Research On Shortcut Nitrification Boundary And Kinetic Model

The short-cut nitrification is hard to maintain due to the strict control. The articletherefore studies the issue by mathematical model, which guide the experimentalresearch and parameter selection.First of all, the author achieves a start up of the shortcut nitrification reacto r, andtake advantage of shaking-bottles test and grey relational analysis （GRA） to choosevariables of the model. Shaking-bottles test is single factor experiment, and thebackground parameters was listed as follows: T=30oC, pH=7.5, DO=2mg/L,[NH⁴⁺-N]=80mg/L,[Cl^-]=0,[K⁺]=0. In GRA, resolution ratio p=0. After research, thearticle chose temperature, pH, dissolved oxygen （DO）, ammonia concentration andsludge retention time （SRT） as the basic variable of following models, which havesignificant correlation with nitrite concentration.Then, short-cut nitrification boundary models were built up based on Monodmodel. The current short-cut nitrification was mainly controlled by substrate limitationand SRT regulation, so the author respectively, to establish a subtrate boundary modeland SRT boundary model. The subtrate boundary model is divided three parts, whichtake single component, dual component and inhibitory effect relatively, namely reflectssituations of the ideal, low ammonia and high ammonia.Two boundary models were simulated by MAPLE, and both of control modes wereproved practicable. Research mainly get conclusions as follows: The inhibition of freeammonia （FA） is stronger than free nitrous acid （FNA）. When the FA is high,recommended pH is8. At this time, NOB is eliminated, and the DO range is large. Butunder the condition of low FA, adopting DO or pH control method separately lay aproblem on achieving short-cut nitrification process. To achieve the aim, reducing totalnitrogen and elevated pH （Recommended pH=9） are recommended. At the same time,the bacteria’s minimum densityof donor is quite low,（order of magnitude is0.01mg/L）.It therefore can’t be successful by limiting the density of donor. Moreover, rising oftemperature will improve the sludge loading and reduce the dwell time. Increasing toabove25℃, the generation times of AOB and NOB separate, which lay a good effecton obtaining short-cut nitrification process.Finally, based on ASM3, a short-cut nitrification kinetic model was built up, whichhad8components and8reaction processes. In stimulation, the Pearson correlationcoefficient of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen were as high as0.445**,0.982**, and0.788**, respectively. Stimulating the kinetic model under differentconditions by AQUASIM, the author got recommended condition as follows under the theories: the SRT is1.0-1.5days, the DO is1.0-5.0mgDO/L, the influent ammonianitrogen concentration is more than50.0mgN/L, the pH is7-7.5or8.5-10, thetemperature is20-35℃. The model focus on the process in the mixed reactor and wasbiased towards aerobic reaction, so there is a certain degree of limitation.Some constructive opinions were put forward, such as the control of mass transfer,the increasing of the reflux ratio, the introduction of anaerobic ammonium oxidizingbacteria. In these way, the condition of "high FA, low FNA" will be achieved inmicro-environment, thus to gain short-cut nitrification process, which plays a certainguidance for research of future.