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Study on the phosphorus desorption of sediment from the Three Gorges Reservoir in turbulence state

Phosphorus (P) is one of the main substances to induce the eutrophication of water. The occurrence and migration of P in water are largely affected by the sediment. Although some studies have investigated the adsorption/desorption characteristics of phosphorus by the sediment, how the change of turbulence intensity affects the sediment flocculation and thus changes the desorption characteristics of P is still unknown. Herein, a nearly turbulent multilayer grid vibration device was designed and built to study the desorption characteristics of P by the sediment under different turbulent conditions. Furthermore, the movement and variation of particle size of the sediment that occurred in the event of turbulence have been investigated based on the images collected by the image collection device. The result shows that the secondary pollution to reservoir water may be induced by the sediment in the Three Gorges Reservoir deteriorating the eutrophication in the Reservoir. The desorption flux of P will augment with the enhancing water turbulence, sediment concentration and water temperature, where the turbulent diffusion influences the desorption of P from the sediment significantly. With the increasing intensity of turbulence, more bottom sediment will be incipiently moved and suspended which will impel the desorption of P more obviously. As the intensity amplifies further, the median diameter of the sediment tends to ascend first and then descend, and the variation of particle size caused by the flocculation and deflocculation of the sediment will affect the desorption of P to some degree. However, the dominant factor for the desorption of P is still the hydrodynamic condition, that is, the desorption of P elevates the increasing intensity of turbulence.