Biosorption of copper(II) from aqueous solutions by Spirogyra species

Journal of Colloid and Interface Science 296 (2006) 59–63 www.elsevier.com/locate/jcis

Biosorption of copper(II) from aqueous solutions by Spirogyra species V.K. Gupta a,∗ , Arshi Rastogi a , V.K. Saini a , Neeraj Jain b a Department of Chemistry, Indian Institute of Technology, Roorkee 247667, India b Central Building Research Institute, Roorkee 247667, India

Received 24 June 2005; accepted 17 August 2005 Available online 15 September 2005

Abstract Batch studies were conducted to investigate the kinetics and isotherms of Cu(II) biosorption on the biomass of green alga Spirogyra species. It is observed that the biosorption capacity of the biomass strongly depends on pH and algal dose. The maximum biosorption capacity of 133.3 mg Cu(II)/g of dry weight of biomass was observed at an optimum pH of 5 in 120 min with an algal dose of 20 g/L. Desorption studies were conducted with 133.3 mg/g of Cu(II) loaded biomass using different desorption agents including HCl, EDTA, H2 SO4 , NaCl, and H2 O. The maximum desorption of 95.3% was obtained with HCl in 15 min. The results indicate that with the advantages of high metal biosorption capacity and satisfactory recovery of Cu(II), Spirogyra can be used as an efficient and economic biosorbent material for the removal and recovery of toxic heavy metals from polluted water. © 2005 Elsevier Inc. All rights reserved. Keywords: Adsorption; Biosorption; Spirogyra; Biomass; Copper; Desorption

1. Introduction The presence of heavy metals in the environment has been of great concern because of their increased discharge, toxic nature and other adverse effect on receiving water bodies. Elevated environmental levels of Cu(II) come from a variety of sources [1]. The potential sources of Cu(II) in industrial effluents include metal cleaning and plating baths, pulp, paper and paper board mills, fertilizer industry, etc. Excessive intake of copper results in an accumulation in the lever and may produces gastrointestinal catarrh. It is also toxic to aquatic organisms even at very small concentrations in the natural waters. Safe and effective disposal of heavy metal-bearing wastewater is a difficult task due, in part, to the fact that cost-effective treatment alternatives are not available [2]. Various treatment and disposal methods exist include chemical precipitation, electrode deposition, reverse osmosis, adsorption, etc. Microbial biomass of fungi, bacteria, and algae offer considerable promise for toxic metals removal from waste water streams [3] and the state of art in the field of biosorption has been reviewed [4,5]. * Corresponding author. Fax: +91 1332 73560.

E-mail address: [email protected] (V.K. Gupta). 0021-9797/$ – see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.08.033

The phenomena of biosorption has been described in a wide range of living biomass like fungi [6], bacteria [7,8], yeast [9], moss [10], aquatic plants [11], and algae [12–28]. The investigations have shown that the biosorption of heavy metal cations by microorganisms is a rapid and reversible reaction and is not necessarily mediated by metabolic processes. In general, it is observed that the heavy metal biosorption capacity depends on the type of biomass and the reaction may be selective for certain cations [29]. Many workers have reported the potential of marine macro algae for biosorption of toxic metal ions [12–18]. The uptake capacities of the biomass of a group of nine marine macro algae for cadmium, copper and lead were evaluated and it was observed that the uptake capacities of the biomass ranged between 0.8–1.6 mmol/g [12]. Biosorption performance of marine algae Sargassum, Padina, Ulva, and Gracillaria species has been studied for removal of Cu, Pb, Zn, Cd, and Ni from aqueous solutions [17]. The biosorption capacities were significantly affected by solution pH. The maximum uptake capacities ranging from 0.61–1.16 mmol/g for Sargassum species and 0.63–1.25 mmol/g for Padina species were observed. In an another study, red alga Palmaria palmate has been utilized for the uptake of Pb, Cu, Ni, Cd, and Zn [18]. The highest max-

