Removal of Malachite Green from aqueous solution using degreased coffee bean
Introduction
Dyeing and finishing processes from industries do generate large amounts of colored wastewater which are discharged into natural streams with undesirable consequences to the environment and human health. Apart from the unpleasant aesthetic aspects of dye wastewater, its presence in natural streams can cause serious harm to aquatic life by increasing toxicity, chemical oxygen demand, and as well hindering photosynthetic phenomena through reduction of light penetration [1]. Dyes, such as Malachite Green (MG), though found useful in many industrial applications (dyeing of silk, leather, plastics, paper and others), can cause injuries to humans and animals by direct contact of inhalation and ingestion [2]. Effects such as carcinogenesis, mutagenesis, teratogenesis, respiratory toxicity and reduced fertility in humans have been reported [3]. MG has a complicated chemical structure (Fig. 1); it is resilient to fading on exposure to light and water and is, therefore, difficult to be removed from wastewaters by commonly used techniques such as biological treatment and chemical precipitation. However, since it dissociates in aqueous solutions, it is prone to be strongly adsorbed into solids such as coffee beans.
Globally, coffee has become an established food beverage with its discharge after processing forming large coffee grounds. Part of coffee grounds are reused as compost and animal feed but greater part are burnt as waste which results in production of carbon dioxide, the green house gas [4].
Adsorption processes are being employed widely for large-scale biochemical, chemical, environmental recovery and purification applications [5]. Adsorption application follows a simple design, ease of operation and guarantees relatively high efficiency. Adsorption processes using activated carbons have been widely proposed and used for the removal of both organic and inorganic pollutants from aqueous effluents. However, commercially available activated carbons are expensive and, in recent years, a great deal of effort has been put into the proposal and usage of low-cost adsorbents prepared from naturally occurring materials and wastes for the removal of dyes from wastewaters. Agricultural wastes are the chief raw materials being studied for this purpose, for they are renewable, usually available in large amounts and potentially less expensive [5], [6], [7], [8].
To date, adsorbent such as neem sawdust, rattan sawdust, bentonite clay, bottom ash, orange peel, algae and rice straw have been evaluated for use in the removal of Malachite Green from aqueous solution [6], [9], [10], [11]. This study reports for the first time, on the feasibility of applying degreased coffee beans (DCB) as low-cost alternative adsorbent for Malachite Green color removal from aqueous solution by focusing on the use of discarded (bad) coffee beans. The effects of adsorbent dosage, initial MG concentration, reaction temperature and pH on MG adsorption onto DCB were studied. Adsorption kinetics, isotherms and thermodynamic parameters were also evaluated and reported.
Section snippets
Adsorbent preparation and characterization
There are two species of coffee: Arabica (75% of world coffee production) and Robusta. Arabica coffee bean from Kirkland Signature was used in the study. The raw coffee beans (RCB) were cut into two in order to extract the coffee entirely from its husk. They were washed in warm water (50 °C) and dried in an oven at 105 °C for 24 h. The degreasing of RCB was carried out by contacting 2 g of RCB with 20 mL of NaOH solution at different concentrations (0.01–5 M) for 1–720 min at 25 °C in a mechanical
Characterization of adsorbent
The change in iodine value was investigated as a function of treatment time for different NaOH concentration (Fig. 2). With increase in treatment time of RCB using NaOH, iodine values increases. In Table 1, IV increased gradually with NaOH concentration. The iodine value could be another means of assessing information on the surface area and adsorption capacity of a material. Determination of iodine value is usually a complimentary test to the N2/77 K adsorption isotherms, and assumed to
Conclusion
The study shows that DCB, an agro-based material, can be used as an adsorbent for removal of MG from aqueous solutions. The adsorption characteristics of MG in aqueous solution were shown to be influenced by several factors. The adsorption was highly dependent on initial dye concentration, reaction temperature and pH. The result of the present investigations showed that degreased coffee beans have higher adsorption efficiency than raw coffee beans. The adsorbed amount of MG increased as initial
Acknowledgement
This work was supported by the National Research Foundation (NRF) grant funded by the Korean government (MEST, No. 2009-0093-461).
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