Transformation And Flow Of Iron And Phosphorus In VUCT-MBR

Phosphate rock is not only an important strategic resource and essential nutrient for living organisms,but also a non-renewable resource.The global phosphate rock reserves are decreasing,but the mining rate is increasing which will resulting in the depletion of phosphorus resources.To lay the foundation for improving vUCT-MBR vivianite yield and operating efficiency,in this paper,the study of iron and phosphorus flow combine the speciation distribution of in-situ crystal dephosphorization process(vUCT-MBR)with iron(a-FeOOH)dosing was studied to investigate the in-situ crystal dephosphorization process of vivianite.The analysis techniques such as Mossbauer Spectrum,XRD and SEM-EDX were combined with hydrochloric acid,sodium pyrophosphate and ammonium oxalate extraction to analysis the iron speciation in vUCT-MBR system.Vivianite formed in anaerobic zone cycle to whole system,resulting that half of the iron in the aerobic reaction zone exists in the form of ferrous,the proportion of ferrous iron in the anaerobic zone is 60%,40%in anoxic zone and 50%in aeration zone.According to the analysis of iron speciation,the ferrous iron in vUCT-MBR system mainly exists in the form of vivianite(Fe3(PO4)2·8H2O),and the remaining ferric iron exists in the form of hydrated iron hydroxide or organic complex iron.Among them,the vivianite content of the membrane zone is higher and the oxidation rate is the lowest.It can be found from the Mossbauer spectrum that 55%of the iron in the membrane zone is ferrous iron in vivianite.Perchloric Acid(PCA),NaOH and Cation Exchange Resin(CER)were used to extract phosphorus from vUCT-MBR and iron-free University of Cape Town system(UCT-MBR)sludge,the phosphorus content and phosphorus speciation in the extract were analyzed.The results show that the aerobic zone of the vUCT-MBR system contains more phosphorus than anaerobic and anoxic zone,and the phosphorus content in different reaction zones in UCT-MBR system is relatively uniform.According to 31P Nuclear Magnetic Resonance(31P NMR)analysis of the phosphorus speciation in the extracts of UCT-MBR and vUCT-MBR sludge,it can be found that orthophosphate is the main form of phosphorus in both systems,organic phosphorus content in vUCT-MBR system is relatively lower than the UCT-MBR system,indicating that the addition of iron may affecting the bioavailability of phosphorus inside the sludge.According to the data obtained,it was found that vivianite in vUCT-MBR system distributed in every reaction zone,and highest content of vivianite can be found in the membrane reaction zone.Vivianite can also exist in the aerobic reaction zone.It has also been found that iron affecting the removal of COD and N in the vUCT-MBR system.