Experimental Study On Treatment Of Sludge Digestive Solution By Partial Nitrification Coupled With Anaerobic Ammonia Oxidation

Anaerobic digestion technology has been widely used in sludge treatment due to its green and low-carbon characteristics.However,this process will produce a certain amount of sludge digestion liquid,which contains high concentration of ammonia nitrogen and a large amount of refractory organic matter.It is a typical type of low carbon nitrogen ratio（C/N）high ammonia nitrogen wastewater.When using traditional biological denitrification methods to treat it,there will be problems such as insufficient carbon source,high energy consumption,and poor efficiency.The partial nitrification anaerobic ammonia oxidation（PN-ANAMMOX）process is a cost-effective autotroph nitrogen removal process,which has a low demand for dissolved oxygen and external carbon sources and a low sludge yield.It has a good prospect in the treatment of high ammonia nitrogen and low C/N wastewater.In this study,nitrification and anaerobic ammonia oxidation were first started in a sequencing batch reactor（SBR）and an upflow anaerobic sludge bed（UASB）,respectively,and the effects of key factors such as organic carbon sources on the nitrogen removal efficiency of these two reactors were explored to seek the optimal control parameters.Then,the two reactors were coupled to explore the treatment effect and operational stability of the partial nitrification anaerobic ammonia oxidation coupled process for treating simulated low C/N wastewater and sludge digestion liquid.During the experiment,high-throughput sequencing,scanning electron microscopy,and three-dimensional fluorescence were used to investigate the changes in sludge morphology,microbial community distribution,and fluorescence components in the effluent.The main research contents and conclusions are as follows:（1）The aerobic sludge was inoculated in the SBR reactor,and the nitrosation process was started by continuous low oxygen aeration.After 65 days of successful startup,the average removal rate of NH₄⁺-N and the average accumulation rate of NO₂^--N reached85.74%and 88.78%respectively after stabilization.The relative abundance of Nitrosomonas increased from 1.99%to 44.60%,becoming the dominant genus.Properly increasing the influent NH₄⁺-N concentration can improve the operational efficiency of the nitrosation reactor.When the influent NH₄⁺-N concentration increases from 150 mg/L to250 mg/L,the NH₄⁺-N removal load of the reactor increases from 0.234 kg/（m³·d）to 0.319kg/（m³·d）,but when the influent NH₄⁺-N concentration increases to 300 mg/L,the NH₄⁺-N removal load decreases to 0.248 kg/（m³·d）.（2）Gradually increase the influent COD concentration of the nitrosation reactor with a concentration gradient of 50 mg/L.When the COD≤150 mg/L,the nitrosation reaction is less affected by organic matter,and ideal NH₄⁺-N removal effect and NO₂^--N accumulation effect can be obtained.However,when the COD>150 mg/L,the inhibition effect of organic matter on the nitrosation process is greatly enhanced,leading to a significant decrease in the NH₄⁺-N removal rate and the NO₂^--N concentration in the effluent.（3）When influent NH₄⁺-N=200 mg/L,COD=150 mg/L,and the operation mode is"inlet water for 30 min→aeration for 4 h→sedimentation for 1 h→drainage for 30 min→idle for 2 h",the average value of effluent NO₂^--N/NH₄⁺-N of nitrosation reactor is 1.36,basically meeting the requirements of anaerobic ammonium oxidation.When the influent NH₄⁺-N=250 mg/L,COD=200 mg/L,the original operating conditions were no longer able to meet the requirements of the effluent.After adjusting the operating mode to"inlet water for 15 min→aeration for 6 h→sedimentation for 1 h→drainage for 15 min→idle for 30min",the average value of NO₂^--N/NH₄⁺-N in the effluent was 1.35,which can also meet the requirements of anaerobic ammonia oxidation.（4）Using a UASB reactor,the anaerobic sludge from the anaerobic tank and the aerobic sludge from the oxidation ditch were mixed in a certain proportion as inoculating sludge.The anaerobic ammonia oxidation reaction was initiated at a temperature of（32±1）℃,p H of 7.3～7.8,HRT of 24 hours,and without deoxygenation of the influent water for 77 days.The average removal rates of NH₄⁺-N and NO₂^--N are 97.00%and98.58%,respectively.The dominant genus of bacteria in the reactor is Candidatus Brocadia,with a relative abundance of up to 38.78%.After the successful start-up of the reactor,the TN volumetric load of the reactor was increased by increasing the influent substrate concentration.When the TN load was 0.469 kg/（m³·d）,the TN removal rate reached83.34%,achieving stable operation under high load.（5）By exploring the effects of factors such as temperature,p H,HRT,type and concentration of organic carbon sources on the nitrogen removal efficiency of anaerobic ammonia oxidation reaction,it is concluded that the optimal operating conditions are:temperature at 30～35℃,p H at 7.5～8.0,and HRT=12 h.The degree of difficulty for different types of organic matter to be utilized by denitrification bacteria in the system ranges from easy to difficult:glucose>sucrose>starch;When glucose is used as the organic carbon source,controlling the COD concentration to 120 mg/L,and sucrose or starch is used as the organic carbon source,controlling the COD concentration to 160 mg/L can fully exert the synergistic effect of anaerobic ammonia oxidation and denitrification to achieve the maximum nitrogen removal effect.During the addition of organic carbon sources,the fluorescent components of the reactor effluent are mainly protein-like,fulvic acid-like,and humic-acid like,among which protein-like will significantly increase with the increase in the concentration of organic carbon sources.（6）After commissioning,an effective match can be made between the nitrosation reactor and the anaerobic ammonia oxidation reactor.When treating simulated wastewater,the treatment effect of the coupling system is efficient and stable,with the average removal rates of NH₄⁺-N,TN,and COD reaching 98.92%,90.10%,and 90.05%,respectively.The operation efficiency and stability of the combined process in treating sludge digestion solution slightly decreased compared to that of treating simulated wastewater,but it still achieved a good nitrogen removal effect.The average removal rates of NH₄⁺-N,TN,and COD were 95.61%,82.18%,and 77.04%,respectively.When the combined process is used to treat simulated wastewater,the main fluorescent component in the effluent is protein-like,while when the combined process is used to treat sludge digestion liquid,the main fluorescent component in the effluent is fulvic acid-like.Figure[46]table[14]reference[143]...