Effects Of Aeration Conditions On Nitrogen And Phosphorus In Overlying Water And DOM Fluorescence Spectra

Eutrophication of water is a kind of pollution phenomenon caused by excessive nitrogen and phosphorus content in the water, which causes a large number of cyanobacteria and so on. The release of nitrogen and phosphorus in sediment is the main way to lead to eutrophication, and the decomposition of organic matter in sediment is considered to be the main source of nitrogen in the overlying water. Therefore, the release of endogenous nitrogen and phosphorus of contaminated sediments has attracted more and more attention in recent years. Due to its low cost and quick effect, the technology of aeration and oxygenation is widely used in the treatment of polluted river. But the application of aeration technology for treatment of polluted river focus on ammonia nitrogen removal, so the total nitrogen removal rate is low.The sediments and overlying water in polluted rive located Hefei city as the research object, the experimental method through indoor simulation and analysis in different dissolved oxygen(0.3 mg/L, 2.5 mg/L, 3.5 mg/L, 4.5 mg/L, 5.5 mg/L and 6.5 mg/L) and different aeration modes(continuous aeration, intermittent aeration conditions), analysis the changes of nitrogen forms such as ammonia nitrogen(NH4+-N) and nitrate nitrogen(NO3--N, NO2--N) in the overlying water, and the different removal effect of total nitrogen. The study also use the three dimensional fluorescence spectroscopy to analysis the changes of DOM, also investigated the correlation between DOM fluorescence intensity and ammonia nitrogen. In order to find a method of rapid characterization of ammonia nitrogen, so as to solve the conventional chemical method to measure a large number of chemical reagents, easy to produce secondary pollution, complicated operation inspection, measuring time was long and the lag and other shortcomings. In addition, the removal efficiency of total phosphorus in the overlying water under aeration condition was studied preliminarily, in order to provide some references for the restoration of the urban polluted river.Under the condition of continuous aeration with different dissolved oxygen, the main conclusions are as following:(1) In the dissolved oxygen were 2.5 mg/L, 3.5 mg/L, 4.5 mg/L, 5.5 mg/L and 6.5 mg/L conditions, with the increase of dissolved oxygen concentration, the fluorescence intensity of the protein decreased gradually, fulvic acid fluorescence intensity gradually increased, the study showed that the protein more susceptible to microbial degradation, and fulvic acid chemical properties of a substance is relatively stable, it is difficult to be degrading microorganisms.(2) Under aeration, the nitrite nitrogen concentration in overlying water will appear the phenomenon of accumulation, mainly due to the inhibitory effect of free ammonia in water, with the decrease of the concentration of free ammonia, the inhibitory effect of free ammonia on nitrate was decreased, nitrite nitrogen was converted to nitrate under the action of nitrate.(3) Continuous aeration can effectively reduce the ammonia nitrogen load of the water, and also can effectively inhibit the release of endogenous ammonia nitrogen. But overall the total nitrogen removal rate is not very high, when the dissolved oxygen is 2.5 mg/L, 3.5 mg/L, 4.5 mg/L, 5.5 mg/L and 6.5 mg/L respectively, until the end of the experiment the total nitrogen removal rate of 50%, 41.6%, 31%, 51.9% and 32.5%, respectively. Continuous low dissolved oxygen aeration is more beneficial to the removal of nitrogen in eutrophic water And aerating oxygen can effectively inhibit the release of internal phosphorus, different dissolved oxygen aeration conditions, at the end of the experiment, the total phosphorus removal rate of 76.6%, 81.4%, 82.7%, 85.8% and 90.3%, respectively.Under the conditions of intermittent aeration with different dissolved oxygen, the main conclusions are as following:(1) Intermittent aeration can promote the release of ammonia nitrogen in sediment in polluted river and realize the high efficiency of nitrogen removal. When the dissolved oxygen is 4.5 mg/L, 5.5 mg/L, ammonia nitrogen and total nitrogen concentration can meet the requirements of the class IV water quality standard; when the dissolved oxygen is 6.5 mg/L, ammonia nitrogen and total nitrogen concentration can meet the class III water requirements.(2) Intermittent aeration can effectively inhibit the release of internal phosphorus in sediments. When the dissolved oxygen is 2.5 and 3.5 mg/L, the concentration of TP can reach the standard of class V water; dissolved oxygen is 4.5 mg/L and 5.5 mg/L, the concentration of TP can reach the standard of class IV water; dissolved oxygen is 6.5 mg/L, the concentration of TP can reach class III water standard.(3) Under the conditions of intermittent aeration, the sum of the fluorescence intensity of the low excitation wavelength tyrosine and tryptophan showed a good linear correlation with ammonia nitrogen concentration with correlation coefficient 0.980, 0.974, 0.972, 0.966, and 0.984. It is indicated that the fluorescence intensity of the low excitation wavelength tyrosine and tryptophan can be used as a feasible method to indirection detection the concentration of ammonia nitrogen.The study shows that intermittent aeration may achieved the effective removal of nitrogen in the overlying water against the continuous aeration. The concentration of ammonia nitrogen can be rapidly predicted by detecting the total fluorescence intensity of the low excitation wavelength tyrosine and tryptophan.