Adsorptive removal of hazardous anionic dye “Congo red” from wastewater using waste materials and recovery by desorption

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Abstract

The present investigation assesses the applicability of waste materials—bottom ash and deoiled soya—for the removal of the colorant Congo red from wastewaters. The adsorption characteristics and dye removal efficiency of adsorbents have been determined by investigating factors such as effect of pH, effect of concentration of the dye, amount of adsorbents, contact time, and temperature. Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich isotherm models have been used to evaluate the ongoing adsorption. With the help of adsorption isotherm data different thermodynamic parameters such as free energy; enthalpy, and entropy have been calculated. The estimated free energy has been obtained as −21.52 kJ mol−1 for bottom ash and −16.88 kJ mol−1 for deoiled soya. On the basis of pseudo-first-order and pseudo-second-order kinetic equations different kinetic parameters have been obtained. Column operations depicted good adsorptive tendencies for Congo red with 96.95% and 97.14% saturation of dye on bottom ash and deoiled soya, respectively. Regeneration of the saturated columns has been made by eluting NaOH solution and more than 90% dye has been recovered in both cases.

Graphical abstract

Effect of pH on adsorption of Congo red over bottom ash and deoiled soya.

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Introduction

An increasing population leads to rapid proliferation of industries and their pollution. Dyestuff manufacturing industries and many other dye and pigment-using industries such as rubber, paper, textile, plastics, and cosmetics generate highly colored and toxic effluent. Reports suggest that nearly 10,000 different commercial dyes and pigments are known, with worldwide annual production of over 7 × 105 tons [1]. Among various industries a huge amount of dyes is discharged by textile industries due to improper processing [2]. The water polluted by these industries is characterized by high COD, dissolved and suspended solids, and high color contents [3]. The dye effluents are highly visible and toxic even at very minimum concentrations [4]. The water bodies and dependent flora and fauna are highly affected by these pollutants. Problems related with the water pollution include damage of the aesthetic nature of water, interference with the process of photosynthesis, destruction of the food web existing in water ecosystem [5], etc. The polluted water is also harmful to animals and human beings as the dyes and their metabolites are highly toxic [6], [7] and carcinogenic [8], [9] in nature. The passivity of the dyes in the presence of heat, light, microbes, and even oxidizing agents makes the degradation of coloring material difficult [10]. This is attributed to the complex structure of the dyes. Moreover, increasing water demand for industrial and public uses necessitates the reclamation of the effluents and treatment of wastewater [11]. Thus removal of color is highly desirous.

From several decades various methods have been evolved in wastewater treatment such as electrochemical treatment methods [12], [13], [14], oxidation [15], and ozonation [16]. However, the adsorption process has been proven as a most effective and reliable method for dye removal. The major advantages of an adsorption treatment for the control of water pollution are less investment in terms of initial development cost, simple design, easy operations, free from generation of toxic substances, and easy and safe recovery of the adsorbent as well as adsorbate materials [17]. In the adsorption technique the major concern is the selection of adsorbent material. In the last few years there has been an emphasis to develop waste materials as potential scavengers for the removal of different types of pollutants from water and waste materials such as baker’s yeast [18], tamarind wood [19], agricultural waste biomass [20], gypsum [21], and sludge [22], [23] have been employed. A significant contribution in the removal of toxic dyes from the wastewater has also been made from our laboratories [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36].

The present research deals with the applicability of adsorption techniques in the removal of the dye Congo red from wastewaters. Congo red is a highly water-soluble diazo dye. It exists as brownish-red crystal and is stable in air with a solubility of 1 g/30 mL in water [37]. It is an anionic acid dye used as a laboratory aid in testing for free hydrochloric acid in gastric contents, in the diagnosis of amyloidosis, as an indicator of pH, and also as a histological stain for amyloid. It has a strong affinity to cellulose fibers and thus is employed in textile industries. It is a derivative of benzidine and napthoic acid and metabolizes to carcinogenic products [38]. It is investigated as a mutagen and reproductive effector. It is a skin, eye, and gastrointestinal irritant. It may affect blood factors such as clotting, and induce somnolence and respiratory problems [39].

Thus keeping the toxic effects of the dye in view, attempts have been made to develop an efficient and cost-effective technique for removal of dye from wastewaters by employing two waste materials, namely bottom ash and deoiled soya. The disposal of bottom ash is always a problem for the station authorities so it was worthwhile to employ it as an adsorbent for color removal. The abundantly available soya industries waste, i.e., deoiled soya, was employed as an animal feed but its use is banned nowadays due to formation of antimetabolites in living systems [40].

Section snippets

Materials and methods

Congo red, is an anionic azo dye having IUPAC name as 1-napthalenesulfonic acid, 3,3-(4,4-biphenylenebis(azo))bis(4-aminodisodium) salt. Some other important chemical properties of the dye are noted in Table 1. The dye was obtained from M/s Merck and its stock solution was prepared in double-distilled water. All the test solutions were prepared by diluting the stock with double-distilled water.

Both adsorbent materials, used in the present research work, are waste materials and available easily

Characterization of the adsorbents

The details of the constituents of the adsorbent materials obtained from standard chemical analysis are provided in Table 2, Table 3. Electron microscopy was helpful in analyzing the nature of the surfaces of both adsorbents. SEM photographs ascertained that the particulates of bottom ash and deoiled soya are porous and almost spherical.

Infrared spectroscopy helped in determination of the absorptive nature of the two adsorbents. Bottom ash gave a sharp absorption band in the region of 3700–3500 

Summary

The important outcomes of the developed methodology adapted for the removal of the anionic dye Congo red using bottom ash and deoiled soya as adsorbents are as follows:

  • 1.

    Studies clearly reveal that both waste materials, bottom ash and deoiled soya, are highly efficient adsorbents for the removal of Congo red from wastewaters.

  • 2.

    The value of mean sorption energy (8–16 kJ mol−1) indicates that adsorption of dye over both adsorbents occurs through chemisorption.

  • 3.

    The negative values of free energy (ΔG°)

Acknowledgment

One of the authors (Arti Malviya) is thankful to CSIR, New Delhi, for the award of Senior Research Fellowship.

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