Combined Toxicity Of Heavy Metals And Organic Drugs On Nitrifying And Denitrifying Bacteria And Removal Technology Of Resistance Genes

In recent years,the combined pollution of organic drugs and heavy metals is one of the typical types in the water environment and water treatment process.It has been detected many times in the sewage treatment system,and a large number of studies have shown that organic drugs and heavy metals will have an important impact on the activity of nitrifying and denitrifying bacteria.At the same time,the existence of antibiotics and heavy metals will cause the increase of ARGs abundance in sewage,and the removal of ARGs is a hot issue in sewage treatment at present.Therefore,in this paper,organic drugs（ciprofloxacin（CIP）,diclofenac（DCF））and heavy metals（Zn（Ⅱ）,Cu（Ⅱ）,and Cr（Ⅵ））were selected as research subjects to investigate the effects of microbial activity in the nitrification and denitrification microflora under the combined stress of organic drugs and heavy metals.In addition,the coupling system of ferrate and sulfite was used to treat wastewater containing ARGs to evaluate its removal efficiency of ARGs.Zn（Ⅱ）,Cu（Ⅱ）,Cr（Ⅵ）and DCF alone inhibited sludge activity and nitrifying denitrifying enzyme activity,and the influence degree of heavy metals was Cr（Ⅵ）>Cu（Ⅱ）>Zn（Ⅱ）in turn.Under the combined stress of three heavy metals and DCF,the combined toxicity of Cu（Ⅱ）/DCF pollution on sludge activity and nitrifying denitrifying enzyme activity was synergistic,and Cr（Ⅵ）/DCF pollution on sludge activity was antagonistic.Zn（Ⅱ）/DCF pollution had synergistic effect on sludge activity and enzyme activity,and antagonistic effect on sludge denitrification and enzyme activity.The addition of heavy metals and/or DCF would increase the PN and PS contents in activated sludge EPS,and PN was the main feedback of bacteria to metals,DCF and mixed metals/DCF.The FITR of EPS indicated that protein C=O,C-O group and polysaccharide O-C-O group played a major role in the interaction of EPS with metal and DCF.Heavy metals,DCF and combined pollution of heavy metals/DCF could stimulate the production of ROS and LDH.The changes of ROS production and LDH release indicate that heavy metals and/or DCF have toxic effects on microorganisms in activated sludge.The removal effects of K₂FeO₄/Na₂SO₃ on total genomic DNA and resistance genes gyr A,par C,qnr S and int I1 tended to decrease with the increase of sulfite concentration.Compared with Fe（Ⅵ）alone,the removal effect of K₂FeO₄/Na₂SO₃ on total ARGs was significant.The removal rates of genomic DNA were 87.47%,89.70%,and 96.48%when the ratio of K₂FeO₄/Na₂SO₃ was 2,1,and 0.5,respectively.When the ratio of K₂FeO₄ to Na₂SO₃ was 0.5,the K₂FeO₄/Na₂SO₃ showed the highest removal rate of genomic DNA.At the antagonistic gene level,the removal efficiencies of gyr A,par C,qnr S and int I1 tended to decrease with the increase of sulfite concentration.It was also found that SOS response was affected in the K₂FeO₄/Na₂SO₃,and the abundance of lex A decreased with the increase of sulfite concentration,while the abundance of rec A and umu D increased first and then decreased with the increase of sulfite concentration.ARGs and int I1 could be effectively removed by flocculation in the K₂FeO₄/Na₂SO₃,and the gene copy number in the precipitate was about 0.61-log to3.21-log higher than that in the supernatant.The hyperchromic effect of DNA ultraviolet absorption spectrum indicated that either treatment with Fe（Ⅵ）and K₂FeO₄/Na₂SO₃ would destroy the DNA structure,and the mechanism of removing ARGs was clarified.The free radical quenching experiment further showed that during the removal of ARGs by the K₂FeO₄/Na₂SO₃ both SO₄^·-and·OH free radicals were generated,and the free radical that played the main role was SO₄^·-.The K₂FeO₄/Na₂SO₃coupling system induced oxidative stress in microorganisms,promoted the production of ROS and the release of LDH,and reduced the relative enzyme activities of CAT and SOD.After treatment with K₂FeO₄/Na₂SO₃,the community structure changed significantly.At the gate level,the relative abundance of Actinobacteria and Firmicutes increased firstly and then decreased with the increase of sulfite concentration in the K₂FeO₄/Na₂SO₃,while the relative abundance of roteobacteria decreased firstly and then increased,and at the genus level,The relative abundance of Alphaproteobacteria and Betaproteobacteria decreased gradually,while that of Gammaproteobacteria increased gradually.The removal of ARGs might be related to changes in community structure.