Changes Of Kinetic Parameters Of Nitrifying Bacteria Under Different SRT Conditions And Establishment Of Their Numerical Models

The viability of Nitrifier is affected by conditions such as sludge retention time(SRT),temperature,pH and substrate concentrations.The nitrification process can be simulated,predicted and precisely controlled by using a mathematical model that can integrate the influence of various environmental limiting factors to improve the efficiency of activated sludge treatment and the effect of sewage treatment.At present,most of the studies on the influence of environmental conditions such as temperature,pH and substrate concentration on the kinetic parameters of Nitrifier are carried out under a certain SRT condition.In addition,adding SRT and many other influencing factors into the nitrifier mathematical model to improve the accuracy of the model is also the focus of current research in the field of nitrification simulation.In this research,Nitrifier(including ammonia oxidizing bacteria AOO and nitrite oxidizing bacteria NOO)were cultured at 35±1?,pH 7.5-8.0,DO>2.0 mg-N/L,and the SRT was controlled for 40 d,20 d,10 d and 5 d.The growth rate,decay rate and yield of Nitrifier with different SRTs was measured during the process of acclimation.After the viability of Nitrifier in each reactor was stable,the typical kinetics of Nitrifier under different SRT conditions(including the influence of temperature,pH,and substrate concentration)was determined.And the Nitrifier species was analyzed to explore the physiological reasons for the effect of SRT on the kinetic parameters.Based on the ASMs series models and the determination of kinetic parameters,a more complete multi-factor two-step nitrification mathematical model was established and verified.The specific conclusions are as follows:1)The growth rate and decay rate of Nitrifier,NOO and AOO change significantly with the decrease of SRT.Among them,?m,Nitrifier?Nitrifier??,Nitrifier??m,AOO?b,AOO??,AOO showed an increasing trend,while ?m,NOO?b,NOO??,NOO showed a decreasing trend.The yield coefficient of Nitrifier,YA,Nitrifier,also increased with the decrease of SRT.2)With the decrease of SRT,the temperature parameters TA,AOO increases slightly,TA,NOO decrease significantly,which indicates that NOO is gradually more sensitive to temperature,and AOO was gradually less sensitive to temperature,but TA,Nitrifier was still affected greatly by NOO from the analysis of the temperature parameters of Nitrifier.The temperature sensitivity of Nitrifier increased gradually with the decrease of SRT.3)The optimum pH values were 8.0-8.2 for AOO,8.3-8.7 for NOO and 8.0-8.3 for Nitrifier.With the decrease of SRT,the pH inhibition parameters,pHLL,Nitrifier,pHUL,Nitrifier,pHUL,NOO,pHLL,NOO,pHUL,AOO,and pHLL,AOO did not change significantly.4)With the decrease of SRT,the sensitivity and tolerance of AOO to ammonia nitrogen both increased(KS,NH4,AOO decreased,KI,NH4,AOO increased),which lead to the gradual decreased of the kinetic parameters of Nitrifier,KS,NH4,Nitrifier and the gradual increase of the kinetic parameters of Nitrifier,KI,NH4,Nitrifier.The inhibitory parameter of nitrite nitrogen on NOO,KS,NO2,NOO?KI,NO2,NOO increased gradually,which indicated that with the decrease of SRT,the sensitivity of NOO to nitrite nitrogen gradually decreased,and the tolerance gradually increased.5)With the change of SRT,?max,the maximum specific growth rate of Nitrifier,NOO,and AOO fluctuated and remained stable in general,which may be because the comprehensive consideration of multiple environmental factors would be closer to the true value of the maximum growth rate of microorganisms than only considering the single factor of SRT.Low temperature is more conducive to achieve short-cut nitrification.The smaller the SRT control,the more vulnerable the short-cut nitrification stability is to temperature variations.6)The relative abundance of Nitrifier species showed a wavy trend with SRT,which may be related to the growth of Nitrifier,the amount of sludge discharged,the growth and death of OHO in the reactor(which affect MLVSS)and other situations.AOO and NOO showed directional trend changes within the nitrifier bacterial community structure.The relative proportion of AOO gradually increased and NOO gradually decreased,which may be caused by the gradual elimination of NOO due to the longer sludge age of AOO than NOO with the decrease of SRT.7)The change of Nitrifier's kinetic parameters may be due to the change of the proportion of AOO and NOO,which leads to the directional change of Nitrifier's growth and decay rate and environmental factor tolerance.In addition,the relative abundance of AOO and NOO at the species level also changed in a wavy shape,which may be one of the reasons why the kinetic parameters of AOO and NOO changed with SRT.8)In this research,a multi-factor two-step nitrification mathematical model was established by comprehensively considering the influence of temperature,pH and substrate concentration,based on ASM1 and two-step nitrification process mechanism.The acclimation process under different SRT conditions was simulated and verified by using the self-tested kinetic parameters,and the simulation results maintained a high degree of fit with the measured values.This indicates that the multi-factor two-step nitrification model established in this study can be used to quantitatively describe the nitrification process,thereby improving the integrity and accuracy of the original model.