Isolation, Identification And Degradation Characteristics Of An Aerobic Heterotrophic Nitrifying-Denitrifying Bacterium

In recent years, eutrophication of water bodies has become increasingly prominent,excessive discharges of nitrogen compounds is one of the major factors, and the controlment ofnitrogen pollution has been received abroad attention. Biological denitrification is one of themost widely used, efficient and cost effective method. Traditional denitrification theorysuggests that biological denitrification is completed by nitrification of autotrophs anddenitrification of heterotrophs, but it tends to be time-comsuming and requires a lager system.Bacteria that have heterotrophic nitrification and aerobic denitrification abilities can overcomeproblems inherent in conventional method. By using these microorganisms, a simultaneousnitrification and denitrification process can be established in one reactor, and it has been a hotissue in the field of wastewater treatment.In this paper, an aerobic heterotrophic nitrifying-denitrifying bacterium was isolated fromthe activated sludge of a coking wastewater treatment system. In order to improve nitrogenremoval efficiency, we studied the influence of different culture conditions on strain growth andnitrogen removal charactristics. Moreover, the treatment results of coking wastewater by thebacterial strain were also investigated, which can provide theoretical basis for its application inthe furture.The mian research conclutions are as follows:1. A bacterial strain that has heterotrophic nitrification and aerobic denitrification abilitieswas screened from activated sludge, named strain Y1. Strain Y1was identified as Pseudomonassp. by morphological, biochemical characteristics and16S rDNA sequence analysis.2. Singer factor experiments revealed that C/N rations and shaking speeds were the mainfactors effecting the degradation of ammonium. The optimum conditions for heterotrophicnitrification were C/N9.6,30℃, initial pH9.0and shaking speed250r/min. Under theseconditions, the degradation rate of NH4+-N, TN were97.37%and96.71%with an initialNH4+-N cocentration of152.88mg/L in8h, respectively. During the process, only few nitrite ornitrate were detected and the degradation of ammonium occured mainly on logarithmic phase.3. Singer factor experiments indicated that high reducing carbon resources, high dissolvedoxygen and higher C/N rations would benefit the degradation of NO₃^--N. The optimumconditions for aerobic denitrification were C/N15,30℃, initial pH8.0and shaking speed250r/min. Under these conditions,196mg/L NO₃^--N was degraded to1.28mg/L in13h and the TNdegradation rate was98.39%. During the process, only few nitrite was detected at the beginningof the culture stage.4. When ammonium sulfate and potassium nitrate were added as nitrogen sourcessimultaneously, the denitrification effect and growth of strain Y1were better than that of ammonium sulfate with sodium nitrite, and the bacterial strain would utilize ammonium sulfatepreferentially.5. Strain Y1with activated sludge were used to treat dilute coking wastewater in anaeration equipment. During the stable operation phase, results showed that the removal rate ofCODcr greater than70%, NH4+-N removal rate up to72.78%and a large amount of nitrite wasobserved in the effluent. Besides,51.26mg/L NO3--N in the influent was degraded to20²5mg/L after treatment.