Bohart-Adams Equation Research Articles

Nickel removal by biogenic selenium nanoparticles (SeNPs): Characterization and simulation of non-symmetric breakthrough curves in continuous-flow packed-bed columns

Nanoparticles offer an alternative mean for heavy metals removal from aquatic environment. In this work we study the sequestering of nickel by biogenic selenium nanoparticles (SeNPs) both in native and in immobilized form in alginate matrix (alginate-SeNPs). The apparent sorption like process is attributed to the coordination chemistry of Ni with the functional groups of the extracellular polymeric substances (EPS) covering the SeNPs. The kinetics and the equilibrium of the process are presented, while the morphology and the properties of the adsorption beads are studied by SEM, FTIR and rheological analysis. Langmuir isotherm describes the adsorption equilibrium with maximum loading Q0 29.411 mg Ni/g SeNPs and 0.651 mg Ni/g alginate-SeNPs. The adsorption of nickel is fast and equilibrium is attained within one hour. Continuous flow experiments in packed beds reveal early elution patterns and non-symmetric sigmoidal profiles due to the reduced adsorption capacity of the immobilized SeNPs, the short depth of the beds and the apparent non-uniform flow pattern. The Bohart-Adams equation fits adequately the main sigmoidal part of the breakthrough curves, however fails to predict the early breakthrough data. By using the advection–dispersion-reaction equation (ADR) under two novel aspects: (a) the rapid equilibrium model with the introduction of an efficiency coefficient accounting for all the kinetic and sorption limitations and (b) the split flow model accounting for any non-uniform flow conditions in the column, the model accuracy is significantly improved. Repeated sorption–desorption experiments show that alginate-SeNPs retain 59% of the original adsorption capacity even after eight cycles.

Rebuttal to comment on “Breakthrough curve analysis by simplistic models of fixed bed adsorption: in defense of the century-old Bohart-Adams model”

In a comment on my article [1] published in this journal, Hu and Zhang [2] assert that I had misinterpreted the Bohart-Adams equation derived by Amundson and that the Bohart-Adams equation lacks the bed voidage parameter. I argue that Hu and Zhang are wrong on both counts. I further contend that their version of the Bohart-Adams equation derived by Amundson contains a glaring error of a rudimentary nature.

Breakthrough curve analysis by simplistic models of fixed bed adsorption: In defense of the century-old Bohart-Adams model

In the water and wastewater treatment field several simplistic models of packed bed dynamics such as the Bohart-Adams, Thomas, and Yoon-Nelson models are frequently used by investigators to fit adsorption breakthrough data. The century-old Bohart-Adams model is arguably the best known one which also serves as the foundation of the bed depth-service time equation. In recent years a substantial body of literature on the subject of fixed bed modeling has however claimed that it is inferior to other models. The present paper shows that such claims are incorrect and misleading because of biased comparisons in which the fitting ability of an oversimplified version of the Bohart-Adams model was compared with those of the Thomas and Yoon-Nelson models. The oversimplified Bohart-Adams equation is in effect an exponential function which predicts an exponentially increasing breakthrough value with time. As such, it is unable to fit typical breakthrough curves which are S-shaped or sigmoidal. It can be shown that a proper version of the Bohart-Adams model gives fit quality similar to those of the Thomas and Yoon-Nelson models. This is not unexpected since the three simplistic fixed bed models can be expressed in terms of the logistic equation of population growth; that is, mathematically they are equivalent.

Carboxymethylated bacterial cellulose: An environmentally friendly adsorbent for lead removal from water

Carboxymethylated bacterial cellulose (CMBC) was synthesized under controlled reaction condition to provide a material with a degree of substitution (DS) that guarantees that the characteristic water insolubility of cellulose is retained (DS = 0.17). The CMBC synthesized was fully characterized by conductometric titration, infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis and solubility assays. The suitability of the produced CMBC for lead removal from water was evaluated. Experimental isotherm data were fitted to different models of sorption isotherms: Langmuir, Freundlich, Dubinin-Radushkevich, and Frumkin, with Langmuir equation resulting in the best fit. Kinetic data were also adjusted to pseudo-first-order and pseudo-second-order models and results undoubtedly showed that the pseudo-second-order kinetic equation was the one that most appropriately described the lead adsorption of CMBC, indicating that lead is adsorbed on CMBC predominantly by chemical interaction. The breakthrough curve was fitted to different models: Bohart-Adams, Clark and Modified Dose-Response, being the Bohart-Adams equation the one that gave the best fit. Desorption studies were carried out in order to know the technical feasibility of the reuse of CMBC. Almost 96% of the retained lead was eluted in just 20 mL, and the CMBC lifetime was over 50 adsorption/desorption cycles. Overall, results obtained suggest that the CMBC herein synthesized may result in an alternative economic and environmentally friendly lead adsorbent for water treatment.

