In river systems, transported suspended sediment interacts with in-channel and riparian vegetation. The involved physical processes are complex and still poorly reproduced by numerical models. This study compares the performance of background horizontal eddy viscosity models in reproducing flow fields and suspended sediment transport processes inside partially vegetated flows. Particularly, we selected an experiment with a partly-vegetated flume which we numerically replicated with the Delft 3D-2DH model. We applied three existing horizontal eddy viscosity approaches: constant value, Elder model and hybrid model. Besides, we represented the vegetation by using Baptist formulation. The results show that the Elder viscosity model reproduces the explicit development of vortices along the flume, while all three viscosity models show an underestimate of the sediment deposition in the vegetated area and an overestimation of sediment deposition in the non-vegetated area. Further investigation is needed to reproduce the experimental introduction of the sediment and to link transversal suspended sediment dynamics with the resolved dynamics in numerical models.

Baptist’s method, Drag Force and Single-Stem approaches are the commonly used tools implemented in Delft3D to model water and sediment transport processes in vegetated channels. Despite their wide application, the model reliability has seldom been tested against data of controlled flume experiments with solid suspension. Here, we investigate the ability to reproduce suspended sediment transport through emergent vegetation by comparing the results of 2D simulations to existing experimental data. The results show that in low vegetation density, the Baptist and Drag Force approaches are not sensitive enough to density variations. The Single-Stem approach reproduces detailed flow structure and sediment deposition around stems, but its high computational time is a limitation for long-term simulations or dense vegetation. Furthermore, we observed that the simplification of 2D depth-averaged models and the non-equilibrium of sediment transport in both experiments and numerical simulations may also affect the overall performance of the vegetated modelling approaches.

The accumulation of phosphorus in activated sludge in wastewater treatment plants (WWTPs) provides potential for phosphorus recovery from sewage. This study delves into the potential for releasing phosphorus from waste activated sludge through two distinct treatment methods—thermal hydrolysis and pH adjustment. The investigation was conducted with activated sludge sourced from four WWTPs, each employing distinct phosphorus removal strategies. The findings underscore the notably superior efficacy of pH adjustment in solubilizing sludge phosphorus compared to the prevailing practice of thermal hydrolysis, widely adopted to enhance sludge digestion. The reversibility of phosphorus release within pH fluctuations spanning 2 to 12 implies that the release of sludge phosphorus can be attributed to the dissolution of phosphate precipitates. Alkaline sludge treatment induced the concurrent liberation of COD, nitrogen, and phosphorus through alkaline hydrolysis of sludge biomass and the dissolution of iron or aluminium phosphates, offering potential gains in resource recovery and energy efficiency.