Research On The Removal Of Phosphorus Pollution Simulation Wastewater In Farmland By Akadama Clay Barrier-ecological Ditch System

Eutrophication of water body has attracted global attention as a hot environmental problem to be solved.Phosphorus is the limiting factor causing this environmental problem.At present,most of the materials that can effectively adsorb phosphorus need to be modified to play a better phosphorus removal effect,and it is urgent to develop natural adsorbents with economical and efficient.Ecological ditch is widely used in the removal of phosphorus in agricultural wastewater because of its advantages of convenient construction and low operating cost.However,in the current research,the effect of phosphorus interception in ecological ditches is relatively poor.In order to improve the interception efficiency of phosphorus in farmland drainage,this study selected a large specific surface area,rich pores and good permeability of natural akadama clay as the adsorption material of phosphorus in water.Through characterization and a series of batch experiments,the influence factors and adsorption mechanism of phosphorus adsorption in natural akadama clay were analyzed.In order to explore the practical application ability of akadama clay and develop the key technology of phosphorus removal with both economic and efficient benefits,this study proposed a unique ecological ditch system equipped measures-akadama clay barrier.Through single factor experiment,the setting parameters of akadama clay barrier in ecological ditch were analyzed and optimized.The main findings are as follows:（1）With the help of SEM、XRD、FTIR and XPS characterization,it is found that the surface of natural akadama clay is loose and porous,the main components are Si O₂ and metal oxides of Al、Fe,and there are a large number of hydroxyl groups.The adsorption of phosphorus by natural akadama clay is probably related to the surface complexation of hydroxyl and phosphate.（2）The removal rate of total phosphorus in the simulated farmland wastewater from the five adsorbent materials selected in the experiment can be ranked from high to low:akadama clay>ceramsite>steel slag>zeolite>volcanic rock.Natural akadama clay has the best removal effect on total phosphorus,and the removal rate reaches95.70%,and the removal rate of dissolved phosphorus and particulate phosphorus is higher,97.49%and 94.94%,respectively.（3）The adsorption of phosphorus by natural akadama clay can reach equilibrium within 120 min,and the environmental conditions with high concentration and high temperature can effectively promote the adsorption.At the same time,when the dosage and particle size of the akadama clay are small,its adsorption capacity for phosphorus is also high.When the solution concentration is 60 mg/L,the temperature is 35℃,the dosage is 5 g/L,the particle size is 0.15 mm,the adsorption capacity of natural akadama clay to phosphorus reaches 5.75 mg/g.The acidic conditions are favorable for the adsorption of phosphate by akadama clay.When HCO₃^-is present in the solution,the adsorption capacity of phosphorus by adsorbent will be significantly reduced.Adsorption data of phosphorus in akadama clay are more in line with the fitting of the pseudo-second-order kinetic model and the isothermal model of Freundlich adsorption,indicating that the adsorption belongs to chemisorption and occurs in-molecular layer.Through the intra-particle diffusion model and thermodynamic model,it can be concluded that the total adsorption rate of phosphorus by the akadama clay is controlled by intra-particle diffusion,and this adsorption belongs to the exothermic process.（4）The akadama clay barrier with small particle size and long length has better removal effect on total phosphorus,dissolved phosphorus and particulate phosphorus.Meanwhile the height of barrier was the same as that of the soil layer,the higher removal efficiencies of total phosphorus,dissolved phosphorus and particulate phosphorus were obtained.When the ecological drainage ditch with 10 cm soil layer was combined with 1mm particle size akadama clay barrier at a height of 10 cm,and a length of 90 cm,the removal rates of total phosphorus,dissolved phosphorus and particulate phosphorus were97.30%,96.88%and 93.80%.Moreover,the decentralized location design of the barrier elevated the phosphorus removal efficiency.It can be concluded that an akadama clay barrier-ecological ditch system has a great potential to remove phosphorus from agricultural rainfall runoff.