Behavior Of Endogenous Nitrogen From Malodorous River Sediment With Aeration

Malodorous of the urban river water was representative consequences of environment pollution and ecological destruction in China, of which the overcapacity of nitrogen was an important problem to be resolved. After effective control of external pollution input, the nitrogen released from sediment gradually become the main source of water nitrogen pollution. Although artificially aeration technology is effective to the treatment of malodorous river water, the operation of aeration engineering were comparatively extensive. The quantitative investigation about the water aeration influence on sediments nitrogen release were rarely reported. Therefore, reynolds number (Re) was introduced to quantitatively characterized the effect of aeration on the overlying water disturbance. And the nitrogen migration and transformation characteristics in surface sediment were also investigated under different aeration conditions. Results of our study were aim to determine the optimized aeration operation conditions, which could provide basic data for treatment of the overcapacity nitrogen and offer technical references to the optimization operation of aeration engineering. Results showed that:When water flow velocity were 0.247m/s,0.288 m/s,0.320 m/s,0.372 m/s, the corresponding temperatures were 19.1℃,25.6℃,28.9℃,16.5℃. Under this conditions, distribution of flow pattern and flow field are different in the equipment, but velocity of symmetrical position is identical with the distribution of flow pattern and flow field.The cross-section closing to aeration rotary brush have a large velocity and reynolds number, as well as fierce turbulent fluid-flow conditions. On the contrary, the cross-section faring from aeration rotary brush have a relatively moderate velocity and flow pattern, as well as reynolds number. Therefore, the greater the velocity, the greater the Reynolds number, the higher the temperature,the smaller the dynamic viscosity of water.Under different aeration conditions, distribution of DO and SOD are different in the equipment. Aeration and temperature which benefited for penetration depth of DO have an impact on DO. Specifically, the greater the aeration, the greater the disturbance. In addition, the equipment may exist in a small amount of algae on high temperature,which have a powerful photosynthesis with increasing DO concentration. Under the same water quality, SOD values keep basically constant. Flow velocity of the river is a major factor impacted on sediment oxygen demand, which increased with increasing velocity in the water.Nitrification and denitrification are the main forms of nitrogen transportation and exchange in the water-sediment interface. Ammonia in the upper layer water are transformed into nitrate and nitrite by nitrification. There are inorganic nitrogen and inorganic nitrogen in the sediments. Heterotrophic microorganisms transforms the easily degradation organic nitrogen into ammonia nitrogen which get into interstitial water and fluid mud layer in succession in the form of exchangeable ammonia nitrogen as a result of the adsorption of clay minerals. One part of the ammonia nitrogen in the fluid mud layer is converted into nitrite as a result of nitrification and then nitrate by oxidation, while the other part is diffusing into the upper layer water to increase the concentration of nutrient. A large amount of nitrite are diffusing from the fluid mud layer into the black mud layer. At the same time, nitrate in the upper layer water are diffusing into the fluid mud layer. But in the conditions of aeration, there will be an exchange of nitrate between the fluid mud layer and the upper layer. At the same time the fluid mud layer also released the nitrate into the upper layer, in addition, the fluid mud layer released a large number of nitrite as the result of the mixing. There will be a small amount of oxygen exist in the black mud layer. And nitrate are therefore probably generated by oxidationThe different intensity of flow field in the turbulent have different effect for behavioral characteristics of endogenous nitrogen, according to influence the gradient distribution of DO, it influence the behavior of endogenous nitrogen. When the flow rate is between 0.288 and 0.320 m/s, the value of RE is 1810-2113, the average of DO is 5.08-7.5 mg/L,the value of SOD is-0.08--0.003 mg/(m2.d) and the removal of nitrogen is the best in the upper layer water.Grey correlation analysis was applied to study the relations between the amounts of SOD, DO, Re and the amounts of NH4+-N, NO3+-N, NO2+-N and TN respectively in the overlying water, fluid mud and black mud under the conditions of aeration. The results show that, it is the Re that has the largest correlation with the change performance of NH4+-N in the overlying water and fluid mud, but it is the SOD that has the largest correlation with the change performance of NH4+-N in the black mud. It is the Re that has the largest correlation with the change performance of NO3+-Nin the overlying water, but it is the DO that has the largest correlation with the change performance of NO3+-N in the fluid mud; it is the SOD that has the largest correlation with the change performance of NO3+-N in the black mud. In the overlying water and black mud, it is the SOD that has the largest correlation with the change performance of NO2+-N; in the fluid mud it is the Re that has the largest correlation with the change performance of NO2+-N. It is the Re that has the largest correlation with the change performance of TN in the overlying water and fluid mud, while it is the SOD that has the largest correlation with the change performance of TN in the black mud.