The Aerobic Denitrification Characteristics Of Paracoccus Denitrificans And Its Effect For Nitrogen Transformation In Water

In aquaculture water, moderate concentration of nitrogen could protect the ecological balance of water, but high concentration of nitrogen could poison aquatic animals, pollute the ecological environment. Traditional theory holded that denitrification must take place under anaerobic or anoxic conditions, but aquaculture water needed sufficient dissolved oxygen. Therefore, the application of denitrifiers in aquaculture water had been limited severely.This paper used an aerobic denitrifiers-Paracoccus denitrificans (ACCC10489) as the test strain, then foused on the cell and colony morphology, the physiological and biochemical characteristics, the appropriate growth conditions and growth curve, the aerobic denitrification characteristics and influencing factors, the possible conversion method of nitrogen, the application security and the transformation ability of nitrogen in aquaculture water. The results showed that:1. Paracoccus denitrificans was a facultative bacterial which could survive and grow under aerobic or hypoxic condition. But its characteristics were mainly reflected in the aerobic aspect, the higher the oxygen concentration, the faster the growth.2. Regardless of aerobic or hypoxic condition, the appropriate growth temperature of Paracoccus denitrificans was30℃, the optimum pH value was7.0. The temperature and pH ranges were very conducive to the practical application of Paracoccus denitrificans in the field of aquaculture.3. Paracoccus denitrificans could carry out the denitrification under aerobic condition, and this process occurred mainly in the logarithmic phase of cell growth. In five kinds of carbon sources of glucose, methanol, sodium acetate, sodium potassium tartrate, and glycerin, for aerobic denitrification of Paracoccus denitrificans, the best carbon source was glucose, and the optimum C/N molar ratio were15～20. 4. Under different dissolved oxygen conditions, Paracoccus denitrificans had good conversion removal efficiency for three forms of inorganic nitrogen (NO3--N、NO2--N and NH4+-N) which existed alone or mixed, but the methods of transformation were different.When NO3--N or NO2--N alone in water, Paracoccus denitrificans used two paths to complete the conversion function, the assimilation and the denitrification, and the main influencing factor was dissolved oxygen. The higher the oxygen concentration, the lower the activity of in vivo dissimilatory nitrate reductase and nitrite reductase of Paracoccus denitrificans, the weaker the denitrification capacity, the stronger the assimilation capacity;When NH4+-N and NO3--N or NO2--N coexistence in water, regardless of the concentration of NH4+-N and dissolved oxygen in water, Paracoccus denitrificans always preferentially used NH4+-N to synthetic bacterial substances via assimilation, and almost transformed all NO3--N or NO2--N via aerobic denitrification. Only when NH4+-N had been depleted and NO3--N or NO2--N was still remaining, Paracoccus denitrificans began to assimilate the NO3--N or NO2--N partly for cell growth.5. Paracoccus denitrificans of10g·L-1was non-toxic for zebrafish through the way of water contact. Moreover, Paracoccus denitrificans existed in natural water environment, so it was safe to be applied to control the nitrogen pollution of aquaculture water.6. Paracoccus denitrificans was applied to fish culture ponds under the dissolved oxygen concentration of4.0～5.1mg·L-1, it had good transformation and removal effect on NH4+-N, NO3--N, NO2--N, and all of the average removal rates>40%, while it also had an removal effect on COD. Within a certain range, the bigger the dosage of Paracoccus denitrificans and the longer the duration of action, the better the water control effect. Taking into account the economic effectiveness of the practical application, the appropriate dosage was1000mL·(acre·m)-1(bacterial concentration≥109CFU·mL-1), and the effective duration of action was10d.The details of the aerobic denitrification of Paracoccus denitrificans resolved the contradiction of aquaculture water must be aerobic and denitrification must be anaerobic or anoxic, and provided a new idea for nitrogen removal of aquaculture water.