气水比对污泥水中以鸟粪石形式回收氮磷的影响

污泥水富含氮磷,其回流经常造成污水处理厂出水水质的不稳定。以模拟污泥水为对象,采用套筒式流化床结晶装置,通过曝气吹脱CO2提高pH值并添加镁盐的方式以促进污泥水中鸟粪石的结晶,研究气水比对模拟污泥水中氮磷的去除效果以及对晶体产物的产量、分布、形态、粒径和成分的影响。结果表明,随着气水比的增加,污泥水的出水碱度降低、pH值升高、PO43--P和氨氮的去除率均增加,当气水比为15:1、30:1、60:1时,PO43--P的平均去除率分别为73%、82%和87%,氨氮的去除率均在17%~23%之间。同时,气水比影响晶体产物的产量、粒径和分布,但对晶体形态和组成的影响较小。同一气水比条件下,反应器底部和内壁晶体的形态存在明显差异,其中底部晶体大多纤细碎小,内壁晶体则均呈硕大的楔形,但X衍射谱图分析表明,以上二者的主成分均为鸟粪石。

Effect of gas-water ratio on struvite recovery in removal of phosphorus and nitrogen from reject water

The supernatant of a waste sludge treatment system (or reject water) was rich in phosphorus and nitrogen, and its recycling always led to unstable effluent in the wastewater treatment plant. In this study, a fluidized bed reactor with tube-in-tube was employed to crystallize struvite from treatment reject water by CO2 stripping and addition of magnesium salts. The effect of the gas-water ratio on the removal of phosphorus and nitrogen was studied, and further research on the quantity, distribution, morphology, size, and components of the crystal products was pursued. The results showed that the removal rate of phosphorus and nitrogen, as well as the pH, increased, while the alkalinity decreased, with increase of the gas-water ratio. When the gas-water ratios were 15:1, 30:1, and 60:1, the removal rates of phosphorus in the reject water were 73%, 82%, and 87%, respectively, and about 17% to 23% of nitrogen was removed. On the other hand, the gas-water ratio also influenced the quantity, distribution, and size of the crystal products, but had little effect on the morphology and components of the crystals. However, there was a recognizable difference between the crystals formed at the bottom and those formed on the inner wall of the reactor. The former crystals were in smaller pieces and the latter were formed as larger cuneiform. Despite the size difference, XRD analysis revealed that both the crystal products were mainly struvite.