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imum adsorption capacity derived from Langmuir model was 15.17 mg/g for Pb (pH 5) and 6.65 mg/g for Cu (pH 5–6). The affinity of metals for Palmaria palmate was found to decrease in the order: Pb > Cd > Cu > Ni > Zn. Many workers have also investigated the performance of fresh water green algae Chaetophora elegans, Scenedesmus, Chlorella, Spirogyra, Chlamydomonas globas, Zygnema species, etc. for the removal various heavy metal ions (Ni, Cu, Pb, Zn, Cd, and Al) from wastewater [19–28]. Biosorption potential of Spirogyra species was studied along with Lemna and Microcystis for removal of Pb, Cu, Cd, and Zn in single, bi-, tri-, and multimetallic mixture and differential pulse anodic stripping voltammetery was used for the measurements [22]. It has been observed that the biomass of all the organisms exhibited the following order of metal biosorption: Pb > Cu > Zn > Cd. The adsorption kinetics of six metal ions (Al, Zn, Hg, Pb, Cu, and Cd) onto green micro alga (Scenedesmus subspicatus) and siliceous earth have also been investigated [24]. The results reveal that alga exhibited a high capacity of metal uptake and mechanism of adsorption onto algae is a mixture of adsorption and accumulation. The biosorption of Zn, Cu, and Co on Oscillatoria angustissima from single, binary, and ternary metal solution was studied as a function of pH [27]. The sorption capacities for single metal decreased in the order Zn > Co > Cu and the adsorption capacities were 0.33 mmol/g Zn, 0.26 mmol/g Co, and 0.12 mmol/g Cu. In view of the above, it is observed that a very little work has been reported on the metal uptake capacity of alga Spirogyra species which is found in abundant in fresh water. The purpose of this study is to evaluate the biosorption capacity of the fresh water alga Spirogyra species for Cu(II) from aqueous solutions. The biosorption capacities were evaluated using Langmuir isotherms and the results indicated that the biomass is a suitable material for the development of high capacity biosorbent for Cu(II) removal. Biosorption capacities observed in the present study have also been compared with the capacities observed by other workers utilizing different biomass for Cu(II) removal from aqueous solutions. 2. Materials and methods 2.1. Materials

2.3. Biomass (adsorbent) Algal biomass of Spirogyra species was collected from a fresh water pond. It was washed with distilled water to remove dirt and was kept open on a filter paper to reduce the water content. After this, the biomass was sun dried for 6–8 h and ground to a particle size of 200–300 µm. 2.4. Experimental procedure Batch biosorption experiments were conducted to obtain rate and equilibrium data, using 250 ml conical flasks kept at room temperature (22 ± 2 ◦ C). The reaction mixture containing 100 ml Cu(II) solution of known concentration and required dose of dry biomass was agitated on a rotary shaker. The solution pH was maintained at a constant value of 5 by adding either 0.1 M HCl or NaOH. Each flask was removed after 120 min of contact time and the solution was filtered using a 0.45 µm membrane filter. The filtrates were analyzed for residual Cu(II) concentration. All the experiments were run in duplicate and mean values are reported. 2.5. Effect of pH To study the effect of various pH viz. 2.5, 4, and 5 on biosorption of Cu(II) on Spirogyra biomass, experiments were conducted with fixed biomass dose of 15 g/L. The concentration of Cu(II) solution was varied from 100 to 250 mg/L and then followed the same procedure as described above. 2.6. Kinetic studies Kinetic studies for biosorption of Cu(II) were conducted at various concentration of Cu(II) solution (150 and 200 mg/L) and biomass doses were ranged from 10 to 20 g/L. Samples of 5 ml were collected at definite time intervals viz. 30, 60, 90, 120, 150, and 180 min to analyse the residual Cu(II) concentration. As the biosorption studies have been carried out using adsorption technique, the following mathematical relation between contact time and percent removal of Cu(II) has been used to find out biosorption kinetics constant for algae R = a(t)b ,

All the reagents were of AR grade either from Merck, Germany or S.D. Fine-Chem Ltd., India. A stock solution of Cu(II) (1000 mg/L) was prepared in double distilled water with copper sulfate and 10 ml of HNO3 was added in the stock solution to check the precipitation of copper. All working solutions were prepared by diluting the stock solution with distilled water.

where R is percent removal, a and b are the constants, and t is the contact time in minutes. The linearized relationship of Eq. (1) can be expressed as

2.2. Equipment

2.7. Adsorption isotherms

pH measurements were made using a pH meter (Model CT No. CL 146, Toshniwal, India). The concentration of copper was determined by inductive coupled plasma (Model Plasmalab 8440) at a wavelength of 324.75 using argon gas.

To determine the maximum biosorption capacity of the biomass, isotherms studies were conducted with varying initial Cu(II) concentration from 50 to 250 mg/L at different biomass dose of 5, 10, 15, and 20 g/L.

log R = log a + b log t.

