Transformation trend of nitrogen and phosphorus in the sediment of the sewage pipeline and their distribution along the pipeline.

Microorganisms transform nitrogen and phosphorus in the sediment of sewage pipelines. When the sediment was scoured by water flow, these elements migrate. This work studied the changes in biofilm morphology and microbial community structure, and focused on the differences in the transformation of nitrogen and phosphorus along the pipeline. The results showed that the nitrogen and phosphorus concentrations varied systematically with time and space (the front, middle, and posterior segments of the pipe). With time, amino acid nitrogen (AAN) concentration in the sediment gradually decreased, NH-N concentration slowly increased, NO-N concentration began to increase after 25 days, and TP concentration continued to increase after 9 days. The AAN, NH-N, and TP concentrations were highest in the posterior segment of the pipe and lowest in the front segment. However, NO-N showed two stages: its concentration was highest in the front segment and lowest in the posterior segment during the first 17 days, after which the opposite was observed. Changes in the nitrogen and phosphorus concentrations were related to the microbial communities in the sediments. The abundances of Rhodobacter (0.001 <p ≤ 0.01), Trichococcus (p ≤ 0.001), Nakamurella (0.01 <p ≤ 0.05), and norank_f__norank_o__PeM15 (0.001 <p ≤ 0.01) in the terminal sediments were significantly higher than those in the initial sediments. Meanwhile, the abundances of Clostridium_sensu_stricto_1, Rhodobacter, norank_f__norank_o__PeM15, and Brevundimonas were different in the front, middle, and posterior segments. Furthermore, nitrogen and phosphorus were easily adsorbed on the small particles and were scoured and re-deposited on the posterior segment of the pipe, resulting in enrichment. The temporal variation in nitrogen and phosphorus and its spatial distribution along the pipeline were due to the combination of biotransformation and migration.