Primary Exploration Of Nitrogen Removal And Metabolic Pathway Of Alcaligenes Faecalis Strain NR

Heterotrophic denitrification was defined as: some heterotrophic microorganismscan complete the transformation from ammonium (NH4+-N) to gaseous nitrogen inaerobic condition. Alcaligenes faecalis strain NR was separated from a membranebioreactor which owed a high simultaneous nitrification and denitrification nitrogenremoval efficiency. Previous studies have confirmed the heterotrophic denitrificationperformance of the srain NR. In this paper, the heterotrophic denitrificationperformance of Alcaligenes faecalis strain NR and the influence factors of it werestudied. By using the response surface method (RSM), the bacterial culture conditionsare optimized. Then a laboratory scale continuous flow reactor was established to studythe denitrification performance of strain NR in wastewater with different ammoniumconcentration and further study it in piggery wastewater. Finally the denitrificationpathway of strain NR was discussed by using the stable isotope technology.In the optimization experiment for culture conditions of bacteria NR, a relationshipmodel between the response values of29experiments and their influence factors(temperature, pH, speed，carbon and nitrogen ratio(C/N)) was established. Then the3Dresponse surface and2D planar isoline figure were described to further analyze theoptimization range of each factor. Then a quadratic model predicted that the maximumremoval of ammonium obtained under the conditions with shaking speed of121.6rpm,temperature of29.6°C, pH of7.2and C/N ratio of9.7, the ammonia nitrogen removalefficiency can reach72.7%.In the continuous reactor, ammonium removal efficiency can reach about77.0%when the inflow was the wastewater with150mg/L ammonium concentration.At thesame time the reactor obtained about75.0%total nitrogen (TN) removal efficiency.Then the ammonium concentration of the inflow water was increased to200mg/L,ammonium removal efficiency can reach about75.0%and total nitrogen removalefficiency can reach about70.0%. Finally, the ammonium concentration of the inflowwater was decreased to90mg/L and the C/N was increased to20, the ammoniumremoval efficiency can be as high as85.1%and the total nitrogen removal efficiencycan be76.4%. At the beginning of the reactor operation, the total organic carbon (TOC)removal efficiency was improved.Then with the operation of the reactor, the removalefficiency of TOC reached as high as90%. After operation for94days, the piggery wastewater was changed to be the reactorinflow instead of the artificial wastewater. Strain NR was used to treat piggerywastewater and the denitrification performance of it was test in batch experiments, dueto the complexity of its composition. In the batch experiments(60h), the NH4+-Nremoval efficiency can reach76.8%and the TN removal efficiency can reach64.3%inpiggery wastewater within suspended solid (SS), the NH4+-N removal efficiency canreach78.3%and the TN removal efficiency can reach65.1%in piggery wastewaterwithout suspended solid. In order to avoid blockage in the reactor, piggery wastewaterwithout SS was chosen as the reactor inlet to investigate denitrification performance ofthe reactor.The results reflected that the reactor also owned70.0%NH4+-N removalefficiency and71.0%TN removal efficiency.Finally, according to the possible metabolic pathways of heterotrophicdenitrification, the intermediate products which maybe produced in the process ofmetabolism of strain NR were labeled with isotope, respectively. Then they were usedas N source in medium to culture NR bacteria in aerobic condition. The15N micrometerdifference (δ15N) in N2got from the gaseous product was test by using gas isotope massspectrometer (GC-IRMS), the results confirmed the existence of N2. At the same time,using isotope mass spectrometer to test the15N atoms abundance in nitrous oxide partatoms abundance, the results also confirmed the gas N2O. Finally, it is concluded thedenitrification pathway of strain N: firstly, NH4+-N was oxidized as NH2OH, then theNH2OH was oxidized as NO2--N, the NO2--N was nitrified to NO3--N, finally theNO3--N was denitried to produce N2O, and then generated the end gas N2.