(643b) Comparative Study for Adsorption of Saxitoxin Onto Waste Biomass Derived Biochar and Its Effect on Thermochemical Process Parameters

Harmful Algal Bloom (HAB) events involve the growth of microalgae which release lethal toxins into fresh and brackish water bodies due to climatic and anthropogenic activities. Saxitoxin, a popular HAB neurotoxin has shown serious concern to humans as consumption of shellfish can results in paralytic shellfish poisoning. This study highlights the use of loblolly pine derived biochar for the useful removal of Saxitoxin (STX) in water. Biochar samples were procured at varying pyrolysis temperatures at 400, 600 and 800 °C for 60 min, which demonstrated favorable physicochemical properties for adsorption. Material characterization revealed that procurement provided both extremes in porosity and surface functionality, which dictate different adsorption behaviors with STX. 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 surveyed (1338.54 µmol/g to 74.55 µmol/g). Important adsorption parameters were investigated to reveal adsorption behavior between STX and biochar, including dosage amount, contact time, initial concentration, and initial pH. Maximum adsorption was favored for biochar prepared at 400 °C 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 Ï€-Ï€ interactions. From applied kinetic models, both Pseudo-First Order and Pseudo-Second Order models showed best fit relationships which indicates both physisorption and chemisorption interactions for three biochar samples. Adsorption isotherm analysis showed the best fit suited the Freundlich isotherm. These findings support the viable use of cost-efficient biochar material for the remediation of STX waters.