Regulation Of Single-stage Autotrophic Denitrification Treating Domestic Sewage And Response Mechanism At Low Temperature

Single-stage autotrophic denitrification,based on nitrification-anammox,has become a research hotspot in biological denitrification field.Current research and application of this technology are mainly concentrated in the high temperature,high ammonia nitrogen wastewater treatment,and research on urban sewage denitrification process is still very limited.This paper targets at the stable growth of nitrosation and anaerobic ammonia oxidation in a single-stage autotrophic denitrification system,inoculats with granular sludge and flocculent sludge as mixed carrier,for startup and running stability of low concentration level condition autotrophic denitrification process.The objective of this project is to construct the cause and effect relationship among temperature conditions,morphological characteristics,biochemical reactivity,and microbial community structure and nitrogen removal efficiency,to reveal influential mechanism of the impacts of low temperature on the competition among main function bacteria.The result will guide the application of autotrophic nitrogen removal process to municipal sewage treatment at low temperature.Thesis mainly draws the following conclusions:?1?Combined with two models of influent patterns,the rapid and stable startup of single-stage autotrophic denitrification can be realized,and the denitrification efficiency remains steady at around 90%.In the building of SBR single-stage autotrophic denitrification system with low concentration,conclusions are:with the average DO concentration remains 0.25-0.30mg/L,the TN removal rate of SBR single-stage autotrophic denitrification system can reach 95%.?2?At the early stage of 20?and 15?,the performance and metabolic of single-stage autotrophic denitrification system declined obviously.At 217-230d,initial atage of 20?,the activity of functional bacteria was significantly decreased for not adapting to the low temperature environment,and the ammonia nitrogen removal rate was 56%on average,the nitrate content accumulation due to the higher activity of NOB.At 231-247d,system had obvious adaptation to low temperature,nitrogen removal efficiency stabled at around 92%.At 249d when the temperature was decreased to 15?,the function bacterias of system were inhibited by a certain degree,with ammonia accumulated in large quantities,and NO₃^--N concentration increased obviously,and NOB can accommodate low temperature environment more better than AOB and AAOB.?3?After temperature decreased to 20?,the AOB and AAOB activity were reduced by 19.1%and 11.9%.Then denitrification performance of system began to rise slowly,AMO and HDH activity tended a rising trend at 235d.The activity of two key enzymes changed in a similar way at 15?.As the extension of time under low temperature,denitrification performance and key enzyme activity of the autotrophic denitrification system had a certain degree of recovery,compared with the corresponding activity level at 30?.Low temperature conditions of autotrophic denitrification system has inhibition to key enzyme activity,and the inhibition degree of HDH was greater than the AMO,characterized by AAOB more vulnerabled to the effects of low temperature than AOB,which affected single-stage autotrophic denitrification system as the denitrification performance and stability during the operation process.?4?Compared to the initial stage,the reaction rate and activity of autotrophic denitrification system increased significantly,and got an effective inhibitory of NOB activity.After temperature decreased to 20?,the reaction activity of nitrosation,anaerobic ammonia oxidation and autotrophic denitrification was reduced by 25.6%,18.7%and 31.2%,respectively,and reduced by 29.6%,22.8%and 47.9%,respectively,under 15?.The results showed the process of lower temperature decreased the denitrification activity of the system by influencing the different reaction activity and the reaction balance,and compared with AAOB,NOB reactivity degreed lower.?5?The AAOB was more sensitive to the adverse effects of low temperature,which affects the balance of two types of reaction process in the system and relatively activity of the single stage,eventually reduced the stability of the system;Through superfine electron microscopy?sem?to the cells of different low temperature period of anaerobic ammonia oxidation,we found that as the system temperature decreased gradually,the cell membrane structure was blured and damaged in a certain degree,at the same time increase in the number of individual cells exist alone,and the distribution density of the bacteria in cooling phase has a tendency to reduce,single cells exist after cooling and blank areas significantly increased,and the cells arranged between desultorily,distribution is irregular;Vision can be observed and loosely arranged inside the bacteria,some bacterial cells appear even autolyzed or death phenomenon.?6?Relative hydrophobicity of flocculent sludge and particles sludge under different temperatures were different,and the influence of temperature on relatively hydrophobic was obvious.At 32?,RH of flocculent and granular sludge reached42%and 42%respectively,sludge settling performance was good,with the particle dense;after running a month under 20?,with RH of granular and flocculent sludge decreased to 29%and 63%,respectively,with hydrophobic extracellular protein decreased relatively,PS/PN ratio increased,and the sludge sedimentation performance was poor;At 15?,RH turned out a rising trend under the same condition.According to these,we speculated that cells could change the surface properties by changing the relative content of extracellular polymer,in turn,to offset parts of the negative impact under low temperature.