Isolation, Screening Of Denitrifying Bacteria And Study On Its Application

The deterioration of aquarium water,especially nitrite pollution which was difficult to prevent,had being becoming an usual harmful factor of national aquiculture development in our country. Biodenitrification is one of the effective methods to remove nitrite from water at present.202 denitrifying strains were separated from numbers of samples. Their respective denitrifying activities were idetified quantitively in the condition that the CODMn of water sample controlled by sterilized LB medium was about 25 mg/L.At last,thinking the characters of denitrification about DNF409, A13 was obtained. Physiological and biochemical tests besides the analysis of 16SrDNA revealed that the A13 stain was Bacillus Licheniformis.The research result indicated that CODMn was the critical facters which affected denitrification efficiency. when CODMn was below 10.5 mg/L,they could denitrify slenderly.Adding carbon source,especial ethanol,could enhance denitrification obviously.In the range of pH from 6.0 to 8.0,the denitrification efficiency had no difference.In other words, the value of pH would not be a limited facter in actual water.When temperature exceeded 20℃, they could denitrify smoothly.The bacterial concentration also affected denitrification clearly.And they could play the role of eliminating the CODMn .The result showed that denitrification efficiency in actual water was much higher than that in sterilized water.Comparing Yezhi lake water with distilled water,the former advanced the latter obviously.Maybe it was the cooperation of microorganisms in denitrification.So the two strains were applied.Their respective denitrification characters were checked .The research revealed that DNF409 advanced A13 for the degradation of nitrate before 12 hrs,while DNF409 accelerated accumulation of nitrite heavily.They could both degradate nitrate to the low level,but DNF409 also exceeded A13 in the terms of the accumulation of nitrite.With time extending to 156 hrs,nitrite would both elevate.According to this result and the principle of cooperation,the combination application model was confirmed that DNF409 strain was used first,then 24 hrs later A13 strain was applied. Compared with the use of single strain, the combination application of DNF409 and A13 increased the percentage of denitrification about 30%.On the base of this model, response surface analysis was implemented. The result showed that the optimum denitrification condition included as follows: COD_Mn 35.1 mg/L, temperature 32.5℃, bacterial concentration 6.2×10⁶ cfu/mL, time 114.2 hrs.This article studied the dinitrification in the outstanding condition.For example,organic nitrogen existing,it could accelerate denitrification.Too much oxygen would inhibit denitrification.