal of the metals is considerable and it causes an increase in the removal efficiency of the composites. Besides, the morphology was tested by scanning electron microscopy (SEM) to characterize the surface of PPy nanocomposites at very high magnification at an accelerating voltage of 15kV, and chemical structure was tested by Fourier Transform Infrared spectroscopy (FTIR) in the wavelength range of 400–4000cm−1, respectively. It was found that PPy/RHA can be used as an effective adsorbent in the removal of anions, heavy metals and COD from textile wastewater.

Removal of Pb(II) using polyaniline composites and iron oxide coated natural sand and clay from aqueous solution

In this research, natural sand and clay coated with polyaniline and iron oxide were used to remove Pb(II) from contaminated water. Fixed bed column and batch studies were performed to evaluate the influence of various experimental parameters such as pH, adsorbent dosage, and contact time. Based on the results, optimum conditions for Pb(II) removal were found to be pH 11, adsorbents dosage of 10g/L, and contact time of 45min. In addition, the morphology and chemical structure of the adsorbents were studied via scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The column tests were conducted with a flow rate of 4mL/min with different bed depths of 10 and 25cm. It was found that when iron oxide/clay, iron oxide/sand, polyaniline/clay and polyaniline/sand were used as adsorbent in a fixed-bed column method, the removal percentages of Pb(II) were 97.50, 99.24, 72.99, 68.80% and for the completely mixed batch reactor (CMBR) method were 99.84, 99.89, 93.91 and 90.77%, respectively. These results indicated that iron oxide coated sand and clay are an attractive source of adsorbents that can be used for removal of Pb(II) in water treatment processes.

Experimental determination of intraparticle diffusivity and fluid film mass transfer coefficient using batch contactors

The mass transfer properties of adsorbates are generally critical factors for design of a fixed bed adsorber. For single-component systems, the completely mixed batch reactor (CMBR) method is a convenient and frequently used experimental technique for determining mass transfer properties. However, the effect of fluid film mass transfer resistance is neglected in the conventional analytical technique of CMBR method when estimating the intraparticle diffusivity ( D S). This effect should be considered to determine the diffusivities more accurately. In this study, a new analytical technique was proposed for determination of D S and fluid film mass transfer coefficient ( k F) from one concentration decay curve and it was applied in practical experiments. This technique will be useful to estimate diffusivities when the fluid film mass transfer resistance cannot be regarded as being negligible. Under the experimental conditions of this study, the fluid film mass transfer resistance could be neglected at high stirring speeds (i.e., >200 rpm). Therefore, values of D S can be estimated by the conventional technique from kinetic experiments performed at relatively high stirring speeds. On the other hand, values of k F obtained by the proposed technique showed a similar tendency to values estimated from Hixson's empirical equation.

Performance evaluation of modified calcined bauxite in the sorptive removal of arsenic(III) from aqueous environment

This research was aimed at evaluating the effectiveness of the adsorbent, modified calcined bauxite (MCB), in removing As(III) from aqueous environment by completely mixed batch reactor (CMBR) and continuous flow fixed bed studies. It was observed that an adsorbent dose of 5 g l −1 could effectively remove 99.2% and 93.4% of As(III), from initial concentrations of 1 and 2 mg l −1, respectively. The sorption kinetics was found to follow pseudo-second-order model. Freundlich isotherm model was well fitted to the experimental equilibrium data rendering a maximum adsorption capacity of 1.362 mg g −1. The sorption process was found unaffected by temperature variations. The removal of As(III) was observed almost consistent over a pH range of 2–8, producing effluent within pH range of 6–7.5. It appears that the mechanism of arsenic removal is dependent on pH, surface charge of the adsorbent and nature of the As(III) speciation. The fixed bed study performed in a 20 mm diameter column at a feed flow rate of 8 ml min −1, demonstrated that an adsorbent bed depth of 10 cm could effectively treat 428 bed volumes of As(III) spiked influent water with 1 mg l −1 concentration, before the attainment of breakthrough. Logit method was used to evaluate the column parameters, adsorption rate constant and adsorption capacity co-efficient.

Acidogenesis characteristics of natural, mixed anaerobes converting carbohydrate-rich synthetic wastewater to hydrogen

The fermentative metabolisms of mixed anaerobic bacteria taken from an anaerobic digester treating dairy manure and stressed in various ways to enhance hydrogen production from a carbohydrate-rich synthetic wastewater were evaluated in batch culture tests by monitoring intermediate metabolites. First, fermentative metabolism was evaluated in batch vial experiments to evaluate various bacterial stresses for enhancing hydrogen production. The results showed that the bacterial stresses tested promoted hydrogen production, and butyric acid was the primary product of acidogenesis. Completely mixed batch reactor (CMBR) experiments were then performed with pH controlled at 4.6, 5.7, and 6.8. Hydrogen-producing species enriched from mixed anaerobic bacteria by stressing with chemical acidification were used because they gave the best result in batch vial tests. The results of the CMBR experiments showed that butyric acid formation was significantly related to higher hydrogen yield. The CMBR operated at pH controlled at 5.7 showed higher hydrogen yield than did the other pH values, and butyric acid (as 50.8–75.8% of total acidogenic liquid products) was dominant. The presence of propionic acid and ethanol indicated decreased hydrogen production.

