Biofilm Growth Law And Population Metabolic Characteristics Of Sewage Pipelines With Different Materials

The metabolism of microorganisms in urban sewage pipelines is an important factor affecting water quality transformation.The roughness,hydrophobicity and other factors of the surface of sewage pipes will change the adhesion and colonization of microorganisms,resulting in differences in the community structure of attached microorganisms and their metabolic transformation characteristics of carbon and sulfur pollutants in sewage.In order to explore the influence of pipe material on the community composition and metabolic transformation ability of attached microorganisms,this paper constructed a set of experimental system of urban sewage pipeline.Using the different pipe material composition of the device,the biofilm formation characteristics of HDPE double-wall corrugated pipes,ductile iron pipes and concrete pipes at different flow rates,the distribution and metabolic characteristics of microorganisms in the membrane were analysed.The results provide a theoretical basis for clarifying the influence of pipeline material on the microbial community composition and carbon and sulfur metabolism in sewage pipelines.The main findings of the paper are as follows:(1)The growth morphology,internal environment and mechanical stability of biofilms in different pipes were analyzed and detected.The results showed that the biofilm structure of the concrete tubes was the roughest,loose and porous,while the biofilm of the other two tubes had a smooth surface and compact internal structure.Concrete pipe biofilm has the highest maximum thickness(2150 μm),followed by double-wall corrugated pipe(1500 μm)and ductile iron pipe(1300 μm)the smallest.The minimum redox potential inside the biofilm of ductile iron pipe is-336 m V,that of concrete pipe is-325 m V,and that of double-wall corrugated pipe bellows is only-276 m V.In addition,the highest adhesion force and Young ’s modulus(deformation resistance)of the double-wall corrugated pipe bellows biofilm are only 15 n N and 0.39N/m,the concrete pipe is 16 n N and 0.47 N/m,and the ductile iron pipe reaches 21 n N and 0.58 N/m.After comprehensive comparison,it can be seen that different pipeline materials make the structure and physicochemical properties of the attached biofilm different.Among them,the stability of the double-wall corrugated pipe biofilm is the worst,and the anaerobic and anoxic range in the membrane is lower.The differences in the above traits will affect the microbial population distribution of biofilms in different tubes.(2)After comparing the microbial diversity and community composition of different pipe biofilms,it was found that the shannon index of bacteria in the double-wall corrugated pipe bellows biofilm was 7.0±2.5,the ductile iron pipe was 7.5±0.7,and the concrete pipe was 7.5±0.7.The Shannon index of archaea in the corresponding pipes were6.0±2.2,4.6±1.5 and 3.8±1.3,respectively.The diversity index of bacteria in the doublewall corrugated pipe bellows biofilm was the lowest,and the diversity index of archaea in the concrete tube biofilm was the lowest.The dominant bacteria at the genus level with the highest content of double-wall corrugated pipe bellows were Pseudomonas(0-30%,degradable plastics produce acetic acid and other substances into the TCA cycle),ductile iron pipe was Acinetobacter(5-28%,widely used organic acid as carbon source),and concrete pipe was Acinetobacter(6-28%).Methanosaeta(Consumption of acetic acid to produce methane)is the dominant archaea at the genus level with the highest content of the above three pipes,with relative abundance of 3-52%,7-71% and 7-82%,respectively.(3)The distribution characteristics of genes encoding key enzymes of carbon and sulfur metabolism in biofilms of different pipes were compared by metagenomic sequencing.The results showed that the abundance of genes encoding key enzymes involved in carbon and sulfur metabolism in the double-wall corrugated pipe biofilm was much lower than that in the other two pipes.The highest abundance of acetate-consuming enzymes(EC: 2.7.2.1)in carbon metabolism was only 434 in double-wall corrugated pipe,583 and 651 in concrete tubes and double-wall corrugated pipe,respectively.The formic acid-consuming enzymes(EC: 1.17.1.9)were 546,831,and 922 in the above pipelines,respectively.Among them,the relative abundance of Methanobacterium,which metabolizes formic acid,was only 0-5% in the double-wall corrugated pipe,3-36% in the concrete pipe,and 1-19% in the ductile iron pipe;Double-wall corrugated pipes have relatively higher sulfur oxidation capacity,and the relative abundance of dominant sulfuroxidizing bacteria is 2-30%,and the relative abundance in other pipelines is less than 6%.It can be seen that the carbon and sulfur metabolism capacity of the double-wall corrugated pipe biofilm is much lower than that of the other two pipelines,and the sewage quality is more stable during the transmission process of the pipe,which reduces the metabolic generation capacity of toxic and harmful gases in the pipeline,and is conducive to the carbon source retention of the influent water of the sewage plant.