Properties And Principal Factors Of Biofilm In Water Supply System

Restricted by the oligotrophic environment, most of bacteria in water supply network attach, grow and slowly form into biofilm on pipe wall. In this case, biological safety problems in water supply system are directly related to the characteristics and stable of these biofilms. Therefore, it’s necessary to study the colonies properties and influencing factors of the pipe biofilm.At present, the researches based on experimental platform in actual water supply network concerning biofilm are rare. From the perspective of biology, based on the pilot research platform in actual water supply network, this paper studied and analyzed the bacteria quantity, species diversity and influencing factors of pipe biofilms by using scanning electron microscopy, laser confocal microscope, flow cytometry instrument and high-throughput sequencing. Meanwhile, the impacts of hydraulic stagnation to microbial quantity in pipe network were also studied in this paper.By direct observation, the results showed that corrosion made the pipe wall become loose and uneven on nodular cast-iron pipe while biofilms on polyethylene pipe were relatively smooth and with certain viscosity. By using the scanning electron microscope and laser confocal microscope, there had both coccus and bacillus on the biofilm, both living bacteria and dead bacteria which were staggered with each other in different density.From the perspective of influence factors, pipe, pipe diameter, water quality indicators had direct impact on bacteria quantity of biofilm. Bacteria density in biofilm on the surface of nodular cast-iron pipe wall was greater than that on the polyethylene pipe wall. Bacteria density in biofilm on the surface of DN100pipe wall was greater than that on the DN200pipe wall.From the perspective of microbial community structure, microbial species on the biofilm in water supply network was very rich. In different levels of classification, the factors influencing biofilm microbial community structure were different. At the Phylum level, pipe material was the dominant influencing factor. At the Class level, water quality was the dominant influencing factor. At the Order level, pipe diameter was the dominant influencing factor. At the Family level pipe material became dominant influencing factor again.Finally, stagnation experiments showed that serious water quality deterioration happened after short term stagnation, especially in the downstream pilot platform. After1h stagnation, residual chlorine, turbidity, microbial indicators could not reach drinking water health safety standards, and the total colonies exceeded100CFU/mL. Therefore, there were serious security hidden dangers under the stagnation condition.