Mechanism Of Atrazine Degradation In Water Via Different PMS Activation Methods

Atrazine(ATZ)is one of the most widely used preemergence and post-emergence chemical herbicides all over the world.Characteristically,it has biological toxicity with strong water solubility and long duration,which can remain in surface water and groundwater for a long time,posing a serious threat to water ecosystem and human health.China is a big agricultural country,and the production and use of ATZ rank among the top in the world.In recent years,the continuous detection of residual ATZ in water environment has caused more and more human health and safety problems.However,the conventional water treatment processes is difficult to remove ATZ from water efficiently.Thus,it has become an urgent problem to explore safer and more efficient methods for ATZ degradation in the water treatment industry.In view of this,Peroxymonosulfate(PMS)is used as an oxidant in this research to investigate the degradation efficiency,influence factors,kinetics and degradation mechanism of ATZ in water under three different activation modes:ultrasonic(US),Heat(Heat)and UV(UV).The main work finished is as follows:(1)The effects of key factors,such as the temperature,PMS concentration,p H,US strength,ATZ concentration,anions(Cl^-,HCO₃^-,NO₃^-)concentration,on the ATZ degradation efficiency and kinetics are investigated.Particularly,the degradation mechanism of ATZ is studied.The results show that the degradation rate of US/PMS is45.85%when the reaction temperature,PMS concentration,reaction solution p H,US strength,ATZ concentration and reaction time are 20?,200 mol/L,7,0.88w/m L,1.25mol/L and 60 min,respectively.Compared with reaction system of US and PMS alone,the degradation rates were 32.43%and 41.75%higher.In the US/PMS system,the anions(Cl^-,HCO₃^-,NO₃^-)display inhibition in the degradation process of ATZ.Moreover,the strong-to-weak sequence of the inhibiting ability is Cl^->HCO₃^->NO₃^-.Furthermore,in the degradation process of ATZ,the US/PMS/Cl^-and US/PMS/HCO₃^-systems are in line with quasi-first-order kinetics,while the the US/PMS/NO₃^-system is more in line with quasi-second-order kinetics.US can activate PMS to produce HO^·and SO₄^·-,thus the oxidative degradation of ATZ by US/PMS mainly depends on dealkylation,dechlorination and hydroxylation.At last,a total of 10 kinds of intermediate products are produced in the degradation process.(2)The influencing factors,kinetics and mechanism of Heat/PMS system on ATZ degradation rate in water are studied.The results show that,when the initial p H value of solution is 7,the reaction temperature is 50?,PMS concentration is 400 mol/L,ATZ concentration is 2.5 mol/L,and reaction time is 60 min,the degradation rate of ATZ in Heat/PMS system could reach 96.28%.HCO₃^-has an inhibitory effect on the degradation of ATZ in Heat/PMS system,while Cl-and NO₃^-have catalytic effects on degradation rate.Further,NO₃^-has a more obvious catalytic effect comparing to Cl^-.Thermal activation can stimulate PMS to produce HO^·and SO₄^·-.The dominant radical types are different under different p H conditions.When ATZ concentration is fixed as 2.5?mol/L,the p H of reaction solution are 6,7 and 8,the ratio of HO^·and SO₄^·-oxidation degradation ATZ is 1.7:1,1:2.4and 1:1.3,respectively.The degradation reaction of Heat/PMS system to ATZ conforms to the pseudo-first-order kinetics,and there are 4 possible pathways in the degradation process.The main reaction types include dealkylation and dechlorination hydroxylation.Finally,a total of 8 intermediate products are produced.(3)By adopting UV to activate PMS,the influence of the reaction temperature,PMS concentration,p H,UV intensity,ATZ concentration and Cl^-,HCO₃^-and NO₃^-concentration on ATZ degradation in UV/PMS system are explored.Also,the degradation kinetics and mechanism of UV/PMS system are studied.The results show that the removal rate of ATZ by UV/PMS system is up to 98.24%when the reaction temperature,PMS concentration,p H,UV intensity,ATZ concentration and reaction time are 20?,50 mol/L,7,50 m W/cm²,2.5mol/L and 20 min.Both Cl^-and HCO₃^-have inhibitory effects on ATZ degradation in UV/PMS systems,but Cl^-has more obvious inhibitory effects.Instead,NO₃^-has promoting effects on the degradation process of ATZ.Kinetic analysis shows that the reaction process of UV/PMS degradation of ATZ is in line with pseudo-first-order kinetics.Both HO^·and SO₄^·-exist in UV activated PMS system.When p H is 7,the ratio of oxidation degradation of ATZ by HO^·and SO₄^·-is close to 1:1.The results of product analysis show that six intermediate products are produced in the degradation process of ATZ by UV/PMS system.Finally,the reaction types include dechlorination hydroxylation,dealkylation,deethylation and dehydration.(4)The UV/PMS system is employed to remove the ATZ in wastewater including Bai Tiao He water(BTH),a water inlet(DWW)of life sewage treatment plant,an industrial wastewater treatment plants(IWW-1)and the water biochemical pool water(IWW-2).The results show that,at room temperature without adjusting the p H of the water sample,the removal rate of ATZ of the above actual water species by UV/PMS system is 100%,76.76%,79.33%,97.23%successively when the concentration of ATZ is 2.5?mol/L,the concentration of the PMS is 20?mol/L,the UV intensity is 50 m W/cm²,and the reaction time is 20 min.The high COD content in DWW and IWW-1 is the major factor for the degradation efficiency reduction of ATZ.As a conclusion,US,Heat and UV can all activate PMS.Among them,UV activation of PMS system has more significant advantage in the degradation of ATZ in water bodies.The research results can provide scientific reference and practical guidance for the efficient treatment of wastewater containing ATZ,and have good application value and prospect.