Study on phosphate and Ammonium Removal using Magnesium Ammonium Phosphate Crystallization

考虑到大都市污泥处理基地的概念，需要开发去除污泥处理过程中排出的废水中的氨氮和磷酸盐的工艺。在本研究中，对结晶特性与可去除性之间的关系进行了基础研究。通过批量实验验证了MAP的结晶特性(水质特性和选择性结晶的操作条件)，得到了选择性结晶的条件(温度、pH、Mg/P摩尔比和NH4/P摩尔比)。在此基础上，进行了间歇反应结晶实验，通过扫描电子显微镜测量晶体大小和形状的动态变化，考察了镁磷去除过程与MAP结晶之间的关系，阐明了获得最佳去除效率的操作pH和镁磷摩尔比，并考虑了基于成核和晶体生长现象的MAP结晶，并考察了乙醇加入法对固液平衡的影响。醇类的加入降低了MAP的溶解度积，MAP的结晶过程被认为是由离子反应、扩散和表面积分步骤组成的，当需要合适的产物尺寸时，积分步骤决定了反应的速度。在考虑结晶速率与结晶器设计方法的关系的基础上，提出了物料平衡和结晶速率的设计方法。

Development of Ammonium and Phosphate ions removal process has been needed for removing them from wastewater exhausted in the process of sludge treatment, considering the concept of sludge treatment base in the metropolitan urban cite. In this research, basic investigation was done on the relation between crystallization characteristics and removability. Batch experiments were done to verify the crystallization characteristics of MAP (characteristics of water quality and operational conditions to crystallize MAP selectively), and selective crystallization conditions (temperature, pH,Mg/P molar ratio and NH4/P molar ratio) was obtained. Based on the results above, batch reactive crystallization experiments were performed, to investigate relation between the process of Magnesium and Phosphate removal and crystallization of MAP,and to clarify operational pH and Mg/P molar ratio for obtaining optimum removal efficiency and consider MAP crystallization based on nucleation and crystal growth phenomena, by measuring the dynamic change of crystal size and its shape through SEM.And also Alcohol addition method was investigated, to make clear the effect of alcohol on the solid-liquid equilibrium. Addition of alcohol lowered the solubility product.Process of MAP crystallization was considered to consist of reaction of ions, diffusion and surface integration stpes, and it was recognized that integration step determined the rate, when desirable product size was needed. Consequently design method on the material balance and crystallization rate was proposed, considering relation between crystallization rate and design method of the crystallizer.