| Activated sludge method is the most common treatment technology of urban sewage.In the severe ecological environment,the standard and energy saving have become the focus of the operation of the sewage plant.A large number of academic research and engineering practice have shown that low dissolved oxygen?DO?operation mode can effectively reduce the energy consumption of sewage treatment,but low-do operation mode can easily induce the filamentous bulking of sludge.The existing research shows that the sludge in the micro-bulking state,using the characteristics of the filamentous bacteria with large surface area,can obtain better effluent effect by catching the pollutants in the sewage.However,the sludge bulking is difficult to control,and the bulking sludge in the uncontrolled state is easy to be lost,and the long running time will make the system completely collapse and difficult to recover.Therefore,lower the DO filamentous bulking mechanism,can run for the low dissolved oxygen mode or micro bulking for the stable operation of the sewage treatment control technology to provide theoretical basis and technical support,which is of great significance.In this study SBR process was used,low DO running mode,with different degree of bulking activated sludge as the object,based on the study of the SBR system pollutants removal efficiency,test the degree of bulking of active sludge EPS components,surface properties and microscopic structure,microbial population structure and analyze the variation characteristics,and reveal the filamentous bacteria and zoogloea bacteria between the surface of the mechanism,providing theoretical basis for construction of filamentous fungi microscopic mechanism of expansion.The main contents include:?1?The effect of the bulking of activated sludge on the removal of water treatment system and the properties of sludge;?2?The influence of the bulking of activated sludge filamentous bacteria on EPS component and surface characteristics of sludge;?3?Analysis of microorganism population structure of filamentous bacteria.The results show that:?1?Under the condition of low dissolved oxygen,the filamentous bacteria of activated sludge expanded,and the COD was rapidly increased in the stage of sludge microexpansion,and the removal rate dropped rapidly to about 60%.The nitrification activity decreased sharply to about 55%.The difference between phosphorus removal efficiency and normal dissolved oxygen?DO=2 mg/L?was not significant,and the average efficiency of phosphorus removal was about 85%.At the stage of sludge expansion,the COD concentration reached 300 mg/L,and the removal rate was reduced to about 40%.The removal rate of ammonia nitrogen was low to 38%,which seriously affected the effluent effect.Phosphorus removal efficiency gradually decreased to 60%.?2?In the study of activated sludge filamentous fungi expansion effect components of sludge EPS,EPS components of polysaccharide and protein/protein content in proportion with the increase of SVI value and gradually reduce,combined with relevant literature that EPS changes of protein components are the key factors influencing the bacteria between gathered,is difficult to form stable expansion activated sludge flocs.The ir spectra of EPS amide I region(1700-1600-cm-1)points of analysis,the results show that with the activated sludge filamentous fungi expansion process,EPS of random coil protein secondary structure of the relative content increase,the alpha helix/?beta fold+random coil?is the ratio of the overall increase.This not only makes the loose structure protein content reduced and EPS of internal have hydrophobic functional group also difficult to outward show,lowered the bacterial surface hydrophobicity and gathered the difficulty between the bacteria.This is another reason for the expansion of the activated sludge filaments.?3?Activated sludge filamentous bacteria influence on the characteristic on the surface of the sludge expansion,EPS before and after the extraction of Zeta potential,it found that negative charge on the surface of a declining trend,show that the expansion process of filamentous bacteria in causing bacteria the change of surface charge,charge drops increased bacterial aggregation difficulty.The decrease of protein content is the main reason for the decrease of Zeta potential.The hydrophobicity of EPS before and after extraction also showed a decreasing trend with the increase of the expansion degree.It is concluded that the decrease of protein content and the decrease of hydrophobic functional groups is one of the reasons for the decrease of hydrophobicity.The change of protein secondary structure leads to the difficulty in releasing hydrophobic functional groups.?4?In the process of activated sludge expansion,the dominant bacteria gate is Proteobacteria,and the dominant bacteria is Thiothrix,and the relative abundance of both increases with the increase of SVI.The dominant filamentous bacteria of activated sludge filamentous bacteria under the condition of low dissolved oxygen is the genus of thiothrix in benazotiaceae.On the one hand,the non-filamentous bacteria were reduced in relative abundance,and on the other hand,non-filamentous bacteria were difficult to adhere to the filamentous bacteria,which ultimately resulted in the failure to form the active sludge flos with stable structure. |
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