Variation of microbial population in sewer networks

A 1200 m-long municipal sewer network was built and the pH, DO, thickness, structure and microbial population variation of the biofilm were investigated along the network. The results showed that the biofilm pH varied little, while DO decreased from 0.35 mg·L^-1 to 0.26 mg·L^-1. The average biofilm thickness increased from 300 μm to maximum 560 μm at 800 m and then decreased gradually due to the hydrological flush and the decrease of the substrate. The surface of biofilm was smooth initially and then became rough along the network, which was beneficial to the growth of microorganism because of the specific surface area increase. At the same time, the microbial population tended to decrease and change along the pipeline as well. At 200 m, the main populations were Pediococcus, Streptococcus, Brevibacillus, Streptobacillus, Bacillus, etc., while were Enterococcus, Desulfovibrio and Thiomonas at 400 m and 600 m and Methanococcus, Denitrifiers and Thiobacillus denitrificans over 1000 m. In sum, along the pipeline, the microbial population decreased but was more stable.