Preparation Of Aerobic Denitrification Inoculum For Domestic Sewage Treatment

Biological denitrification is regarded as the most promising technology for wastewater denitrification due to its advantages of high efficiency,environmental friendliness,and economy.Compared to autotrophs,aerobic denitrifying bacteria have a short generation cycle,fast growth rate,and high denitrification efficiency,showing good prospects for application in enhanced biological nitrogen removal from wastewater.However,most aerobic denitrifying bacteria studies focus on the actual denitrification effect.There is still a need for systematic and in-depth research on improving their operational stability and reducing application costs.Based on this,this study was conducted to evaluate the effect of nitrogen removal from simulated domestic wastewater and MBR effluent by using the strains stored by the group,to obtain a formulation of aerobic denitrification inoculum and to optimize the mixed fermentation process conditions of the resulting inoculum to increase the concentration of the bacteria and thus reduce the preparation cost.Further,the resulting aerobic denitrification inoculum was injected into the aerobic tank of the A/O-MBR to study the effect of enhanced biological nitrogen removal and the microbial community succession in the reactor.The preliminary analysis of the denitrification pathways of the essential aerobic denitrifying bacteria,combined with nitrogen balance analysis and changes in the enzymatic activity of key denitrification enzymes,is intended to enrich the knowledge of aerobic denitrifying bacteria nitrogen removal and provide technological support for the development and application of aerobic denitrification inoculum,which is of great academic significance and practical value.The main research contents and results are as follows:（1）Evaluation of the denitrification effect for aerobic denitrifying bacteria.The nitrogen removal capacity of aerobic denitrifying strains B301,B308,B601,P6,X01,and Y11 were limited by C/N.In systems with a relatively low C/N,strains could grow slower and not perform nitrogen degradation.Strains could carry out normal metabolism and effective nitrogen removal in a suitable carbon source system.The six aerobic denitrifying strains had no competitive antagonism with each other and could be combined into the aerobic denitrification inoculum for subsequent tests.（2）Optimization of mixed fermentation conditions for aerobic denitrification inoculum.The components and process conditions of the fermentation medium were optimized by shaking bed tests,in which the nitrogen source was 2.3 g/L NH₄HCO₃,the carbon source was 20 g/L glucose,the metal ion was 0.1 g/L Fe³⁺,the fermentation p H was 7.5,the incubation temperature was 40℃,and the loading volume was 100 m L.The 3 L fermenter experiment results showed that the maximum OD₆₀₀ obtained was 4.13 at 9 h,24 h,and 48 h,which was significantly better than the control group without replenishment（2.31）,and the highest viable count of 39 billion CFU/m L at 96 h.The fermentation broth’s dry weight and cell yield were 12.73 g/L and 0.29g/g,respectively.（3）Study on aerobic denitrification inoculum enhanced nitrogen removal in domestic wastewater.The total nitrogen（TN）removal rate of the experimental group with the aerobic denitrification inoculum was 60.34%,17.55%higher than that of the control group,and the effluent TN concentration was 12.75±2.72 mg/L,in line with China’s Standard for the Discharge of Pollutants from Urban Wastewater Treatment Plants（GB 18918-2002）.With the combination of microbial community analysis,it was clear that the addition of aerobic denitrification inoculum not only improved the microbial community structure,increasing its abundance and diversity,but also helped to promote the enrichment of dominant genera in the community,thus enhancing the nitrogen removal performance of the A/O-MBR system.（4）Preliminary investigation on the physiological,biochemical,and denitrification pathways of aerobic denitrifying bacteria strain B301.The results show that strain B301removed nitrogen via heterotrophic nitrification and aerobic denitrification（HN-AD）without nitrite accumulation.It exhibited the optimal nitrogen removal efficiency under 30℃,citrate as the carbon source and C/N ratio of 15.The maximal rates of ammonium,nitrate and nitrite achieved 2.11 mg NH₄⁺-N/（L·h）,1.62 mg NO₃^--N/（L·h）and 1.41 mg NO₂^--N/（L·h）,respectively,when ammonium,nitrate and nitrite were employed as the only nitrogen source under aerobic conditions.Ammonium nitrogen was preferentially consumed via HN-AD in the coexistence of three nitrogen species.Nitrogen balance analysis suggested that 83.25%of ammonium was converted to gaseous nitrogen.The HD-AD pathway catalyzed by strain B301 followed NH₄⁺→NH₂OH→NO₂^-→NO₃^-→NO₂^-→N₂ supported by the results of key denitrifying enzymatic activities.This strain exhibited excellent nitrogen removal ability and had great potential in disposing of nitrogenous wastewater.