Release,Transformation And Recovery Of Phosphorus In Sludge Pretreatment And Anaerobic Digestion System

For the issues of sludge treatment and disposal,sludge pretreatment and anaerobic digestion are the effective method to achieve sludge reduction and utilization.As a kind of resource,sludge is rich in phosphorus.If not recovered,phosphorus could cause the eutrophication and the waste of phosphorus resource.Based on the issue of phosphorus recovery during sludge treatment,this study first investigated on the impacts of sludge pretreatment and anaerobic digestion for phosphorus release and transformation.Then the influences of sludge pretreatment for anaerobic digestion on phosphorus release and transformation were also discussed.In view of anaerobic digestion,the thermodynamics and dynamics of vivianite to removal phosphate from aqueous solutions was also studied.To analyze the relationship between phosphorus release and other characteristics,the concentrations of phosphorus,COD and nitrogen and EMM(Excitation-emission-matrix)were measured.SMT(Standards,Measurements and Testing)method and 31P-NMR(nuclear magnetic resonance)method were also used to study the principle of phosphorus release and phosphorus species transformation by pretreatment.The results showed that acid and alkali treatments were more effective to release P from the sludge,with the phosphorus concentration of 171-321 mg/L and 143-295 mg/L respectively in supernatant after pretreatment.The release of P from the sludge biomass was not well correlated to the profiles of COD and nitrogenous compounds,indicating the different mechanisms.Although the phosphorus could not released though anaerobic digestion the most of phosphorus translated to phosphate.On the base of vivianite crystallization in anaerobic digestion system,the water environment chemical equilibrium software(Visual MINITEQ)was used to simulate the effects of CO32-and S2-on vivianite formation.The solubility product(KSp)in 25-55? and metastable zone of vivianite were also measured.The effect of pH and seed on vivianite crystallization and the dynamics of vivianite crystallization was studied.The result indicated that the pH level of vivianite formation was 5 to 10.CO32-and low concentration of S2-(<0.5 mmol/L)have few influence on the vivianite crystallization.The pKsp of vivianite was 39.8-40.7 at temperatures from 25-55 0C and the temperature effect was insignificant.The saturation index(SI)of metastable zone of vivianite crystallization was from 0 to 11.Effective nucleation and growth of vivianite was observed at pH 7.Adding seeds could increase the reaction rate of vivianite crystal growth pH 7.