Study On The Process Characteristics And Influence Factors Of Dissimilatory Nitrate Reduction To Ammonium By Strain Desulfovibrio Sp. CMX

Nitrogen cycle is one of the most important geochemical cycles in nature. Dissimilatory nitrate reduction to ammonium is an important process in nitrogen cycle and it is a way of dissimilatory nitrate reduction which is different from denitrification. In some certain circumstances, DNRA is the most important way of the dissimilatory nitrate reduction. At present, there are few studies on the DNRA process under pure culture conditions. To solve this problem, we choose the strain Desulfovibrio sp. CMX which was isolated previously in our laboratory and could reduce Fe(II)EDTA-NO to ammonium. The characteristics and influencing factors of DNRA process of the strain were investigated under pure culture conditions.The ability, influence factors of Desulfovibrio sp. CMX on DNRA process was investigated. The results showed that the production rate of ammonium reached 85.8% and 97.3% with the presence of NO3- and NO2- (10 mmol/L) as the sole electron donor and nitrogen source respectively. Meanwhile, there were no by-products such as N2 and N2O. We optimized the DNRA process with the conditions such as external nitrogen source, the amount of inoculation amount and carbon source. As a result, extra nitrogen, yeast extract, could promoted DNRA process by improving both growth and metabolism of the strain, the best inoculation amount was 20 mg/L(protein concentration) and when the initial nitrate concentration was 10 mmol/L, the best amount of carbon source was 5 mL/L.Then the effect of different concentrations of ammonium chloride, nitrate and sulfide on DNRA process were also investigated. The results showed that high concentrations of ammonium chloride had no effect on DNRA process of Desulfovibrio. sp. CMX which proved the ability of resistant to high ammonium chloride concentrations of this strain. But different initial concentrations of nitrate and sulfide have a significant impact on DNRA process. When the initial concentration was low(10 mmol/L or less), the ammonium was the major product without the generation of nitrous oxide. When the initial concentrations was high(15 mmol/L or more), the final product was ammonium, nitrous oxide and nitrogen. The effect of sulfide on DNRA process was observed. Both the growth and two stages of the DNRA process were inhibited in the presence of sulfide. Inhibition was enhanced with the increase of sulfide concentration. It’s noticeable that the inhibition on nitrate reduction was stronger than the inhibition on nitrite reduction with 6 mmol/L of sulfide, leading to the lower reduction rate of nitrate than that of nitrite. In these conditions, no accumulation of nitrite was observed in the system either.The study on the process of reduction and the effect of impact factors was investigated when the nitrate and sulfate existed simultaneously in the system. It turned out the strain reducted the nitrate first and then reducted the sulfate. The yeast extract could promote the process and affect the final product of DNRA by the strain. Sulfate had different effects on two transformation stages of DNRA by the strain. It promoted the nitrate reduction stage while inhibited the nitrite reduction. Overall, the DNRA process by Desulfovibrio sp. CMX was inhibited by sulfate. The amount of carbon affected the reduction process of the two substances. In the case of sufficient amount of carbon, the strain conducted DNRA process first at the condition of low carbon source, and then the reduction of sulfate was carried out. The reduction of sulfate would be strengthened with the increasing of carbon source, but the DNRA process would be inhibited because of the competition of sulfate reduction and the inhibition of sulfide formed in the reduction of sulfate. On another experiment, the effect of different carbon sources add-ways were investigated. It showed that separate addition of excess carbon source would a the inhibition of sulfate reduction on DNRA process. But the sulfate reduction rate was reduced when the excess carbon was added separately. And there was no promoting on DNRA process and sulfate reduction when metal ions such as Fe or Zn2+ were added.