Environ Sci Pollut Res DOI 10.1007/s11356-013-1516-1
Heavy metals removal from wastewaters using organic solid waste—rice husk S. Sobhanardakani & H. Parvizimosaed & E. Olyaie
Received: 13 November 2012 / Accepted: 22 January 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract In this study, the removal of Cr(III) and Cu (II) from contaminated wastewaters by rice husk, as an organic solid waste, was investigated. Experiments were performed to investigate the influence of wastewater initial concentration, pH of solution, and contact time on the efficiency of Cr(III) and Cu(II) removal. The results indicated that the maximum removal of Cr(III) and Cu(II) occurred at pH 5–6 by rice husk and removal rate increased by increased pH from 1 to 6. It could be concluded that the removal efficiency was enhanced by increasing wastewater initial concentration in the first percentage of adsorption and then decreased due to saturation of rice husk particles. Also according to achieved results, calculated saturation capacity in per gram rice husk for Cr(III) and Cu(II) were 30 and 22.5 mgg−1, respectively. The amounts of Cr(III) and Cu(II) adsorbed increased with increase in their contact time. The rate of reaction was fast. So that 15–20 min after the start of the reaction, between 50 and 60 % of metal ions were removed. Finally, contact time of 60 min as the optimum contact time was proposed. Keywords Rice husk . Chromium . Copper . Adsorption . Wastewater
Responsible editor: Philippe Garrigues S. Sobhanardakani (*) Department of the Environment, Hamedan Branch, Islamic Azad University, Hamedan, Iran e-mail: [email protected]
H. Parvizimosaed : E. Olyaie Young Researchers & Elites Club, Hamedan Branch, Islamic Azad University, Hamedan, Iran
Introduction Industrial used water is one of the major sources of aquatic pollution. A large volume of effluents with hazardous species, namely heavy metals and semimetals, is being discharged every day from industries into aquatic systems (Seko et al. 2005; Guerra et al. 2009). Sustainable water supplies are vital for agriculture, industry, recreation, energy production, and domestic consumption. Thus, there is a need to improve the efficiency of water purification technology (Gupta et al. 2003). Different materials were used for the removal of dyes by use of adsorption processes (Gupta et al. 2006a, b, 2007, 2010; Gupta and Sharma 2003; Jain et al. 2004). A number of workers have used different adsorbent systems, developed from various industrial waste materials, for the removal of toxic metals and organic waste pollutants (Saleh and Gupta 2012; Karthikeyan et al. 2012). This issue has been a matter of serious concern worldwide for the last few decades, and rigorous emphasis is being given to get rid of this unavoidable risk. Due to the discharge of large amounts of metal-contaminated wastewater, industries bearing heavy metals, such as Cr, Cu, Cd, Ni, As, Pb, and Zn, are the most hazardous among the chemical-intensive industries. Because of their high solubility in the aquatic environments, heavy metals can be absorbed by living organisms. Cr compounds are widely used by modern industries, resulting in large quantities of this element being discharged into the environment. Some of the main used of Cr compounds is plastic coatings, electroplating of metal for corrosion resistance, leather tanning and finishing, and in pigments and for wood preservative. Thus, Cr occurs in wastewater resulting from these operations in both trivalent and hexavalent forms. Cr exists in the environment mainly in
