Hydrothermal carbonization of biomass waste and application of produced hydrochar in organic pollutants removal

Abstract

This novel research, presents the study of utilizing the wild almond shell as biomass waste to fabricate hydrochar using the hydrothermal carbonization (HTC) method based on a central composite design (CCD) with two independent variables (time and temperature) and three responses; productivity, higher heating value (HHV) and norfloxacin (NOR) adsorption capacity. The prepared hydrochar at 200 °C and 8 h was then employed to produce activated carbon (AC) by chemical-thermal activation technique. Hydrochar and AC were characterized using XRD, BET, SEM-EDX, Raman, and FTIR techniques. The pore development, resulting in a rise in the SBET (637.46 m2/g) value occurred after the activation process. Moreover, the results of XRD and Raman analyses revealed a decrease in graphitization degree. The adsorption of norfloxacin, methylene blue (MB), and sunset yellow (SY) by prepared hydrochar and AC were studied to assess the impact of the pH of the solution, initial concentration, temperature, and contact time. The maximum adsorption capacity for NOR, MB, and SY using hydrochar and AC were 85.37, 153.46, 93.35, and 384.1625, 556.465, 264.93 mg/g, respectively. The experimental data for the adsorption of NOR, MB, and SY using hydrochar and AC illustrated a good fit with the PSO model. Besides, the Langmuir and Freundlich models indicated better fitting with empirical data obtained for the adsorption of NOR, MB, and SY, respectively. Thermodynamic study outcomes validated the exothermicity and spontaneity of the adsorption process for both absorbents. This study presents a new opportunity to develop the circular economy by fabrication of sustainable adsorbents with high adsorption capacity for organic pollutants from biomass waste.