The Effect Of C/N Ratio And Free Ammonia On Extracellular Polymeric Substance(EPS)and Microbial Diversity Of Activated Sludge

Activated sludge is formed by extracellular polymeric substances?EPS?,bacteria,and bacterial micelles,besides EPS is considered as the third component except water and microbial cells in activated sludge flocs,moreover microbial metabolism and autolysis is one of the sources of EPS.So the change of free ammonia?FA?concentration?FA is the function of NH₄⁺-N concentration,pH,and temperature?and carbon ratio nitrogen?C/N?will affect the function of microbial metabolism,causing the variety of content of EPS and its components.In order to further explore the chang of extracellular polymer?EPS?in the process of denitrification in activated sludge system.Based on three-dimensional excitation-emission matrix?3D-EEM?fluorescence spectroscopy,high throughput Sequencing,scanning electron microscopy?SEM?and scanning electron microscopy-X-ray enery spectrometer?SEM-EDS?,we take the long-term effect of the ratio of carbon to nitrogen?C/N?and free ammonia?FA?on the performance of nitrogen removal,extracellular polymeric substance?EPS?and its compositions,sludge dewaterability,settling performance and microbial diversity in the sequencing batch reactor?SBR?treating synthetic wastewater.Based on the effect of four C/N conditions?0,5,10,15?on the performance of nitrogen removal,extracellular polymeric substance?EPS?and its compositions?PS,PN and DNA?,sludge dewaterability,settling performance and microbial diversity.Mainly obtained the following conclusions:?1?Four systems achieved high removal efficiency of NH₄⁺-N,and the phenomenon of simultaneous nitrification and denitrification?SND?occured in the R₁₀and R₁₅systems,the result indicated that high C/N was favorable for SND;?2?With C/N rose from 0 to 15,the contents of EPS and tightly bound EPS?TB-EPS?increased,while the loosely bound EPS?LB-EPS?gradually decreased,indicating high C/N was favorable for the production of EPS.Moreover,protein?PN?,Carbohydrate?PS?and DNA in EPS and TB-EPS increased with the C/N ratio increased.However,PN,PS and DNA in LB-EPS decreased with the C/N ratio increased.?3?With the C/N increased,the value of capillary suction times?CST?,specific resistance to filtration?SRF?,and sludge volume ratio?SVI?increased significantly.The result indicated that with the C/N increased,dewaterability and settling performance of sludge deteriorated significantly,and C/N had a significant impact on dewaterability and settling performance of sludge,moreover EPS was positively correlated with CST,SRF and SVI;?4?The EEM fluorescence spectra of LB-EPS,TB-EPS and EPS.?1?The EEM fluorescence spectra of LB-EPS.Comparing the fluorescence intensity values of peak A?protein-like substances?,peak B?humic substances?,and peak C?fulvic acid-like?in the R₁₅system at the beginning of nitrification,the fluorescence intensity of peak A,peak B,and peak C increased after nitrification,so it could indicate that high C/N was beneficial to accumulate protein-like substances,humic substances and fulvic acid-like during nitration.?2?The EEM fluorescence spectra of TB-EPS.During the nitrification process,protein-like substances,humic substances,and fulvic acid-like substances were accumulated in TB-EPS in the R₀ system,however they decreased in the R₅,R₁₀,and R₁₅systems.?3?The EEM fluorescence spectra of EPS.During the nitrification process,protein-like and fulvic acids accumulated in the R₀ system,however the content of humus substances decreased,at the same time,protein-like substances,humic substances,and fulvic acid-like substances were not conducive to accumulated in the R₅,R₁₀,and R₁₅systems.?5?SEM and SEM-EDS of activated sludge.The results showed that with the C/N increased,the microbial population characteristics changed significantly in activated sludge under different substrate,and a large number of filamentous bacteria infested.Besides the surface main elements of activated sludge were C,N,O and P.The elements of C was the carbon scaffold of the microbial cells,so its content was the highest,N took the second place?the material was provided as the microbial synthesis of protein?,besides with the C/N increaseed,the apparent concentration of C,N,and O and its percentage decreased.?6?The analysis of microbial community structure and microbial diversity based on high-throughput sequencing.?1?The sample size was sufficient to reflect the richness of the community and could meet the analysis requirements of microorganisms.Besides the number of OTUs were 1513,1023,1410,and 1139 in the samples of four C/N conditions.?2?With the C/N increased?0?5?10?15?,the number of unique OTUs showed firstly decreased then slight upward trend?715?293?221?382?in the samples of activated sludge.Besides microbial species of R₁₀at the level of gate,class,order,familiy,and genu was the highest,R₁₅took the second place,and the R₅ system was the least.At the level of species level,microbial species of R₁₀was the highest,R₀ took the second place,and the R₅ system was the least.?3?The microorganisms of Proteobacteria,Bacteroidetes,Cyanobacteria,Microcolumbia,Nitrospira,and Float were the main flora of the activated sludge systems.The relative abundance of the six gates was approximately 90.6%,at the same time with the C/N increased,the abundance of Nitrosomonas decreased?3.43%?0.27%?0.20%0.13%?.Based on the effect of four FA conditions?0.5,5,10,15?on the performance of nitrogen removal,extracellular polymeric substance?EPS?and its compositions?PS,PN,DNA?,sludge dewaterability and settling performance.Mainly obtained the following conclusions:?1?Four systems achieved high removal efficiency of NH₄⁺-N,and the systems of R₁₀and R₁₅achieved stable short-cut nitrification[the accumulation rate of NO₂^--N was?96.6.%⁹9.3%?],indicating that high FA was conducive to achieve short-cut nitrification.?2?The contents of LB-EPS and TB-EPS at the end of nitrification were slightly higher than the contents of LB-EPS and TB-EPS at the beginning of nitrification and at the end of denitrification,besides DNA in LB-EPS and TB-EPS decreased in the nitrification process and increased significantly in denitrification process.In addition,PS in TB-EPS was significantly higher at the end of nitrification than PS was at the beginning of nitrification and at the end of denitrification,The result indicated that the nitrification process was beneficial to accumulate PS in TB-EPS.?3?When FA concentration increased from 0.5 to 10,the contents of EPS,TB-EPS and LB-EPS increased in the R_0.5,R₅,R₁₀and R₁₅during denitrification process,however when FA rose from 10 to 15,the contents of EPS,TB-EPS and LB-EPS decreased.Compared to EPS,TB-EPS,and LB-EPS in R_0.5,R₅,and R₁₀,R₁₅was not conducive to accumulate the content of EPS,TB-EPS and LB-EPS.?4?PN was the main constituents in LB-EPS and the percentage of PN/LB-EPS was?44%⁷3%?,PS took the second place?the percentage of was 21%⁵3%?,DNA was subtle?the percentage of was 3%¹1%?,besides PS was dominant component in TB-EPS and EPS,PN took the second place,DNA was subtle.With FA rose from 0.5 to 10,PS and PN in TB-EPS and EPS increased,however FA increased from 10 to 15,the contents of PN and PS decreased.?5?When the FA concentration was in the range of?0.5⁵?mg·L^-1,the values of CST,SRF,and SVI increased with the FA increased,the result indicated that dewaterability and settling performance of sludge deteriorated with the FA increasing.When the FA concentration was in the range of?5¹5?mg·L^-1,the values of CST,SRF,and SVI decreased with the FA increasing,the result indicated that dewaterability and settling performance of sludge improved with the FA increasing.