Influences of process conditions on particle size in struvite precipitation for phosphorus recovery from wastewater
工艺条件对磷回收过程中鸟粪石沉淀颗粒粒径的影响

In the process of struvite precipitation for recovery of phosphorus from wastewater,the particle size of struvite would directly affect the settling rate,thereby affects the phosphorus recovery efficiency.The average size of struvite was measured by laser particle size analyzer,and variation of struvite particle size with different process conditions in a small scale continuous stirred tank reaction-precipitation device was studied detailly,and then the struvite particle settling rate at the outlet of wastewater flow was calculated with Stokes formula in order to provide some references for the design of settlement tank.The results showed that the average particle size of struvite is in range of 12~25 μm,and the settling rate is between 5.46×10-5 and 2.37×10-4 m/s.With the hydraulic retention time(HRT) in the reactor increasing,the struvite particle size increases,but it becomes almost the same size when the HRT is more than 18 mins.With the HRT in the settlement tank increasing,the average size of struvite particles increases slowly,and when the HRT is more than 70 mins,the particle size changes little.The particle size changes little when the initial concentration of phosphorus is within 62~248 mg/L,but it significantly increases when the initial phosphorus concentration is greater than 496 mg/L.The pH has little effect on the average particle size.With molar ratio of nitrogen and phosphorus increasing,the average size of particles increases slowly,however,it decreases with increaing of the molar ratio of magnesium and phosphorus,and the settling rate is significantly reduced.