Use of various agricultural wastes for the removal of heavy metal ions

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Use of various agricultural wastes for the removal of heavy metal ions Article  in  International Journal of Environment and Pollution · October 2008 DOI: 10.1504/IJEP.2008.020797

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Int. J. Environment and Pollution, Vol. 34, Nos. 1/2/3/4, 2008

Use of various agricultural wastes for the removal of heavy metal ions Sibel Kahraman* Faculty of Education, Department of Sciences, Inonu University, 44280 Malatya, Turkey E-mail: [email protected] *Corresponding author

Nukhet Dogan Institute of Sciences, Department of Biology, Inonu University, 44280 Malatya, Turkey E-mail: [email protected]

Sema Erdemoglu Art and Science Faculty, Department of Chemistry, Inonu University, 44280 Malatya, Turkey E-mail: [email protected] Abstract: There is a need to develop innovative and alternative technologies that can remove toxic heavy metal pollutants from wastewater. In this study, two agricultural residues, cotton stalks and apricot seeds, were used to adsorb copper and lead in solutions. Sorption capacities of agricultural wastes were significantly affected by solution pH, adsorbent mass and adsorbent particle size. The adsorption efficiency of two agricultural waste was in the order cotton stalk > apricot seed and the agricultural wastes adsorbed metal ions in the order of Pb > Cu. Treatment of these metals with agricultural wastes reduced their toxic effects on P. aeruginosa. This reduction in toxic effect is important both in respect of environmental biotechnology and waste detoxification. This study has indicated that cotton stalk and apricot seed could be employed as low-cost alternatives in wastewater treatment for the removal of heavy metals. Keywords: agricultural waste; apricot seed; biosorption; cotton stalk; heavy metal; toxicity. Reference to this paper should be made as follows: Kahraman, S., Dogan, N. and Erdemoglu, S. (2008) ‘Use of various agricultural wastes for the removal of heavy metal ions’, Int. J. Environment and Pollution, Vol. 34, Nos. 1/2/3/4, pp.275–284. Copyright © 2008 Inderscience Enterprises Ltd.

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S. Kahraman et al. Biographical notes: Sibel Kahraman received her first Degree from the Department of Biology (1992) at Inonu University (Turkey). She was awarded to Master Degree (1994) and PhD (1998) from the same department and she is currently an Assistant Professor in the Department of Sciences at Inonu University. She has published 12 papers in refereed journals and participated in 11 scientific meetings. Her main specialisation is in environmental biotechnology, wastewater treatment, industrial biotechnology and enzyme biotechnology. Nukhet Dogan did her Master Degree (2005) in the Department of Biology at Inonu University (Turkey) under the Supervision of Dr. Kahraman. Sema B. Erdemoğlu gained the Degree of BSc in chemistry from Inonu University, Malatya in 1989. She was subsequently awarded a MSc in analytical chemistry by the same University in 1992 and her PhD 1998. She has been serving as research assistant between 1990–2001 in İnönü University and she is currently employed as an Assistant Professor in the Department of Analytical Chemistry the same university. She has published 14 papers in refereed journals and participated in more than 20 scientific meetings. Her main specialisation is in chromatographic and spectroscopic techniques, element speciation and photocatalytic degradation.

1

Introduction

Heavy metals are present in nature and industrial wastewater. Owing to their mobility in natural water ecosystems and their toxicity, the presence of heavy metals in surface water and groundwater poses a major inorganic contamination problem (Yesilada, 2001; Yan and Viraraghavan, 2003). The heavy metals lead and copper are among the most common pollutants found in industrial effluents. These metals can be toxic to organisms, including humans. For instance, lead is extremely toxic and can damage the nervous system, kidneys and reproductive system, particularly in children. Although copper is an essential trace element, high levels can cause harmful health effects. Copper is also toxic to a variety of aquatic organisms, even at very low concentration (Sheng et al., 2004). Conventional methods for removing heavy metals include chemical precipitation, ion exchange, oxidation/reduction, filtration, electrochemical processes, membrane separation and evaporation. These methods have several disadvantages like high cost, incomplete removal, low selectivity and high-energy consumption (Celeya et al., 2000). In order to qualify for industrial applications, biosorbents have to be produced at a low cost. Among many new technologies, utilising plant residue as adsorbents for the removal of dyes and metal ions from wastewater is a prominent technology (McKay et al., 1987; Kanchana, 1991). Several agricultural wastes have already been tested to remove heavy metals such as apple residues (Chong et al., 1998), olive mill solid residue (Pagnanelli et al., 2002), plant root tissues (Chen et al., 1998), cassava peel (Rajeshwarisivaraj et al., 2001), sawdust (Garg et al., 2004), tree fern (Ho, 2003; Ho et al., 2004) and so on. New, economical, easily available and highly effective adsorbents are still needed. This study presents the first outcoming results about the possible use of cotton stalk and apricot seed as heavy metal biosorbents. These materials were chosen considering its large amount availability and the basic cellulosic structure. The heavy metals selected as sorbates were Cu and Pb. The aim of the present work was to study the adsorption