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Cr3+ (bioelement) and Cr6+ (mutagenic) states. The drinking water guideline recommended by USEPA is 100 μgL−1. The legal discharge limit of Cr(III) varies from 0.5 mgL−1 (in surface water) to 2.0 mgL−1 (in sewers) depending on the processing, country, and wastewater treatment methods (Mohan et al. 2006). The discharge of industrial acidic effluents containing Cu may cause serious environmental problems due to its highly toxicity and non-biodegradability, and expensive heavy metal is also being wasted too (Chmielewski et al. 1997; Santos et al. 2004). Cu, a widely used metal in industry, is an essential trace element for human health and plays an important role in carbohydrate and lipid metabolism and in the maintenance of heart and blood vessel activity. The adult human body contains 100– 150 mg of Cu, but excess amount in the body can be toxic (Gong et al. 2008). Cu are among those hazardous materials that are most commonly found in an industrial wastewater; thus, their removal is of utmost importance (Wong et al. 2003). The main treatment processes for heavy metal removal from wastewaters include lime precipitation, membrane alteration, ion exchange, adsorption into activated carbon, and electrolytic methods. The characteristics of the main species used in the industrial wastewater treatment are presented in Table 1. Although these methods have been widely employed, they have several drawbacks such as high operating and waste treatment costs, high consumption of reagents, and large volume of sludge formation (Olyaie et al. 2012). However, due to their high cost and sometimes low availability, their use is not as feasible as it should be (Bishnoi et al. 2004). Therefore, cost-effective alternative technologies or adsorbents for the treatment of metalcontaining wastewaters are needed (Kadirvelu et al. 2001). Interest has risen recently in removing heavy metals from solution by binding with agricultural materials such as waste wool, tea waste and coffee, hazelnut straws, peanut hull, saw dusts, husk, corncobs, papaya
wood, maize leaf, leaf powder, nut wastes, modified cotton, and sawdust (Yu et al. 2000; Asrari et al. 2010). Biosorption is a promising technique for the removal of heavy metals from aqueous environments especially when adsorbents are derived from lingnocellulosic materials (Asrari et al. 2010). Rice is the strategic crop all over the world. Every year, large amount of rice husks is produced. Structurally, rice husks consist of cellulose, hemicellulose, and lignin. Agricultural residues, especially rice husk, the by-product of the rice milling industry, are produced in large quantities as a waste, creating environmental problems. Rice husk that mainly consists of crude protein (3 %), ash (including silica 17 %), lignin (20 %), hemicellulose (25 %), and cellulose (35 %) renders it suitable for metallic cations fixation. Rice husk has been used in the removal of some of the metal ions (Ajmal et al. 2003; Bishnoi et al. 2004; Dadhlich et al. 2004). But little attention has been paid to the biosorption of many metal ions together, metal speciation, involvement of functional groups, and the identification of cations for ion exchange onto the biomatrix (Krishnani et al. 2008). In recent years, attention has been focused on the utilization of unmodified or modified rice husk as a sorbent for the removal of heavy metals. Rice husk has been evaluated for their ability to heavy metal ions (Ajmal et al. 2000; Khalid et al. 2000; Kumar and Bandyopadhyay 2006; Zulkali et al. 2006; Gao et al. 2008). Various modifications on rice husk have been reported in order to enhance sorption capacities for metal ions and other pollutants (Wong et al. 2003). In this study, an attempt was made to use rice husk as an adsorbent, since the main components of the adsorbent are lignin and silica which had been recognized to facilitate the adsorption process. The aims of the present investigation are to detect the performance of rice husk on Cr(III) and Cu(II) removal from aqueous solution and to evaluate the effect of various parameters including pH, initial Cr(III) and Cu(II) concentration, reaction time, and the amounts of sorbent.