Separation of ethanol/water azeotrope using compound starch-based adsorbents

Comparing breakthrough cures of five starch-based materials experimentally prepared for ethanol dehydration, a compound adsorptive agent ZSG-1 was formulated with high adsorption capacity, low energy and material cost. The selective water adsorption was conducted in a fixed-bed absorber packed with ZSG-1 to find the optimum conditions yielding 99.7wt% anhydrous ethanol with high efficiency. The adsorption kinetics is well described by Bohart–Adams equation. The adsorption heat, ΔHabs, was calculated to be −3.16×104Jmol−1 from retention data by inverse gas chromatography. Results suggested that water entrapment in ZSG-1 is a exothermic and physisorption process. Also, ZSG-1 is recyclable for on-site multiple-use and then adapt for upstream fermentation process after saturation, avoiding pollution through disposal.

Copper biosorption on immobilized seaweed biomass: Column breakthrough characteristics

Abstract The biosorption of copper by the brown seaweed Sargassum baccularia, immobilized onto polyvinyl alcohol (PVA) gel beads, was investigated with fixed-bed experiments. Laboratory-scale column tests were performed to determine breakthrough curves with varying flow rates and feed concentrations. A theoretical fixed-bed model, known as the Bohart-Adams equation, was evaluated in simulating the experimental breakthrough curves. The Bohart-Adams model qualitatively predicted the breakthrough trends. PVA-immobilized seaweed biomass beads were amenable to efficient regeneration with aqueous solution containing the chelating agent ethylenediaminetetraacetic acid (EDTA). The biosorbent retained most of its original uptake capacity over three cycles of use. The excellent reusability of the biosorbent could lead to the development of a viable metal remediation technology.

Determination of model parameters for zinc (II) ion biosorption onto powdered waste sludge (PWS) in a fed–batch system

Biosorption of zinc (II) ions onto pre-treated powdered waste sludge (PWS) was investigated using a completely mixed tank operating in fed–batch mode instead of an adsorption column. Experiments with variable feed flow rate (0.05–0.5 L h −1), feed Zn(II) ion concentrations (37.5–275 mg L −1) and amount of adsorbent (1–6 g PWS) were performed using fed–batch operation at pH 5 and room temperature (20–25 °C). Break-through curves describing variations of aqueous (effluent) zinc ion concentrations with time were determined for different operating conditions. Percent zinc removal from the aqueous phase decreased, but the biosorbed (solid phase) zinc ion concentration increased with increasing feed flow rate and zinc concentration. A modified Bohart–Adams equation was used to determine the biosorption capacity of PWS ( q′ s) and the rate constant ( K) for zinc ion biosorption. Biosorption capacity ( q′ s=57.7 g Zn kg −1 PWS) of PWS in fed–batch operation was found to be comparable with powdered activated carbon (PAC) in column operations. However, the adsorption rate constant ( K=9.17 m 3 kg −1 h −1) in fed–batch operation was an order of magnitude larger than those obtained in adsorption columns because of elimination of mass transfer limitations encountered in the column operations. Therefore, a completely mixed tank operated in fed–batch mode was proven to be more advantageous as compared to adsorption columns due to better contact between the phases yielding faster adsorption rates.

Prediction of protein breakthrough behavior using simplified analytical solutions

The predictability of the breakthrough behavior of lysozyme on the strong cation exchanger SP Sepharose FF was evaluated using two different but related analytical solutions. The first solution, known as the Thomas equation, assumes that adsorption can be represented by a pseudo second-order reaction rate law which translates into a Langmuir isotherm at equilibrium. The second solution, known as the Bohart–Adams equation, assumes that adsorption can be described by a quasi-chemical rate law which reduces to a rectangular isotherm at equilibrium. The Bohart–Adams solution can be regarded as a limiting form of the Thomas solution. The equilibrium and rate parameters embedded in the two solutions were extracted from batch experiments. Predictions using the two simplified solutions agreed with experimental breakthrough data. When the isotherm is highly favorable the simpler Bohart–Adams solution can be used as a practically useful modeling tool in lieu of the mathematically complicated Thomas solution.

