Investigation of adsorption parameters of saxitoxin onto loblolly pine-derived biochar synthesized at various pyrolysis temperature.

This study highlights the use of loblolly pine derived biochar for the removal of harmful algal bloom toxin, Saxitoxin (STX), from water. Biochar samples were prepared at varying pyrolysis temperatures (400, 600 and 800 °C) for 60 min. As pyrolysis temperature increases, enhancement in surface porosity was observed (S_BET = 7.26 ± 0.2 m²/g to 408.15 ± 6.19 m²/g) while a decline in oxygen-containing functional groups was observed (1517.80 ± 14.98 μmol/g to 823.01 ± 7.72 μmol/g). This study aimed to discover the effects of adsorption parameters such as biochar dosage amount, contact time, initial concentration and initial pH on Saxitoxin adsorption. These studies revealed impressive results with >90 % toxin removal with dosage rate of 0.01 g/L, contact time of 30 min, and increasing percent removal with increasing initial STX concentration and initial pH in water. Maximum uptake was calculated for P400 with adsorption capacity of 314.37 μg/g. This showed that surface functionality showed higher affinity for STX uptake, which may be possible due to hydrogen bonding, electrostatic interactions, ion-exchange, and π-π interactions. Applied kinetic models indicated both physisorption and chemisorption interactions with best fit supporting the Elovich models. Complementary, adsorption isotherm analysis confirmed the multilayer adsorption behavior of the Freundlich model. Therefore, these findings support the viable use of biochar material for the remediation of STX waters.