Inorganic Nutrient Transformation In Sewer Networks

Nitrogen and phosphorus in municipal sewage is a major pollutant. The form of nitrogen in the wastewater are mainly composed of organic nitrogen and ammonia nitrogen, phosphorus in the aqueous phase are composed of phosphorus orthophosphate, polyphosphate and other forms of inorganic phosphorus and organic phosphorus. The presence of nitrogen and phosphorus nutrient is not only the main cause of eutrophication and dissolved organic nitrogen(DON) in the water is a precursors of nitrogen-containing disinfection by-products. In recent years, with the development of urban drainage science, sewage pipe network playing a "bioreactor" role is gradually recognized by people. Research shows that in the transportation process that the sewage conveying to sewage treatment plant, physical, chemical and microbial action occurring within the pipe network will change the content and composition of pollutants in water to a certain extent. These changes only affect the water quality of sewage treatment plants, while the impact on the operating efficiency of nitrogen and phosphorus removal in subsequent water treatment plant. For this reason, this paper studies the changes of organics, nitrogen and phosphorus in wastewater along with the pipe network.By the established urban sewage pipe network simulation system, we study the variation of the main pollutants in sewage pipe network. It indicates that the average removal rate of the dissolved organic matter is 22.55% in sewage after passing through the 1200 m pipe. Ammonia(NH3-N) concentrations decreased 3.66mg/L, it is Associated with the microbial assimilation in pipe network.(the concentrations of dissolved organic nitrogen increased by 2.99 mg/L); Dissolved organic nitrogen(DON) are mainly composed of amino acids, and the remaining components include proteins, nucleic acids and other nitrogen-containing organic compound(amino sugars, humus, etc.). Along the entire process the total nitrogen solubility(DTN) levels essentially unchanged, which is associated with the relatively stable anaerobic environment in the sewage.The changes of orthophosphate, pyrophosphate along with the pipe network were studied at the same time.The results showed that the content of phosphate in the sewage pipe network along the entire process changed little. Only a small part is converted to pyrophosphate. The concentration of pyrophosphate reduces by 2.87mg/L(a concentration of orthophosphate increased by 2.07 mg/L) in sewage after passing through the 1200 m pipe, which is associated with the action of microorganisms.By three-dimensional fluorescence spectroscopy(3DEEMFS) and Fourier transform infrared spectroscopy(FT-IR), we analyzed the fluorescence properties and the functional group of dissolved organic matter in water. The results showed that aromatase protein substances humic substances increased significantly with the length of sewage pipe network. Under the action of sewage microorganisms the content of the amino compounds along with the pipe shows a gradual increasing trend, which caused by dissolved organic nitrogen. On the one hand,ammonia in the water is converted by microbes into essential free amino acids under a variety of amino acid biosynthesis pathway. On the other hand, these free form amino acids synthesis complex nitrogenous organic compounds,such as protein, by different microbial metabolic.