Degradation Of Atrazine By Persulfate Activated By Cold Plasma

Atrazine（ATZ）is one of the most widely used chloro-s-triazine herbicides for agricultural production in many countries/regions（such as Brazil,China and the United States）,and its the total usage has been steadily increasing since its inception.Due to its strong mobility in the soil and moderate water solubility,ATZ can easily migrate to groundwater and surface water,causing pollution in soil,ground water,and drinking water.Since ATZ is a potential human carcinogen and endocrine disruptor,its negative effects may occur when it migrates to the aquatic ecosystem,and it is urgent to develop efficient treatment methods for ATZ water pollution control.Pollutants removal based on persulfate（PS）advanced oxidation process has been extensively explored.Heat,ultraviolet rays and carbon material have been used for PS activation separately.Therefore,it is imperative to investigate the high-efficiency,safe,no secondary pollution activation method.Dielectric barrier discharge（DBD）,as an advanced oxidation technology,can generate a variety of free radicals,such as·OH,HO₂·,H·,ions and free electrons（e^-）.In addition,physical effects such as ultraviolet rays,shock waves,and heat can also be generated during discharge.These combined effects are all conducive to activate PS.At the same time,in order to improve the gas-liquid mass transfer efficiency of the plasma reactor,microbubbles（MBs）are introduced into the system.In this work,a DBD/MBs activated PS process was designed,ATZ was selected to be the target contaminant.The operating conditions were optimized.Effects of common anions/cations in water,humic acid and the actual water matrix on ATZ degradation were investigated.The activation mechanism of PS and the degradation mechanism of ATZ were also explored.The main research contents and results are as follows:（1）The ATZ degradation efficiency by DBD/PS,MBs/PS and DBD/MBs/PS was separately investigated.The resluts showed that the existence of PS greatly promoted the generation of free radicals,the presentation of MBs enhansed the gas-liquid mass transfer as well as the PS non-radical activation,and DBD was the main driving force for PS activation.Compared with DBD/PS and MBs/PS alone,the DBD/MBs/PS system showed obvious synergistic effects.（2）Effects of solution temperature,discharge power,PS dosage and initial solution pH value were investigated.The results showed that the heat energy generated by DBD slowly heated the treated solution,which is beneficial for PS activation and ATZ degradation.Besides,the higher discharge power or PS dosage were detrimental to the ATZ degradation,and correspondingly the highest removal efficiency was achieved at a discharge power of 85 W and PS dosage of 2 m M,respectivly.Moreover,the degradation efficiency under acidic and neutral conditions was better than that under alkaline conditions.（3）Effects of different anions and cations,humic acids and several actual water matrix on ATZ removal were studied.The presence of SO₄^2-,Cl^-,CO₃^2-,and HCO₃^-inhibited ATZ decomposition,while a slight promotion effect was observed as the addition of humic acid.Besides,surface water,groundwater water and secondary sedimentation tank effluent had a significant inhibitory effect on ATZ abitation,but after 75 min treatment,the degradation efficiency of ATZ in tap water coud reach 56%.（4）Free radicals identification by different radical trapping agents,electron paramagnetic resonance（ESR）and optical emission spectroscopy（OES）were conducted.The degradation products of ATZ were also detected by HPLC-MS,and the possible ATZ degradation pathway was speculated.The results showed that HO·,SO₄^-·,¹O₂ and RNS were the main active spcises involved in ATZ removal,and the degradation pathways of ATZ included alkylenation,alkyl oxidation,dealkylation and dechlorination.