Application of biorefinery by-product of Nigella sativa L. herb for green treatment of synthetic dye impurity in aquatic environment: a circular economy based approach to water purification

Abstract

In this work, the performance of residual biomass of Nigella sativa L. plant from the process of bio-oil production toward the green removal of synthetic dye pollution from aquatic medium was systematically studied for the first time based on the circular economy strategy. The characterization of material was performed using Electron Microscope of Scanning and Infrared Spectrometer of Fourier Transform. The main process variables like pH, biosorbent amount, synthetic dye loading, and contact duration were optimized by the batch biosorption experiments to achieve the maximum remediation yield. The analyses of kinetics, equilibrium, and thermodynamics were conducted to understand the possible mechanism of purification. The experimental dynamics and equilibrium data were in better agreement with the pseudo-second-order and Langmuir models. For the targeted model synthetic dye compound (C. I. Basic Red 46), the biosorption capacity was obtained as 136.2 mg g⁻¹ at the optimized conditions of pH of 8, biosorbent amount of 10 mg (100 mg L⁻¹), synthetic dye loading of 30 mg L⁻¹, and duration of 360 min. The treatment process was favorable, spontaneous, and physical. The characterization operation showed that the dye molecules were restrained on the rough surface of biosorbent. This study reveals that the reuse of herbal oil refinery residue as a biosorbent can present an economic, efficient, and eco-friendly option for the remediation of synthetic dye pollution in aqueous medium.

Novelty Statement

Here, by adopting the circular economy based approach, an exemplary study was conducted using the waste biomass of Nigella sativa L. left over from the bio-oil production process for the removal of synthetic dye pollution from water environment. N. sativa L. (Black seed, Ranunculaceae plant family) is an annual herb containing many different bioactive molecules. Mostly, the seed part of plant is widely used for domestic and industrial purposes (such as food, medicine, cosmetic, and biofuel) almost all over the world. Most of the bioactive compounds of plant are concentrated in the oil content of seed (30–38%). A huge amount of waste seed biomass remains after the extraction process to obtain this rich oil ingredient. The reuse of this vegetal oil refinery by-product as a biosorbent material for the remediation of synthetic dye pollution in aqueous environment has not been investigated so far. A cationic azo dye (C. I. Basic Red 46) extensively employed in the textile industry was selected as the model synthetic dye compound to test the treatment efficiency of novel biosorbent. The optimization, dynamics, equilibrium, thermodynamics, characterization, and comparison analyses were performed to evaluate the performance of synthetic dye removal of biosorbent from water medium. This work showed that the application of N. sativa L. oil refinery residue as a novel biosorbent could offer a promising option for the treatment of synthetic dye impurity in water medium.

Keywords:

• Biorefinery by-product
• circular economy
• Nigella sativa L.
• synthetic dye pollution
• water purification

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.