Non-radical mechanism and toxicity analysis of ß-cyclodextrin functionalized biochar catalyzing the degradation of bisphenol A and its analogs by peroxydisulfate.

Bisphenols (BPs) are distributed in worldwide as typical environmental hormones, which potentially harm the ecological environment and human health. In this study, four BPs, i.e., bisphenol A, bisphenol F, bisphenol S, and bisphenol AF, were used as prototypes to identify the intrinsic differences in degradation mechanisms correlated with the molecular structures in peroxydisulfate (PDS)-based advanced oxidation processes (AOPs). Electron transfer was the main way of modified biochar to trigger the heterogenous catalysis of PDS, which can cause the degradation of BPs. Phenolic hydroxyl groups on bisphenol pollutants were considered as possible active sites, and the existence of substituents was the main reason for the differentiation in the degradation efficiency of various bisphenols. Results of ecotoxicity prediction showed that most intermediates produced by the degradation of BPs in the ß-SB/PDS system, which was dominated by the electron transfer pathway, had a lower toxicity than the parent molecules, while the toxicity of several ring cleavage intermediates was higher. This study presents a simple modification scheme for the conversion of biochar into functional catalysts and provides insights into the mechanism of heterogeneous catalytic degradation mediated by modified biochar as well as the degradation differences of bisphenol pollutants and their potential ecotoxicity.

Flocculation performance and mechanism of fungal pellets on harvesting of microalgal biomass.

In this study, a bioflocculation method assisted by fungal pellets was developed for highly efficient microalgae harvesting. Effects of critical parameters, including flocculation type, temperature, rotation speed and initial pH, on the bioflocculation of fungal Aspergillus niger for microalgae Scenedesmus sp. were investigated. Results showed that the maximum flocculation efficiency of 99.4% was obtained when the fungal pellets were inoculated in the algal solution at the initial pH of 8.0, temperature of 30 °C and rotation speed of 160 rpm for 48 h in BG-11 medium. Furthermore, microscopy examination, scanning electron microscopy, Fourier transform infrared spectroscopy, Zeta potential measurement and three-dimensional excitation emission matrix fluorescence spectroscopy were used to explore the mechanism of bioflocculation process. It was found that the interaction of fungi and microalgae was related to the surface functional groups of fungal pellets. This study provides a interpretation of conceivable mechanism for microalgal bioflocculation by fungal pellets.