Effects of flow rate and wastewater concentration on the transformation of nitrogen in sediment-water system of sewage pipelines.

In this work, the transformation law of nitrogen in sediment-water system under different flow rates and wastewater concentrations were investigated in a simulated sewage pipeline system. Results showed that the different flow rates and wastewater concentrations in the pipeline caused differences in microbial community in sediments and nitrogen transformation. When the flow rate increased from 0.05 to 0.2 m/s, the scouring effect was enhanced, resulting in higher concentrations of NH4 + -N and NO3 - -N in the overlying water. At 0.2 m/s, the relative abundance of Clostridium_sensu_stricto_1 in sediments was higher, resulting in a greater conversion of amino acid nitrogen (AAN) to NH4 + -N. Meanwhile, many denitrifying bacteria (Trichococcus, Dechloromonas, norank_f__norank_o__Gaiellales, Thiobacillus) had high relative abundance in the sediments, and the denitrification process was common. When the wastewater concentration was high, the nitrification reaction was great in overlying and interstitial water. Moreover, the ammoniation process was great in the sediments, and the variation flux of AAN was large (remarkably reduced). PRACTITIONER POINTS: AAN transformed to NH4 + -N in sediment under different flow rate and concentration. Scouring was enhanced at 0.2 m/s, increasing nitrogen contents in overlying water. Difference in microbial community led to more AAN conversion to NH4 + -N at 0.2 m/s. The ammoniation process was greater in sediment at a high concentration of sewage. NH4 + -N migrated from overlying water to sediment at a high concentration of sewage.

Changes in the transformation of nitrogen and phosphorus under different microbial communities in sewage pipes.

Microbial communities living in different environments can affect the transformation of nitrogen and phosphorus in sewage pipes. Two different environments were simulated to investigate the differences in the transformation of nitrogen and phosphorus under different microbial communities in the pipe. Results showed that the concentration of nitrogen and phosphorus changed greatly in the first 25-33 days and the first 21 days, respectively, and then remained stable. The decrease in amino acid nitrogen (AAN) concentration and the increase in ammonia nitrogen (NH4 + -N) concentration in the sediments were evident in the contrast group. The concentrations of total phosphorus (TP), dissolved total phosphorus (DTP), and dissolved reactive phosphorus (DRP) in the overlying water and interstitial water decreased, and that of TP in the sediment increased. Some microorganisms in the sediments of both groups are related to the transformation of nitrogen and phosphorus, such as Clostridium_sensu_stricto_1, Sporacetigenium, Norank_f__Anaerolineaceae, Norank_f__norank_o__PeM15, and Caldisericum. The relative abundance of these microorganisms was remarkably differed between the two groups, which partly caused the difference in nitrogen and phosphorus transformation among overlying water, interstitial water, and sediment in the two environments. PRACTITIONER POINTS: The concentration of N and P changed greatly in the first 20-30 days. AAN and NH4 + -N in sediments had greater concentration variation in contrast group. In two groups, TP, DTP, and DRP of water decreased, and TP of sediment increased. Microbe related to the transformation of N and P differed between the two groups.