Bed Depth Service Time Approach Research Articles

Arsenic mitigation by chitosan-based porous magnesia-impregnated alumina: performance evaluation in continuous packed bed column

Dissolved arsenic in contaminated groundwater is a major concern on a global scale due to its extreme toxicity. This paper reports a magnesium oxide-impreg- nated mesoporous alumina synthesized using biopolymer chitosan template. The adsorbent was first characterized by BET, SEM and EDAX analysis. The packed column per- formed effectively over wide range of pH and exhibited a maximum adsorption capacity of 17.2 mg/g for an input arsenic concentration of 20 mg/L. The experimental data fitted well with pseudo-second-order kinetics. Thermody- namic study on the adsorption phenomena revealed that arsenic adsorption on the porous adsorbent was sponta- neous, and the process was exothermic. The arsenic sorp- tion capacity at breakthrough point was greatly dependent on bed depth. A bed depth service time approach was adopted to describe the continuous flow system. The col- umn after exhaustion was regenerated by eluting the bound arsenate (As(V)) with *15 bed volume sodium hydroxide solution. The adsorbent could retain its capacity up to five cycles of such regeneration. The influence of different operating conditions such as bed depth, flow rate and initial arsenic concentration was investigated statistically by the two-level full-factorial experimental designs to evaluate optimum operating conditions. Graphical abstract

Fixed Bed Column Adsorption Studies Using Fly Ash for Removal of Cadmium from Aqueous Solution

In the present paper, adsorptive removal of cadmium from synthetic wastewater using a 2 cm diameter fly ash column was studied through three column adsorption experiments by varying column depths (10, 15 and 20 cm). Study results showed fly ash to be an effective adsorbent for cadmium removal. Column design parameters such as depth of adsorption zone (6 cm), critical bed depth (1.3 cm), adsorption capacity (480.82 mg/l) and adsorption rate constant (0.0111 l/mg min) are calculated using bed depth service time approach. Using the same method effect of varying flow rate (5, 8 and 10 ml/min) and initial cadmium concentration (15 and 20 mg/l) was studied and the corresponding model predicted service times conformed well with the experimentally obtained results from three more column studies. Negligible leaching of adsorbed cadmium from exposed fly ash column was observed during two desorption studies.

Biosorption of Pb(II) and Cr(III) from aqueous solutions: breakthrough curves and modeling studies

The sorption capacity parameters obtained for batch studies provide useful information about biosorption system. However, such data fail to explain the process under continuous-flow conditions. The present study is an attempt to explore the biosorption of Pb(II) and Cr(III) by straw from local wheat (Triticum aestivum). The biosorbent has been characterized by using Fourier transform infrared spectroscopy and surface area and elemental analyses and found to be porous and polyfunctional. S-shaped breakthrough curves were obtained at different column heights for the both metal ions. Various breakthrough parameters and saturation times have been determined. The column data have been successfully used to study the Bohart-Adams' bed depth service time (BDST) model and Yoon and Nelson's model. It was found that BDST model quite efficiently explained the whole column data whereas Yoon and Nelson model could explain it below 90% breakthrough concentration. The predicted and calculated BDST parameters were in agreement with each other. Yoon and Nelson's constant decreased with an increase in the column height for both metal ions. Effect of change in flow rate on the Pb(II) biosorption has also been discussed with respect to BDST approach.

The Effect of Zeolite Fixed Bed Depth on Lead Removal from Aqueous Solutions

The effect of zeolite bed depth on lead removal from aqueous solutions by the column method has been examined. The results indicate that the increase of bed depth delays the breakthrough point and exhaustion point, and increases the contact time of the zeolite – lead solution, and the height of the mass transfer zone, hz. The increase of the bed depth lowers the effect of axial dispersion on the mass transfer process. In order to predict the time necessary for exceeding the defined effluent concentration for a constant bed depth, the bed depth service time (BDST) approach has been used. Experimentally obtained breakthrough curves for the flow rate of 1 ml/min were used to derive the BDST approach equations. These equations were successfully used for modelling of the system for flow rates of 2 and 3 ml/min. The BDST equations have yielded modelled linear equations used for calculation of hz. The increase of the flow rate increases hz, which indicates that the zeolite–solution contact time is not sufficient. This may be attributed to the affect of axial dispersion on mass transfer on the solid-liquid interface.

