Effect Mechanism Of Composite Substrates On The Stability Process Of Granule-based Enhanced Biological Puosphorus Removal System

In recent years, granular sludge has been paid more attention to by the resear-cher at home and abroad because of its good settlement performance, high process-ing load and the strong removal capacity of nitrogen and phosphorus. Currently, the research about granular sludge technology combining with enhanced biological phosphorus removal (EBPR) technology was only a little. This research was based on mature granular sludge and best mixed carbon sources ratio, through the metho-ds of16S rDNA molecular biology techniques of PCR-DGGE, cloning and seque-ncing, and fluorescence in situ hybridization (FISH) technique, also including the detection of polyhydroxyalkanoates (PHA), extracellular polymers (EPS), particle size and conventional water quality parameters, the effect mechanism of complex substrates on the stability process of granule-based EBPR systems was studied. The experimental s about composite substrates were consisted of two parts, includ-ing the orthogonal test composed by three factors (C/N/P) and levels and shocking loadings (carbon source). The experiment(orthogonal test)proljected around40d,which was about the effect of composite substrates on the stability process of granule-based EBPR system.The results showed that great changes have taken place of every system, including the setting characteristics,particle morphology and size, removal efficiency of phosphorus and COD,lnicrobial community structure alld so on.2#(C/N/P=400:10:5),3#(C/N/P=600:10:10)and5#(C/N/P=400:20:15)systems expanded filamentous bulking to grantiIar sludge；there were many granular fraglnents resulting subsidence in poor performance of6#(C/N/P=600:20:5) system,the performance retumed back to nomal after the particulate debris removing out of the system；and the granular of9#(C/N/P=600:30:15)system changed for better setting cllaracteristics and granular structure becaine tight.The size of granular sludge has been gradually decreased for all systems,especially in3#,8#and9#system,and the average particle size was only0.3mm at the elld of operating.The CODcr(the same with below)of1#(C/N/P)=200:10:15),4#(C/N/P=200:20:10)and7#(C／N／P=200:30:5)system was consumed more than95％in anaerobic,phosphours release/uptake rates were relatively stable and fluctuated within the rang of60-100mg/(g·h),60-80mg/(g·h) and40-60mg／(g·h),respectively.However,COD of other systems were consumed mainly in anaerobic changing to in aerobic and phosphorus release/uptake rates gradually declined,some system even decreased to0mg/(g·h).Phosphate average removal rate of each system was(from1#system to9#system)83.5％,52.8％,7.1％,96.7％,19.7％,72.2％,79.7％,28.1％and48.7％,respectiVely.The content of protein in EPS was about50％,and stability of granular sludge was relatively with high protein content in EPS. When the system expanded filamentous bulking to granular sludge, content of polysaccharides and DNA was reduced, PN/PS of system was first increased then reduced and indicated that the granular sludge experienced the process of unstable to stable.Detected with FISH technology, PAOs accounted for more than50%of1#,4#,6#and7#systems, and the rest systems have a high proportion of GAOs or the total amount of bacteria was few. Through the detected of PHAs for each system at the end of operating, only1#,4#,7#and8#(C/N/P=400:30:10) systems have obviously synthesis and consumption of PHAs, the rest almost none. The metabolic mechanism of microbiological has been disorder. Combined with the16S rDNA molecular biology techniques of PCR-DGGE, cloning and sequencing, we knew that the microbial community structure for all systems became rich from single expect the3#system which the bacteria became few. Summary, we can get that after different composite substrate treatment,1#,4#and7#systems were still normal granule-based EBPR system, but the rest has lost the EBPR performance, because the bacterium were gradually replaced by other heterotrophic microorganisms or occurred to filamentous bulking.Apply two analytical methods, visual analysis and variance analysis, to analyze the results of orthogonal tests and results are consistent. The best composite substrate condition for the granule-based EBPR system for stable operation was that C/N/P=200:20:15.The effect of impact loading on the stability process of granule-based EBPR system was studied, and the resluts showed that when influent concentration of carbon source were200mg/L and400mg/L, the granule-based EBPR system has good EBPR performance and the average phosphate removal rates were97.1%and96.1%, respectively. But when the influent concentration of carbon source increased to600mg/L, the system occurred sludge bulking similar filamentous after running for some time, and phosphorus release/uptake rate gradually decreased from100mg/(gh) to0mg/(gh), and the phosphate removal rate was only34%. At this time, the COD was consumed mainly in aerobic.When the influent concentration of carbon source was600mg/L, the granular sludge secreted315mg/gVSS EPS and was twice of the rest concentrations, and more EPS was conducive to withstand the adverse external environment. At this moment, there was no PHA synthesis and consumption, the content of PAOs was only24%and GAOs was only about15%. Combined with PCR-DGGE technique, it found that other heterotrophic bacterium was dominated in the system, and PAOs and GAOs have been gradually replaced by other heterotrophic bacterium. Therefore, the normal granule-based EBPR system can not bear the impact loading when influent concentration of carbon source was600mg/L for a long time. This may be caused by the high influent concentration of carbon source and the unreasonable proportion of carbon, nitrogen and phosphorus.