Scholarly article on topic 'Thermodynamic and kinetics studies of the adsorption of phosphorus by bioretention media'

Thermodynamic and kinetics studies of the adsorption of phosphorus by bioretention media Academic research paper on "Chemical engineering"

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Academic research paper on topic "Thermodynamic and kinetics studies of the adsorption of phosphorus by bioretention media"

THERMODYNAMIC AND KINETICS STUDIES OF THE ADSORPTION OF PHOSPHORUS BY BIORETENTION MEDIA

Ying MEI3b, Xiao-Hua YANG3*, Ya-Nan GUO3, Jun HE\ Rong JIANG3, Yu-Qi LP, and Jian-Qiang LId

a State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, China b Department of Environmental Science and Engineering, School of Energy and Power Engineering, Inner Mongolia University of Technology, Hohhot, China c School of Geography and Remote Sensing Science, Beijing Normal University, Beijing, China d Water Resources and Hydropower Planning and Design General Institute, MWR, Beijing, China

Short paper DOI: 10.2298/TSCI1205506M

The objective of this study is to explore the mechanism ofphosphorus adsorption in the bioretention media. The phosphorus adsorption characteristics of four media of bioretention are studied by four isothermal adsorption experiments. The result indicate that the maximal adsorption capacity (qm) of phosphorus of the four bioretention media are found to be media I (0.3365 mg/g), media II (0.3302 mg/g), media III (0.2751 mg/g) and media IV 0.8435 mg/g), respectively. The negative values of Gibbs free energy of phosphorus indicate that each of the phosphorus adsorption process by the four bioretention media is a spontaneous process. The mean sorption energies obtained from DR isotherm were 0.0758, 0.0772, 0.0803 and 0.0632 kJ/mol respectively, which indicate the physical nature of the adsorbate/adsorbent interactions. Two kinetic models including pseudo first-order and pseudo second-order equation were selected to follow the adsorption process. The results showed that the adsorption of phosphorus with the four types of bioretention media could be described by the pseudo second-order equation. The media IV was the better media of bioretention with high phosphorus removal capacity.

Key words: bioretention media, phosphorus adsorption, isotherm models, kinetic models

Introduction

Bioretention is a urban stormwater low-impact development (LID) best management practice (BMP) by mulch, soil, and plants [1-3]. However, soil phosphorus sorption capacities can vary widely [4]. Although sand media are widely used in the bioretention, only few stu-

* Corresponding author; e-mail: xiaohuayang@bnu.edu.cn

dies have reported on what kind of sand media which acts as effectively removal capacities of phosphorus. In this study, the mechanism of phosphorus adsorption onto four bioretention media was discussed.

Methods and materials

Materials

Four types of bioretention media were used. The four media used in the experiments were excavated from the coastal area of the Yong Ding river in Beijing. All media were washed thrice using deionized water prior to the experiments.

Adsorption studies

The adsorption isotherms were determined with 100 ml solutions with varying initial concentrations of phosphorus from 20 to 100 mg/L. The initial pH of solution was adjusted to the 7.0 by using NaOH or HNO3 solution prior to addition of adsorbent. All reagents used in this study were of AR grade. These solutions were shaken at 298 K in an orbital shaker at the rate of 100 strokes per minute for time of 48 hours. Following centrifugation at 400 rpm for 10 minutes, and then filtered through a 0.45 ^m filter paper. At last, the concentration (Ct) of the residual phosphorus was prepared. All samples were filtered using a 0.45 ^m membrane filter to analyze their total phosphorus. Total phosphorus was analyzed using an inductively coupled plasma-atomic emission spectrometry (ICP-AES).

Batch adsorption experiments were carried out for an adsorption period of 50 minutes in a glass container with 250 ml solution. Based on equilibrium tests at different time, the procedures of kinetic experiments were completed. The aqueous samples were taken at setting intervals time, and the concentrations of phosphorus were measured under the identical condition.

Adsorption isotherms

The data of adsorption of phosphorus on the bioretention media was used to Freundlich, Langmuir, Dubinin-Rudushkevish (D-R) and Flory-Huggins (F-H) models [5]. Different parameters calculated from these models are given in tab. 1.

