Utilization of powdered peanut hull as biosorbent for removal of anionic dyes from aqueous solution
Introduction
Because of their ease of use, inexpensive cost of synthesis, stability and variety of color compared with natural dyes, synthetic dyes have been increasingly used in the textile, paper, rubber, plastics, cosmetics, pharmaceutical and food industries [1], [2], [3]. Today there are more than 10,000 dyes available commercially [4], most of which are difficult to biodegrade due to their complex aromatic molecular structure and synthetic origin [5]. The extensive use of dyes often poses pollution problems in the form of colored wastewater discharge into environmental water bodies. Even small quantities of dyes can color large water bodies, which not only affects aesthetic merit but also reduces light penetration and photosynthesis. In addition, some dyes are either toxic or mutagenic and carcinogenic [6]. In industries, the methods employed for treating dye wastewaters include coagulation and flocculation [7], oxidation or ozonation [8], [9], membrane separation [10] and activated carbon sorption [11]. These technologies do not show significant effectiveness or economic advantage. Activated carbon is the most popular and widely used dye sorbent, but its relatively high price, high operating costs and problems with regeneration hamper its large-scale application. Activated carbon is expensive and the higher the quality the greater the cost; furthermore, regeneration using solutions produces a small additional effluent, while regeneration by refractory technique results in a 10–15% loss of sorbent and its uptake capacity. Therefore, there is a growing need to find low cost, renewable, locally available materials for the removal of dye colors. Some agricultural byproducts have been investigated for this purpose. These sorbents can be used once and then disposed as fuel for power generation or as ferment substrate to produce high protein animal feed.
Many sorbents based on low cost agricultural byproducts had been used for dye sorption from wastewater, which included orange peel [12]; cassava peel [13]; banana pith [14]; plum kernels [15]; apple pomace, wheat straw [16]; cotton waste, rice husk, teakwood bark [17]; sawdust [18]; bagasse pith, maize cob [19]; palm fruit bunch [20], [21]; coir pith [22]. But new, economical, locally available and highly effective dye sorbents were still needed.
The purpose of this work was to investigate the possibility of peanut hull as a biosorbent for removal of anionic dyes from aqueous solution. Peanut hull is an abundant and low cost agricultural waste residue and is easily available in large quantity in China. The dyes selected as sorbate were amaranth (Am), sunset yellow (SY) and fast green FCF (FG). Their chemical structures and general data are shown in Fig. 1 and Table 1, respectively. The effects of various operating parameters on biosorption such as initial pH and dye concentration, sorbent dosage, particle size, ion strength, contact time were monitored and optimal experimental conditions were decided.
Section snippets
Preparation of peanut hull sorbent
The peanut hull used in this study was obtained from a local market. The collected biomaterial was extensively washed with tap water to remove soil and dust, sprayed with distilled water and then dried in an oven at 80 °C to a constant weight. Dry biomass was crushed into powder, sieved to different particle sizes and then preserved in a desiccator for use.
Preparation of anionic dye solutions
Three anionic dyes (Am, SY and FG), in 80–85% purity, were used without further purification. The dye stock solutions were prepared by
Effect of initial pH
Because the initial pH of solution can significantly influence biosorption of dyes, the effects of pH on dye biosorption by the powdered peanut hull was studied first. The value of pH used ranged from 2 to 11. As elucidated in Fig. 2, for all three dyes, the dye removal ratios were maximum at the initial pH 2. The ratios of dyes sorbed decreased as the initial pH was increased from 2 to 5, and, the dye removal ratios were kept constant beyond pH 5. For this reason, pH 2 was selected for all
Conclusions
The present study showed that the powdered peanut hull is a promising biosorbent for the removal of anionic dyes from aqueous solution, since the raw material peanut hull was easily available in large quantity and the treatment method of biomaterial seemed to be economical. At initial pH 2, three dyes studied could be removed effectively. The isothermal data of biosorption followed both Langmuir and Freundlich models. The sorption capacities were found to be 14.90 mg, 13.99 mg and 15.60 mg dye per
Acknowledgments
The first author is thankful to the financial supports by the Key Laboratory of Bioresource Protection and Utilization of Anhui Province, the Anhui Educational Bureau and the Anhui Normal University, China.
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