Composite Toxic Effects And Mechanisms Of Agnps And Phenol On Pure Denitrifying Bacteria

Now silver nanoparticles are widely used in our daily life, with the widely application of the Ag NPs, the potential environmental biological effects aren’t also allow to ignore.Ag NPs releasing from the consumer goods are most likely with the sewage into the sewer system,and then into the sewage treatment plant.however, the existence of the Ag NPs has a certain toxic on the microorganism of wastewater biological treatment system’s. At the same time,phenol is commonly in waste water of a wide range of industries,which also has high biological toxicity.Part of the studies have proved that Ag NPs and phenol respectively have certain inhibition on microorganism,the research of their impacts on the denitrifying bacteria is less.So this thesis takes Brachymonas denitrificans as model strains, Studing the effect mechanism and influences on the activity of denitrifying bacteria by respectively building the Ag NPs and phenol exposure experiment.And exploring joined poisoning effects on bacteria through building the Ag NPs with phenol compound pollution.In this paper,the bacteria were exposed to the medium which contained different concentrations of Ag NPs(0.1~30mg/L) and phenol(0.05~6mg/L),detecting the denitrification ability.When the casting concentration of Ag NPs is 1.0 mg/L, the bacteria of NO3-- N reduction rate is 0.15mg/(L·h), denitrifying bacteria capacity is affected by a certain degree. By transmission electron microscopy observation can be found the bacterial cell membrane surface is rough, and lactate dehydrogenase(LDH) release rate was 149%, intracellular bacteria produce reactive oxygen species(ROS) content is 6.97 times that of blank group.With the increase of Ag NPs concentration, bacteria denitrification capacity is decreased obviously. Phenol to bacteria toxicity is higher, when the concentration of phenol dosing is 0.1 mg/L, the NO3-- N reduction rate was only 0.17mg/(L·h), bacteria cell membrane integrity were affected, and LDH release rate was 132%, NR activity was 0.14.And when the concentration of phenol dosing?5mg/L, activity of bacteria was almost completely loss.Changing the bacteria culture temperature and p H, bacterial growth and enzyme activity is affected by the serious, and organic metabolic main way canchange.When p H<6 or p H?8, bacteria NO3--N reduction rate significantly decreased,and the medium bacteria Numbers have plummeted.But the change of culture does not reduce the biological toxicity of Ag NPs and phenol,the bad cultivation environment makes the poor state of bacterial growth,low concentration of silver nanoparticles and phenol can obviously decrease activity of denitrifying bacteria.The LDH release rate is higher than the best environment to cultivate.Ag NPs can adsorb some amount phenol, and the different contact temperature will effect the adsorption equilibrium between Ag NPs and phenol and adsorption quantity.The mixture of Phenol and Ag NPs has higher toxicity,which has Microbial bigger threat for communities in water treatment system, which provides a theoretical basis for composite toxicity research conclusion.