Study On Degradation Of New Neonicotinoid Pesticide Wastewater By Potassium Sulfate Oxidation

Persulfate(S₂O₈^2-)can be thermally or chemically activated to produce a powerfol oxidant sulfate free radical?·SO₄^-,E0=2.6 V?which can degrade many organic pollutants,such as new neonicotinoid pesticide,imidacloprid,clothianidin,dinotefuran.Main research contents of this article are as follows: The first part was degradation of imidacloprid and clothianidin by heat activated persulfate oxidation process,the second was degradation of clothianidin by microwave-activated persulfate,and the third was degradation of dinotefuran by evaporation combined persulfate.The various factors on the degradation of pesticides were studied in detail,including the temperature,pH,dosing quantity of S₂O₈^2-,the concentration of inorganic ion,microwave radiation time,distillation volume,etc.The free radical species in the reaction system were detected by free radical detection.The degradation products were detected by LC-MS and GC-MS,and the possible degradation mechanism was speculated.The degradation of 70% imidacloprid WDG by heat-activated persulfate showed that the degradation rate increased with the increasing temperatures.The removal imidacloprid with persulfate follows the first order kinetics.The half time of reaction were 173.28,101.93,60.80,31.36,20.32 min when the temperature increased from 50 ? to 90 ?.Activation energy of reaction is 53.291kJ/mol.When the temperature was 80?,and the concentration of potassium sulfate was 20mmol/L,the degradation rate of imidacloprid was slightly higher at neutral conditions than at alkaline and acidic condition.The degradation rate change is only 1.57% as the pH of the starting solution increases from 3 to 11.The addition of chlorine ion?Cl^-?inhibited the degradation of imidacloprid.The basic nitrate?NO₃^-?had no effect on potassium persulfate oxidation of imidacloprid.The presence of bicarbonate?HCO₃^-?had adverse effects on imidacloprid degradation.However,inhibitory effects were observed in the case of existing chlorine ions.The intermediate product of imidacloprid are mainly 6-Chloronicotinamide and 2-chloropyridine by GC-MS.Study on the kinetics of the degradation of clothianidin by heat activated persulfate.The various influence factors on clothianidin removal efficiency were evaluated in this word.The free radical species could be detected in the reaction system by free radicals probe.The results showed that the degradation of clothianidin exhibited a pseudo first-order reaction.The half time of reaction were 8058.13,990.00,150.65,35.00,18.00 min,when the temperature increased from 30? to 80?.Activation energy of reaction is124kJ/mol.The higher persulfate concentration favored clothianidin degradation.When the temperature was 60?,and the concentration of potassium sulfate was 20mmol/L,the degradation rate of clothianidin reached the maximum when the pH of the solution was 4.6.Acidic and neutral pH were more favorable for clothianidin oxidation than basic pH.Degradation of the clothianidin was inhibited by the presence of Clunder the neutral and acidic conditions.Under alkaline conditions,the low concentration of Cl^-promoted the degradation of clothianidin.The presence of HCO₃^-inhibited the degradation of clothianidin.Radical scavenger ethanol and tert-butyl alcohol test indicated that sulfate radical was the advantage of radical species at acidic and neutral p H,while hydroxyl radical was more at basic pH.In order to effectively degrade pesticide wastewater containging clothianidin,the oxidation technology of microwave-activated persulfate were studied.Main impacting factors of degradation rate were investigated,including the microwave radiation time,dosing quantity of K₂S₂O₈,pH of the solution and the concentration of Cl^-and HCO₃^-in aqueous solution.The results showed that the combination of potassium persulfate and microwave radiation can effectively remove clothianidin.The process of clothianidin degradation was accelerated by longer microwave irradiation time and higher persulfate dose in the MW/PS system,with the increase of microwave radiation time,the degradation rate of clothianidin increases.Acidic pH values were more favorable for clothianidin oxidation than basic p H values.The higher degradation was noticed at the pH of 4.5.Clothianidin was not degraded by the action of microwave alone,or by the action of persulfate alone.High level of Cl^-and HCO₃^-showed inhibition on the clothianidin degradation.N-?2-chloro-1,3-thiazole-5-ylmethyl?-N-methyl guanidine and 2-chloro-5-aminomethylthiazole were identified as the major degradation intermediate products by LC-MS.The process of combining evaporation with potassium persulfate oxidaton for degradation of dinotefuran was first proposed in this paper.Experimental results show that with the increase of concentration of potassium persulfate,the degradation rate of dinotefuran increased,and the COD content in the steam condensate decreased.The greater the volume of the distillation,the lower the COD content in the steam condensate became.With the increase of the initial pH,the COD content in the steam condensate decreased.Addition of Fe²⁺ to the solution promoted the decline of COD in the steam condensate.Addition of nitrate to the solution had little effect on the decline of COD in the steam condensate.Addition ofchloride ion had adverse effect on the decline of COD in the steam condensate and that of bicarbonate had positive effect on the decline of COD in the steam condensate.Qualitative detection of the residual liquid and condensate showed that The vast majority of dinotefuran was mineralized,and a small amount was converted into acetic acid.Organic nitrogen was mainly converted to ammonia nitrogen and nitrate nitrogen.