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Wine processing waste sludge (WPWS) has been shown to be an effective sorbent for the sorption of heavy metals (i.e., chromium and nickel), but the mechanism of removal of hexavalent chromium [Cr(VI)] by WPWS remains obscure. The aims of this study were to determine the effects of temperature, initial concentration of Cr(VI), and particle size on the removal Cr(VI) using WPWS. The characteristics of WPWS were determined, and sorption mechanism studies were also performed. The WPWS used was a deposit mixture containing considerable quantities of chemical coagulation as well as activated sludge precipitation from the settling basins of a wastewater treatment plant. Differential scanning calorimetry (DSC) analysis revealed that the WPWS comprised abundant labile carbohydrates and few aromatic structures. According to the IR spectrum, carboxylic groups were the most important functional group in WPWS, interacting with chromium species by protonation and redox reaction. All kinetic experiments were conducted at an initial pH of 2.0, and all of them had reached steady state within 240 min. The final pH values of the suspensions were approximately 4.2, and the increase of the pH caused low Cr removal. In addition, about 2-18% of the Cr(III) remained in the liquid phase. The Cr removal percentage increased with increasing temperature (i.e., 14-25%), but it was less affected by particle size (17-22%). All kinetic data obtained from different conditions showed good compliance with a pseudo-second-order model, and the rate constant k 2 was found to range from 0.032 to 0.074 g mg -1 min -1 . Some of the Cr(VI) ions were reduced to Cr(III) ions as a result of oxidation of organic components in WPWS, as indicated by monitoring using the X-ray absorption near-edge spectroscopic (XANES) technique.

Rainfall intensity and slope gradient are important factors that affect soil erosion; however, contradictory observations have been made due to different experimental conditions and materials. Colluvial deposits with loose, coarse material and steep slopes are easily erodible, but the erosion mechanism of colluvial deposition remains obscure. This work investigated the effects of heavy and storm rainfall intensity and steep slope gradients on the infiltration, runoff, and soil loss of colluvial soil. The rainfall intensity ranged from 1.00 to 2.33 mm min−1, and the slope gradient ranged from 36 to 84%. The infiltration rates declined sharply in the initial stage, whereas an opposite trend was observed for runoff rates until a steady state was reached after 5 min. Single‐ and multiple‐peak models illustrated the two types of changes for the sediment yield process. The infiltration volume and the coefficient increased with increasing rainfall intensity and decreased with increasing slope, whereas the runoff coefficient decreased with increasing rainfall intensity and increased with increasing slope. Runoff volume and sediment yield increased with increasing rainfall intensity but had a critical slope gradient of 58% and >47%. The sediment concentration increased with increasing rainfall intensity, and first increased and then decreased with increasing slope gradients at rainfall intensities of 1.00 and 1.33 mm min−1 but increased at rainfall intensities of 1.67, 2.00, and 2.33 mm min−1. The findings of this study can be used to clarify the erosion mechanisms in disturbed soils with high coarse particle content.

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