Biosorption of copper(II) ions onto powdered waste sludge in a completely mixed fed-batch reactor: Estimation of design parameters

Biosorption of Cu(II) ions onto pre-treated powdered waste sludge (PWS) was investigated using a fed-batch operated completely mixed reactor. Fed-batch adsorption experiments were performed by varying the feed flow rate ( 0.075–0.325 l h −1), feed copper (II) ion concentrations (50–300 mg l −1) and the amount of adsorbent (1–6 g PWS) using fed-batch operation. Breakthrough curves describing the variations of effluent copper ion concentrations with time were determined for different operating conditions. Percent copper ion removals from the aqueous phase decreased, but the biosorbed (solid phase) copper ion concentrations increased with increasing the feed flow rate and Cu(II) concentration. A modified Bohart–Adams equation was used to determine the biosorption capacity of PWS and the rate constant for Cu(II) ion biosorption. Adsorption rate constant in fed-batch operation was an order of magnitude larger than those obtained in adsorption columns because of elimination of mass transfer limitations encountered in the column operations while the biosorption capacity of PWS was comparable with powdered activated (PAC) in column operations. Therefore, a completely mixed reactor operated in fed-batch mode was proven to be more advantageous as compared to adsorption columns due to better contact between the phases yielding faster adsorption rates.

Adsorption of tetrahydrothiophene on faujasite type zeolites: Breakthrough curves and FTIR spectroscopy study

Adsorption of tetrahydrothiophene (THT) on NaX, CaX, AgX, and H-USY was studied by dynamic adsorption method and FTIR spectroscopy. The stoichiometric adsorption capacities are not very different for all materials, which is indicative of a complete micropore filling. In contrast, the overall rate constant of adsorption, determined from fitting the breakthrough curves with Bohart–Adams equation, is two times greater for H-USY than for type X zeolites. For NaX, CaX and H-USY, heating under N2 flow at 300°C allows to restore completely their initial adsorption capacities. In the case of AgX the same treatment results in a twofold lose of capacity accompanied by a collapse of the zeolite structure as evidenced by XRD. The nature of interaction between THT molecules and zeolites was characterized by FTIR spectroscopy. Only a weak interaction through hydrogen bonding was observed for THT on H-USY leading to an almost complete desorption at 100°C. For NaX and CaX adsorbed molecules are gradually eliminated when heated to 300°C while completely different pattern was observed for THT adsorbed on AgX on which the amount of the adsorbate remains nearly constant between 25 and 200°C, but rapidly decreases on further heating. Such a behavior is indicative of much stronger interaction between THT molecules and Ag+ cations in agreement with the data on the regeneration of the adsorbents.

Dynamic Adsorption of Vapours by Activated Carbons and by Polymer-Derived Adsorbents: 1. Adsorption at 0% R.H.

The uptakes of volatile organic compounds from a nitrogen carrier gas at 0% R.H. onto packed beds of adsorbents have been measured by monitoring the effluent vapour concentration profile as a function of time. The profiles have been quantitatively fitted by a modified Bohart-Adams equation which was then integrated to yield the adsorbent capacities. Traditional activated carbons, carbonised macroreticular resins and a macroreticular polymer were used in the study. Performance in the dynamic tests has been related to the pore volume characteristics and surface areas determined from nitrogen adsorption isotherms. Whilst the extent of micropore filling basically increased as the sorbate boiling point increased and increased capacities reflected increased micropore volumes, these trends were interrupted by size exclusion and specific polar interaction effects.

The quantitative use of the Bohart-Adams equation to describe effluent vapour profiles from filter beds

In studies of the removal of gases and vapours of varying volatility from a N 2 stream by adsorbent filter beds it is shown, for the first time, that the Bohart-Adams equation, first proposed over 70 years ago, can with slight modification be used to give good quantitative fits to the effluent vapour profiles at 0% R.H. This was true for conventional carbons and both carbonised and uncarbonised macroreticular resins, and for vapours reversibly adsorbed. Desorption profiles could only be fitted to the equation for the most volatile sorbates. Under conditions of high humidity, when water displacement competes with sorbate uptake, then adherence to the equation only occurs at intermediate vapour volatility.