In this study, Aspergillus niger was isolated from the solid waste generated during mushroom fermentation and was employed as an eco-friendly bioflocculant for the treatment of high-turbidity water. A comprehensive evaluation of the flocculation performance and underlying mechanisms of A. niger was conducted. Characterization of its physical and chemical structures was performed, and parameters, such as adsorbent dosage, culture time, pH, and agitation, were investigated to optimize turbidity removal. In addition, kinetic, thermodynamic, and isotherm analyses were carried out. Under optimized conditions, an adsorbent dosage of 5.25 g/L, a culture time of four days, and a pH range of 4.0-10.0, a remarkable turbidity removal rate of 98% was achieved. Moreover, A. niger manifested a high adsorption capacity for kaolin at 318 K. The kinetics and isotherm processes were well-described by the pseudo-first-order and the Langmuir models, respectively. Advanced analytical techniques, including zeta potential, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and density functional theory analyses, revealed that turbid colloidal particles were eradicated through the synergy of physisorption, charge neutralization, van der Waals interactions, and the functional groups (amino, carboxylic, and hydroxyl) present in the fungal structure. These findings suggest that A. niger reaches adsorption equilibrium rapidly and is effective for treating turbid water across a broad pH range.
