Study On The Characteristics And Mechanism Of Inactivating Indicator Microorganisms By Activated Persulfate

The use of recycled water can greatly alleviate the problem of water shortage.However,conventional disinfection techniques always produce more disinfection by-products（DBPs）and have poor inactivation effect on disinfectant-resistant pathogenic microorganisms.Therefore,there is an urgent need for a disinfection technology that can effectively inactivate pathogenic microorganisms and produce fewer toxic and harmful DBPs.Advanced oxidation technology based on persulfate has become a research hotspot due to its high efficiency and less generation of environmental DBPs.In this experiment,the characteristics and mechanism of activated persulfate inactivation indicator microorganisms were studied.The main conclusions are as follows:（1）Fe SO₄ activated persulfate（PDS）was used to compare the sterilization characteristics of Fe²⁺/PDS and Fe²⁺/H₂O₂ with the indicator microorganisms of Escherichia coli（E.coli,Gram-negative bacteria）and Enterococcus faecalis（E.faecalis,Gram-positive bacteria）as research objects.The results showed that under the conditions of Fe²⁺/oxidant molar ratio of 2:5 and p H=7,the technology of Fe²⁺/PDS inactivated 6 log E.coli and 2.71 log E.faecalis,respectively.The technology of Fe²⁺/H₂O₂ inactivated 0.98 log E.coli and 0.51 log E.faecalis in 180 min,respectively.The results indicated that Gram-negative bacteria are more likely to be inactivated than Gram-positive bacteria.（2）When both Fe²⁺and oxidants were 0.5 m M and p H=7,the technologies of Fe²⁺/PDS and Fe²⁺/H₂O₂ inactivated E.coli for 6 log（10 min）and 3.37 log（180 min）,respectively.The two technologies inactivated E.faecalis for 4.2 log and 0.84 log in180 min,respectively.It was concluded that Fe²⁺/PDS has better disinfection effect on indicator microorganisms than Fe²⁺/H₂O₂.（3）The effective Fe²⁺content in the system was controlled by adding medium strength reducing agent such as Na₂S₂O₃·5H₂O,Na HSO₃ and organic chelator like citric acid,and then Fe²⁺/PDS technology was promoted to inactivate E.coli.The results showed that when the ratio of Fe²⁺/PDS/reducing agent was 1:5:1 and under neutral conditions,the inactivation effect of E.coli in 120 min was 1.6 times that of the control Fe²⁺/PDS system（3.76 log）.Under the same conditions,only 0.08 log E.coli was inactivated by adding organic chelating agent.It was concluded that the medium strength reducing agent has an enhanced effect on the Fe²⁺/PDS technology inactivated E.coli,while the organic chelating agent completely inhibites the sterilization ability of Fe²⁺/PDS.（4）The low cost and high efficiency siderite was selected to activate PDS,and the more representative E.faecalis was used as the indicator bacteria to study the inactivation characteristics of siderite/PDS technology.Results showed that the inactivation effect of this technique on E.faecalis was better when p H was 3.The sterilization effect increaseed with the increase of siderite dosage,PDS concentration and temperature.The inactivated rate was not sensitive to the initial concentration of bacteria.The inorganic ions and natural organic matter（NOM）on the technology of inactivated effect had inhibitory effect,and the strength of the inhibition was followed by NOM>HCO₃^->NO₃^-.The inactivation ratio of E.faecalis decreased from 3.07 log to 1.98 log after four cycles of siderite,and 2.38 log of E.faecalis was inactivated in the fifth experiment after cleaning.（5）The mechanism of activated persulfate inactivation of indicator microorganism was studied by free radical quenching and the determination of extracellular proteins and DNA.The results showed that SO₄·^-played a major role in sterilization of Fe²⁺/PDS technology,and the free radical contribution was SO₄·^->O₂·^->HO·.In Fe²⁺/H₂O₂ technology,both HO·and O₂·^-played an important role in bacterial inactivation.HO·was the main oxidizing substances in siderite/PDS technology sterilization process.In addition,the extracellular protein and DNA levels first increased and then decreased after bacterial inactivation.It was indicated that highly reactive oxygen species could destroy the cell wall of bacteria and release intracellular organic compounds,leading to bacterial inactivation.The late decreasing trend indicated that highly reactive reactive oxygen species might degrade or even mineralize extracellular organic substances.