Biological Phosphorus Removal Granular Sludge And Denitrifying Phosphorus Uptake

Discharging waste-water with high levels of phosphorus (P)and nitrogen (N)can result ineutrophication of receiving waters.The biological nutrient removal processes are main methods to remove P and N in wastewater.In this paper firstly the formation,the stability and phosphorus removal characteristics of biological phosphorus removal granular sludge werestudied;secondly the denitrifying characteristics of the anoxic granular sludge wereresearched;finally the induction and characteristics of the denitrifying phosphorus uptake granular sludge were investigated.The main results and conclutions are as follows.(1) The granulation processes of the seed floccular sludge without and with filamentousbacteria in SBRs fed with sodium acetate were compared for biological phosphorous removalby means of hydraulic selection.The complete granulation was observed at the 82nd (withoutfilamentous bacteria)and the 20th (with filamentous bacteria)day respectively.The granularsludge formed was characteristic with 1.0～2.0mm in diameter,20～30m/h in settling velocity,1.0439 in specific gravity,94% in concentration of water,11.4mg/gSS,3.21mg/gSS and 0.17mg/gSS in concentration of Ca,Mg and Fe,and below 30mL/g in SVI.The max.specificphosphorus release rate (SRPR)and the max.specific phosphorus uptake rate (SUPR)were67.93 mgP/gVSS·h and 60.08mgP/gVSS·h respectively,the ratio of SRPR and COD degradation rate (Δρ_P／ΔCOD)was 0.35～0.49,the phophorus content of MLSS (TP/SS)was5.6～7.8%.(2) When the filamentous bacteria on granular sludge overgrew,the settling ability andphosphorus removal ability would deteriorate.In biological phosphorus removal granular sludge system the fine and distant bacterial filament didn't affect the reactor.But when the bacterial filamentous bacterial grew strong and dense,and its length was over 2.5 times thegranule diameter,the bulking occurred.Not only the SVI,the effluent SS and the MLSS achieved 112mL/g,100mg/L and 2000mg/L respectively but also the phosphorus removal efficiency droped below 60%,and the max.SRPR and SUPR were 14.97mg/gVSS·h and 10.95mg/gVSS·h respectively,and theΔρ_P／ΔCOD and TP/SS were only 0.21 and 3.66% respectively.The bulking system could recover by one of three strateges,that is extending sedimentation time,combining extending sedimentation time with increasing stirring speedand adding non-bulking granular sludge,and the required recovery time was 53,26 and 20days respectively.(3) The anoxic granular sludge was formed in SBR fed with sodium acetate and NO₃^- bymeans of hydraulic selection.The granule was characteristic with 1.2～1.8mm in diameter,25⁶0m/h in settling velocity,93～96.7% in concentration of water and 65²27mg/gSS inconcentration of Ca.The anoxic granular sludge had fine biological activity and adapted tohigh pH value.The max.specific denitrifying rate (SDNR)was 95.46mgNO₃^--N/gVSS·h,and the max.SDNR was about 45.51mgNO₃^--N/gVSS·h eventhough the pH value was over 8.5.(4) The biological phosphorous removal granular sludge could be induced into thedenitrifying phosphorus uptake granular sludge by swithing A/O to A/A/O.When the initialNO₃^--N concentration was from 5mg/L to 20mg/L,the content of the anoxic phosphate uptakewas increased from 28% to 80%,and max.SUPR was elevated froml3.6mg/gVSS·h to27.87mg/gVSS·h.The granular sludge was characteristic with 1.0～2.0mm in diameter,in settling velocity,1.0470 in specific gravity,44.34mg/gSS,27mg/gSS and 0.21mg/gSS inconcentration of Ca,Mg and Fe,and below 50mL/g in SVI.Compared with the granularsludge formed in EBPR,the one formed in DNEBPR had a high settling velocity (29～51m/h)and the concentration of Ca,Mg and Fe (44.34mgCa/gSS,27Mgmg/gSS and 0.21mgFe/gSS).The max.SRPR,SUPR and SDNR were 29.97mg/gVSS·h,27.87mg/gVSS·h and16.9mgNO₃^--N/gVSS·h respectively at anoxic stage,and when 1g N was removed the 1.4g Pcould be uptaken;the max.SDNR was 18.83mgNO₃^--N/gVSS·h which used nitrate,and themax.SDNR was 2.29mgNO₃^--N/gVSS·h which used nitrite.(5)According to the electron acceptors PAOs could be categorized into 3 groups:PAOsutilizing oxygen only,PAOs utilizing both oxygen and NO₃^- and PAOs utilizing oxygen,NO₃^- and NO₂^-.The percentage of DNPAOs in PAOs was increased from 14.9% to 80.7%after 212 days operation.(6)The granular sludge had a high threshold for NO₂^--N inhibitation.When the NO₂^-N was 4.69mg/L,the inhabitation occurred; when the NO₂^--N was 20.81mg/L,DNPAOs wascomplete inhibited.