The date seeds (DS) biochar produced at 550°C was found to be appropriate for remediation of metal-contaminated water. This was evident in the data, which showed that applying the biochar to Raphanus sp. and Arabidopsis sp. reduced metal stress and toxicity. The LC50 of all tested metals solutions on seed germination was increased significantly (P<0.05) in Raphanus sp. by 10.4, 2.3, 5, 1.8, and 3 folds, respectively, for Cu, Zn, Cd, Pb, and metals combination, and by 5, 3.4, 6, 5.5, and 2.5 folds in Arabidopsis sp. For seedling growth, the DS biochar enhanced the LC50 significantly (P<0.05) of the same metals in Raphanus sp. by 9.6, 9.2, 13.8, 12.1, and 1.6 folds, and in Arabidopsis sp. by 7, 3, 2.3, 2.9, and 2.7 folds, respectively. The LC of all metals was increased by 1.5 to 8 times and 1.5 to 12 times, respectively, for the seed germination and seedling growth of Raphanus sp. and Arabidopsis sp. Both plants were able to grow shoots at higher metal concentrations when the DS biochar was employed, as compared to the case when no DS biochar was utilized. In terms of shoot length, similar results were achieved, with the DS biochar application significantly enhancing shoot length (P<0.05), as compared to the case when no biochar was applied. Despite the fact that Arabidopsis sp. was more sensitive to metals than Raphanus sp., both plants raised their RGR and TI and reduced their phytotoxicity values in all metals following the DS biochar application, and sprouted at higher metal concentrations than before. These findings introduce a successful eco-friendly adsorbent for metal removal from aquatic environments, paving the way for more investigations.
It was found that date seeds are suitable for biochar production due to their low moisture content 8.92%, low ash yield 1.05%, and high organic matter content 78.3%. The biochar was produced by pyrolysis at 350, 450 and 550°C. The effect of pyrolysis temperature on the physicochemical characteristics of biochar was investigated. It was found that the porosity, water holding capacity, ash content, pH, organic matter, fixed carbon, and the elemental content of Na, K, Ca, Mg, Fe, Mn, P, Zn, Ba, Cr, Cu, Ni, Pb, Ti, and V were increased along with pyrolysis temperature. Meanwhile, the biochar yield, bulk density, and the total content of N and S were decreased. The biochar was tested as a sustainable adsorbent to investigate the adsorption of Cd from contaminated water. The adsorption isotherms of Cd on biochar were determined based on Langmuir equation. The maximum adsorption of Cd at 25°C and pH 7 were 667, 714, and 833 mg/kg for the biochars produced at 350, 450, and 550°C, respectively. On the basis of the physicochemical characteristics of the biochar and the findings from Langmuir equation that showed the biochar produced at 550°C has the highest adsorption capacity for Cd, the desorption/adsorption experiment was carried out using the biochar produced at 550°C. The adsorption of Cd by biochar was directly proportional to the Cd concentrations. It was increased from 0.009 mmol/0.5g at 0.01 mmol Cd to 0.12 mmol/0.5g at 0.2 mmol Cd concentration. The desorption of Cd from biochar was increased proportionally to cadmium concentrations from 0.01 to 0.05 mmol and became constant above 0.05 mmol, regardless of the increment of cadmium concentrations. High retention potential for the cadmium that adsorbed within the biochar was proven in this study with desorption/adsorption percentage of 16%. These findings provide a successful example of date seeds converting into the sustainable adsorbent for Cd removal from aquatic environment to achieve the conception of eco-friendly production, which should be studied further.
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