Degradation Kinetics And Mechanism Of Atrazine By Fe~0 Activated Peroxymonosulfate

As the most widely used herbicide in the world,atrazine（ATZ）is one of the most commonly detected agents in groundwater.The concentration of ATZ in groundwater is the highest in Northeast China.ATZ is difficult to be decomposed naturally in the environment,and is a strong secretion disruptor that can interfere with the hormonal system of human and animals.ATZ can reduce frog fertility,tadpole cardiac tissue disorders,affect the neuroendocrine function of rats and so on.ATZ not only affects the health of animals,but also increases the incidence of breast cancer,prostate cancer and other cancers in humans.Therefore,a green,economical and efficient water treatment technology is needed to remove ATZ from groundwater.Advanced oxidation technology（AOPs）is the best method to degrade organic pollutants which are difficult to decompose under natural conditions because of its strong oxidation capacity and fast degradation rate.Persulfate can also be activated by different kinds of transition metal elements,including Mn,Co,Cu,Fe,etc.Because iron is an abundant metal in the earth’s crust,it plays a very important role in the diversification process from physiological research to industrial processing and manufacturing.Peroxymonosulfates（PMS）are more easily activated than perdisulfates due to the asymmetry of the groups on both sides of the-O-O-bond.In this paper,the advanced oxidation technology of zero valent iron activated persulfate was selected to degrade ATZ in water.Firstly,the effects of operating conditions,such as initial pH value of reaction solution,Fe⁰dosage,PMS dosage and initial concentration of ATZ,on the degradation of ATZ in water by PMS/Fe⁰advanced oxidation system were studied,and the main parameters that had significant effects on the degradation of ATZ were analyzed by principal factor analysis.Secondly,the ratio of free radical species to yield was identified by the method of competitive free radical of pollutants.Furthermore,the influence of main water quality parameters on the degradation of ATZ in water by PMS/Fe⁰advanced oxidation system was studied,and the removal effect of ATZ in real water was simulated.Finally,the cost of ATZ removal was analyzed based on energy input and agent addition.The results show that in the pH range（2.5-9）,the degradation efficiency of ATZ decreases with the increase of pH value.When the pH value is 2.5,3,4,5,the degradation law of ATZ conforms to the pseudo-first-order kinetic model.When the concentration of PMS increased from10μmol/L to 200μmol/L,the degradation efficiency of ATZ first increased and then decreased.The pseudo-first-order rate constant increases with the addition of zero-valent iron（0.05 g/L-0.25 g/L）.This is because when the concentration of PMS is too high,excessive PMS in the solution reacts with HO^·and SO₄^·-,thus reducing the available amount of HO^·and SO₄^·-,and excessive SO₄^·-will also appear quenching.The SO₄^·-in the system is reduced,the oxidation effect is weakened,and the degradation rate of organic matter is slowed down.Increasing the concentration of target pollutant ATZ（1.7μmol/L-3.4μmol/L）reduced the pseudo-first order rate constant.Among the above factors affecting the degradation effect of ATZ,PMS concentration,Fe⁰dosage and initial pH value have the greatest influence on the degradation effect of ATZ.When methanol and tert-butanol were added into the system,it was found that both methanol and tert-butanol could inhibit the degradation of ATZ.The competitive results of nitrobenzene and ATZ showed that the active species in PMS/Fe⁰system were sulfate radical(SO₄^·-)and hydroxyl radical（HO^·）.The yield ratio of the two free radicals was 10.5:1.The anions in actual water affected the degradation of ATZ,and CO₃^2-,Cl^-and NO₃^-inhibited the degradation of ATZ.The inhibition effect of Cl^-on ATZ increased with the increase of concentration（2mmol/L,10mmol/L）.The degradation of ATZ could be inhibited by the use of dilute hydrochloric acid to adjust the initial pH of the solution.In the simulated groundwater condition,most of ATZ was degraded after 24h of reaction,indicating that PMS/Fe0 had a good removal effect on ATZ under the background of simulated groundwater quality.Finally,the electrical energy（EE/O）required to reduce pollutant concentration by one order of magnitude per 3785 litres of water at different pH values was studied,and the energy input and pharmaceutical costs for different pH values（pH=2.5,3,4,5）were calculated respectively.When pH=2.5,the total EE/O value is the minimum.