工艺条件对鸟粪石晶体的粒径和沉降速度的影响

采用激光粒度仪实验测定了小型套管式空气曝气填料层磷回收装置中不同条件下生成的鸟粪石晶体的体积平均粒径，考察了其变化规律，并结合Stokes公式计算了晶体的沉降速率，同时考虑鸟粪石晶体形状的影响，进行了相应的修正。实验结果表明，鸟粪石的粒径在10—200μm之间，主要集中于20～100μm；在磷回收装置中添加填料并通人空气有利于增大鸟粪石晶体的粒径和沉降速度，无填料无空气时和有填料有空气时的平均粒径分别在30～55μm和40～65μm之间。随着pH值的增大，鸟粪石晶体的粒径和沉降速度逐渐增大，但当pH大于9．0后，鸟粪石晶体的粒径和沉降速度又逐渐减小；氮磷比值从1：1增大到2：1，鸟粪石晶体的粒径和沉降速度小幅度增加，氮磷比进一步增大，鸟粪石晶体的粒径和沉降速度基本不变；镁磷摩尔比在1：1—1．2：1的范围内时，鸟粪石晶体的平均粒径和沉降速度随镁磷比的增大而增大；镁磷摩尔比大于1．2：1后，鸟粪石晶体的平均粒径和沉降速度随镁磷比的增大逐渐减小；初始磷浓度越高，鸟粪石晶体的平均粒径和沉降速度越大。

Effect of process conditions on the average particle size and settling velocity of struvite crystal

The average particle size of struvite crystals was measured under different process conditions in a double pipes/CO2 stripping packed layer phosphorus recovery pilot unit with the aid of laser particle size analy- zer, and its variations was in detail investigated. The settling velocity of the struvite crystals was evaluated with Stokes formula which was modified by taking into account the influence of struvite crystal shape. The results show that the particle sizes of struvite crystals are in the range of 10 to 200 μm, with mainly between 20 - 100μm. Packing and airing will be beneficial for enhancing average particle size from 40 to 65 μm and settling velocity of struvite crystals in the phosphorus recovery equipment compared to no packing and airing with the average size from 30 to 55μm. The particle size and settling velocity of struvite crystals increase with an increase of pH, whereas inversely, for pH 〉 9, the size and settling velocity decrease. Ammonia-nitrogen/phosphorus molar ra- tio from 1：1 to 2：1 results in a slight increase in the particle size and settling velocity of struvite crystals, but fur- ther increase in ratio does not change the particle size distribution and settling velocity. The particle size and set- tling velocity of struvite crystals are elevated when magnesium/phosphate molar ratio spans from 1 ： 1 to 1.2： 1, while magnesium/phosphate molar ratio exceeds 1.2： 1, the size and settling velocity decrease. Additionally, it should be noted that the particle size and settlement velocity of struvite crystals increase at higher initial phos- phorus concentration.