Study On Isolation And Nitrogen Removal Characteristic Of Aerobic Fungal Denitrifiers

Aerobic denitrifiers that include bacteria, actinomycetes and fungi are a kind of microorganism, they can remove nitrogen by denitrification in the aerobic condition. Since the discovery of aerobic denitrification phenomenon, most isolated aerobic denitrifiers were bacteria and aerobic fungi were less isolated. It was discovered that fungus obtained a wider range of application of carbon source and nitrogen source and better environmental adaptability. Therefore, this study isolated five effective aerobic fungal denitrifiers from the sediment of a river of Kiaochow bay through the combinative method of limiting dilution analysis, BTB selective medium method and nitrite indicator method, and then the five fungi were identified and studied. The identification result showed that the five fungi belonged to Penicilium, Alternaria, Alternaria, Ascomycetes and Fusarium respectively.As to the four nitrogen sources and eight carbon sources that were tested, the five fungi that can use ammonia, nitrite, nitrate and carbamide as nitrogen sources all can use sodium acetate, glucose, soluble starch and sucrose as carbon sources. However, they all can’t use sodium citrate, sodium oxalate and sodium carbonate as carbon sources. Furthermore, Penicillium and Alternaria can’t use sodium succinate which was used by Ascomycetes and Fusarium.The five fungi remove ammonia only by the aid of assimilation. Glucose, soluble starch and sucrose were easier assimilated by fungi than sodium acetate, and so, higher ammonia removal rates and more cell dry weights were obtained in the three carbon source mediums. Carbon source type and strain species both influenced the change of medium pH. Overhigh and too low solution pH were the restrictive factors that was most likely to appear in the ammonia removal process. The removal way of nitrite and nitrate by fungus included fungal assimilation and denitrification. High nitrite and nitrate removal rates were got when glucose, soluble starch and sucrose were acting as carbon sources. However, too high initial nitrate concentration had inhibitory action on strain growth in the nitrate removal process. Initial nitrate concentration, initial solution pH and carbon nitrogen ratio (C/N) did not much affect nitrite accumulation but temperature and salt concentration had some effect on nitrite accumulation in the nitrate removal process of some fungi.About30℃was the optimum temperature for the growth of the five fungi. The best C/N were4-6,12～16and12～20respectively for the five fungi, and the best salt concentration for all the fungal strain were all less than20g/L. Ammonia was first removed when ammonia, nitrite and nitrate coexisted in the solution, and nitrite was then removed. Nitrate was the most difficult to be used among the three nitrogen compounds.The experimental result showed that aerobic fungal denitrifiers were excellent in the respect of carbon and nitrogen source using range and capacity, viability in the real environment and adaptive capacity in the change of environmental conditions. Fungi can not only remove nitrogen compounds but also the COD. Penicillium and Ascomycetes even can be used as nitrogen removers in the seawater. Therefore, aerobic fungal denitrifiers have huge potential for the nitrogen removal in the organic-rich real water environment.