| Currently,the activated sludge process is the most widely used technology for wastewater treatment.However,it has been restrained by the sludge bulking since the process was proposed.So,researchers from all over the world have conducted a great deal of work from the aspects of water quality,environmental factors and operational conditions,and have achieved a lot.As the microorganisms are the main functional role of the process,however,there are few reports on microbiological metabolism or predominant species and their correlations with sludge settling ability.In this study,the evolution of microbial community structure of sludge was tracked,and the composition of microbial metabolites was detected.The internal factors affecting the sludge settling ability were investigated under different operational conditions.The aim of the study is to enhance the knowledge of sludge settlement / bulking.The main results of the study are as follows:(1)For the same influent fed and sludge inoculated the non-filamentous bulking and filamentous bulking respectively in the two reactors operated under different conditions were induced.The carbon source of the influent were sodium acetate and soluble starch(ratio of COD contributed was 3:2).Non-filamentous sludge bulking took place in the No.1 reactor which was operated at low level of dissolved oxygen and higher of organic loading.However,Type 0914 filamentous bacteria proliferated in the No.2 reactor operated at that of normal level of dissolved oxygen and organic loading led to filamentous sludge bulking finally.The results of 16 S rDNA high throughput sequencing analysis showed that the higher organic loading and lower dissolved oxygen stimulated the growth of Bradyrhizobiu in the No.1 reactor.Increase of extracellular polysaccharides in extracellular mucus secreted by Bradyrhizobiu was the main reason for non-filamentous sludge bulking.The abundance of Chloroflexi and Saprospiraceae were 13.13% and 10.14% in the No.2 reactor,respectively.It is believed that the soluble carbon source is main reason for the overgrowth of both types of bacteria and result in the subsequent filamentous sludge bulking.(2)In the three processes of AAO nitrogen and phosphorus removal(process I),AO nitrification-denitrification(process ?)and aerobic carbon removal(process ?I),the settling ability of activated sludge was different.The best settling ability was found in process I,followed by process ?I and then process ?.The types of dominant bacteria and microbial community structure of the system changed significantly.The relative amount of Thiothrix which was the dominant bacteria affected the sludge settling ability.The abundance of Thiothrix was only 0.08% and 1.51% in inoculation sludge and process I,increased to 9.41% in the process ? and decreased to 4.29% in the process ?I.The anaerobic zone of process I had an inhibitory effect on the growth of the bacterium,but the anoxic zone of process ? stimulated its growth.The microbial population diversity among the three processes was different.The highest was in the process I,and followed by process ? and then process ?I.The introduction of anoxic and anaerobic zone led to increase of environment complexity and function of system,and the increase of microbial community diversity.The change of microbial community structure had a significant effect on the composition of EPS,which might improve the settling ability of sludge or aggravate the bulking.The sludge settling ability was positively correlated with the ratio of protein and polysaccharide of loosely bound EPS.As the functions of the reactor changed,the types of filamentous bacteria varied significantly.The dominant filamentous bacteria of inoculation sludge and of the sludge in the process I,? and ?I were Type0092,Sphaerotilus natans,Thiothrix spp.and Nostocoida limicola ?,respectively. |
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