Adsorption of microcystin contaminants by biochars derived from contrasting pyrolytic conditions: Characteristics, affecting factors, and mechanisms

The growing incidence of microcystins (MCs) in the environment has become an issue of global concern for the high ecological and human health risks. Herein, a comparative adsorption of three MCs (MC-LR, MC-YR and MC-RR) by spent mushroom substrate (SMS)-derived biochars from contrasting pyrolytic conditions (temperature: 600/300 degrees C; and gas steam: CO2/N2) was surveyed to better understand the mechanisms and factors affecting the adsorption performance. For biochar preparation, 600 degrees C and CO2 led to greater levels of aromaticity, ash, SBET, and porosity, while 300 degrees C and N-2 created more surface functional groups. The adsorption of MCs by biochars was a pH-dependent and endothermic physisorption process, following the pseudo-second-order kinetics (R-2 = 0.99) and linear isotherm model (R-2 > 0.88). The distribution coefficients K-d (0.98-19.2 L/kg) varied greatly among MCs (MC-YR > MC-RR > MC-LR) and biochars (BC600 > BN600 > BC300 > BN300), which depends on the combined effects of hydrophobicity, electrostatic attraction, H-bonding, cation bridging, and the amounts of adsorption sites on biochars. Higher ash, SBET, and total pore volume of BC600 facilitated the adsorption capacity for MCs relative to other biochars. Furthermore, the co-adsorption efficacy for MCs (K-d = 1.09-8.86 L/kg) was far below those for the single adsorption, indicating strong conflicts among competing MCs. This study sheds light on the roles of pyrolytic temperature and gas steam in biochar properties, and elucidates the mechanisms and factors affecting the adsorption performance of different MCs, which lays a foundation for MCs removal from water. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found that different pyrolytic temperatures and gas conditions significantly influence the properties of biochars, affecting the adsorption performance of microcystins. The adsorption process is pH-dependent and follows pseudo-second-order kinetics and a linear isotherm model, with distribution coefficients K-d varying greatly among different MCs and biochars.