The Performance And Mechanism Of PN-ANAMMOX Coupling Denitrification In Constructed Rapid Infiltration System

Constructed rapid infiltration?CRI?is a novel wastewater eco-treatment technology developed from traditional soil infiltration system,with such advantages as low construction cost,simple operation and low consumption.It has significant advantages and important popularization value in treating domestic sewage from small and medium-sized towns,rural decentralized sewage,polluted surface water and remote area sewage that has not yet been covered by municipal pipe network.However,the application of CRI system is limited for its low TN removal efficiency.Partial nitrification?PN?and anaerobic ammonia oxidation?ANAMMOX?provides a new way to solve the problem of carbon source shortage in traditional biological denitrification.Previous studies have mainly focused on the achievement of PN and ANAMMOX in such activated sludge systems as SBR,MBR,ABR or UASB,which were mostly suitable for high-ammonia wastewater treatment.However,few studies on the performance and mechanism of PN-ANAMMOX coupling denitrification in CRI system have been reported.In order to provides a new method for denitrification of high efficiency and low consumption in CRI system,the start-up characteristics and stability control methods of PN and ANAMMOX in CRI system were discussed,the kinetic models were constructed,the coupling denitrification performance of PN-ANAMMOX were investigated,the microbial community structures in the PN and ANAMMOX reactors were analyzed,and the mechanism of PN-ANAMMOX coupling denitrification was revealed.The main results are as follows:?1?The regularity of nitrogen transformation and activity changes of AOB and NOB under different starvation time and pH values were investigated.The optimum starvation time and pH value for partial nitrification were determined.After 15 days starvation,NH₄⁺-N removal rate and NO₂^--N accumulation rate in CRI system were stable at about60%and 65%,respectively.When adjusting the influent pH value to 8.7,the activity of NOB was further inhibited and the accumulation of NO₂^--N increased.The NH₄⁺-N removal rate and NO₂^--N accumulation rate were stable at 60%and 90%,respectively.The effluent NO₂^--N/NH₄⁺-N ratio was 1.21¹.33.Partial nitrification in CRI system was achieved successfully based on the synergistic regulation of starvation and pH.On this basis,the effluent water quality could meet the requirement of the following ANAMMOX process when the CRI system was operated at the influent pH value of 7.2⁷.8,wet-to-dry ratio of1:3¹:4,hydraulic loading of 1.0 m·d^-1,temperature of 20³0°C,NH₄⁺-N concentration of45⁵0 mg·L^-11 and COD concentration of 100¹50 mg·L^-1.?2?Through the investigation of denitrification characteristics in CRI system after inoculating different sources of activated sludge,a fast start-up method for ANAMMOX in CRI system was proposed based on the inoculation of sludge mixed by aerobic nitrification sludge and heterotrophic denitrification sludge according to volume ratio of 1:2.After four periods,namely adaptation period?1¹5 d?,activity retardation period?16³5 d?,activity improvement period?36⁸7 d?and activity stabilization period?88⁹2 d?,the ANAMMOX process was successfully achieved.The VS,Heme,EPS and SAA in activity stabilization period were 113.2±3.9 mg·g^-1,1.17±0.13?mol·g VS^-1,138.28±3.66 mg·g VS^-11 and95.96±3.79 mgN·g VS^-1·d^-1,respectively.The average TN removal rate was 91.5%and volumetric nitrogen removal rate was 0.0827 kgN·?m³·d?^-1.On this basis,the TN removal rate of ANAMMOX could remain at above 90%steadily when the CRI system was operated at the influent NO₂^--N/NH₄⁺-N ratio of 1.3,hydraulic loading of 1.0 m·d^-1,pH value of7.0⁸.2,DO concentration of 0.5³.0 mg·L^-11 and temperature of 20³5°C.?3?Based on the investigation of nitrogen transformation rule along the path,kinetic models of PN and ANAMMOX under different influent substrate concentrations and hydraulic loadings were constructed.For PN reaction,the kinetic models of NH₄⁺-N removal under NH₄⁺-N concentration of 10.2⁶1.3 mg·L^-11 and hydraulic load of 0.2¹.2m·d^-11 were S_h/S₀=exp(-1.0033S₀^-1.1337h)and S_h/S₀=exp(-0.0127q^-0.8991h),respectively.For ANAMMOX reaction,when the influent concentration ratio of NO₂^--N and NH₄⁺-N was 1.3,the kinetic models of NH₄⁺-N and NO₂^--N removal under NH₄⁺-N concentration of 5²5mg·L^-11 were S_h/S₀=exp(-0.6244S₀^-0.714h)and S_h/S₀=exp(-0.7633S₀^-0.7178h),respectively;the kinetic models of NH₄⁺-N and NO₂^--N removal under hydraulic loading of 0.4¹.1 m·d^-1were S_h/S₀=exp(-0.07302q^-0.8019h)and S_h/S₀=exp(-0.07614q^-0.7104h),respectively.The calculated values of the models were in good agreement with the experimental measured values,indicating that the kinetic models were of relatively high accuracy.?4?The PN-ANAMMOX coupling process showed high-efficient and stable denitrification performance under stable influent conditions.Its average COD,NH₄⁺-N and TN removal rates were higher than 90%,98%and 90%,respectively.PN reactor played a leading role in the conversion of NH₄⁺-N in sewage,and its NH₄⁺-N removal rate was 60.23±1.381%.ANAMMOX reactor played a leading role in the removal of TN in sewage,and its TN removal rate was 84.56±3.477%.The average TN removal rate decreased to62.11%when the influent NH₄⁺-N concentration decreased to 27³3 mg·L^-1.The average TN removal rate decreased to 81.94%when the influent hydraulic loading decreased to 0.8m·d^-1.The ratio of?NO₂^--N/?NH₄⁺-N dropped to about 1.3 and the average TN removal rate recovered to more than 90%after adjusting the PN reactor height to 60 and 45 cm,respectively.The coupling denitrification of PN-ANAMMOX process could be effectively realized under the condition of water quality or quantity fluctuation via appropriate regulation.?5?16S rRNA high-throughput sequencing technology was used to analyze the OTU abundance,microbial community type,Alpha diversity and Beta diversity of stable-operated PN and ANAMMOX reactors,and the mechanism of PN and ANAMMOX in CRI system was revealed.Three kinds of ammonia oxidizing bacteria or archaea?Nitrosomonas,Nitrosovibrio,Nitrosopumilus?and one kind of nitrite oxidizing bacteria?Nitrospira?were detected in five filter layers of PN reactor.Among them,the relative abundance of Nitrosomonas was 5.33%⁷.25%,which occupied a dominant position in total microbial community.While the relative proportion of Nitrospira was only 2.53%⁶.34%of the total of Nitrosomonas,Nitrosovibrio and Nitrosopumilus.NH₄⁺-N could be successfully oxidized to NO₂^--N,while the oxidation of NO₂^--N to NO₃^--N was hindered,resulting in the occurrence of partial nitrification.Two kinds of anammox bacteria?Candidatus Brocadia,Candidatus Kuenenia?were detected in five filter layers of ANAMMOX reactor.Among them,the relative abundance of Candidatus Brocadia was 1.25%⁵.33%,and it was the key functional genus for simultaneous removal of NO₂^--N and NH₄⁺-N in ANAMMOX process.In addition,some other types of denitrification bacteria,such as Nitrosomonas,Nitrospira,Dechloromonas,Bdellovibrio,Thauera and Flavobacterium were detected in ANAMMOX reactor.They coexisted in the ANAMMOX reactor and affected the denitrification performance together.