Advanced Nitrogen Removal Process And Optimized Control Strategy For Endogenous Partial Denitrification (EPD) Coupling With Anammox

Anaerobic ammonia oxidation（Anammox）,as a new type of autotrophic nitrogen removal process,is one of the key technologies to realize energy self-sufficiency or output of sewage plants.However,successful application of Anammox in mainstream municipal wastewater treatment is still hindered by the unstable acquisition of its reaction matrix nitrite and the process produces nitrate（～11%）,which also limits the further nitrogen removal improvement.This project intended to use endogenous partial denitrification（EPD,NO₃^--N→NO₂^--N）as a new approach for Anammox to obtain nitrite,and developed an innovative combined EPD+Anammox process（EPD-AMX）to achieve organic compound removal for advanced nitrogen removal.In addition,the long-term performance,optimal control,nitrogen removal mechanism and microbial community structure of the process were studied,which might provide theoretical basis and technical support for the popularization and application of Anammox process.The primary contents and innovations of this research work are as follows:（1）Study on the start-up of EPD process and efficient nitrate accumulation characteristicsIn order to establish successfully the EPD process,a single sequencing batch reactor（SBR）fed with synthetic high-strength nitrate and municipal wastewater and operated under anaerobic/aerobic（A/O）and anaerobic/anoxic/aerobic（A/A/O）modes successively.The start-up and long-term operation characteristics of EPD process with sodium acetate as carbon source（EPD_A）were mainly investigated,and the intracellular carbon source（polyhydroxyalkanoates,PHAs）conversion and nitrite accumulation characteristics in the system were analyzed.The results showed that:EPD_A process was established successfully by controlling the influent ratio of COD and PO₄^3--P,which promoted the selective growth of glycogen accumulating organisms（GAOs）,under A/O operation for 120 days.Intracellular carbon source storage rate remained above 85%.Efficient nitrite accumulation was achieved by increasing influent nitrate rate concentration under A/A/O operation.The nitrate-to-nitrite transformation ratio and specific nitrate reduction rate were 88.4%and7.41 mg N/（gVSS·h）,respectively,without remaining nitrate in the effluent to ensure the continuous provision of nitrite for Anammox.The EPD process was constructed and optimized to become the key pathway for Anammox to obtain nitrite.（2）Difference of intracellular carbon storage and nitrite accumulation characteristics in EPD process with discordant influent carbon sourcesThe EPD system with glucose as carbon source（EPD_G）was established under the same operation mode as EPD_A by inoculating activated sludge in another SBR for investigating the difference of intracellular carbon storage,nitrate reduction and nitrite accumulation characteristics and analyzing the mechanism of carbon and nitrogen transformation.The results showed that:higher intracellular carbon storage efficiency（89.2%）was observed in EPD_A than that in EPD_G（85.3%）;better performance of nitrate reduction and nitrite accumulation in EPD_A than that in EPD_G.The nitrate-to-nitrite transformation ratio and specific nitrate reduction rate in EPD_A were 88.4%and 7.41mg N/（gVSS·h）,while 82.5%and 6.88 mg N/（gVSS·h）in EPD_G.In addition,the fundamental reason for the different performance of EPD lies in the different composition of PHAs.the PHB/PHAs were 0.43 and 0.33 mol C/mol C,in EPD_A and EPD_G,respectively,while PHB was regarded as to be helpful for EPD to achieve high NTR.（3）Characteristics of nitrogen removal and microbial community in simultaneous treatment of municipal wastewater and nitrate wastewater by EPD-AMX processTwo-stage SBR+UASB reactor with sodium acetate and glucose as carbon sources was utilized to establish EPD-AMX processes（termed as EPD_A-AMX_A and EPD_G-AMX_G）to treat municipal wastewater and nitrate wastewater to achieve deep nitrogen removal.The long-term nitrogen removal performance of the system was investigated,and the microbial community structure was identified by high-throughput sequencing technology.The result showed that:the efficient nitrogen removal performance was both observed in EPD_A-AMX_A and EPD_G-AMX_Gand the total nitrogen（TN）removal rates were 88.7%and 91.3%,respectively;Anammox was the main pathway to reduce nitrogen,and the contribution percentage of nitrogen removal reached 87.8%and 89.4%respectively.The functional bacterium was also shifted to Defluviicoccus from Candidatus＿Competiacter in two systems.at different phases.The relative abundance of EPD_G was lower than that of EPD_A（30.6%>25.8%）;Candidatus＿Kuenenia was detected in Anammox process,accounted for16.58%in AMX_A and only 2.3%in AMA_G,which explained the difference of nitrogen removal performance from the microscopic point of view.（4）Investigation on a novel N-SBBR+EPD-AMX process based on anammox,endogenous partial-denitrification and completed nitrificationIn order to supply nitrate,a novel biofilm process of N-SBBR+EPD-AMX was established,which was fed with synthetic municipal wastewater.The nitrogen and phosphorus removal performance of the process was investigated,and the microbial community structure was identified by high-throughput sequencing.The results showed that:N-SBBR could supply stable nitrate for EPD-SBBR when municipal sewage was treated.EPD-SBBR was operated for nitrite which was necessary for following Anammox with NTR lasting to 87%during long-term operation;Through the combination of N-SBBR and EPD-SBBR,the suitable ratio of NO₂^--N and NH₄⁺-N for Anammox process could be obtained,which was about 1.05.TN removal efficiency of 93.9%and a TP removal efficiency of 94.2%with the concentrations of effluent TN,NH₄⁺-N and PO₄^3--P being3.6 mg/L,2.1 mg/L and 0.3 mg/L,respectively.were achieved this process.High-throughput sequencing showed that Anammox（Candidatus＿Kuenenia,8.4%）、GAOs（Defluviicoccus,34.4%）were functional microorganism in Anammox and EPD,respectively,potentially responsible for nitrite accumulation and nitrogen removal.