PREPARATION, KINETIC STUDY, AND EFFICIENCY EVALUATION OF DATE PALM STONE-DERIVED BIOCHAR AND HYDROCHAR FOR METHYLENE BLUE REMOVAL
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Date
2024
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UNIVERSITI TEKNOLOGI MALAYSIA
Abstract
Freshwater shortages are a critical challenge in agriculture and food security, especially in arid regions such as desert areas. A promising solution to these irrigation water shortages lies in the reuse of treated wastewater. However, effective removal of contaminants, including dyes, heavy metals, and organic pollutants, is essential for ensuring water quality. The date palm (Phoenix dactylifera) is a significant cash crop in many regions. Harvesting of its fruits would normally result in huge production of biomass including dried leaves, stems, pits, and seeds. Based on its high carbon and biochemical contents, these biomass offers interesting alternative to be used as raw materials to produce biosorbents. In view of this, it was the objective of this study to evaluate the feasibility of producing biochar and hydrochar from date palm stones for wastewater treatment and to determine the adsorption mechanism of these materials. In this study, samples of date palm stones (DPS) were collected from the Hail region in Saudi Arabia. Two types of adsorbents were then prepared namely date palm stone biochar (DPSB) and date palm stone hydrochar (DPSH). DPSB was produced through pyrolysis at a temperature of 300 °C for 2 hours, allowing for carbonization in an oxygen-limited environment, while DPSH was synthesized using hydrothermal carbonization at 250 °C for 3 hours in a liquid medium. Fourier-transform infrared spectroscopy (FTIR) analysis of DPSB and DPSH showed the presence of C=C, C=O, CO, and OH groups, scanning electron microscopy (SEM) micrographs indicated the presence of a highly porous structure with open pores and sharp edges, critical for enhancing surface area and, consequently, adsorption capacity. Thermogravimetric analysis (TGA) indicated a total weight loss of 21.76% across both samples between 30 °C to 450 °C, confirming their thermal stability and suitability for reuse in environmental applications. The contaminant removal capacity was evaluated using methylene blue (MB), a model dye representative of many industrial pollutants. Maximum removal capacity of 85.6% for DPSB and 89.4% for DPSH were achieved under optimized experimental conditions determined as follows; initial MB concentration of 10 mg L-1, 2 g of adsorbent and 30 to 45 minutes contact time to reach equilibrium. Kinetic studies indicated that both first-order and second-order reaction models accurately described the adsorption process, highlighting the complex interactions between dye molecules and the adsorbent surfaces. Additionally, molecular dynamics studies utilizing density functional theory (DFT) were performed to propose the geometry of the adsorbents and explore the adsorption mechanisms. Results from the DFT calculations indicated an increase in band gap energy (-0.00956 eV) and dipole moment (8.803487 D) for DPSH compared to DPSB, suggesting a higher resistance of DPSH to chemical and environmental degradation, relative to DPSB. As a conclusion, this study successfully demonstrated the potential of DPSB and DPSH derived from date palm stones, as alternative adsorbents to remove contaminants such as methylene blue from aqueous solution. This finding shall form part of the overall global initiative of addressing the issue of freshwater shortages, better agricultural waste management and having a more sustainable and economically viable solution for wastewater treatment, as well as contributing to the circular economy in agricultural practices.