Table 1 Current treatment technologies for removal of heavy metals involving physical and/or chemical processes Physical and/or chemical methods
Oxidation Ion exchange Membrane filtration Coagulation/flocculation Electrochemical treatment Lime softening Electrokinetic coagulation Fentons reagent
Rapid process for removal Good removal of a wide range of heavy metals Good removes of heavy metals Economically feasible Rapid process and effective for certain metal ions Most common chemicals Economically feasible The oxidation rate is faster than hydrogen peroxide and oxidant solution more stable Feasible in removing some metals
High energy costs and formation of by-products Absorbent requires regeneration or disposal Concentrated sludge production, expensive High sludge production and formation of large particles High energy costs and formation of by-products Re-adjustment of pH is required High sludge production Operator error in mixing the Fe(II) compound with the hydrogen peroxide can degrade the results Technology yet to be established and commercialized
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Materials and methods Rice husk was obtained from a rice mill. Some experiments were performed to determine the physical and chemical properties of absorbent. Table 2 shows the physicochemical characteristics of rice husk. Aggregation in the adsorption of metal ions by the rice husk particles is effective because decreasing particle size of rice husk would lead to decrease in total surface area of the sorbent. So in order to keep the size of the husk particles in a fixed range, 500 g of rice husk were washed for several times with deionized water, dried at 60 °C for 24–48 h, and stored at room temperature for subsequent studies. Rice husk was ground to pass through a 1-mm sieve. In this study, the synthetic wastewater was used under laboratory conditions. The stock solution of Cr(III) and Cu (II) were prepared by dissolving their salts such as Cr (No3)3·9H2O and CuCl2·2H2O in distilled water separately. All chemicals used in this study were analytical grade, obtained from Merck (Germany) which were used in their commercial forms without further purification. All experiments were carried out in a series of 200 mL glass beakers. The test solutions containing single Cr(III) or Cu(II) ions were prepared by diluting a 1-gL−1 stock metal ion solution. The initial metal ion concentration ranged 100 mgL−1, for Cr and Cu. The pH of each solution was adjusted to the required value with HCl or NaOH before mixing the biosorbent. The beaker was mixed by magnetic stirrer (125 rpm) for 10 min at ambient temperature (25±1 °C). After continuous stirring, over magnetic stirrer for a predetermined time interval, the aqueous samples in each bottle were centrifuged at 3,000 rpm for 10 min and the supernatant passed through a Whatman-42 filter paper (0.45 μm) before being analyzed for heavy metals concentration. The remaining Cr(III) or Cu(II) concentration was determined by atomic absorption (PerkinElmer 2380). Every experiment was run in triplicate and the average value is reported here. Solutions were allowed to react with sorbent for a period of time (10, 20, 30, 60, 90, and 120 min). The study on the effect of pH on sorption was carried out by adjusting the pH of the metal solution to values in the range of 1–7 with the Table 2 The physicochemical characteristics of rice husk
Solid density Moisture content Insoluble materials Total soluble particles Organic materials Fe2O3 CaO
1.8 9.5 75 105
gcm3 % % mgL−1
82 0.16 0.24
% % %
addition of 1.0 M HCl or 1.0 M NaOH. In all experiments, pH was measured with a pH meter (290A and 410A) and the pH meter was calibrated with three buffers (pH4.0, 7.0, and 10.0) daily. The experiments were carried out with 100 mg L−1 of sorbent dose in metals solutions. The effect of other parameters such as sorbent dosage (1, 1.5, 2, 2.5, 3, 3.5, 4, and 5 mgL−1) and initial Cr(III) or Cu(II) concentration (100, 200, 400, 600, and 800 mgL−1) were studied in terms of their effect on reaction processes. The amount of metal ion adsorbed was calculated as: Adsorption% ¼ ðC0 Ce Þ=C0 100
Where C0 and Ce are the initial and final concentration of Cr and Cu, respectively.
