Characterization Of The Biofilm Formation Process In Urban Sewer System

In this paper,the changes of internal environment and microbial morphology in the biofilm during the the biofilm formation process were studied by a 1200 m long urban sewer system.The distribution of the characteristical microbial in the biofilm were analyzed.The results of the study are of great significance for the effect of microbial on the treatment of pollutants in pipe network.The result showed that the DO in the biofilm was less than 2 mg / L,the ORP was between-480 and 150 mV,and the pH was in the range of 6 to 7.6.With the increase of biofilm formation time,the membrane environment changed from anoxic to anaerobic,the film thickness gradually increased and stabilized at 75 d.The maximum film thickness was 1.06 mm.The environment along the pipe also changed from anoxic to an anaerobic.The results of energy spectrum and scanning electron microscopy showed that the biomass increased and the biofilm became more dense.The extracellular polymeric substance(EPS)increased and then slightly reduced at 60 days.The Ca,Mg and Si elements gradually increased.While along the pipe sysems,the biomass decreased gradually,and the EPS increased first and then decreased,and the Ca,Mg and Si elements decreased.The increase of EPS in the biofilm leads to the densification of the biofilm,and the microbial morphology changed from Gibberella,Streptococcus to Brevibacterium and Micrococcus.The results of fluorescence in situ hybridization(FISH)showed that at the same point of the pipe during the biofilm formation,the abundance of nitrifying bacteria(AOB)decreased gradually from the initial 2%,and disappeared at about 10 d.And the abundance of fermented bacteria(FB)increased significantly to 17% at 75 d and stabilized.The abundance of hydrolyzed acid bacteria(HPA)increased gradually and stabilized at 5% at 75 d.The sulfate-reducing bacteria(SRB)abundance increased to 2.3% at 30 days and then decreased to 0.9% at 60 days.The total abundance of the functional microbes increased,and the microbial community changed significantly.From the whole,the abundance of AOB,FB and HPA decreased,while the abundance of MA and SRB increased along the pipe.The total abundance of functional microbes decreased by an average of 3% per 400 m,and the microbial flora structure changed significantly.The results of water quality analysis showed that,in the process of the biofilm formation,about 60 ~ 150 mg / L COD was converted into the substances which was easier to use for microorganisms.About 3 ~ 9mg / L sulfate was conversed to sulfide.The total nitrogen(TN)in the influllent and efflullent was almost constant.The concentration of organic nitrogen increased and the concentration of ammonia increased,and the decrease of organic nitrogen was consistent with the increase of ammonia nitrogen,which showed that the organic nitrogen was changed to the ammonia nitrogen because of the microbiols.