Preliminary Research On Aerobic And Dissimilatory Nitrate Reduction To Ammonium By Bacteria

A biofilm was taken out of a contact oxidation reactor which was used for treating high temperature oil field waste water. The bioflim was cultured in Giltay medium, which would become blue after enrichment. And bacteria enriched from the bioflim could educe granulated ammonium crystals from the agar plate below 4°C. Mixed strains were enriched from the agar plate. The effects of four environmental factors such as carbon, citrate-C / N-nitrate mole ratios, dissolved oxygen and ammonium on the ability of nitrate reduction to ammonium were studied. The data indicated that mixed strains were notablely influenced by carbon, citrate-C/ N-nitrate mole ratios, dissolved oxygen and ammonium, and that mixed strains can utilized citrate well with staple of ammonium. The data also indicate that all of the rates of ammonium production were more than 20% when citrate-C/N-nitrate mole ratios were given 3:1-8:1. The capacity of nitrate reduction under aerobic environment was higher than that capacity under anaerobic environment. It's difficult to control rates of ammonium production in batch-tests of mixed strains steadily. The decline in nitrate concentration coincided with an elevation in nitrite levels, which was followed by a substantial increase in ammonium concentration. It was proved to be a dissimilatory nitrate reduction to ammonium pathway.There were six dissimilatory ammonium producers isolated from mixed strains. Because the entire nitrate reduction process was affected by the coact of the bacteria of mixed strains, physiological and biochemical characteristics of the six bacteria were tested and we made a 16S rDNA sequences analysis of the preponderant Q1—3. On the basis of their morphological observation and physiological and biochemical characteristics, the strain Q1-3 was classified as Pseudomonas alcaliphila. The pure culture of strain Q1-3 was performed. The effects of four environmental factors such as citrate-C/N-nitrate mole ratios, temperature, dissolved oxygen and nitrogen source on the ability of dissimilatory nitrate reduction to ammonium were studied. In addition, the strain Q1-3 can absorb heavy metal, such as Ag⁺, CrO₄^2- and Cu²⁺, from synthetic wastewater. The bottles were kept statically at room temperature after 72h batch-test. And there were indissoluble crystals at the bottom of some cultures after some time. It was supposed that formation of crystals be concerned with biomineralization in agar-gel system induced by strain Q1-3. Elemental analyses show that the crystals consisted mainly of NH₄⁺-N, Mg, P and K. Aerobic DNRA was studied in present manuscript. The study of DNRA is of theoretical significance with respect to conservation of nitrogen in soil. It is certain that strain Q1-3 be of significant value on wastewater treatment through a series of researches.