Emerging Contaminants (Jan 2022)
Batch equilibrium studies on the adsorptive capacity of powdered and pelleted maize tassel to remove PFOA and PFOS from aqueous medium
Abstract
This study was aimed at evaluating the potential of raw maize tassel powder and pellets to remove PFOA and PFOS from water. Batch experiments were first conducted using ultrapure water to investigate the effects of pH, adsorbent dosage, initial PFASs concentration, contact time and temperature in adsorption efficiency of powdered and pelleted maize tassel. The optimum conditions for the removal of PFOA/PFOS observed for both maize tassel powder and pellets were as follows: pH 2.0, adsorbate initial concentrations of 20 mg g−1, adsorbent dosage of 0.5 g (20 pellets), 1 h contact time, all at 25 °C. These optimum conditions were, thereafter, applied to surface water samples from Apies River in Pretoria, spiked with 20 mg L−1 PFOS/PFOA. Shimadzu LC-MS/MS was employed in analysis and the Langmuir and Freundlich isotherm models were used to determine the types of adsorption mechanism. High percentage removal 91.3% and 89.7% for PFOA and PFOS respectively using both MT powder and pellets were achieved. The maximum adsorption capacities identified for the monolayer of the Langmuir isotherm model was found to be between 41.6 mg g−1 and 58.82 mg g−1 for PFOA using powder and pellets respectively; and between 42.37 mg g−1 and 176.5 mg g−1 for PFOS for the same adsorbents respectively. These results showed very insignificant conformity to the Langmuir model; therefore it can be assumed that the Langmuir model was not obeyed. However, the experiments proved to be primarily consistent with the Freundlich model, with high correlation coefficient (R2) values ranging from 0.900 to 0.998 for both PFOA and PFOS. Maximum adsorption capacities of 142.8 mg g−1 and 78.57 mg g−1 for PFOA and 107.4 mg g−1 and 85.7 mg g−1 for PFOS at 25 °C using both powder and pellets respectively were obtained suggesting that adsorption took place on heterogeneous layers for both targeted PFASs.
