Enhanced Simultaneous Nitrogen And Phosphorus Removal From Wastewater By Coupling Denitrifying Phosphorus Removal And Anammox

The nitrogen and phosphorous removal from wastewater had becom e a research hotspot in recent years.Due to the low C/N ratio and carbon sources shortage of municipal wastewater in China,it is difficult to achieve the discharge standards by using the traditional biological nitrogen and phosphorus removal process.In view of the C/N characteristics of municipal wastewater in China and the technical difficulties of tradiational biological nitrogen and phsosphorus removal processes,this study proposed novel processes to enhance nitrogen removal by coupling denitrifying phosphorus removal and anaerobic ammonia oxidation（Anammox）.Denitrifying phosphorus accumulating organisms（DPAOs）were employed to remove phosphorus from wastewater by anaerobic phosphorus release and anoxic phosphorus uptake.During this process,the oxygen consumption and the production of excess sludge are low.Nitrogen could be removed by anammox bacteria without adding carbon source,which effectively enduced energy consumption and CO₂emissions.Moreover,the performance of nitrogen and phosphorus removal,microbial community structures,and removal mechanisms were investigated in partial denitrifying phosphorus removal coupled partial nitritation（PDPR-PN）and endogenous partial denitrification and phosphorus removal（EPDPR）respectively coupling with Anammox.This study aimed to provide theoretical basis and experimental data support for development and application of novel nitrogen and phosphorus removal process to treat low C/N wastewater,and the following results were obtained:（1）A sequencing batch reactor（SBR）was used and inoculated with ordinary activated sludge to treat municipal wastewater and simulated nitrite wastewater.The start-up and stable operation of PDPR-PN system was achieved through regulating influent NH₄⁺-N and COD concentrations and aerobic time.The experiment results showed that when the aerobic time was 150 minutes（DO concentration was 0.5-1.2 mg/L）and the influent concentrations of NH₄⁺-N and COD were about 58.7 mg/L and 237.5 mg/L respectively,partial denitrification-phosphorus removal in the system could be achieved in 16 days.The effluent concentrations of PO₄^3--P and COD were 3.1 mg/L and 49.9 mg/L,respectively,and the removal efficiencies of PO₄^3--P and COD were 65.7%and 68.9%,respectively.When the influent concentrations of NH₄⁺-N and COD increased from 49.9 mg/L and 220.0 mg/L to95.6 mg/L and 300.0 mg/L,respectively,nitritation in the system could be achieved in 38,and the partial denitrification-phosphorus removal performance was improved;The effluent concentrations of NO₂^--N and NH₄⁺-N were 15.6 mg/L and 24.1 mg/L respectively,with the effluent concentration of PO₄^3--P was below 0.5 mg/L.When the influent concentration of NH₄⁺-N was 110-120 mg/L and the aerobic time was 320 minutes,the conversion from nitritation to partial nitritation of the system could be achieved,and the partial denitrification-phosphorus removal performance was stable;The effluent concentrations of NO₂^--N and NH₄⁺-N were 23.4 mg/L and 20.1 mg/L respectively,and the average removal efficiency of PO₄^3--P was 91.4%.In the stable operation phase of the system,the effluent concentrations of NO₂^--N and NH₄⁺-N were 23.6 mg/L and 20.2 mg/L,respectively,which achieved a stable ratio of NO₂^--N/NH₄⁺-N（about 1.32）.Meanwhile,the removal efficiency of PO₄^3--P could achieve 100%,and the average removal efficiency of COD was 76.2%.Thus,the effluent of PDPR-PN system was achieved the subsequent influent conditions of Anammox for deep nitrogen removal.After 83 days of acclimation,the ammonia oxidizing bacteria（AOB）of PDPR-PN system increased from 3.12%to5.43%,which ensured the stable accumulation of nitrite（about 24.7 mg/L）.The increase of phosphorus accumulating organisms（PAOs）from 4.21%to 9.82%,which ensures the efficient removal of phosphorus and COD of the system.（2）A SBR was used and inoculated with ordinary activated sludge to treat simulated municipal wastewater and simulated nitrate wastewater.The start-up and stable operation of EPDPR system was achieved through regulating influent NO₃^--N concentrations of anoxic stage and anoxic time.The experiment results showed that,in the EPDPR system,the anaerobic（180 min）/aerobic（120 min）operation mode was adopted.After 42 days of acclimation,the system achieved the efficient removal of PO₄^3--P by released phosphorus in anaerobic time and absorbed phosphorus in aerobic time.The effluent concentration of PO₄^3--P and COD reached 0.45 mg/L and 52.13 mg/L,respectively,and the removal efficiencies of PO₄^3--P and COD reached 95%and 78.3%,respectively.Subsequently,the influent concentration of NO₃^--N in the anoxic stage was gradually increased（from 50 to120 mg/L）,and the anoxic time was prolonged（from 120 to 180 minutes）to achieve the start-up and optimization of the endogenous partial denitrification phosphorus removal in the system.The effluent concentration of PO₄^3--P,COD,NH₄⁺-N and NO₂^--N were 0,26.7,22.14,and 24.31 mg/L,respectively.The removal rate of PO₄^3--P was stable above 95%,and the removal efficiency of COD was about 86.3%.In the stable operation phase of the system,the ratio of NO₂^--N/NH₄⁺-N reached 1.32.Thus,the effluent of EPDPR system was achieved the subsequent influent conditions of Anammox for deep nitrogen removal.The dominant PAOs in the system were:Norank＿f＿＿caldilineaceae,Norank＿f＿＿comamonadaceae,Hyphomicrobium;The main GAOs were Candidatus＿Competibacter and Defluviicoccus,which provided sufficient endogenous carbon sources for endogenous partial denitrification phosphorus removal and endogenous denitrification in anoxic stage.（3）A upflow anaerobic sludge blanket（UASB）was inoculated with anammox sludge which had good performance of nitrogen removal.Subsequently,it was coupled with PDPR-PN and EPDPR systems,respectively,for investigating feasibility of deep nitrogen removal.The experimental results showed that,after 22 days,the effluent concentrations of COD,PO₄^3--P,NH₄⁺-N and NO₂^--N decreased to 35.13,0.16,0.37 and 0.21 mg/L,respectively,and the removal efficiency of TN was stabe at about 93.1%in PDPR-PN coupled with Anammox-UASB.Simultaneous treatment of low C/N municipal wastewater and nitrite wastewater has been achieved.After 23 days,the effluent concentrations of COD,PO₄^3--P,NH₄⁺-N and NO₂^--N decreased to 34.62,0.12,0.39 and 0.27 mg/L,respectively,and the TN removal efficiency was stable at about 85.1%in EDPPR coupled with Anammox-UASB.Simultaneous treatment of low C/N municipal wastewater and nitrate wastewater also has been achieved.