(1)

(2)

V.K. Gupta et al. / Journal of Colloid and Interface Science 296 (2006) 59–63

The Langmuir adsorption model was adopted for the estimation of maximum Cu(II) biosorption capacity at different initial concentration, where they could not be reached in the experiment [19]: 1/qe = 1/(Xm bCe ) + 1/Xm ,

(3)

where qe is the metal biosorption per unit weight of dry biomass (mg/g), Ce is the equilibrium concentration (mg/L), Xm is biosorption capacity (mg/g), and b is the Langmuir constant (L/mg). 2.8. Desorption studies Desorption studies were conducted with 133.3 mg/g of Cu(II) loaded biomass using different desorption agent including HCl, EDTA, H2 SO4 , NaCl, and H2 O. The concentration of HCl, H2 SO4 , and NaCl was 0.1 M and 0.25 M for EDTA. The solid to liquid ratio was kept to 2 g/L and shaked on a rotary shaker for 15 min. The reaction mixture was filtered and supernatant was used to determine the Cu(II) concentration after desorption. 3. Results and discussion 3.1. Effect of pH It has been consistently shown that the solution pH is an important factor which affects biosorption of metal and that cation biosorption increases as solution pH increases [8,9]. The effect of pH on the biosorption capacity of Cu(II) with biomass of Spirogyra has been in shown Fig. 1. It reveals that on increase in pH from 2.5 to 5, the biosorption capacity increases

Fig. 1. Effect of pH on biosorption of Cu(II) at various concentrations by Spirogyra.

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at all the select Cu(II) concentrations. The maximum biosorption capacity at pH 5 with 100, 150, 200, and 250 mg/L of Cu(II) concentration were about 71, 78, 75, and 70%, respectively. The mechanism of biosorption at different pH can be explained considering the nature of the biosorbent at different solution pH and metal biosorption is mainly due to ionic attraction. At lower pH, the cell wall of Spirogyra becomes positively charged due to increase in hydrogen ion concentration responsible for reduction in biosorption capacity. In contrast, at higher pH (5) the biosorption capacity of Cu(II) is high due to attraction between biomass and metal, since the cell wall surface is more negatively charged. The study at pH higher than 5 were not conducted because insoluble copper hydroxides get precipitated and restricted the true biosorption studies. 3.2. Kinetic studies Kinetic studies were carried out for biosorption of Cu(II) as a function of contact time at various algal doses (10, 15, and 20 g/L) with initial Cu(II) concentrations ranging from 100 to 250 mg/L and the results for 150 and 200 mg/L of initial Cu(II) concentration are shown in Figs. 2 and 3. The figures show that the biosorption of Cu(II) increases with increase in contact time from 0 to 120 min and after that becomes almost constant up to the end of the experiment (180 min). However, the biosorption rate was fast during first 30 min of contact time and most of the removal takes place during this period. The figures also show that Cu(II) biosorption increases with increase in algal dose and maximum biosorption has been observed at 150 mg/L concentration of Cu(II). The maximum removal of Cu(II) ranges from 72 to 81% for select Cu(II) concentrations with an algal dose of 20 g/L in 120 min.

Fig. 2. Effect of contact time on the biosorption of Cu(II) at various doses of Spirogyra.

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Fig. 3. Effect of contact time on the biosorption of Cu(II) at various doses of Spirogyra.

Fig. 4. Effect of Cu(II) concentration on biosorption at various doses of Spirogyra.

Table 1 Values of biosorption kinetic constants Cu(II) (mg/L)

Algal dose (g/L)

log a

a

b

100

10 15 20

1.56 1.57 1.59

36.0 37.1 39.2

0.08 0.13 0.10

150

10 15 20

1.51 1.61 1.65

32.3 40.5 44.7

0.17 0.13 0.16

200

10 15 20

1.56 1.60 1.63

36.2 39.6 42.8

0.12 0.14 0.14

250

10 15 20

1.43 1.50 1.61

26.9 31.6 40.7

0.15 0.14 0.11

Figs. 2 and 3 show that a linear relationship exists in percent biosorption of Cu(II) and contact time. Hence Eq. (1) was fitted in the experimental data and the values of constants a and b are shown in Table 1. A perusal of Table 1 shows that values of a range from 26.9 to 44.7 and highest value of a is observed at Cu(II) concentration of 150 mg/L with an algal dose of 20 g/L. The value of a decreases with increase in algal dose for the same initial Cu(II) concentration which suggests that biosorption capacity increases with increase in algal dose. The values of b range from 0.11 to 0.16 and lower values of b suggest that with increase in time, rate of percentage removal decreases. 3.3. Adsorption isotherms The results of isotherms studies conducted at various initial Cu(II) concentrations at different algal dose are shown in Fig. 4. It is observed that with increase in initial Cu(II) concentration

