Isolation And Characteristics Study Of A Heterotrophic Nitrification-aerobic Denitrification Fungus

With the development of coking industry, a lot of coking wastewater discharge and have caused serious environmental pollution and ecological problems. The coking wastewater is a kind of complex industrial waste water, which contains not only phenolic organic but inorganic materials such as nitrides and sulfur cyanide. The nitrogen pollution has become a problem needed to be solved. The chemical or physico-chemical methods could decontaminate the wastewater but cause secondary pollution, meanwhile, the treatment cost is relatively high. At present, the traditional biodenitrification has been adopted widely, and its operation is simple and practical. However, this process need long time to start and insufficient energy to consume. New denitrification technology and microbe have provided new ideas for removing nitrogen in coking wastewater treatment. Heterotrophic nitrification can proceed in inorganic or organic carbon source conditions, and need few environmental requirements; Aerobic denitrification is no longer strictly confined by anaerobic condition, and can proceed in aerobic environment smoothly. Then, heterotrophic nitrification-aerobic denitrifying bacteria can simultaneously conduct nitrification and denitrification in the same reactor, and highly complete nitrogen removal.A filamentous fungus, which was isolated from the activated sludge of a coking wastewater treatment facility, exhibited effective high-strength ammonium removal ability, and was named A60. This fungus was provisionally identified as Fusarium sp., according to its colonial and individual morphological characteristics and 26S rDNA-ITS sequences analysis. It was named Fusarium sp.A60.In order to discuss the growth and ammonium removal performance of Fusarium sp.A60, culture experiments were designed with different carbon sources, nitrogen sources, C/N ratios and pH value. The result indicated that the strain performed strong adaptation to the environment; sucrose and ammonium sulfate were the best carbon source and nitrogen source, respectively; the best C/N ratio (mol/mol) was 12, and the optimum initial pH value of the medium was 6.0. Under the optimal culture, the strain performed effective ammonium removal ability, and an initial concentration of 450 mg/L NH4+-N was removed by 94.97% with the fastest removal rate of 14.83 mg/L/h, while total nitrogen was reduced by 88.35%. During the whole process, there were a few accumulations of nitrite and nitrate. In the optimum medium, the denitrification ability of the strain was improved greatly because of the optimal C/N ratio and pH. In different concentration experiment of ammonia nitrogen, Fusarium sp.A60 could not only quickly remove low concentration ammonium but also adapt to high concentration ammonium wastewater environment. The nitrogen removal ratios were about 95% and 92% in initial concentration of 450 mg/L and 800mg/L NH4+-N mediums, respectively.The experiment was designed to analyze its use and transformation of ammonium, nitrite and nitrate with ammonium sulfate, nitrite, and nitrate as a sole nitrogen source in aerobic condition, respectively, while to detest the nitrogen gas (N2) and discuss the denitrification ability. The result indicated that in nitrite and nitrate mediums, the strain could make good use of nitrite or nitrate and convert them to nitrogen gas with the ratio of about 35%. It confirmed that the strain Fusarium sp.A60 could use products of nitrification as substrates of denitrification and exhibited effective heterotrophic nitrification-aerobic denitrification characteristics. Based on the principle of nitrogen balance, about 30% to 50% nitrogen was used to growth and converted to cells nitrogen by the strain. The possible nitrification sequence of Fusarium sp.A60 was suggested as NH4+â†'NO2-â†'NO3-, and the rationality of denitrification sequence (NO3-â†'NO2-â†'N2) was testified by nitrate experiment.In order to make the strain adapt to coking wastewater and perform the best denitrification ability, the experiment was designed to domesticate Fusarium sp.A60 by increasing the proportion of coking wastewater. After domestication, the strain could further adapt to coking wastewater. The nitrogen removal ratio of the strain was increased to 89.91% from 78.10%.