Sponge effect of aerated concrete on phosphorus adsorption-desorption from agricultural drainage water in rainfall

In the initial stage of the rainfall, the nutrient element phosphorus (P) in the farmland, one of the most important factors causing agricultural non-point source pollution, flows into agriculture drainage ditches rapidly, and an instantaneous phosphorus peak value in the ditch water often occurs. Aerated concrete with high P adsorption properties was chosen as the experiment material in the laboratory to reduce the instantaneous P peak value in the drainage water in the initial stage of the rainfall. The three total P (TP) concentrations of the simulated drainage water (1.0, 2.0, and 3.0 mg/L) stood for three treatments were designed in the adsorption experiment; the same three TP concentrations of the simulated drainage water and the three TP concentrations of the simulated natural water (0.2, 0.3, and 0.4 mg/L) stood for nine treatments in the desorption experiment. The sponge effect of the aerated concrete on the P adsorption-desorption was explored by studying the dynamics of the P adsorption-desorption of the aerated concrete with an increase in the experiment’s time. The results showed the following details: (1) Both the adsorption rate and desorption rate of the aerated concrete decrease with an increase in the experiment’s time. The initial adsorption is dominant during the entire adsorption, as with the initial desorption during the entire desorption. (2) The adsorption capacity of the aerated concrete slightly decreases with the increase in the re-adsorption, whereas the desorption capacity of the aerated concrete significantly decreases with the increase in the re-desorption. Thus, the aerated concrete can be introduced into the agricultural drainage ditch to reduce the instantaneous P peak value in the drainage water in the initial stage of the rainfall, and potential further studies should explore the relationship between the different drainage water loads and the amount of the aerated concrete.