Control Conditions And Mathematical Simulation Of Partial Nitrification Process

Shortcut nitrification and denitrification process is a kind of high efficiency and energy saving technology, but the condition is harsh, and it is easy to convert to the nitrification denitrification.By studying the start-up and maintenance process of shortcut nitrification,this topic explores how to consider the various factors that control the type of nitrification and realize long-term stable nitrite accumulation, and carry on analysing the shortcut nitrification process from the point of dynamics, to provide a theoretical basis for explaining and achieving shortcut nitrification better.The results show that:(1)By increasing the influent ammonia nitrogen load, the SBR reactor can start and stabilize shortcut nitrification. Reduce the influent ammonia nitrogen load to a certain extent, the shortcut nitrification was quickly destroyed. Shortcut nitrification in the treatment of wastewater with high ammonia nitrogen is relatively easy to implement, because microbial specific growth rate is high under high ammonia load. Besides, ammonium oxidation bacteria(AOB) has good nitrification ability and is able to resist impact load, and the high FA concentration can achieve inhibition on nitrite oxidation bacteria(NOB), the impact of short-term high FA did not cause fatal influence to the shortcut nitrification.(2)Reasonable control of the settling time is conducive to the formation of short-cut nitrification granular sludge and washing off the poor sedimentary properties and small sludge in reactor. Compared with the floe sludge, granular sludge has good settle ability and high methanogenic activity and is not easy to drain. In addition,it can increase the oxygen mass transfer resistance which is conducive to maintaining the stability of shortcut nitrification and denitrification.(3)The experiment finds that the KoAOB value is higher than KONOB,not only NOB can not washed out under low dissolved oxygen(DO), but the growth of AOB is inhibited. In the CSTR reactor, the shortcut nitrification is realized under low DO, which results in the decrease of the removal rate of ammonia nitrogen, then the concentration of ammonia nitrogen in the mixed solution is relatively high, which increases the specific growth rate of AOB. At the same time high pH value is needed to be maintained in the reactor to make high FA to suppress NOB, and then through the control of sludge retention time(SRT) NOB is washed out.Multiple factors should be comprehensively controlled to achieve shortcut nitrification.(4)SBR realized and stability maintained shortcut nitrification under high DO, it shows that in high ammonia nitrogen low DO is not a necessary condition, once the AOB became the dominant species, the shortcut nitrification still can be maintained stable operation even in adverse conditions.(5)The effect of pH on the growth rates of AOB and NOB was analyzed, and the mathematical model for AOB and NOB growth was established based on the Monod equation. Then fitted the model to the measured data by MATLAB software, and the simulation results were good. After that the model was used to predict the startup of partial nitrification, the prediction results show that short-cut nitrification could be achieved on the condition of SRT of 6d, DO of 1.5mg/L and pH of 7.3-8.