Study On Phosphorus Removal From Anaerobically Digested Liquid By Using Dolimite Lime In Fluidized-Bed Crystallizer

Phosphorus (P) is almost non-renewable with one-way circulation in nature. With the wide use of P resource, it makes the resources exhausted. And a lot of phosphate substances discharged into the water bodies, for example, city sewage discharge, which lead to serious eutrophication of ocean and lakes. Therefore, P removal and recovery is good for P sustainable use and water environmental protection.Researches on P removal from synthetic anerobically digested liquid were conducted by "active seed", dolomite lime, in a new fluidized-bed crystallizer (FBC). The reactor was operated with intermittent and continuous modes, and outside circulation operation for investigating P removal efficiency. Single-factor investigation and Response Surface Methodology were used in the research. The results showed that P removal efficiencies could reach up to86%under the optimum experimental parameters, i.e., pH value9.5, reaction time2.0h, and settling time2.0h for batch process; dolomite dosage650mg/L, hydraulic retention time (HRT)5.0h, and aeration rate50ml/min for FBC by natural dolomite; pH value9.5, Mg/P molar ratio2.2, and HRT3.0h for FBC by acidified dolomite. But the influence of outside circulation operation on P removal efficiency was not significant in high pH value (pH=9.5) system. The morphology and structure of product solids were characterized by using Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX), X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometry (FTIR). The results showed that in this lower P concentration (20mg/L) and higher alkalinity system (20mM), P was mainly removed by magnesium ammonium phosphate (MAP). Through the research on interactive effects of Ca2+and CO32-on MAP reaction, CO32-effectively eliminate the negative influence of Ca2+in coexistence system, which made P mainly removed by MAP reaction.