Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials

Abstract

This article describes the use of bottom ash [a power plant waste] and de-oiled soya [an agricultural waste] as effective adsorbents for the removal of a hazardous azo dye [Chrysoidine Y] from its aqueous solutions. This paper presents an experimental study and discussion of the adsorption characteristics of this dye on the two adsorbents. The adsorbents have been characterized, and also the effects of time, temperature, concentration, pH, and sieve size on the extent of adsorption have been evaluated. Batch adsorption measurements, kinetic studies, and column operations have been performed to elucidate the dye uptake capacity of the adsorbents. The monolayer adsorption capacities at 30 °C have been found from Langmuir analysis to be 7.27 × 10⁻⁵ mol g⁻¹ and 3.35 × 10⁻⁵ mol g⁻¹ for bottom ash and de-oiled soya, respectively. Adsorption kinetics experimental data are indicative of pseudo-second order kinetics during these processes. Column experiments indicate practical utility of the adsorbents for eradicating hazardous dyes from effluents. The recovery of the adsorbed dye from bottom ash and de-oiled soya, have been found to be 85% and 99%, respectively.

Introduction

Azo dyes are a class of dyes characterized by the presence of the azo-group [NN]. These dyes are widely used in the textile, leather, rubber, plastic, and food industries. Due to high usage of these azo dyes, large volumes of colored effluents are discharged into environmental water sources. The colored wastewater is unsightly, and also may inhibit vital photosynthetic processes [1]. Due to their complex structures, water-soluble azo dyes exhibit considerable resistance to biodegradation, as well as high thermal and photo-stability. The release of azo dyes into the environment is of further concern due to their toxic, mutagenic and carcinogenic characteristics of the dyes and their biotransformation products [2]. Azo dyes cause chromosomal damage [3]; reductive cleavage of azo-groups forms carcinogenic aromatic amines [4], [5]. Thus, removal of colored dyes from wastewaters is a major environmental issue.

Among the various techniques for removal of dyes from wastewater, such as chemical coagulation [6], electrokinetic coagulation [7], oxidation and ozonation [8], adsorption [9], [10] has been found to be an effective removal method, due to its efficiency, simplicity, and applicability. Various researchers have studied the adsorption of dyes on various types of materials. Activated carbon has been found to be an effective adsorbent having high surface area and high adsorption capacity. However, it has relatively high operation costs, which hamper its large-scale application. Therefore, a number of low-cost adsorbents have been examined for the treatment of wastewaters, such as activated sludge [11], coconut bunch waste [12], kaolinite [13], Rhizopus oryzae [14] and castor seed shell [15]. In recent years, versatile methods for cleaning of wastewater by employing cost effective and efficient adsorbents have been developed [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36].

In the present investigations, bottom ash and de-oiled soya are investigated as adsorbents for the removal of a common hazardous coloring agent [Chrysoidine Y] from wastewater. Chrysoidine Y is a synthetic azo dye, which is used widely in the textile industry. Being an azo dye, Chrysoidine Y may also undergo reduction followed by a chain of reactions leading to formation of other toxic compounds, which are potentially harmful to humans and animals. It has been demonstrated that oral administration of Chrysoidine Y results in liver-cell adenomas, carcinomas and leukemia in animals [37]. Some case studies also suggest that the dye is carcinogenic [38]. Thus, removal of Chrysoidine Y by methods such as adsorption has important potential applications. Therefore, the adsorption potential of bottom ash and de-oiled soya as adsorbents for the removal of Chrysoidine Y from wastewater has been investigated.

Bottom ash is a waste material obtained from thermal coal-fired power generation plants. It is a dark gray, granular, porous material. When pulverized coal is burned, about 80% of the unburned material can be recovered as fly ash, while the remaining 20% of the ash is bottom ash, which is collected in a water filled hopper at the bottom of the furnace [39]. De-oiled soya is a by-product of the soybean oil industry. It is a dry, yellow colored, porous, flaky material obtained after extracting all of the nutrients and proteins from the soybean. In processing of soybeans, hexane is sometimes used as a solvent to extract the oil. Improper processing can result in lipoxygenase activity, which gives the de-oiled soya a bitter taste, rendering it unfit for human and animal consumption. Published reports suggest that more than 170 ppm hexane residue in the de-oiled soya makes it toxic to birds, animals and fish [40]. India is one of the largest producers of soy beans; the state of Madhya Pradesh is the largest producer of soya beans. Thus the ready availability of this material in our vicinity has attracted our attention to it as an adsorbent for removal of toxic dyes from wastewater.