Study On Biodegradation Of EDTA In Sulfate-reducing System

This dissertation aims to study the biodegradation of EDTA by a mixed culture YAZ and strain CMX in sulfate-reducing system. The mixed culture YAZ is composed of Desul-fovibrio sp.YAZ1 and Enterococcus sp.YAZ2. Strain CMX belongs to Desulfovibrio sp.. Effects of oxygen content,carbon source and organic nitrogen source on the biodegradation of EDTA were investigated. Influences of the complex compound morphology on the biodegradation of EDTA were also studied. In addition to this, the biodegradation of EDTA by the mixed culture YAZ in the presence of sodium molybdate and in aerobic were investigated too. Bacteria morphology were observated by SEM.The biodegradation rate of EDTA increases with the increase of oxygen content in the experimental range.Sodium lactate as the carbon source, partial biodegradation of EDTA by mixed culture YAZ was achieved accompanied by a efficient removal of sulfate. The degradation rate of EDTA was 15.4% in 72 hours. In contrast, with fructose, sucrose and glucose as carbon sourc, due to the fermentation of Enterococcus YAZ2, pH values dropped to 4.5-5.0, inhibiting the sulfate reducing process. Due to the biodegradation of EDTA while the Desulfovibio sp.YAZ1 was inhibited, we concluded that EDTA was degradated by Enterococcus YAZ2 in the mixed culture YAZ.With yeast extract, peptone, urea as organic nitrogen source, the effects on EDTA degradation was unconspicuous.Morphology of the complex compound had a important influence on the biodegradation of EDTA by the mixed culture YAZ and strain CMX. The degradation rate of Ca-EDTA was higher than that of Fe-EDTA, but a better sulfate reducing rate in Fe-EDTA system.After the addition of sodium molybdate, Desulfovibrio sp.YAZ1 was inhibited absolutely, the sulfate-reducing process came to a termination. In this case, the biodegradation of EDTA still appeared. So, we further concluded the contribution of Enterococcus YAZ2 to the biodegradation of EDTA in the mixed culture YAZ.In aerobic condition, the Desulfovibrio sp. YAZ1 was inhibited by oxygen, the sulfate-Reducing process stopped while a efficient removal of EDTA was achevied.The degradation rate of EDTA was 38.9% in 96 hours. Oxygen concentration is an important affcet factor on biedegradation of EDTA. This is a futher evidence for that EDTA was degradated by Enterococcus YAZ2.Bacteria morphology were observated by SEM. Desulfovibrio sp. YAZ1 were short rods, Enterococcus YAZ2 were spherical and ova, CMX were short rods too. In aerobic conditions, Enterococcus YAZ2 were in a dominant position in the mixed culture YAZ.