Adsorption of phosphate by sediments in a eutrophic lake: Isotherms, kinetics, thermodynamics and the influence of dissolved organic matter

Adsorption and desorption of phosphorus (P) at sediment-water interface is one of the key processes of biogeochemical cycling of P in lakes. Thus, adsorption of phosphate by sediments from Lake Dianchi, a eutrophic lake, was investigated in this study. Importantly, the influence of dissolved organic matter (DOM) with fulvic acid (FA) as a representative example on these processes was further studied. The results showed that the presence of FA in the solution did not change the tendency of phosphate adsorption by sediments from Lake Dianchi. Compared with Freundlich equation, Langmuir model fitted better in describing the adsorption isotherms. And the pseudo-second-order kinetic model predicated well the adsorption kinetics for adsorption of phosphate by sediments. Under low concentrations of phosphate, FA promoted desorption of phosphate adsorbed on the sediments. However, adsorption behaviors including capacity and efficiency would be enhanced by presence of FA under high concentrations of phosphate. Based on adsorption thermodynamics, temperature and DOM (FA in this study) were two most important factors for adsorption of phosphate by sediments. Adsorption of phosphate on sediments was a spontaneous endothermic reaction process, which was a chemical-physical process rather than a simple physical adsorption. The influence of FA on the adsorption of phosphate by sediments was closely related with characteristics of sediments such as contents of Fe-Al oxides and organic matter. Aggressive results showed that increasing DOM due to algal blooming was likely an important way for dominant algae to maintain the nutrients such as P in lakes.