Naphthalene Biodegradation from Non-Aqueous-Phase Liquids in Batch and Column Systems: Comparison of Biokinetic Rate Coefficients

The kinetics of microbial degradation of naphthalene from a two-component non-aqueous-phase liquid (NAPL) coated onto uniformly sized nonporous particles were evaluated in a completely mixed batch reactor (CMBR) system and in flow-through column systems to examine the differences in the biodegradation kinetic coefficients, micro(max), the maximum specific growth rate coefficient, and K(s), the half saturation constant in the two systems. The values of these coefficients were estimated by nonlinear least-squares regression of the naphthalene mineralization profiles obtained from both CMBR and column biodegradation experiments. The results show that the range of values for micro(max) and K(s) obtained from column systems are very similar to the range of values obtained from CMBR systems. This suggests that coefficients estimated from CMBR or column systems are equally applicable for modeling studies. The presence of microorganisms and the development of biofilms at the NAPL-water interface reduced the mass transfer rates of naphthalene from the NAPL by 60% in CMBR and by 70% in column systems. If such changes in mass transfer coefficients are not accounted for, significantly erroneous values of biokinetic coefficients may be obtained.

A kinetic model for H 2O 2/UV process in a completely mixed batch reactor

A dynamic kinetic model for the advanced oxidation process (AOP) using hydrogen peroxide and ultraviolet irradiation (H 2O 2/UV) in a completely mixed batch reactor (CMBR) is developed. The model includes the known elementary chemical and photochemical reactions, and literature reported photochemical parameters and chemical reaction rate constants are used in this model to predict organic contaminant destruction. Unlike most other kinetic models of H 2O 2/UV oxidation process, the model does not assume that the net formation rate of free radical species is zero (pseudo-steady state assumption). In addition, the model considers the solution pH decrease during the process as mineral acids and carbon dioxide are formed. The model is tested by predicting the destruction of a probe compound, 1,2-dibromo-3-chloropropane (DBCP) in distilled water with the addition of inorganic carbon. The new model developed in this work gives better predictions of the destruction of the target organic compound than the model based on the pseudo-steady state assumption. The model provides a comprehensive understanding of the impact of design and operational variables on process performance. Accordingly the ability of the model to select optimum process variables, such as hydrogen peroxide dosage, is illustrated.

The influence of natural organic matter (NOM) on the desorption kinetics of pyrene and naphthalene from quartz

The influence of natural organic matter (NOM) on the desorption kinetics of pyrene and naphthalene adsorbed on quartz was examined in batch experiments. Online determination of the concentration of the polycyclic aromatic hydrocarbons (PAH) in the aqueous phase was performed using fluorescence detection. Desorption experiments were done in a Completely Mixed Batch Reactor (CMBR) using PAH loaded quartz as model soil. A diluted pyrophosphate extract and a water extract of a well characterized soil, water of a bog lake (Hohlohsee, Black Forest), and deionized water were used as aqueous phases. The experimental data were fitted to two mathematical models: (1) an empirical model and (2) the diffusion film model. Both models were able to describe the concentration profile of the dissolved PAH quite well. Whereas the desorption rate of naphthalene decreased in the presence of NOM, no significant influence of NOM on the desorption kinetics of pyrene was observed. In this context, neither the origin nor the concentration of the different NOM had a significant impact on the values obtained.

Influence of the mode of reactor operation on the rate and yield of fermentation of the model solid substrate, wheat bran, by a microbial consortium under non-axenic anaerobic conditions

Anaerobic fermentation of wheat bran, a model solid substrate, was conducted under non-axenic conditions, in two reactors operated under different modes, all other conditions being strictly identical. The first reactor was a completely-mixed batch reactor. The second reactor was a percolator into which the liquid phase was recirculated in closed loop through the solid substrate acting as a stationary bed. The final yield of fermentation was obtained after 27 days in the completely-mixed batch reactor, and after 14 days only in the percolator. Scanning electron microscopy revealed that numerous micro-organisms adhered to the solid substrate acting as a carrier in the percolator, whereas only very few micro-organisms adhered to the solid substrate in the completely-mixed batch reactor. The results show that obtaining a durable direct contact between micro-organisms and their solid substrate improves the rate of solids degradation.