Table 1. Analysis of the results of adsorption of phosphorus on the bioretention media at 298 K

Isotherms models Parameters Media I Media II Media III Media IV

Langmuir model qm [mg g-1] 0.3365 0.3302 0.2751 0.8435

Kl 0.0237 0.0374 0.0409 0.2187

R2 0.9993 0.9972 0.9854 0.9931

Frendlich model n 0.8983 0.8922 1.1604 1.0019

Kf 0.0052 0.0086 0.0199 0.0234

R2 0.9938 0.9951 0.9842 0.9470

D-R model E [kJ mol-1] 0.0758 0.0772 0.0803 0.0632

R2 0.9768 0.7487 0.5562 0.8575

F-H model AG [kJ mol-1] -18.5403 -20.0923 -26.1801 -30.7505

R2 0.9985 0.9881 0.8876 0.9682

Adsorption kinetics

In order to assess the kinetic rank of the adsorption process, pseudo first-order rate equation and pseudo second-order rate equation were used.

The pseudo first- and second-order rate equation is generally represented as [6]:

- pseudo first-order model: —L = K(qe~qt) (1)

- pseudo second-order model: —1 = k-, (qe - qt)2 (2)

where qt [mgg1] is the amount of adsorbate per unit wet of adsorbent at any time t, qe [mgg1]

- the adsorption capacity at equilibrium, and k1, and k2 are the rate constants of pseudo firstorder and second-order adsorption, respectively. These parameters can be calculated from the two kinetic models and the plotting as shown in fig. 1. Values of k\, k2, qe, and R2 are summarized in tab. 2.

-2 -■- Media 1

о Media II

-3 -a- Media III

Media IV

40 50 Time, t [min.]

Time, t [min.]

Figure 1. Plot of pseudo-first and pseudo-second order kinetic model for the adsorption of phosphorus in the bioretention media at 298 K

Table 2. Parameters calculated for pseudo-first and pseudo-second order kinetic models

Media First-order kinetic model Second-order kinetic model

type R2 qe [mgg 1] k1 [min. 1] R2 qe [mgg 1] k2 [gmg '-min. ']

Media I 0.9064 0.1188 0.4133 0.9902 0.2933 2.2260

Media II 0.8789 1.9380 0.1824 0.9809 0.8665 8.0586

Media III 0.9438 0.9892 0.31344 0.9937 0.4176 0.02457

Media IV 0.9440 2.6753 0.1982 0.9557 2.3186 0.1958

Conclusions

According to the batch adsorption experiments, it can be concluded that the media IV was more effective for removing phosphorus. The adsorption capacity of phosphorus by

the Langmuir model are found to be media IV > media I > media II > media III. The adsorption of phosphorus with four media preferably fits to the Langmuir adsorption isotherm. Mean sorption energy obtained from D-R isotherm was less than 8 kJ/mol which showed that the adsorption process was dominated by physical adsorption. The negative AG values for phosphorus of four bioretention media indicated that the phosphorus adsorption by four media was a spontaneous proces. The experimental data were found to be better fitted to the pseudo second order kinetic model in the whole bioretention media.

Acknowledgments

This work is supported by the Project of National Natural Science Foundation of China (Nos. 51079004 and 50939001), the National Basic Research Program of China (No. 2010CB951104), the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20100003110024), and the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0809).Youth Fund of Inner Mongolia University of Technology (No. X201217).

References

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[2] Kim, H., Seagren, E. A., Davis, A. P., Engineered Bioretention for Removal of Nitrate from Stormwater Runoff, Water Environment Research,75 (2003), 4, pp. 355-367

[3] Mei Y., et al., Comprehensive Assessment of Pollutants Removal in Bioretention, Advanced Science Letters, 10 (2012), 1, pp. 698-699

[4] Sawhney, B. L., Hill, D. E., Phosphate Sorption Characteristics of Soils Treated with Domestic Waste Water, Journal of Environment Quality, 4 (1975), 3, pp. 342-346

[5] Biswas, K., Gupta, K., Ghosh, U. C., Adsorption of Fluoride by Hydrous Iron(III)-Tin(IV) Bimetal Mixed Oxide from the Aqueous Solutions, Chemical Engineering Journal, 149 (2009), 1-3, pp. 196-206

[6] Malana M. A., Qureshi R. B., Ashiq M. N., Adsorption Studies of Arsenic on Nano Aluminium Doped Manganese Coppe Ferrite Polymer (MA, VA, AA) Composite: Kinetics and Mechanism, Chemical Engineering Journal, 172 (2011), 2-3, pp. 721-727

Paper submitted: July 1, 2012 Paper revised: August 3, 2012 Paper accepted: August 13, 2012