| Sludge bulking problem has always been one of the difficult problems in domestic and foreign sewage treatment plants.Although a lot of related research has been done,the fundamental method to solve this problem has not been found yet.Most of the sewage treatment plant by changing the inlet water quality and adjust the factors such as operation mode to optimize the sewage treatment effect,the water quality characteristic of this kind of wastewater in the actual operation,seasonal changes in temperature and in the operation of low dissolved oxygen,and easy to induce the occurrence of sludge bulking,increased the difficulty of the sludge bulking control.With the emergence of new methods,new technologies and new equipment,a large number of studies have systematically summarized the physiological and ecological characteristics of filamentous bacteria in sludge bulking.However,due to the fact that pure culture technology is still difficult to achieve in the laboratory,the existing research results are not comprehensive and in-depth.In recent years,with the development and application of molecular biology technology,the research on the overall diversity of microbial flora and the competition between microorganisms in the swelling sludge system has become more and more abundant,which provides the possibility for the further control of the sludge bulking.This paper takes expanded sludge as the research object,starting with three typical causes of filamentous bacteria sludge bulking caused by water quality conditions,operating conditions and external environment,in the process of filamentous bacteria sludge bulking,With the help of High throughput sequencing technology,the diversity changes of different taxonomic levels,different microbial flora and microbial genus,the diversity changes of microbial flora with different functions and their classification under the whole microbial flora,In addition,Quantitative real-time PCR（q PCR）was used to investigate the abundance change and correlation of dominant filamentous bacteria and functional bacteria in expanded sludge under different conditions.The specific research contents and results are as follows:（1）The influence of filamentous bacterial expansion induced by using long chain fatty acid-starch mixed carbon source as influent carbon source on sludge settling performance and pollutant removal rate.Using traditional nitrification and denitrification process under atmospheric pressure,with oleic acid-starch mixture and stearic acid-starch mixture for carbon source induced by filamentous bacteria sludge expansion,the water of different concentration of long chain fatty acids on sludge sedimentation performance has a great influence,when the content is 20%,SVI value increases gradually,COD and TN removal rate was 80%and 70%,When the content increases to 40%,the SVI value increases rapidly,and the removal rates of COD and TN decrease.After the removal of long-chain fatty acids in the influent water,the SVI and pollutant removal rates of the two reactors are recovered.During the expansion process,the SVI1 value is always greater than SVI2,and the pollutant removal rate in SBR1 is also greater than that in SBR2.FISH confirmed that the dominant filamentous bacteria were all microfilaments,indicating that long-chain fatty acids were exclusive carbon sources of microfilaments,which could still maintain a good treatment effect after the malignant expansion of activated sludge..（2）Effect of low temperature and low dissolved oxygen on sludge settling performance and pollutant removal rate with 20%oleic acid-starch mixture as carbon source.Under the condition of low temperature,the lower the temperature of SVI value the faster,the greater the increase,resulting in decreased the removal rate of pollutants in wastewater,and removal rate of pollutants with volatile of sludge bulking is not s Tab,when temperature 16℃,pollutant removal rate has remained at the normal level,COD removal rate of over 80%,TN removal rate over 70%,This indicates that the functional bacteria in this experiment still maintain normal growth and metabolism at low temperature 16℃.Compared under the condition of low dissolved oxygen,and the conditions of low temperature,low dissolved oxygen on pollutants removal rate is larger,the influence of COD and TN removal rate reduced to 70%and 50%respectively,because the microorganisms need oxygen when using long chain fatty acids,and low dissolved oxygen can cause microorganism on the substrate using incomplete,thus causing sludge bulking caused a series of problems.（3）Changes of microbial community structure in expanded sludge with long chain fatty acid-starch mixture as carbon source at low temperature or low dissolved oxygen.Proteobacteria（Proteobacteria）accounted for the largest proportion in all the sludge samples.The abundance of Proteobacteria increased at different ranges in the three experiments under different conditions.The greatest increase was found in the low temperature operation condition,which increased from 48.63%to76.85%at 13℃.It indicated that low temperature was more conducive to the metabolic growth of this phylum.The Proteobacteria of Proteobacteria showed an increase in its relative abundance compared with seed mud under the experimental conditions of low temperature and low dissolved oxygen,indicating that it had strong competitive ability under the conditions of low temperature and low dissolved oxygen,and guaranteed a good total nitrogen removal effect after sludge expansion.（4）Effect of long chain fatty acid-starch mixture as carbon source and low temperature or low dissolved oxygen on microbial species in expanded sludge.Five filamentous genera,M.parvicella,Thiothrix,Haliscomenobacter,Tetrasphaera,and Tessaracoccus,were found in the nine mud samples.In experiments under different conditions,M.parvicella was the first dominant filamentous bacterium with the largest proportion of relative abundance,and Thiothrix was the second dominant filamentous bacterium at the genus level.Both of them were more sui Tab for growth and proliferation at low temperature and low dissolved oxygen.（5）The competitive relationship between microfilaments and functional bacteria with long chain fatty acid-starch mixture as carbon source and low temperature or low dissolved oxygen.In the process of activated sludge bulkup,when 20%oleic acid-starch mixture was used as carbon source,the abundance of microfilaments reached the maximum of（8.74±0.51）×10~8gene copies/g MLVSS,indicating that this condition was more conducive to the growth and proliferation of microfilaments.When stearic acid-starch mixture was used as carbon source,AOB abundance of nitrifying bacteria was the most affected,and AOB abundance was reduced by 63%,which had a negative effect on sludge denitrification effect.At low temperature and low dissolved oxygen,the abundance of microfilaments increased gradually,and at low temperature was positively correlated with the abundance of functional bacteria,while at low dissolved oxygen,the abundance of microfilaments was positively correlated with the nitrifying flora of functional bacteria. |
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