| To actively respond to the increasingly strict discharge standard of sewage nitrogen pollutants in sewage treatment industry of our country, this work focused on the analysis throughout the generation, transmission, and treatment of sewage. With the goal of continuing cuts of the concentration of nitrogen in sewage effluent. The migration law of nitrogen speciation between the sewage generation and entrance to the municipal pipe network had been analyzed. The transforming discipline and removal mechanism among different forms of nitrogen component in sewage networks had been clarified. The conversion and removal process of nitrogen pollutants in waste water treatment plants had been mastered. This research provided reliable evidence for the control of nitrogen pollution in urban waste water, and had important uses and practical value.The composition and sources of nitrogen pollutants in waste water had been analyzed. Results showed that more than 70% of sewage nitrogen was contributed by urea in the urine which accounted for less than 1% of the total waste water. The nitrogen contamination in faeces, of which main form is organic nitrogen(ON), consumed 14% of total nitrogen(TN) in waste water. Urea in the urine would rapidly hydrolyze to ammonia nitrogen when it contacted septic tank sludge and sewer biofilms. Organic nitrogen in faeces could hydrolyze and convert when it exposed to septic tank sludge. Ultimately leading to the fact that sewage nitrogen speciation occurred mainly in organic nitrogen when the waste water had been produced, and quickly converted into ammonia nitrogen in the municipal waste water pipe. It had been determined by overwhelming superiority of nitrogen compounds in faeces and urine of urban sewage and transformation properties of ON in early process of sewage collecting, that ammoniacal nitrogen was the main form of nitrogen in sewer and sewage treatment systems.The distributing rule of nitrogen pollutants along the sewer had been monitored, and the results showed that the concentrations of ammonia nitrogen was gradually increased while TN was decreased. The experimental results also indicated that nitrogen pollutants had been removed by sewer biofilms. Simulation experiment was conducted to study the migration and transformation characteristics of nitrogen compounds in sewer with the ammonium chloride, soy protein isolate used as nitrogen source of synthetic waste water. Results showed that the concentrations of dissolved total nitrogen(DTN) were decreased by 1.30mg/L, 1.58mg/L and 2.09mg/L respectively. In addition, microorganisms which attached to the sewer biofilms could make use of the ammonia nitrogen and protein to synthesize various amino acids for metabolic activity. It showed that sewer microbes could give priority in use of the protein for metabolic activity by Three-dimensional fluorescent spectroscopy and δ15N stable isotopes analytic results. While it did not have protein in sewage, ammonia nitrogen, which was a inorganic nitrogen source would be used for synthesis and metabolism by microorganisms. The results further indicated that humic acid substances would be released by metabolites of microorganisms, which increased the content of refractory biodegradation organic nitrogen in effluents.Species and removal approaches of nitrogen pollutants at different compartments in municipal waste water treatment process had been studied. Results showed that more than 10% of TN could be removed by aerated grit chamber and primary settling tanks. It had been confirmed that the nitrogen was mainly due to sedimentation of particulate nitrogen by δ15N stable isotopes analysis. Moreover, there had been a certain ammonia volatilization in aerated grit chamber, which result in ammonia nitrogen decreasing during the process. The migration and transformation characteristics of nitrogen compounds in secondary biological treatment processes had been studied. Results showed that the denitrification occurred both in anaerobic and anoxic reactor. The effect of hydrolysis and ammonification in anaerobic and anoxic reactor were much better than aerobic tank. The experiment results also indicated that the dissolved organic nitrogen(DON) was generated at entire biological treatment process, but the yield of DON by assimilation in the anaerobic and anoxic reaction only accounted for 29.6% and 17.5% of DON yield in aerobic reaction. Furthermore, some of DON which generated at aerobic reaction were degraded and utilized by microorganisms in anaerobic and anoxic reactor as sludge recirculation. |
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