Research On Phosphorus Removal From Rural Domestic Sewage By Iron Cyclic Reloading

China has vigorously promoted domestic sewage treatment in rural areas and achieved a preliminary success in recent years.However,it still remains a problem to be solved that the total phosphorus in effluent from treatment facilities exceeds the standard owing to the simple process of phosphorus removal in rural domestic sewage and the poor effect of phosphorus removal.In view of this,this research proposes an efficient and convenient phosphorus removal method of enhancing the phosphorus absorption capacity by chemically modifying phosphorus adsorbents with iron-loaded cycling.The main research conclusions are drawn as follows:（1）Vermiculite was selected as the research material for enhanced phosphorus removal by using FeSO₄ to modify different materials and conducting static adsorption tests.The Freundlich Isothermal Adsorption Model and the Quasi-second Order Kinetic Model can be used to describe the adsorption process well with the theoretical phosphorus adsorption capacity is 4.29 mg·g^-1,and the phosphorus removal process is mainly chemisorption.（2）The phosphorus removal device was constructed with vermiculite as phosphorus absorbing material.The influencing factors of iron load of cyclic ferric reflux and the optimal conditions for iron cyclic reload were studied.Adopting single factor test and Box-Behnken response surface test,the parameters of iron loading efficiency were optimized.The optimal process parameters of iron loading were obtained as follows:reflux rate of 24 m L·min^-1,concentration of 10.7 g·L^-1（in Fe）and aeration flow of 0.1 L·min^-1.（3）Dynamic phosphorus removal experiments were carried out under the optimal iron loading conditions.The results showed that with the increase of influent phosphorus concentration,the phosphorus adsorption capacity of iron-loaded materials increased,but the overall phosphorus removal efficiency decreased and the influent flow rate had no significant effect on phosphorus adsorption capacity and phosphorus removal efficiency.The total phosphorus adsorption capacity and effective running time can be significantly increased by iron cyclic reloading when the saturated phosphorus absorption failure occurs.However,with the increase of cycle times,the iron loading efficiency decreases as well as phosphorus removal efficiency.Under the single iron load,the effective phosphorus removal time of the plant is the longest under the inlet phosphorus load of 0.031 kg·m^-3·d^-1 and hydraulic load of 3 m³·m³·d^-1,and the phosphorus adsorption capacity and phosphorus removal efficiency are relatively high.If the parallel operation mode of adsorption columns is adopted,continuous influent phosphorus removal process can be implemented,so as to adapt to the current operation and maintenance management of rural domestic sewage facilities.（4）According to the continuous operation results of the actual rural domestic sewage,the total effective operation period of phosphorus removal is 71d and the average effluent total phosphorus concentration is<0.5 mg·L^-1 after three iron-loaded cycles under the condition of the influent average phosphorus concentration of 7.22 mg·L^-1 and hydraulic load of 3 m³·m³·d^-1.The result of characterization analysis shows that the phosphorus absorption material mainly enhance phosphorus removal through the chemical precipitation of Fe³⁺on the surface and the combined action of iron hydroxides and oxides on PO₄^3-coordinated complexation adsorption.These research conclusions show that the phosphorus removal efficiency of phosphorus absorption materials can be greatly improved by iron cycle reloading,and the long-term and stable phosphorus removal effect can be realized by using the parallel and alternative cyclic operation of iron-loaded and phosphorus adsorption process.In conclusion,this research provides a practical method with good application prospect for phosphorus removal in rural domestic sewage.