Short Term Kinetics Of Phosphorus Adsorption By Resuspended Sediments In The Rigs-to-reefs Area

Studies have shown that phosphorus has become the key factor to control eutrophication of the Bohai Sea.The interaction between suspended sediment and phosphorus plays an important role in the prevention and control of marine eutrophication.After transforming oil production platforms to fish reefs,water dynamic conditions has changed in the sea area near the project.Under the action of reciprocating flow,the sediment resuspension-settlement phenomenon occurred periodically,and the water residence times in the project sea area is short.Therefore,it is very important to study the short-term kinetics of the interaction of sediment-phosphorus for understanding the eutrophication process occurred at the rigs-to-reefs area..Batch experiment is a powerful technology to study adsorption,but it is difficult to capture the short-term kinetic information because of its complicated operation process.The stirred flow experiment technology not only has an open system,but also can realize continuous sampling,so it has greater potential in the study of short-term kinetics.In this study,phosphorus adsorption by resuspended sediments,sampled from Chengdao sea area of Bohai Sea,was discussed by short-term stirred flow kinetics experiments under different influent phosphorus concentrations,solid concentration and flow rate.And the distinction between batch experiments and stirred flow experiments under different phosphorus concentrations were discussed.In addition,the influence of different conditions on the equilibrium time are predicted according to the kinetic equation and parameter fitting equation.Based on the R language,a zero dimensional model was established to simulate the adsorption kinetics in the flow stirring experiment,and predicted the phosphorus concentration in the effluent.The main conclusions are as follows:(1)Although the pseudo-second order kinetic model is a better description equation for both flow experiments and batch experiments,the equilibrium adsorption capacity Q_e2and rate constant k₂determined by the two methods were significantly different.k₂from batch experiments were significantly higher and Q_e2was significantly lower than those from flow experiments.Moreover,the initial adsorption rate from batch experiments were significantly higher than those from flow experiments.1/n<1(convex)in Freundlich adsorption isotherm equation obtained by batch experiment,while 1/n>1(concave)obtained by stirred flow method.(2)The phosphorus adsorption was significantly affected by the influent phosphorus concentration.According to the relationship between influent phosphorus concentration and kinetic parameters in stirred flow experiments,the kinetic equation in terms of influent phosphorus concentration was established.The equation can not only express the change of unit resuspended sediment adsorption amount with time and influent phosphorus concentration,but also directly express the distribution relationship of phosphorus between resuspended sediments and aqueous phase.(3)The results show that the phosphorus adsorption was significantly affected by the solid concentration and flow rate,and the adsorption rate increases with the decrease of solid concentration and with the increase of influent flow rates.According to the relationship between kinetic parameters and solid concentration or flow rates,the comprehensive kinetic equations of adsorption were obtained respectively.(4)According to the pseudo-second order kinetic equation and kinetic parameter fitting equation,the equilibrium time is predicted under different conditions.It shows that the equilibrium time decreases with influent concentration and flow rate,but with the decrease of solid concentration.(5)The zero dimensional model for the stirred flow experiment was established in R language software to predict the effluent phosphorus concentration.It shows that the removal efficiency of phosphorus would increase with increasing phosphorus concentration and decreasing flow rate in the predicted period,but there was no monotonous relationship between phosphorus removal efficiency and solid concentration.