Fig. 5. Langmuir isotherms of Cu(II) biosorption at various algal doses.

from 50 to 150 mg/L, the biosorption efficiency increases and becomes maximum (81%) at 150 mg/L. On further increase in initial Cu(II) concentration up to 250 mg/L, decrease in biosorption efficiency has been observed. Fig. 4 also shows that on increase in algal dose from 5 to 20 g/L, Cu(II) biosorption efficiency increases at all the select initial Cu(II) concentrations as is observed during kinetic studies. The values shown in Fig. 4 were used to fit in Langmuir model (Eq. (3)) to calculate the maximum biosorption capacity (Xm ) and Langmuir constant (b). The adsorption isotherms at different algal doses have been shown in Fig. 5 which shows that biosorption of Cu(II) followed the Langmuir model well, as is shown by high values of the coefficient of correlation (r 2 ) given in Table 2. The values of biosorption capacity (Xm ) and Langmuir constant (b) are shown in Table 2. As is observed from Table 2, biosorption capacity for Cu(II) increases with increase in algal dose and varies from 59.5 to 133.3 × 103 mg Cu(II)/g of dry weight of biomass. Hence maximum Cu(II) biosorption capacity (133.3 mg Cu(II)/g of dry weight of biomass) is observed at an algal dose of 20 g/L with initial Cu(II)

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4. Conclusions

Table 2 Langmuir parameters for adsorption isotherms Algal dose (g/L)

Xm (mg/g)

b (L/mg)

r2

5 10 15 20

59.5 79.4 106.4 133.3

0.34 0.13 0.15 0.10

0.99 0.99 0.92 0.99

Table 3 A comparison of biosorption capacity (Xm ) of different biomasses for Cu(II) removal Biomass

Xm (mg/g)

Reference

P. palmate (red alga) O. angustissima (green alga) P. aerogenosa (bacteria) S. subspicatus (green alga) P. pupureum (red alga) P. tricornutum (diatom) C. cryptica (diatom) Siliceous earth Spirogyra (green alga)

6.65 7.62 23.00 13.28 0.27 1.67 26.28 0.07 133.30

[17] [25] [8] [21] [21] [21] [21] [21] [This work]

The batch studies conducted in the present study provides significant information regarding biosorption of Cu(II) on green algae Spirogyra species in terms of optimum pH and biomass dose for maximum removal of Cu(II) from the aqueous solution. The studies indicate that Spirogyra species is an effective biosorption for Cu(II) removal. The maximum Cu(II) biosorption capacity has been found to be 133.3 mg Cu(II)/g of dry weight of biomass at an algal dose of 20 g/L in 120 min of contact time with initial Cu(II) concentration of 150 mg/L and optimum pH of 5. At pH higher than 5, the precipitation of insoluble metal hydroxides takes place restricting the true biosorption studies. With the advantage of high metal biosorption and desorption capacities, the biomass of Spirogyra has the potential to be used as an effective and economic biosorbent material for the removal and recovery of heavy metals from wastewater streams. Acknowledgment The authors are thankful to CSIR, New Delhi, India, for providing financial assistance to carry out the present work. References

Fig. 6. Effect of various agents on desorption of Cu(II) from Spirogyra.

concentration of 150 mg/L, which is much higher than the biosorbents used by other workers. A comparison of biosorption capacities of various biomasses used for Cu(II) removal has been given in Table 3. A perusal of Table 3 shows that the biomass of Spirogyra used in the present study is an efficient biosorbent for removal of Cu(II) from aqueous solutions. 3.4. Desorption studies The results of desorption experiments are shown in Fig. 6, which clearly indicates that effective desorption of Cu(II) was observed with mineral acids (HCl and HNO3 ) and chelating agent EDTA after 15 min. The maximum desorption of 95.3% was obtained with HCl, while desorption using distilled water (H2 O) and NaCl was almost negligible (4.4 and 8.6%, respectively).

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