Removal of methylene blue from aqueous solution by rubber (Hevea brasiliensis) seed shell in a fixed‐bed column

AbstractThe present study investigated the dynamic sorption of methylene blue (MB) from solution using rubber seed shell (RSS) in a fixed‐bed column. The process of sorption of MB from solution was analyzed using five different isotherm models (Langmuir, Freundlich, Temkin, Harkins–Jura, and Halsey isotherm equations), and the monolayer sorption capacity (82.64 mg/g) obtained from the Langmuir plot was compared with the bed depth service time (BDST) capacity (703.42 mg/l) obtained from the BDST model plot. The effect of two process variables (RSS bed height and initial MB concentration) on the dynamic sorption of MB on RSS was studied using the breakthrough curve. The total time (tx) for the establishment of primary adsorption zone (PAZ), the time required for the movement of the PAZ down the length of the RSS bed (tδ), the fractional capacity (f), and the length or depth of PAZ (δ) were evaluated. The operating design of the fixed was altered using serial dynamic sorption study, and the sensitivity of the RSS bed to drought was monitored when the Ci/Cf approached 0.5. The operational parameters of these variations were also estimated. The process variables were correlated with the BDST model, and a linear graph with high linear correlation (R2 > 0.9) values was obtained (0.9944 and 1.0000 at Tb10 and Tb50 respectively). The results obtained from the correlation of the process variables with the BDST model were used to predict the effect of changing the process variables on the system by using the BDST approach. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Sorption of anionic surfactants on a fixed bed of rubber granules

The performance of a fixed-bed adsorber (FBR) column for the removal of anionic surfactants from aquatic environments has been studied. Waste tyre rubber granules were used as the adsorbent material, and sodium dodecyl sulfate, an anionic surfactant, as the adsorbate. The FBR column design parameters were evaluated using the column breakthrough data at different bed depths. The Bohert and Adams model was used with the bed depth service time approach for the design of the column. The bed efficiency obtained was 90.97%.

Development of Fixed Bed Adsorber for Abatement of Endosulfan in Aqueous Media

In this paper an attempt was made to develop and evaluate the performance of a fixed bed adsorber (FBR) column to remove endosulfan, an organochlorine pesticide from the water environment using wood charcoal as an adsorbent. The FBR column design parameters were evaluated using the column breakthrough data at different bed depths. The Bohert and Adams model was used with bed depth-service time (BDST) approach for the design of the adsorber. Similarity in service time values estimated from BDST approach and experimental curves revealed that BDST approach could be adapted for the design of this system. Desorption of the exhausted column with 10% methanol solution took 1hr with maximum desorption occurring at 0.5 hrs with a maximum endosulfan concentration of 47 mg l−1. A laboratory column study for 3 successive cycles of operation (adsorption-desorption) revealed that the column could treat 47.27 bed volumes of endosulfan-contaminated water up to breakthrough and 158.45 bed volumes up to exhaustion. It showed a promising performance with more than 89% of its original efficiency even after the 3rd cycle of operation. It clearly demonstrates adaptability of the present study in developing adsorber columns for rural areas.

Sorption and desorption of lindane by wood charcoal in fixed‐bed reactor

Sorption and desorption of lindane (y‐HCH) by wood charcoal (WC) and wood charcoal treated by 1N HNO3 (WCT) in fixed‐bed reactor (FBR) were investigated in this study. WCT revealed a better performance than WC, in removing lindane in FBR. The breakthrough of lindane was significantly affected by the size of WCT, flow rate to the FBR, and depth of WCT bed. The removal of lindane in the presence of mixture of other pesticides was considerably reduced. The design parameters for FBR were calculated based on the bed‐depth service time (BDST) approach. Many parameters Viz. depth of sorption zone, velocity of sorption, sorbent use rate, critical bed‐depth, bed efficiency, and service time, were determined for design of the fixed‐bed. Using the material balance principle, the characteristics of the wave‐front were evaluated and found that the wave‐front velocity is approximately equal to the sorption velocity determined from the BDST approach. Desorption studies were performed in dilute organic solvent media and they gave an excellent performance in regeneration process.