Establishment And Application Of Short-cut Nitrification And Denitrification Dynamics Model

Along with the rapid development of society and the constant improvement of people’sliving standard in china, the nitrogen element pollution problem of water becomes more andmore serious. Traditional biological nitrogen removal process is characterized by the highsludge production, high operation costs, high infrastructure construction costs and large area.In recent years, researchers actively study the development of new nitrogen removal processand the improvement of traditional process. Short-cut nitrification and denitrification processhas received increasing attention for its advantages of energy-saving, saving carbon source,shorten the hydraulic retention time and reducing emissions of excess sludge.In this study, on the basis of experimental studies on short-cut nitrification, a modeldescribing the SBR short-cut nitrification and denitrification processes was established, andthe model was used to simulate and theoretically analyze the realization, destruction andstabilizing process of short-cut nitrification. Conclusions are elicited as follows:(1) In this study, the strategy of high temperature (32℃), high pH (8.0～8.7) and lowaeration rate (25L/h) was adopted to achieve a fast start of short-cut nitrification anddenitrification processes. The SBR reactor experienced the realization and destruction ofshort-cut nitrification, and the nitrite accumulation rate decreased from80%to nearly zero.The test proved excessive aeration can easily lead to the conversion from short-cutnitrification to complete nitrification.(2) In order to avoid excessive aeration phenomenon, the operating conditions of SBRreactor have been adjusted. The cycle of reactor operation was increased, and the aerationtime in a single cycle was shortened at the same time, so that ammonia cannot be transformedcompletely in the aeration phase. After about30days of acclimation, ammonia removal rateand nitrite accumulation rate of the SBR reactor reached80%and the system run stably.Afterthe aeration rate increased to37.5L/h, the ammonia removal rate reached90%and the systemrun stably.(3)After correction and calibration of the Activated Sludge Model No.3(ASM3), a model describing the SBR short-cut nitrification and denitrification processes was established.The model was applied to the fitting of measured data of the nitrification stage withMATLAB software programming, and the simulation results were good.(4) The model was used to simulate the realization of short-cut nitrification process. Thesimulation results show that, in the environment of high temperature, high pH and lowdissolved oxygen (DO), with the increase of operating cycle, the ammonia-oxidizingbacteria(AOB) multiplied rapidly, while the nitrite-oxidizing bacteria(NOB) growth wasinhibited due to the lack of DO, which benefitted the realization of short-cut nitrification.(5) The model was used to simulate the destruction of short-cut nitrification process. Thesimulation results show that, If the reactor keep aerating after the ammonia convertedcompletely, NOB will convert nitrite into nitrate quickly and multiply rapidly. With theincrease of the operating cycle, the amount of NOB became more and more, and the short-cutnitrification converted to complete nitrification eventually.(6) The model was used in single factor analysis of DO. The simulation results show that,realization of short-cut nitrification merely by controlling DO need to control the aerationstrictly, and the system could not achieve the best running effect with the excessive ordeficient aeration. However, effluent quality is easy to fluctuate in actual project. Even if theaeration rate can be controlled in the best value, changes in water quality can also make theideal running effect difficult to maintain.(7) The model was used to simulate the effect of real-time control on short-cutnitrification, and the simulate results were compared with the timing control mode. Theresults of comparison show that, the short-cut nitrification operation effect of real-time controlmode was superior to the timing control mode indeed. Real-time control mode does notrequire a strict DO control, as long as an accurate grasp of ammonia oxidation end-time，ideal effect and stable operation of short-cut nitrification process can be relatively easy to beachieved.(8) In the simulation curves of the timing control mode and real-time control mode, wefound a law that the greater the aeration, simultaneous nitrification and denitrification (SND) phenomenon is less obvious.In order to optimize the short-cut nitrification and denitrificationprocess and facilitate the achievement of SND, the combination strategy of real-time controland low DO control was recommended to achieve stable operation of the short-cutnitrification and denitrification processes.