The Study On Degradation Of Pesticides In Water By Activated Persulfate Oxidation

The application of pesticides in agriculture is essential to manage many pests at various stages of crop production and storage for an easy availability of food to growing population of world.However,the reckless use of pesticides has also resulted in the pollution of soil and water resources.The water pollution by pesticides has become major environmental concern around the world due to the toxic nature of pesticides.Therefore,developing a cost-effective technology has been essential to remove the pesticides from waters and wastewaters.Advanced oxidation process based on activated persulfate(PS)oxidation is one of the most effective techniques to degrade the organic pollutants.The degradation of pollutants by PS oxidation is primarily based on the sulfate(SO4·-)radicals,which can also be assisted by hydroxyl(·OH)radicals.PS oxidation has received much attention for the degradation of pollutants from waters due to its higher efficiency,rapid reaction,higher stability,simple application and the mildness of reaction conditions.This study emphasized on the degradation of most commonly applied pesticides in water by chemical activated PS oxidation at laboratory scale.In the first part,copper oxide(Cu O)and Cu O/biochar(BC)composite were synthesized and applied to degrade imidacloprid(IMI),a worldwide widely applied pesticide of neonicotinoids family.The results revealed that BC did not positively influence the efficiency of Cu O.Both Cu O-PS and Cu O/BC-PS systems were inefficient for degradation and have been effective at a short p H range.The degradation by Cu O-PS and Cu O/BC-PS systems was majorly carried out by ·OH.Further,Cu O activated PS oxidation was not effective for degradation in real water matrices.So,it was essential to test another activator to activate PS for IMI degradation.Hence,iron(Fe)-based activators were applied and degradation was monitored.In the second part,hematite(Fe2O3)coated magnetic biochar(MBC)was synthesized and its efficiency for PS activation was compared with the efficiencies of ferrous-ferric oxide(Fe3O4)and iron disulphide(Fe S2,Py R).The results revealed that BC enhanced the activation potential of MBC,which suggested its applicability for PS oxidation of organic pollutants.Fe3O4 was inefficient for activation,hence Fe3O4-PS system resulted the lowest degradation.Py R was relatively more efficient than MBC and Fe3O4 and degradation of 30.0 mg/L IMI by Py R-PS system was 87% within 180 min.Py R-PS system was efficient in p H range of 3.0-9.0;however,the rapid degradation was achieved at p H 3.0.Further,the degradation become rapid by increasing the temperature from 25.0°C to 40.0°C.A degradation of less than 55% after 300 min in sewage and tap waters demonstrated that Py R-PS system was less effective for degradation in real waters.So,another activator,zero-valent iron(ZVI,nanoscale)was applied for PS activation to degrade IMI.In the third part,n ZVI-PS system was applied for degradation,which showed that it was the most efficient degradation system for PS oxidation of IMI.81% degradation of 30.0 mg/L IMI occurred within 20 min at optimum experimental conditions.The degradation by n ZVI-PS system increased by decreasing p H from 9.0 to 3.0,where more than 80% degradation occurred within 10-80 min.The ·OH was mainly responsible for IMI degradation by n ZVI-PS system,which was also assisted by SO4·-.The major intermediates,generated during the degradation were 2-chloro-N-(1H-[1,2,4]-triazol-3-yl)-nicotinamide and 6-Chloronicotinamide.Moreover,n ZVI-PS system resulted a degradation of more than 75% in tap,kitchen and sewage waters,which supports the applicability of the system for degradation in real water channels.In last,ZVI-PMS and Py R-PMS systems were applied to degrade methomyl(MET),a pesticide of carbamate family.Further,the efficiency of PMS was compared with the efficiency of PS to degrade MET.The results demonstrated that PS has been effective in the presence of activators compared to PMS,who have been effective with and without activators.However,the final degradation of MET by PMS-Only was almost equal to its degradation by Py R-PMS and ZVIPMS systems.It was observed that degradation by PMS-Only,Py R-PMS and ZVI-PMS systems was majorly carried out by singlet oxygen(1O2).1.0 mmol/L PMS was sufficient for more than 70% degradation of 20.0-60.0 mg/L MET.Further,degradation was influenced by variation in initial p H.However,the variation in temperature did not significantly influence the degradation.4-Morpholinecarbothioamide,1-methyl N-hydroxy methylcarbamoyloxyethanimidothioate,Methomyl sulfoxide and 2-(Methylthio)acetamide were identified as products after degradation.The PMS-Only system also resulted in more than 70% degradation in real water matrices,which confirmed the applicability of PMS-Only for the degradation of MET in water channels.The present study is first research study,which reports the Cu and Fe activated PS or PMS oxidation of IMI and MET.Further,present study is the first research study,which reports the comparison of Cu O-PS system,Cu O/BC-PS system,MBC-PS system,Fe3O4-PS system,Py R-PS system and n ZVI-PS system for IMI degradation in a single study.Furthermore,it is the first study,which explains the comparison of Py R-PS system,Py R-PMS system,ZVI-PS system and ZVIPMS system for MET degradation in a single study.The comparison of various activator-oxidant systems for the degradation of one pollutant in one research study has not been carried out in PS oxidation,to date.Further,the potential applicability of applied systems was determined through experiments in real water matrices,which provides an attractive insight into the application of the applied systems in field.The study revealed that activated PS oxidation is an efficient,rapid and viable technique,which can be applied for effective in situ degradation of pesticides from waters and wastewaters.