Study On The Structure,Activity Of Biofilm And The Distribution Of Nitrifying Bacteria

Biofilm is a complex micro-ecosystem consisting of microorganisms,microbial-secreting extracellular polymeric substances(EPS)and microbial adsorption or degradation.EPS is the main component of biofilm in addition to microorganisms,its composition and content not only affect the properties of biofilm,such as porosity,adsorption properties,diffusion and microbial metabolic activity,and determine the living environment of microorganisms in biofilm.Therefore,the study of biofilm structure has very important theoretical and practical value in understanding biofilm and the design,operation and management of biofilm sewage treatment system.The object of this study are two typical suspened carriers biofilm,one from the xi'an fifth WWTP and the other from a Lab-scale cultivated SBBR reactor.The biofilm was treated with micro-cutting technique and the macroscopic structure of biofilm was observed directly.The distribution of EPS in biofilm was investigated by fluorescent staining.The effects of different extracting methods on EPS content in biofilm were investigated by different extraction methods.In situ analysis of microorganisms in biofilm is used to study the distribution characteristics of different functional strains in biofilm.By comparing the real morphology of these two kinds of different biofilm,study the similarities and differences between laboratory biofilm and municipal sewage plant biofilm in structure,EPS content and microbial composition are studied,which provided theoretical basis for recognizing biofilm and applying its sewage treatment.The main results are as follows:(1)At the microscopic level,the two kinds of biofilm exhibit typicalheterogeneous porous structure,and the internal irregular distribution of voids and pores with different shapes.Compared with the actual biofilm in the municipal sewage treatment plant,the biofilm is more thick in the lab reactor,the surface is more rough and the VSS/SS value is higher,and the oxygen consumption rate of the corresponding microorganism is higher.(2)The EPS content in the lab biofilm is less than the actual biofilm in the municipal sewage treatment plant,but the EPS distribution features are identical.EPS is a mesh structure,forming the matrix of biofilm,microorganism fills in them;The EPS component in the biofilm has a gradient change along the thickness direction,the surface layer protein content is high,the biofilm depth direction gradually decreases,and the polysaccharide is opposite.(3)The content of EPS in biofilm is related to the extraction method,formaldehyde +NaOH is the largest,the heating is second,and the CER is minimal.The EPS content obtained by image analysis(FISH and FS)is significantly higher than that of chemical or physical extraction method,and the EPS value obtained by FISH and FS is close.(4)The distribution of microorganisms in biofilm has obvious spatial heterogeneity.The microorganism is mainly distributed in the surface layer of biofilm,less in the inner layer of biofilm.and the bacteria in the surface is more heterotrophic,the nitrifying bacteria is less.