A novel biowaste-based biosorbent material for effective purification of methylene blue from water environment

Abstract The biowaste left over from the fixed oil biorefinery process of Nigella sativa L. plant was used as a new biosorbent for the biosorption of synthetic dye of methylene blue from water environment in this study. The main variables of biosorption operation such as methylene blue concentration, time, pH, and biosorbent amount were optimized by the batch-type experiments. The characterization, kinetics, equilibrium, and thermodynamics works were conducted to show the nature of methylene blue biosorption. The studies of Fourier transform infrared spectroscopy and Scanning electron microscopy indicated that the biosorbent possessed an inhomogeneous surface morphology including many cavities and protuberances, and a rich functional group profile. The optimum values of operating variables studied for the biosorption of methylene blue were determined as methylene blue concentration of 15 mg L−1, time of 360 min, pH of 8, and biosorbent amount of 10 mg. The experimental data of methylene blue biosorption followed the kinetics and isotherm models of pseudo-second-order (R 2: 0.98, AdjR 2: 0.98, and RMSE: 8.97) and Dubinin-Radushkevich (R 2: 0.99, AdjR 2: 0.98, and RMSE: 6.84), respectively, based on the statistical tests of coefficient of determination (R 2), adjusted coefficient of determination (AdjR 2), and root mean squared error (RMSE). The biosorption of methylene blue was a physical, spontaneous, and energetically favorable process (E DR: 3.48 kJ mol−1 and ΔG°: (−14.51) − (−10.02) kJ mol−1). This residual biological material from the fixed oil biorefinery process exhibited higher biosorption performance (187.46 mg g−1) than own unrefined (virgin) form and its modified, activated, and composite forms and many other sorbents reported in the literature. Hereby, the current work showed that this novel biowaste-based material could be used as an environmentally and economically promising biosorbent to effectively purify methylene blue from aquatic environment. NOVELTY STATEMENT Nigella sativa L. (black cumin) is a well-known annual medicinal and aromatic plant from the family of Ranunculaceae. Its seed part has a rich profile containing a wide variety of valuable compounds (fixed oil, carbohydrates, proteins, vitamins, pigments, essential oil, various bioactive substances, etc.), which are widely used in many fields such as cosmetics, food, medicine, and biofuel. After the refinery process to obtain these valuable compounds, a large amount of waste biomass remains. Considering the circular bioeconomy motion, a novel study was conducted on the use of biowaste left over from the fixed oil biorefinery process of N. sativa L. in the field of synthetic dye biosorption in the current work. The synthetic dye of methylene blue was used as a model to test the biosorption behavior of this novel biowaste-based biosorbent material. The main variables of biosorption operation such as synthetic dye concentration, time, pH, and biosorbent amount were optimized by the batch-type experiments. The characterization, kinetics, equilibrium, and thermodynamics studies were performed to show the nature of methylene blue biosorption operation. This residual biological material from the fixed oil biorefinery process exhibited higher biosorption performance than own unrefined (virgin) form and its modified, activated, and composite forms and many other sorbents reported in the literature. Hereby, the current work showed that this novel biowaste-based material could be used as an environmentally and economically promising biosorbent to effectively purify methylene blue from aquatic environment.