Study On The Effect Of Free Ammonia And Free Nitrous Acid On Nitrification Process

Biological nitrogen removal has the advantages of low cost and high efficiency,which has been widely used in sewage treatment systems.Free ammonia(FA)and free nitrous acid(FNA)are the key factors that affect the microbial nitrogen removal.There are great differences on the threshold concentrations of FA and FNA for nitrification inhibition.And the suitable range of FA and FNA concentrations for stable operation of nitrification process has not been obtained yet.In this study,according to the single factor experiments,the response of denitrification performance and metabolic activity of nitrifying bacteria under FA short-term stress,FA long-term stress as well as FNA short-term stress(two ways of addition)was explored.Based on the response of bacteria under FA and FNA stresses,the influence of ammonia concentration,nitrite concentration,pH and temperature on the inhibition of FA and FNA concentrations were investigated,and the correlation among denitrification performance,ATP content,initial FA and FNA concentration was analyzed.The main findings are as follows:Short-term FA stress:Pearson correlation analysis showed that the SATP level was closely related to SAOR,SNaAR and initial FA concentration(Correlation coefficient R>0.8).The Haldane inhibition kinetic model was suitable for describing the inhibitory effects of FA on the activity of nitrifying bacteria(R~2>0.92).The inhibition constants of ammonia nitrogen concentration and pH were 41.869 mg/L,61.833 mg/L for ammonia oxidizing bacteria,and 5.511 mg/L,21.670 mg/L for nitrite oxidizing bacteria,respectively.The order of ammonia concentration,pH and temperature on the inhibition effects of FA were ammonia concentration>pH>temperature.Long-term FA stress:The influential FA concentration of the seven systems began to be stabilized after 7 days ofexperiment.When ammonia was fixed as a univariate variable,the accumulation rate of nitrite was more than 90%,and the NIAR(accumulation rate of nitrate nitrogen)was always kept at a low level.When pH was a univariate variable and the average influent FA concentration was 3.94 mg/L,the accumulation of nitrite was not obvious.When the average influent FA concentration was up to 21.67 and 65.94 mg/L,the NIAR was lower than 1 mg/L/h while the accumulation rate of nitrite was higher than 95%.The response of ATP content was:continuous decline(1-6d),gradual rise(6-16d)and stabilization(17-24d).Microbial community structure analysis showed that the richness and diversity of microorganisms were decreased,and the relative quantity of AOB and NOB were increased decreased respectively after 24 days of experimental period.Short-term FNA stress:Starved cells of AOB had a higher tolerance than normal cells under different FNA stress conditions.The shorter exposure time results in less obvious accumulation of nitrite.The order of nitrite concentration,pH and temperature on the inhibition effects of FNA were pH>nitrite concentration>temperature,and the correlation between SATP and SAOR,SNaAR,initial FNA concentration was higher when ammonia and nitrite were added at the same time.The order of nitrite concentration,pH and temperature on the inhibition effects of FNA were nitrite concentration>pH>temperature when adding nitrite first and then adding ammonia.This paper could provide theoretical guidance for uncertainty of FA and FNA concentration threshold and difference of nitrifying bacteria response.It was conducive to design stable activated sludge process and maintain the stability of the activated sludge process.