Study On Degradation Of Atrazine In Soil By Microwave Activated Persulfate

In recent years,with the acceleration of urbanization and the adjustment and transformation of industrial structure,soil pollution caused by the relocation of a large number of industrial enterprises has become a major problem affecting the use of urban land resources.As a common herbicide,atrazine（ATZ）has great demand because of its remarkable effect and low cost.The relocation of pesticide plants producing ATZ has led to a large number of ATZ contaminated sites in urgent need of treatment.The advanced oxidation process based on persulfate（PS-AOPs）has a more significant effect on the remediation of site contaminated soil.Microwave（MW）heating technology has more application prospects because of its fast-heating speed,low energy consumption and high degradation efficiency.At the same time,the thermal and non thermal effects of MW have a dual mechanism in the process of activating PS.In this paper,a MW activated PS system has been developed by combining MW heating technology with PS-AOPs technology for remediation of organically contaminated soils at sites,and using ATZ a kind of target pollutant,we determined the superiority of the MW/PS system for degrading ATZ in soils;The reaction conditions for the degradation of soil ATZ by the MW/PS system were optimized;The effect of environmental factors on the efficacy of ATZ from soil degraded by MW/PS system was investigated;The mechanism of ATZ degradation by MW/PS system and the related degradation path were analyzed;and the suitability of MW/PS system for other typical contaminants was evaluated,the main research results were presented as follows:（1）The experiments results of four different systems,PS alone,MW/PS alone,and PS with traditional thermal activation（CH/PS）,on the degradation of ATZ showed that the removal of ATZ by PS alone at 60 min was only 18.8%,and similarly MW alone was only 16.7%;The degradation rate of ATZ by CH/PS system was only 27.9%within 30 min,while the removal rate of ATZ by MW/PS system reached 92%within 30 min,the corresponding reaction rate constant(k_obs)reached0.0842 min^-1,and the degradation rate of ATZ was nearly 100%at 60 min.The study showed that the MW/PS system was significantly superior in both efficiency and rate of degradation to ATZ.（2）The effects of reaction parameters PS dosing concentration,activation temperature,MW power,initial concentration of ATZ,and water/soil ratio on the efficacy of ATZ degradation by MW/PS system were investigated,and the results showed that the increase of PS concentration,activation temperature,and MW power promoted the degradation of ATZ in MW/PS system in a certain range.However,an excessive amount of PS as well as an excessive activation temperature and MW power would increase the MW/PS system radical content rapidly,accelerate the consumption of free radicals and increase the remediation cost at the same time;The increasing initial concentration of ATZ could decrease the degradation rate of ATZ to some extent,but the MW/PS system was able to achieve complete degradation of ATZ at different concentrations within 60 min;The removal efficiency of ATZ by MW/PS system could reach 80%in both water and soil comparisons with more or less water;The optimum removal efficiency of ATZ was 97.9%by optimization at PS dosing concentration of 24 mmol/L,activation temperature of 80 ^oC,MW power of 400 W,initial ATZ concentration of 50 mg/kg,and water to soil ratio of 1:1.（3）The effects of major environmental factors,such as soil organic matter（plus humic acid5%,10%and 20%）and inorganic anions（Cl^-,HCO₃^-andH₂ PO₄^-）on the degradation of ATZ from soils with different organic matter fractions were investigated,and the results showed that soils with different organic matter fractions had little effect on the degradation of ATZ from soils with different MW/PS fractions,and ATZ could be removed up to 98%from soils with different organic matter fractions,demonstrating that this system could play a significant role in ATZ removal from soils with different organic matter fractions;Low concentration of inorganic anions（Cl^-,HCO₃^-）had no effect on the degradation of ATZ in MW/PS system,while high concentration of inorganic anions（Cl^-,HCO₃^-）may quench free radicals and thus slightly inhibit the degradation rate of ATZ,butH₂ PO₄^-had no effect on the degradation of ATZ in MW/PS system.The system as a whole showed a higher tolerance to soil organic matter content as well as to inorganic anions presented in the system.（4）The mechanism of ATZ degradation by MW/PS system was analyzed by radical quenching,radical trapping,and intermediate product identification,and the results showed thatSO₄^?-,?OH,O₂^?-and ¹O₂existed in MW/PS system and all contributed to the ATZ degradation,whereO₂^?-played a stronger contribution to the degradation of ATZ thanSO₄^?-,?OH and¹O₂and played a major role in the degradation of ATZ;Nine ATZ degradation intermediates were detected by LC-MS,and the degradation pathways of three ATZ were deduced,i.e.,they could be finally mineralized to CO₂and H₂O by dealkylation,dechlorination hydroxylation,and oxidation of the alkyl chain,respectively.