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capacity of these agricultural wastes for heavy metal removal from aqueous solution under different experimental conditions. The effect of various operating parameters on biosorption such as initial pH and metal concentration, adsorbent amount and adsorbent particle size were studied and optimal experimental conditions were decided. Another purpose of this study was to test the toxic effect of heavy metals on a soil bacterium Pseudomonas aeruginosa ATCC 10145 before and after biosorption with agricultural wastes.

2

Materials and methods



Adsorbents preparation: Two agricultural residues, cotton stalk and apricot seed that were collected from fields in and around east Turkey and southern-east Turkey, respectively, were used as biosorbent. These were ground and the size distribution was determined by using a sieve [particle size; 25–60–100–270 British Standard Sieve (BSS) mesh].



Metal solutions: Stock metal solutions at various concentrations were prepared by dissolving lead nitrate and copper sulphate in distilled water (Analytical reagent grade, Merck). The pH of each metal solution was adjusted to the desired value using 0.1 NaOH and 0.1 HCl.



Biosorption studies: Different amounts of agricultural wastes were transferred to 250 l flask that contained 50 l of metal-containing distilled water. The effect of the pH on the biosorption capacity of the agricultural wastes with Pb and Cu ions was investigated in the pH range of 2.0–6.0 at 50 mg l–1 concentration at 30°C. The effect of the initial metal concentration on the biosorption was studied between 50–250 mg l–1 at 30°C. All experiments were carried out at fixed agitation rate (150 rpm). All the biosorption experiments were run in duplicate. Controls without the adsorbent were also run parallel. The metal concentrations in the samples were determined with a Flame Atomic Adsorption Spectrophotometer (FAAS).



Desorption studies: Desorption of Cu and Pb ions were performed with a 0.1 M HCl solution. The metal-loaded biosorbent after biosorption was dried, and then this biosorbent was brought into contact with 50 ml of the 0.1 M HCl for 30 minute on a rotary shaker (150 rpm) to study the removal of biosorbed metal ions. The final metal concentrations in the aqueous phase were determined by FAAS as described above. Desorption ratio was calculated from the following equation: Desorption ratio = (amount of metals desorbed)/(amount of metals biosorbed) Percent desorption values were obtained by multiplying the above ratio by 100 (Bayramoglu et al., 2002). The desorbed biosorbent was dried, and so the regenerated biosorbent was used in biosorption–desorption cycles to determine reusability of the agricultural wastes.

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Toxicity assay: Pseudomonas aeruginosa ATCC 10145 that is a soil bacterium was used to test the toxicity of before biosorption and after biosorption of heavy metals. For this, P. aeruginosa was incubated for 18 hours at 37°C in nutrient broth medium. Each toxicity test was carried in test tubes in a final volume of 5 ml, containing 100 µl bacterial suspensions, 1 ml nutrient broth and the metal sample to be tested. After incubation for 24 hours at 37°C, viable cell counts (colony forming units, cfu ml-1) were estimated by plating on nutrient agar plates. Samples of 100 µl were taken from the tubes and serial dilutions were prepared with saline. After that, 100 µl of the diluted sample was spread onto duplicate nutrient agar plates. The plates were incubated at 37°C for 24 hours and then the number of viable cell counts was expressed as mean colony forming unit per ml (cfu ml–1) (Yesilada and Sam, 1998).

3

Results and discussion

Effect of adsorbent particle size and adsorbent amount: To investigate the effect of particle size and the amount of cotton stalk and apricot seed on Cu biosorption, agricultural wastes in the range 0.1–1.0 g 50 ml–1 and 25–60–100–270 mesh particle size were subjected to biosorption tests in the test solution while keeping the initial metal concentration (50 mg l–1), temperature (30°C), agitation (150 rpm) and pH (natural) constant for 30 minute (Figure 1 (A–B)). As shown in Figure 1, the percent adsorption was increased with adsorbent dose. The ratios of Cu adsorbed increased as the adsorbent particle size decreased. This can be because of the larger specific active surface of small particles. While most effective particle size for cotton stalk was 100 and 270 meshes, it is 270 mesh for apricot seed. So, further experiments for cotton stalk and apricot seed were done using 1.0 g and 100 mesh and 1.0 g and 270 mesh, respectively. Increase in the adsorption with adsorbent dose can be attributed to increased adsorbent surface area and availability of more adsorption site (Garg et al., 2004). Adsorption increased from 32% to 86% as the adsorbent dose of cotton stalk was increased from 0.1 to 1.0 g 50 ml–1, and it increased from 13% to 69%, depending on the enhancement of the adsorbent dose of apricot seed from 0.1 to 1.0 g 50 ml–1. Figure 1