Description
Currently, wastewater from industries such as textiles, leather, paper, plastics, and others are produced in significant quantities, particularly wastewater containing methylene blue (MB) dye, which may threaten humans and animals. The dyeing industry not only generates large amounts of wastewater but also releases effluents with traits like a dark colour, high levels of aromatic pollutants, alkaline properties, substances that resist biodegradation, and various complex compounds. Current treatment technologies are expensive, not dynamically feasible and generates huge amount of secondary waste such as solid sludge. Granular activated carbon is usually installed in the wastewater treatment system as a polishing system. Nevertheless, upon repeated usage, the exhausted activated carbon needs to be disposed of as sludge. This provides an opportunity for researchers to continue in the development of adsorbent materials with high efficiency but produced from cheaper and more sustainable materials. Biochar and hydrochar are some examples of adsorbent materials which is widely used in wastewater treatment operations. Hydrochar for example stands out as an adsorbent primarily due to the abundance of oxygen-rich functional groups (such as hydroxyl, phenolic, carbonyl, and carboxylic) on its surface. It is also equally important to fully understand the mechanism of pollutant removal by these types of adsorbents. Nevertheless, at present not many studies reported on meaningful interactions between pollutants and functional groups present on biochar/ hydrochar. In-silico approach such as using density functional theory (DFT) provide insight into the reaction models, structures, and binding capabilities of adsorbents, while offering qualitative understanding of the mechanisms governing the adsorption process and the behaviour of adsorption. Thus, it was the aim of this study to evaluate the feasibility of producing biochar and hydrochar from one kind of agricultural waste namely date palm stone (obtained from Saudi Arabia's Hail region). Then the methylene blue (one type of common dye pollutant in water system) removal characteristics for the adsorbents were determined followed by in-silico analysis of the methylene blue and functional groups interaction, which would give some indication on the mechanism of removal involved.
Keywords
date palm, Hail region in Saudi Arabia, date palm stones (DPS), date palm stone biochar (DPSB), date palm stone hydrochar (DPSH)
Citation
Freshwater shortages are a critical challenge in agriculture and food security, especially in arid regions such as desert areas. A promising solution to these irrigation water shortages lies in the reuse of treated wastewater. However, effective removal of contaminants, including dyes, heavy metals, and organic pollutants, is essential for ensuring water quality. The date palm (Phoenix dactylifera) is a significant cash crop in many regions. Harvesting of its fruits would normally result in huge production of biomass including dried leaves, stems, pits, and seeds. Based on its high carbon and biochemical contents, these biomass offers interesting alternative to be used as raw materials to produce biosorbents. In view of this, it was the objective of this study to evaluate the feasibility of producing biochar and hydrochar from date palm stones for wastewater treatment and to determine the adsorption mechanism of these materials. In this study, samples of date palm stones (DPS) were collected from the Hail region in Saudi Arabia. Two types of adsorbents were then prepared namely date palm stone biochar (DPSB) and date palm stone hydrochar (DPSH). DPSB was produced through pyrolysis at a temperature of 300 °C for 2 hours, allowing for carbonization in an oxygen-limited environment, while DPSH was synthesized using hydrothermal carbonization at 250 °C for 3 hours in a liquid medium. Fourier-transform infrared spectroscopy (FTIR) analysis of DPSB and DPSH showed the presence of C=C, C=O, CO, and OH groups, scanning electron microscopy (SEM) micrographs indicated the presence of a highly porous structure with open pores and sharp edges, critical for enhancing surface area and, consequently, adsorption capacity. Thermogravimetric analysis (TGA) indicated a total weight loss of 21.76% across both samples between 30 °C to 450 °C, confirming their thermal stability and suitability for reuse in environmental applications. The contaminant removal capacity was evaluated using methylene blue (MB), a model dye representative of many industrial pollutants. Maximum removal capacity of 85.6% for DPSB and 89.4% for DPSH were achieved under optimized experimental conditions determined as follows; initial MB concentration of 10 mg L-1, 2 g of adsorbent and 30 to 45 minutes contact time to reach equilibrium. Kinetic studies indicated that both first-order and second-order reaction models accurately described the adsorption process, highlighting the complex interactions between dye molecules and the adsorbent surfaces. Additionally, molecular dynamics studies utilizing density functional theory (DFT) were performed to propose the geometry of the adsorbents and explore the adsorption mechanisms. Results from the DFT calculations indicated an increase in band gap energy (-0.00956 eV) and dipole moment (8.803487 D) for DPSH compared to DPSB, suggesting a higher resistance of DPSH to chemical and environmental degradation, relative to DPSB. As a conclusion, this study successfully demonstrated the potential of DPSB and DPSH derived from date palm stones, as alternative adsorbents to remove contaminants such as methylene blue from aqueous solution. This finding shall form part of the overall global initiative of addressing the issue of freshwater shortages, better agricultural waste management and having a more sustainable and economically viable solution for wastewater treatment, as well as contributing to the circular economy in agricultural practices.