Sequestration of a food dye (sunset yellow) from wastewater using natural adsorbent: a kinetic, isotherm and interference study

Abstract

Cocos nucifera, commonly known as coconut is rich in coir dust (CCD) at its outer surface, which is a very significant agri waste used as biosorbent for wastewater treatment. The current work addresses use of CCD for removal of hazardous Sunset Yellow dye (SY) FCF widely used as coloring agent in food industry, from wastewater. The uptake capacity in batch and column mode is 82 mg/g and 160 mg/g respectively. Characterization study including SEM, FTIR and BET results also supported the adsorption process. The comparative analysis with other natural biosorbents showed best results of biosorption with CCD. The output was better at high pH (10) and lower concentration of dye (5 mg/L). The kinetic study suggested pseudo second order rate revealing both adsorbate-adsorbent interdependency. The presence of covalent bonding or valence forces between the interfaces, suggested chemisorption as the rate limiting mechanism with valence forces, hydrogen bonding and pi-pi stacking being the chief forces responsible in binding of the dye molecules to the surface. The isotherm supported Langmuir model with monolayer and uniform adsorption at the interfaces. The interference test confirmed slight decrease in percent adsorption with interference from chloride and sulfate as dominating ions. The techno-economic feasibility highly recommended in field application of the substitute (net profit value, 1.256 Rs/m³, input cost, 0.052 Rs/m³). The industrial sample analysis with lab to land approach justified sustainability and commercial viability of the present work.

GRAPHICAL ABSTRACT

HIGHLIGHTS

• Facile removal of a food dye (sunset yellow, FCF) using Coconut coir dust (CCD).

• Uptake capacity in batch and column mode is 82 mg/g and 160 mg/g respectively.

• Chemisorption as the rate limiting mechanism with valence forces, hydrogen bonding and pi-pi stacking being the chief forces.

• Better uptake efficiency is seen at higher pH (10) and lower concentration (5mg/L).

NOVELTY STATEMENT

Indiscriminate use of dyes in multidimensional industries including food industry makes water bodies unsafe. To address the issue, we have investigated efficient removal of toxic food dye (Sunset Yellow FCF) using coconut coir dust (CCD) which is a naturally available agri waste. Current protocol demonstrates the removal of dye in batch mode encompassing several batch parameters like dose, pH, concentration and time. The uptake capacity obtained in batch mode is highly significant with percent removal of 71% (82 mg/L) which is highly appreciable for a biosorbent material. Column uptake capacity with remarkable value of 160 mg/L was calculated using Thomas model rate equation in order to explore the maximum viable efficiency to extend the research for a possible pilot-scale and field application studies. The mechanism of biosorption is governed by the surface active forces including covalent forces, hydrogen bonding and pi-pi stacking. Since several agricultural/non-agricultural biomasses are available for wastewater treatment, a comparative research analysis of the removal efficiency with three other natural bio sorbents were experimented for removal of food dye and the results showed the highest uptake for CCD than others. The current study advances the understanding of coconut coir’s efficacy in dye removal by comprehensively analyzing physicochemical parameters and conducting column studies to simulate real-world applications. Additionally, it investigates ion interference and validates findings with real wastewater scenarios, enhancing the authenticity and significance of the research. Thus the process firmly stands as low-cost, environment friendly substitute, and does not generate harmful by products. The uniqueness of the work lies in the fact that it is one of the best substitute compared to the other conventional methods of treatment available with a net profit value of 1.256 Rs/m³ and operating cost of 0.052 Rs/m³.The work also meets few principles of green chemistry/engineering and serves as a sustainable protocol to a great extent.

Keywords:

• Biosorption
• coconut coir dust
• natural adsorbents
• phytoremediation
• sunset yellow dye

Disclosure statement

The authors declare no conflict issues associated with this publication.

Data availability statement

The authors declare that there is no such data availability associated with this publication.