Study On Effect Of Sludge Settleability In Biological Nitrogen And Phosphorus Removal System

In the field of sewage treatment,the activated sludge process is favored because of its unique advantages and has become the mainstream process in wastewater treatment plants.However,the problem of sludge bulking in sewage treatment systems with biological nitrogen and phosphorus removal functions has not been solved.In order to find out the mechanism of sludge bulking,molecular biology techniques were used to track the succession of microbial community structure by changing the composition of influent organic matter and running processes with different contaminant removal functions,while analyzing intracellular polymers(PHA)and extracellular polymers(EPS),to explore the influencing factors of sludge settleability changes in the nitrogen and phosphorus removal system,and to provide a theoretical basis for solving the problem of sludge expansion.The main results of this study are as follows:(1)In the AAO system,under the composition of mainly dissolved organic matter(stage ?),all dissolved organic matter(stage ?)and mainly particulate organic matter(stage ?),PHA and EPS were the highest in stage ?,the activated sludge floc structure was the densest,and the sludge settleability was the best,SVI=70 mL/g followed by stages ?(SVI=120 mL/g)and ?(SVI=280 mL/g).There was a significant negative correlation between sludge settleability and PS,PN and Zeta potentials of LB-EPS(r=-0.668,p<0.05;r=-0.818,p<0.01;r=-0.850,p<0.01),whereas the correlation between sludge settleability and TB-EPS was weak.The species and quantity of filamentous bacteria changed significantly as the composition of the organic matter in the influent water changed.The dominant filamentous bacteria in the inoculated sludge were Type 0092 and Haliscomenobacter hydrossis,the dominant filamentous bacteria instage ? were Thiothrix spp.and Nostocoida limicola?,the dominant filamentous bacteria in stage ? was Thiothrix spp.,and the dominant filamentous bacteria in stage ? was Type 1851-like.The composition of different influent organic matter could lead to significant changes in the abundance of dominant bacteria in the system.The changes in the abundance of bacteria of Thiothrix,Trichococcus and Chryseolinea were closely related to the sludge settleability.Among them,acetate could promote the growth of bacteria of Thiothrix and Chryseolinea,and starch could promote the growth of bacteria of Trichococcus.The dominant growth of these filamentous bacteria led to filamentous bulking in the activated sludge.(2)The sludge settleability of activated sludge was different under different operating conditions.Among them,the AAO system(stage ?)had the highest EPS content,the sludge floc structure was densest,and the sludge sedimentation performance is the best,followed by the CAS system(stage ?)and the AO system(stage ?).There was a significant negative correlation between sludge settleability and PS,PN and Zeta potentials in LB-EPS(r=-0.699,p<0.05;r=-0.715,p<0.05;r=-0.684,p<0.05),whereas the correlation between sludge settleability andTB-EPS was weak.As the function of the system changes,the type and abundance of filamentous bacteria changed significantly.The dominant filamentous bacteria in the inoculated sludge were Type 0092 and Haliscomenobacter hydrossis,the dominant filamentous bacteria in stage ? were Type 0914 and Type 0041,the dominant filamentous bacteria in stage ? were Thiothrix spp.,and the dominant filamentous bacteria in stage ? were Type 021 N.Different pollutant removal processes had a greater impact on the abundance of dominant bacteria in the system.Among them,the changes in the abundance of bacteria of Thiothrix and Chryseolinea were related to the sludge settleability.The introduction of an anoxic zone stimulated the growth of bacteria of Thiothrix,and the introduction of an anaerobic zone promoted the growth of bacteria of Chryseolinea.This was the reason for the filamentous bulking in the activated sludge.(3)Sludge settleability was closely related to changes in microbial community structure,intracellular and extracellular polymers.Thiothrix,Trichococcus and Chryseolinea were the key genus of sludge settleability.Among them,Thiothrix spp.was easy to grow in the system containing acetate and anoxic zone;Chryseolinea spp.easily grew in the system containing acetate and anaerobic zone;growth of the Trichococcus spp.was less correlated with process conditions,mainly related to the composition of organic matter in the influent,the genus was susceptible to proliferation in systems containing starch.The change of microbial community structure was the fundamental factor affecting the sludge settleability.The intracellular and extracellular polymers played an auxiliary role in the sludge settleability,which might aggravate the progress of sludge settleability improvement or deterioration.