Preliminary Research On Dissimilatory Nitrate Reduction To Ammonium In Microaerobic Condition

Domestic research of dissimilatory nitrate reduction to ammonium （DNRA） was mainlyfocused on rice flooded soils, relatively few studies of other geographical; Recent studieshave shown that DNRA occupy a position can not be ignored in the total removal nitrate;Most of the DNRA research was under strictly anaerobic environment, which is quitedifferent from realistic conditions. So this research was aim to the impact of growth factor onriver silt mixed flora DNRA process on microaerobic condition, isolate DNRA bacterial strain,study its characteristic of nitrate reduction and relationship with denitrifying strain SB1.By comparing the four different bacterias’ ammonium produce ability and qualitativetests of nitrogen form of separation crystallization which was produced by mixed flora on lowtemperature, confirmed that the mixed flora source was river silt from one of the Zhujiangwharf. The microaerobic condition was obtained by shaking table, the results showed that theratio of ammonium production to total nitrate reducers was highest when made sodiumsuccinate as carbon source, concentration of NH₄⁺-N was15.0～22.0mg/L at the end of theexperiment, DNRA process tend to occur in oxidation degree weaker carbon sourceenvironment; NH₄⁺-N could be detected in the culture medium when C/N rang among2¹0,higher C/N was better to insure the occurrence of DNRA process in oxidation degree strongercarbon source environment. The decline in nitrate concentration coincided with an elevationin nitrite levels, which was followed by a substantial increase in ammonium concentration. Itwas proved to be a dissimilatory nitrate reduction to ammonium pathway. Initial pH6¹0was more conducive to the DNRA pathway, the ratio of ammonium production achievedhighest level （25.71%） when initial pH was7; In the conditions of this experiment, mixedflora produced ammonium obtained the highest rate of47.59%at30℃, after which thetemperature continues to rise, ammonium production rate declined.D1and A7bacterial strains were isolated from mixed flora, nitrate reductioncharacteristic of D1bacterial strain was studied in this experiment, the results showed thatC/N had an important impaction in DNRA pathway, when C/N=10, the average growth rate ofNH₄⁺-N concentration was1.76mg/L·h; D1bacterial strain demonstrated low sensitivity tooxygen in DNRA pathway, when DO was0.6¹.0mg/L, the ratio of ammonium productionachieved44.69%; Because NO₂^-was considered to inhibit bacterial growth it was notsuitable for D1bacterial strain to used NO₂^-as nitrogen source when C/N≤3; More N₂Owould be produced in a neutral and alkaline environment, the highest output of N₂O when pH=7was89.14μg/L, which was about0.1%of the total reduction rate of NO₃^--N; SB1and D1 bacterial strains were inoculated with different quantity proportion into the same media at thesame time, the accumulation of NH₄⁺-N positively correlated to the inoculation quantity of D1bacterial strain in the media. DNRA process would become the main pathway of dissimilatorynitrate reduction in the environmental favorable condition and when the size of DNRAbacterial dominant in one system.