A comprehensive study on flocculation of anionic dyes using the bioflocculant produced by Bacillus thuringiensis: Kinetics, affecting factors, and perspectives.

Bioflocculants have received more and more attention as alternatives to chemical flocculants because of their innocuousness, environmental friendliness, and high effectiveness. This study aims to investigate various factors that influence the performance of the novel bioflocculant produced by Bacillus thuringiensis (BF-TWB10) and analyze its adsorption kinetics to optimize its flocculation performance for real applications. The best-fit kinetic model was pseudo-second order with R2 = 0.999. The effects of pretreatment temperature, pH, and the presence of cations on flocculation were assessed. Further investigations of flocculation, including zeta potential analysis and particle size analysis, were also conducted. Thermal pretreatment of BF-TWB10 or the presence of divalent cations could stimulate the decolorization efficiency of the bioflocculant. BF-TWB10 manifested outstanding dye removal performances with over 90% for all tested anionic dyes at pH 2 and 3. Its decolorization efficiency on anionic dyes decreased with the increase of pH values. Zeta potential analysis revealed that the electrostatic repulsion between anionic dyes decreased after the addition of BT-TWB10 and further diminished by adjusting the reaction mixture to pH 2 before flocculation, suggesting the occurrence of adsorption bridging and charge neutralization. These findings proposed that BF-TWB10 might be a promising bioflocculant for the removal of dyes in textile wastewater. PRACTITIONER POINTS: Bioflocculant BF-TWB10 shows outstanding performance in flocculation. Adsorption process follows pseudo-second-order kinetic model. Flocculation process is pH-responsive. High-temperature pretreatment or divalent cations enhance its flocculation performance. The analyses suggest the occurrence of charge neutralization and adsorption bridging.

Ecological Significance and Processes in Research of the Viable but Nonculturable State in Bacteria / 微生物学通报

The viable but noncuturable (VBNC) state is a survival strategy when bacteria are exposed to en- vironment stress. The VBNC state is part of the life cycle of non-differentiating bacteria, and it has a far-reaching impact on traditional bacteriology. Cells in the VBNC state fail to grow on the routine bacterio- logical media, here its significance in human health and environment science are detailed. Cells entering the VBNC state exhibit dwarfing and a number of metabolic changes in respiration rates and macromolecular synthesis. This paper summarized the variations in DNA and protein comparing to the culturable cells. We also discussed the ability of cells to resuscitate from the VBNC state and return to an actively metabolizing and culturable form. Some new methods for monitoring the VBNC state were listed. Finally the future was suggested.