Study On Removal Of Phosphorus From Effluent Of Wastewater Treatment Plant In Low Temperature By Coagulation With Fine Particle Loading

The traditional biological phosphorus removal technology has great limitations.When the influent water quality is poor or the temperature is low,the removal effect of phosphorus is often poor.The removal phosphorus by conventional coagulation technology is also greatly affected by temperature.At low temperature,the hydrolysis rate of the coagulant is slow,Brownian motion of the colloidal particles is inhibited.These series of reasons leads to poor phosphorus removal in conventional coagulation techniques at low temperatures.The particle loading coagulation technology is based on the conventional coagulation technology,and the small particle size particles such as magnetic powder or micro sand are added to the water before the destabilized colloidal particles have not re-agglomerated.With the help of coagulant,the colloidal particles in the water are wrapped around the fine particles,thereby reducing the free phosphorus-containing particles in the water,increasing the phosphorus removal rate and the clarification speed,and offsetting the effect of low temperature on the phosphorus removal.In this paper,in view of the problem that the phosphorus in the effluent of wastewater treatment plant was too high under low temperature conditions,the optimum conditions for the removal of phosphorus from the effluent of sewage treatment plant under low temperature were studied by loading coagulation technology,and the kinetic model of phosphorus removal at low temperature by particle loading and coagulation technology was established..The results of conventional coagulation and dephosphorization experiments showed that when PAC,Al₂?SO₄?₃ and FeCl₃ were selected as phosphorus removal agents,FeCl₃ had the best phosphorus removal effect.Under the condition of that the pH was 5,the dosage was 60mg/L and the dosage of PAM was 1.5mg/L,the phosphorus removal rate could reach about at 91%at room temperature,and 86%at low temperature.Magnetic loading coagulation experiments showed that the smaller the particle size of the magnetic powder,the better the phosphorus removal effect.When the effluent from the aeration tank of the sewage plant first passed through the secondary sedimentation tank for separation of mud and water and then magnetic coagulation and dephosphorization,the particle size of the magnetic powder was 800 mesh,the dosage was 140 mg/L,and the rotation speed of the flocculation stage was 55⁶0r/min,the operating time was 8 min,the phosphorus removal rate was about 97%at normal temperature,and the phosphorus removal rate was about 95%at low temperature.When the effluent from the aeration tank was directly subjected to magnetic loading and coagulation for simultaneous phosphorus removal,the magnetic powder particle size was 800 mesh,the dosage was 400 mg/L,the flocculation stage speed was 60 r/min,and the time was 8 min.Under the normal temperature,the phosphorus removal rate was about 95%,and at low temperature,it was about 92%.It can be seen that the magnetic loading can enhance the effect of the conventional coagulation treatment,especially under low temperature conditions,the phosphorus removal efficiency can be increased by about 10%.The results of sand loading coagulation and phosphorus removal experiments showed that when the particle size of the micro-sand was 140¹80 mesh,the dosage was 240mg/L,the mixing speed in the flocculation stage was 60r/min and the stirring time was 6min,the phosphorus removal rate of the sand loading coagulation and phosphorus removal was 93.89%at normal temperature and 89.61%at low temperature.It indicated that the sand loading coagulation can also enhance the effect of conventional coagulation and phosphorus removal to a certain extent,and the phosphorus removal rate at low temperature can be increased by about 4%.Comparison of magnetic loading phosphorus removal experiment of 150 mesh magnetic powder and sand loading phosphorus removal experiment of 140¹80 mesh micro-sand showed that magnetic loading coagulation technology was superior to sand loading coagulation not only in phosphorus removal rate and clarification speed but also in coagulant usage.The observation of floc structure by Scanning Electron Microscopy?SEM?and microscope and the measurement of fractal dimension of flocs showed that the magnetic flocs are more compact and larger than the sand flocs.The results of Zeta potential showed that the addition of magnetic powder can reduce the Zeta potential of the system,while micro-sand does not.Therefore,from the perspective of low-temperature phosphorus removal,magnetic powder was the best loading material.According to the analysis of the best working condition of phosphorus removal by response surface analysis method,the best working condition of magnetic loading coagulation and dephosphorization of the secondary sedimentation tank effluent with800 mesh magnetic powder under low temperature condition was that the magnetic powder dosage was 128.7mg/L,the stirring speed was 59.18r/min,and the stirring time was 8.02min.The corresponding phosphorus removal rate was close to 95%.Under the same conditions,the optimum working conditions of 140¹80 mesh micro-sand were that the micro-sand dosage was 243.20 mg/L,stirring speed was57.92 r/min and stirring time was 5.14 min.The corresponding phosphorus removal rate can reach 89.92%.The results of kinetic experiments showed that the loading of phosphorus in low temperature was consistent with the second-order kinetic model.The apparent reaction rate constant of magnetically loaded coagulation and dephosphorization at low temperature was:k=5.446?10^-66 L^-0.3416m¹.2416.2416 v^1.5455,where:?L?represents the particle size of magnetic powder,?m;?m?represents the amount of magnetic powder added,mg/L;?v?represents the stirring speed in the flocculation stage,r/min.The apparent reaction rate constant of sand loading coagulation and dephosphorization of140¹80 mesh micro sand at low temperature was:k=5.055?10^-4m⁰.4892.4892 v^0.9146,where:?m?represents the amount of micro-sand added,mg/L;?v?represents the stirring speed in the flocculation stage,r/min.