Results and discussions Effect of pH It is well known that sorption of heavy metal ions by solid substrates depends on the pH of the solution. For the effect of solution pH, changes in solution pH can alter the chemical nature of the functional groups on the rice husks and then the metal adsorption capacity of the adsorbent (Asrari et al. 2010). To identify the pH effect as one of important factors on the Cr (III) or Cu(II) removal using rice husk, an experiment was conducted using a series of the solutions with initial Cr(III) or Cu(II) concentration of 100 mgL-1 and different initial pH of 1–7 in 90 min as contact time at ambient temperature (25±1 °C). The results of Cr(III) or Cu(II) removal in the pH–effect experiment are presented in Fig. 1. It showed that the sorption amount of Cr(III) or Cu(II) increases with the increase of solution pH, the sorption process is pH-dependent. Finally, metal adsorption between pH 5 and 6 is optimal. It can be observed that the removal of Cr(III) or Cu(II) by rice husk adsorption increases with increasing pH, from its minimum at pH 1.0 to its maximum at a pH of about 6.0. After that, the percent adsorption decreases slightly in pH 7.0. The greatest increase in the sorption rate of Cr and Cu ions on husk were observed in a pH range from 2 to 5. It can be observed from Fig. 3; the percent sorption of Cr(III) or Cu(II) increased with increase in pH and reached maximum 55 and 65 %, respectively, for at pH 6.0. The percentage of Cr(III) removal increased from7 to 55 % with an increase of pH from 1.0 to 7.0. The percentage sorption of Cu(II) increased with increase in pH and reached maximum 67 % at pH6.0. The percentage Cu(II) removal increased from 7 to 66 % with an increase of pH from 1.0 to 7.0. This is consistent with the findings of many previous studies such as Wong et al. (2003). They emphasized that at low pH the surface of the sorbent was surrounded by
Environ Sci Pollut Res Fig. 1 Effect of pH on the adsorption of Cr(III) and Cu(II) using rice husks. Adsorption conditions: initial Cr(III) and Cu(II) concentration of 100 mg L−1, 200 mL of sample, temperature 25±1 °C
hydronium ions (H+), which prevented the metal ions from approaching the binding sites on the sorbent. Therefore, solution pH is of great importance for Cr(III) and Cu(II) removal by rice straw.
of Cu and Cr in solution. This was due to the saturation of the sorption sites on adsorbents (Parekh et al. 2002). The Cu adsorption by rice husk was more of chromium ion. This represents a more efficient adsorbent for removal of Cu.
Effect of initial Cr(III) and Cu(II) concentration Effect of contact time The initial concentration of metal ion provides an important driving force to overcome all mass transfer resistances of metal ions between the aqueous and solid phases (Malkoc 2006). The removal of As using synthetic nanoparticles was investigated by varying initial As concentration, optimum pH (6.0–7.0) at ambient temperature (25±1 °C), and contact time of 90 min. The results are presented in graphical form as percentage removal versus initial Cr(III) and Cu(II) concentration in Fig. 2. The effect of initial metals ion concentrations on Cr(III) and Cu(II) removal was investigated over a range of 100–800 mgL−1. It is clear from Fig. 2 that there is an increase in removal percentage increase in initial concentrations of metal ions by rice husk particles, until it reaches a certain concentration (100 mgL−1). After 100 mgL−1 as initial concentration of both metals, increase in concentrations of metal ions leads to decrease in absorption rate. Therefore, the removal efficiency decreases with increasing concentration Fig. 2 Effect of ion concentration on the adsorption of Cr(III) and Cu(II) using rice husks. Adsorption conditions: initial Cr(III) and Cu(II) concentration of 100 mgL−1, 200 mL of sample, temperature 25±1 °C
The experiment, concerning the influence of reaction time on sorption efficiency, is carried out under the conditions that the pH value is 5.0–6.0, initial concentration of 100 mgL−1 at ambient temperature (25±1 °C), keeping all other parameters constant. Removal of heavy metals at varying contact time of 10, 20, 30, 60, 90, and 120 min was studied. The observed removal rates of Cr (III) and Cu(II) at different initial concentration are presented in Fig. 3. It is evident from this figure that the removal efficiency increased with the elapse of contact time. It is clear from Fig. 3 that adsorption rate is very fast initially, about 45.0 % of Cr(III) and 55 % of Cu(II) are removed within 10 min and equilibrium is reached after 30 min. So the optimum agitating time for adsorption of Cr(III) and Cu(II) ions can be accepted as 30 min. The initial faster rate of metal sorption may be explained by the large number of sorption sites available