Effect of adsorbent dose and adsorbent particle size on biosorption of Cu by Cotton stalk (A) and Apricot seed and (B) (Cu concentration: 50 mg l–1; Contact time: 30 min; Agitation rate: 150 rpm; and pH: natural)

Use of various agricultural wastes for the removal of heavy metal ions Figure 1

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Effect of adsorbent dose and adsorbent particle size on biosorption of Cu by Cotton stalk (A) and Apricot seed and (B) (Cu concentration: 50 mg l–1; Contact time: 30 min; Agitation rate: 150 rpm; and pH: natural) (continued)

Effect of pH: Solution pH is an important parameter that affects the biosorption of heavy metal by biomass. To study the effect of the pH on Cu and Pb adsorption on cotton stalk and apricot seed, the experiments were carried out at 50 mg l–1 initial metal concentration with 1.0 g 50 ml–1 adsorbent dose (100 mesh for cotton stalk and 270 mesh for apricot seed) at 30°C for 30 min and 150 rpm. The effect of initial pH on the biosorption capacity of cotton stalk and apricot seed was investigated in the pH range of 2.0–6.0. There was an increase in adsorption of Cu with increasing pH, from 2.0 to 5.0, but it seemed to decrease at pH 6.0 (Figure 2). Also, there was an increase in adsorption of Pb with increasing pH from 2.0 to 4.0, but it seemed to decrease at pH 5.0 (Figure 3). Figure 2

Effect of pH on biosorption of Cu by Cotton stalk and Apricot seed (Cu concentration: 50 mg l–1; Contact time: 30 min.; Adsorbent dose: 1.0 g 50 ml–1; and Agitation rate: 150 rpm)

280 Figure 3

S. Kahraman et al. Effect of pH on biosorption of Pb by Cotton stalk and Apricot seed (Cu concentration: 50 mg l–1; Contact time: 30 min; Adsorbent dose: 1.0 g 50 ml–1; Agitation rate: 150 rpm)

The low biosorption capacity at pH values below 4.0 was attributed to hydrogen ions that compete with metal ions on the sorption sites (Huang et al., 1991). In other words, at lower pH, owing to protonation of binding sites resulting from high concentration protons, negative charge intensity on the sites was reduced, resulting in the reduction or inhibition of the binding of metal ions (Kapoor et al., 1999). The increase in biosorption by raising the pH from 3.0 to 5.0 and beyond would indicate the involvement of negatively charged groups. Increased pH (i.e., fewer H+ ions) results in more ligands being available for metal ion binding, and hence biosorption is enhanced (Sheng et al., 2004). On the other hand, the formation of sizeable metal precipitates at high pHs (above pH 5.0) inhibited the contact of metal with the adsorbent (Sing and Yu, 1998). Some researches reported similar values of pH, ranging from 2 to 7 (Bhainsa and D’Souza, 1999; Kahraman et al., 2005). Effect of initial metal concentration: The influence of the initial concentration of metal in solutions on the rate of adsorption on cotton stalk and apricot seed was studied. The experiments were carried out at fixed adsorbent dose (1.0 g 50 ml-1) in the test solution, 30°C temperature, pH (5.0 for Cu and 4.0 for Pb) and with different initial concentration of metal (50, 100, 150, 200, 250 mg l–1) and fixed agitation (150 rpm) for 30 minutes. Copper and lead biosorption were clearly dependent on the initial metal ion concentration of the solution (Figures 4 and 5). Percent Cu and Pb removal efficiency of cotton stalk and apricot seed reduced with increase in Cu and Pb concentration. Cu uptake was reduced for cotton stalk from 88% to 27% and for apricot seed from 54% to 4%, as concentration was increased from 50 to 250 mg l–1. Pb uptake was reduced for cotton stalk from 93% to 90% and for apricot seed from 82% to 29%, as concentration was increased from 50 to 250 mg l–1. The use of agricultural wastes might offer advantages for metal removal from industrial effluents that are reported to have a lower metal concentration (