Population Structure,function And Reaction Kinetics Of Nitrifying Bacteria In Biological Nitrogen Removal System

Nitrifying bacteria is the important functional bacteria in nitrogen removal,which plays a key role in biological nitrogen removal system.The population structure,function and reaction kinetics of nitrifying bacteria are key factors for process optimizion of treatment and removal efficiency improvement.However,the quantitative relationship and growth balance between ammonium oxidizing bacteria?AOB?and nitrite oxidizing bacteria?NOB?are relatively ignored.In this study,nitrification activities and microbial populations of nitrifying bacteria were investigated in 10biological nutrient removal wastewater treatment systems in Xi'an.Batch tests were used to determine the nitrifying activities while fluorescence in-situ hybridization?FISH?was used to quantify the fractions of AOB and NOB.Then,Nitrospira was enriched in the activated sludge taken from a municipal wastewater treatment plant?A²/O?by controlling nitrite concentration in the reactor.The kinetic characterization of Nitrospira under 20?was studied.Finally,a“stepwise nitrification-partial denitrification”and a“simultaneous nitrification-partial denitrification”test were designed to explain why a higher proportion of NOB in activated sludge.The main results and conclusions are as follows:1.The surveyed results of 10 wastewater treatment systems showed that each system had a good nitrification performance.Ammonia removal efficiency was more than 90%.The average ammonia oxidation rate was 3.25±0.52 mg NH₄⁺-N/?gVSS·h?and the average nitrite oxidation rate was 4.49±0.49 mg NO₂^--N/?gVSS·h?.The activity of NOB was higher than that of AOB.The proportion of NOB was 1.72⁵.87higher than that of AOB.Nitrosomonas and Nitrospira were the dominant bacteria of AOB and NOB,respectively.2.The surveyed results of the fourth wastewater treatment plant for one year showed that,most time of this year,the activity of NOB was higher than that of AOB.The average activity of NOB was 1.20 times higher than AOB,and the fraction of NOB was 1.25².46 times higher than AOB.The activity and quantity of AOB and NOB decreased obviously in winter when compared with their performance in summer.3.Nitrospira could be successfully enriched from activated sludge under the condition of nitrite concentration less than 2 mg/L in Feed-Batch reactor.The FISH results showed that the fraction of Nitrospira was enriched from 2.9±0.1%to74.3±1.8%.Nitrite oxidation rate increased from 3.42 mg NO₂^--N/?gVSS·h?to 48.72mg NO₂^--N/?gVSS·h?.4.Kinetic parameters of Nitrospira at 20? were investigated.The half-saturation constants of Monond equations for nitrite and oxygen were 0.32±0.03 mg/L and1.52±0.09 mg/L,respectively.The maximum specific growth rate was 0.63±0.06 d^-1.The temperature correction coefficient between 15? to 35? was 1.046.Free ammonia?FA?and free nitrous acid?FNA?have strong inhibition on the activity of Nitrospira.IC₅₀?The half maximun inhibitory concentration?for FNA was 0.02 mg/L and that for FN was 0.39 mg/L.5.By using“stepwise nitrification-partial denitrification”and“simultaneous nitrification-partial denitrification”tests,nitrite loop was confirmed exist in nitrification and denitrification process.NOB could use the intermediate product,nitrite,as the additional substrate to achieve the cell synthesis,which is an important reason for the phenomenon that the proportion of NOB was higher than that of AOB in the sludge.