Environ Sci Pollut Res Fig. 3 Effect of time on the adsorption of Cr(III) and Cu(II) using rice husks. Adsorption conditions: initial Cr(III) and Cu(II) concentration of 100 mg L−1, 200 mL of sample, temperature 25±1 °C
for adsorption. For the initial bare surface, the sticking probability is large, and consequently adsorption proceeded with a high rate. Later, the Cr(III) and Cu(II) uptake rate by adsorbent is decreased significantly, due to the decrease in the number of adsorption sites as well as Cr(III) and Cu(II) concentrations. Decreased arsenic removal rate, particularly, towards the end of experiments, indicates the possible monolayer formation of Cr (III) and Cu(II) ions on the outer surface. For a 100-mg L−1 initial concentration, the removal of Cr(III) and Cu (II) increased from 45 to 57 % and 55 to 68 % during 5 to 40 min contact time, respectively. Effect of sorbent does on biosorption The effect of variation of sorbent does on the removal of metals ions by rice husks is presented in Fig. 4. Amount of sorbent was varied from 1 to 5 g and equilibrated for 90 min at an initial metals ion concentration. It is apparent that the metal ion concentration in solution decreases with increasing sorbent amount for a given initial metal concentration. Since biosorption is highly dependent on the initial adsorbent concentration, the extent of biosorption is proportional to specific area. Specific area can be defined as the portion of the total area that is available for biosorption (Malkoc 2006). The results are presented in Fig. 4 which indicated that the percentage of removal of both metal ions increase with increasing doses of adsorbent. This result was accepted Fig. 4 Effect of sorbent dosage on the adsorption of Cr(III) and Cu(II) using rice husks. Adsorption conditions: initial Cr(III) and Cu(II) concentration of 100 mgL−1, 200 mL of sample, temperature 25±1 °C
because increasing adsorbent doses provides greater surface area and more pore volume will be available for the biosorption (Holan and Volesky 1995; Martin-Dupont et al. 2002; Ho and McKay 2003). Since saturation capacity of the Cr(III) and Cu(II) is 22.5 and 30 mgg−1, respectively, 5 and 4 g of Cr(III) and Cu(II), respectively is needed for total removal of 100 mgL−1 initial concentration.
Conclusions The rice husks are an agricultural waste substance. The rapid uptake and high sorption capacity makes it a very attractive alternative sorbent material. In this study, the role of rice husks in the removal of Cr(III) and Cu(II) from aqueous wastes has been investigated. The investigations are quite useful in developing an appropriate technology for wastewater treatment. For this purpose, various parameters were evaluated on the Cr(III) and Cu(II) removal by rice husks. Adsorption of Cr(III) and Cu(II) by rice husks has been shown to depend significantly on the pH, initial concentration of metal ions, rice husks dosage, and contact time. The optimal initial pH was 5.0–6.0 and the Cr(III) and Cu(II) removal rate increased with decreased in initial concentration and rice husks dosage and with increased in reaction time. Also, it can be concluded that the reaction progress is high, and for a 100 initial Cr(III) and Cu(II) concentration, the removal of metal ions was 45 and 55 %
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during 0 to 10 min contact time, respectively. The maximum adsorption capacity was 22.5 and 30 mgg−1 for Cr(III) and Cu(II), respectively. Finally, after usage of various husks doses, the concentration of heavy metals became to 0 mg L−1. Actually, the percent of removing Cr(III) and Cu(II) reached maximum to 100 % for 5 and 4 g, respectively, as amount of sorbent. Rice husk has been shown to be a potentially useful material for the removal of Cr(III) and Cu(II) from aqueous solution in our study. There are some advantages in using rice husk to remediate Cr(III) and Cu (II)-contaminated wastewaters. The first is that rice straw, which is often burned as waste, is abundant and available at a much lower cost. Thus, recovery of heavy metals is potentially more economical than current process technology. Using rice husks in the Cr(III) and Cu(II) removal do not need continuous nutrient supply and the husk cells are not subjected to constraints of physiological factors such as Cr (III) and Cu(II) toxicity. Therefore, rice husk may be a new kind of cost-effective material which could be used economically in the field to treat Cr(III) and Cu(II)-contaminated wastewaters. This process is environment friendly and reduces the huge amount of indiscriminate effluent discharges around the small industry concerns. It may provide an affordable technology for medium-scale industry.
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