Bioremoval of Malachite green from water sample by forestry waste mixture as potential biosorbent
Introduction
Synthetic dyes are widely used in many areas such as paper, textile, food, cosmetic, leather, plastic and pharmaceutical industries. An important amount of these pollutants are commonly present in the effluents of above industries [1]. Unless properly treated, synthetic dyes may affect aesthetic condition of water bodies and compromise many water uses. Also, they may pose serious risks to aquatic life and human health [2], [3]. Therefore, the effluents containing synthetic dyes need to be treated to minimize their threat to the environment. One of the most used synthetic dyes is Malachite green (MG). MG, a triarylmethane dye, is widely used for different purposes in various industrial fields such as textile, food, paper and other biological fields. However, MG presented many adverse characteristics because of its high toxicity, as well as teratogenic, carcinogenic, and mutagenic properties. Although different authorities all over the world have applied restrictions for the usage of MG, it is still used in many countries due to its low cost and availability [4], [5], [6].
Many different types of treatment processes including ion exchange, coagulation, flocculation, membrane filtration and chemical oxidation have been used to remove such synthetic unsafe dyes from polluted effluents. These methods have some disadvantages such as incomplete removal, high reagent and energy requirements, and generation of toxic sludge or other waste products that require disposal [7], [8]. Hence, the removal of hazardous dyes to an environmentally safe level in a cost effective and environmentally friendly manner assumes great importance. Among the emerging remediation technologies for dye impurity, biosorption of synthetic dyes using natural biomasses or agro-industrial wastes and by-products is known to be a feasible and efficient alternative considering numerous biosorbent sources, low operational costs, high removal efficiency and low secondary pollution risk [9], [10], [11]. As a natural waste biomass, sawdust generated in abundance from forestry and agricultural activities in particular has various important advantages in terms of cost, quantity, renewability and biodegradability. It mainly consists of cellulose, hemicellulose and lignin. These properties make sawdust a suitable biomass for pollutant biosorption. Many biosorption studies involving different unwanted materials and sawdust residues have been performed earlier [12], [13], [14], [15]. However, to the best of our knowledge, performance of different types of sawdust biomass in biosorption system has been evaluated individually. Besides, current studies have focused on applying different modification agents to improve biosorption capacities of biosorbents, and this operation showed a great improvement [16], [17]. Hence, cetyltrimethylammonium bromide (CTAB) as a model modification agent was first applied to modify a novel multi-component biosorbent composed of pine, oak, hornbeam and fir sawdust biomasses, aiming to obtain an effective biosorbent for MG dye in this study. Different process variables were evaluated for optimal biosorption conditions. Performance estimation of batch biosorption system was achieved by appropriate mathematical modeling.
Section snippets
Reagents
Malachite green (MG, Type: triarylmethane, C.I. name: basic green 4, molecular formula: C23H25ClN2, molecular weight: 364.911 g mol− 1, maximum absorbance: 617 nm) was supplied from Carlo Erba. A stock solution of MG (1 g L− 1) was prepared by dissolving required amount of the dye in distilled water. The experimental concentration of MG in the aqueous solution was varied from 10 to 30 mg L− 1 by diluting the dye stock solution with distilled water. Cetyltrimethylammonium bromide (CTAB) was obtained from
Effect of contact time
Fig. 1(a) presents the effect of contact time on the biosorption of MG onto the modified biosorbent. The biosorption capacity of biosorbent significantly increased within the first 60 min and slowly reached to equilibrium within 120 min. Further extending the contact time did not improve the biosorption potential of biosorbent for MG. The initial high rate might relate to the large numbers of available sites on the surface of biosorbent and the subsequently decreased biosorption rate was probably
Conclusions
The CTAB modified multi-component biosorbent is a potential biosorption agent for the removal of MG from aqueous solution. The biosorption process was affected by the medium pH, biosorbent quantity, reaction time and MG concentration. The biosorption data fitted well with Sips and the logistic models, and the maximum biosorption capacity was 52.610 mg g− 1. The pore diffusion and surface biosorption were the main mechanisms involved in dye removal. This natural biosorbent can be a good candidate
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