Continuous biosorption of azo dyes from textiles industry effluents using zinc oxide-chitin nanocomposites.: Continuous biosorption of azo dyes

Abstract

Textile sectors are responsible for major environmental pollution challenge in the world [1]. The textile sector creates the greatest dye effluent (54%) and accounts for over half of all dye effluents discovered in the environment [2]. Textile effluents are highly contaminated and contain various toxic aromatic compounds especially azo dyes which are highly toxic, mutagenic and carcinogenic that, if not treated properly, have a significant negative influence on the environment, causing harm to aquatic ecosystems as well as human health, necessitating treatment prior to discharge into natural reservoirs [3]. To address this issue, it is necessary to create a sustainable, long-term, and effective dye effluent treatment technique. Several strategies are available for the removal of azo dye such as ion exchange, electrolysis, membrane, Fenton oxidation, Coagulation and Flocculation Technique [4-8]. However, these methods pose several drawbacks, such as high operation cost, larger formation of sludge, long retention time and the production of toxic by-products [9-10].

Biosorption technique using nanosorbents has attracted considerable attention due to its technical feasibility, flexibility, operation simplicity, high efficiency, low cost and environmental friendliness [11-12]. The present study aims to synthesis Zno-chitin nanocomposite and evaluating the performance of synthesized Zno-chitin nanocomposite as adsorbent for continuous removal of azo dye from textile effluents. The biosorption of dyes from wastewaters has been widely studied by performing batch studies due to their harmful effects.  However, research on the continuous removal of azo dye by performing column studies are not reported till date.

 Multifunctional ZnO nanoparticles were prepared using Citrus aurantifolia peel extract at low temperature taking care that all the bioactive phytochemicals of the peel were retained, then synthesized ZnO nanoparticles are immobilized with biocompatible and biodegradable chitin to form Zno-chitin nanocomposite. The feasibility and performance of Zno-chitin nanocomposite as nanosorbent for continuous removal of azo dye was evaluated by conducting packed column test. A known amount of immobilized zinc oxide nano particles/chitin nanocomposite will be packed in the packed bed column. Textile effluents collected will be passed over the packed nanocomposite continuously with a known amount of flow rate. The treated water will be analysed for the reduction of dye. The continuous packed column will be operated at different bed heights and flow rates.

Characterization of synthesized ZnO nanoparticles were studied using Fourier transmission infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray diffraction (XRD) and U V spectroscopy.  SEM image reported that the spherical ZnO nanoparticles size was found to be less than 100 nm. XRD confirmed the wurtzite hexagonal ZnO structure by showing peaks at 2Ѳ value of 31.74⁰ and 36.17⁰. FTIR results showed relative peaks for green synthesized ZnO at 452.60 cm-1 and also showed the presence of a high level of phytochemical ingredients of lime peel extract such as phenolics, carboxylic acid, alcohols, ketones, amines, terpenoids, flavonoids which are also responsible for maximum removal of azo dye from waste water. UV spectroscopy confirmed the presence of ZnO in the extract by a strong peak at 345 nm. The findings from Packed column study revealed that synthesized Zno-chitin nanocomposite could remove up to 76.4% of azo dye from waste water and also experimental data obtained from continuous column tests were fitted well to the Thomas model with the correlation coefficient ranges 0.89–0.91. Therefore, practical and economic point of view, synthesized Zinc oxide-chitin nanocomposite could be considered as effective biosorbent for the removal of azo dye from waste water.