Performance evaluation of low cost adsorbents in reduction of COD in sugar industrial effluent

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Abstract

Studies on reduction of chemical oxygen demand (COD) in effluent from sugar industry have been carried out by employing different absorbents optimizing various parameters, such as initial concentration of adsorbate, pH, adsorbent dosage and contact time. Experimental studies were carried out in batches using metakaolin, tamarind nut carbon and dates nut carbon as adsorbents by keeping initial adsorbent dosage at 1 g l−1, agitation time over a range of 30–240 min, adsorbent dosage at 100–800 mg l−1 by varying the pH range from 4 to 10. Characterization of there adsorbents were done using techniques such as Fourier transforms infra red spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental adsorption data fitted well to Langmuir and Freundlich adsorption isotherms. The isotherms of the adsorbents indicate appreciable adsorption capacity. Higher COD removal was observed at neutral pH conditions. Studies reveal that maximum reduction efficiency of COD takes place using metakaolin as an absorbent at a dosage of 500 mg l−1 in a contact time of 180 min at pH 7 and it could be used as an efficient absorbent for treating sugar industrial effluent.

Introduction

Effluents from sugar industries induce environmental pollution. India, being one of the major producers of sugar in the world, is prone to large volume of wastes from sugar industries. The by-products namely bagasse, molasses, distillery wastes and press mud are some of the major objectionable wastes generated by the sugar industries [1].

Activated carbon is one of the major adsorbents used for treatment of sugar industry wastes to reduce chemical oxygen demand (COD) [2], [3]. Ideal adsorbents must obey the following characteristics – a solid, with high surface area, high porosity, inertness – stability to withstand chemical, thermal and climatic changes, cost effective and good physicochemical properties similar to that of commercial activated carbon. An adsorbent possessing the above properties, would be considered as a good adsorbent in water and wastewater treatments [4], [5].

The adsorbents may be classified under four major headings based on their origins namely agricultural wastes, industrial by-products, natural materials and commercial and synthetic activated carbons. When comparing the cost of the above categories with the available literature [6], [7], [8], [9], [10], [11], [12] it is of the order: natural minerals (0.04–0.12 US$/kg) < agricultural wastes (∼0.25 US$/kg) < industrial by-products (∼1 US$/kg) < commercial synthetic carbons (20–22 US$/kg). Many researches have been done to identify a low cost substitute for activated carbon for the treatment of industrial effluents to reduce COD. The low-cost adsorbents can be viable alternatives to activated carbon for the treatment of wastewater. It is important to note that the adsorption capacities may vary, depending on the characteristics of the individual adsorbent, surface modification and the initial concentration of the adsorbate. In general, technical applicability and cost-effectiveness are the key factors that play major roles in the selection of the most suitable adsorbent to treat effluent.

To achieve an economically effective effluent treatment of wastewater, various low-cost materials have been investigated worldwide, such as in India [13], Thailand [14], Nigeria [15], Italy [16] and USA [17]. Further, it has been reported that wool [18], soya cake [19], sawdust [20], maple saw dust [21], distillery sludge [22], cocoa shell [23], sugar beet pulp [24] and zeolite [25] could be used as possible absorbents in conjunction with Cr(VI) to treat the effluents for reduction of COD with high efficacy. Common materials such as sawdust, fly ash, bagasse pith, controlled burnt wood charcoal, etc., have been used for the treatment of industry wastes [26], [27]. Kaolin based adsorbents have been studied to treat other industrial effluents [28], [29]. However, metakaolin has not been studied as an adsorbent for the treatment of wastewater from sugar industry, so far.

Further, use of absorbents for COD reduction has the advantage of easy sludge disposal when compared to conventional precipitation technique. In the present study metakaolin (natural materials) and carbon derived from tamarind and dates nuts (agricultural wastes), which are belonging to low cost category, have been investigated as the possible adsorbents for the reduction of COD from sugar industrial effluents. Characterizations of adsorbents were done through Fourier transforms infra red spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Several parameters like contact time, adsorbent dosage and pH were optimized and the adsorption data were fitted in Langmuir and Freundlich isotherm adsorption isotherms.

Section snippets

Effluent sample

Effluent collected from Dharani Sugar Mills, Vasudevanallur, Tamilnadu, India was used in the present studies. The effluent samples were analyzed for physicochemical characteristics and results are listed in Table 1.

Preparation of adsorbents

Metakaolin, a pozzolana, was prepared by heating kaolin clay to a temperature of 600–800 °C. Kaolin, a fine white clay mineral, consists of alternate layers of silica and alumina in tetrahedral and octahedral co-ordinations having a specific surface area of 15 m2 g−1 was used.

FTIR

FTIR spectra of the absorbent materials viz., metakaolin, tamarind nut carbon and dates nut carbon recorded between wave number 4000 and 450 cm−1 are presented in Fig. 1a–c, respectively. FTIR spectra of metakaolin (Fig. 1a) show three large regions where the main vibration and deformation bands of Si–Al, Ca and OH are concentrated. Vibrational and deformation bands of occult water (O–H) appeared through a broad transmittance reflection around ∼3437 cm−1 region. Vibrational bands corresponding to

Conclusion

An attempt has been made to identify an efficient and low cost absorbent to treat sugar industrial effluent. Metakaolin, tamarind nut carbon and dates nut carbon are investigated as adsorbents with varying conditions to understand its functionality after initial characterization through FTIR, XRD and SEM analysis. FTIR spectra of metakaolin shows three large regions where the main vibration and deformation bands of Si–O, Si–O–Si, Al–O, Al–O–Al, Ca–O, Ca–O–Ca and OH are concentrated. FTIR

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