Study On Resource Treatment Of Glyphosate Wastewater By Persulfate Advanced Oxidation

Glyphosate is a non-specific and destructive organophosphorus pesticide,which is widely used worldwide to protect crops from weeds.During its production and use,a large amount of pesticide wastewater is generated,which is characterized by high phosphorus content,poor biochemical properties,high COD and rich in many toxic and harmful substances.The random discharge of wastewater has caused a series of environmental health issues.therefore,the treatment of glyphosate wastewater has attracted much attention.However,the existing methods of glyphosate wastewater treatment have disadvantages such as incomplete treatment,high investment cost,complicated process,neglecting resource regeneration and generating by-products,which bring burden to the environment and economic development.In this thesis,an electric/high temperature/UV activated peroxynitrite advanced oxidation system is used to treat organophosphorus pesticides in wastewater,and the degradation experiments and various characterization means are combined to recover valuable elements in the subsequent crystallization unit when the The products were characterized and analyzed by degradation experiments and combined with various characterization means for the subsequent crystallization unit to recover valuable elements.The main findings are as follows.（1）The optimization of reaction conditions and the influence of common co-existing substances on the reaction process in the treatment of glyphosate wastewater by an electrically activated peroxynitrite advanced oxidation system were investigated and a comprehensive analysis of the treatment effect and energy consumption was performed.The results showed that glyphosate could be mineralized by 60%in 180 min（60℃,pH=10,d=1 cm,Js=60m A/cm~2,PS=1.29 g,n=200 rpm）.The addition of high concentrations of Cl^-,CO₃^2-and HCO₃^-increased the mineralization efficiency of glyphosate at 180 min from 60%to 98%,72%and 77%,respectively.While several other anions and organic compounds inhibit the mineralization of glyphosate,the special feature of glycine is that the inhibition of glyphosate mineralization decreases with increasing concentration.（2）In addition,in order to improve the treatment effect of glyphosate,high temperature was used to activate the advanced oxidation of glyphosate by peroxynitrite instead.The effects of reaction conditions and coexisting substances on the catalytic degradation of glyphosate were analyzed in depth,and the oxidation mechanism of the process was explored by bursting experiments.The results showed that the optimal mineralization p H of glyphosate was 4.The mineralization rate of glyphosate increased from 16%to 100%at 180 min as the reaction temperature increased from 45℃ to 65℃.Under the optimized conditions,100%mineralization of glyphosate was achieved at 150 min（60℃,PS=1.075 g,p H=3,n=200rpm）.The addition of methanol or tert-butanol to the wastewater before the reaction reduced the mineralization of glyphosate from 100%to 44.89%and 66.7%,respectively.The contribution of two radicals,sulfate radical(SO₄^·-)and hydroxyl radical（HO^·）,in the oxidation process was 40.3%and 59.7%,respectively,after calculation using equation.（3）In addition,to further improve the treatment efficiency of the advanced oxidation of glyphosate by activated peroxynitrite and to investigate the decomposition kinetics of glyphosate,photoactivation was added to the thermal activation for assistance.The effects of reaction conditions and coexisting species on the catalytic degradation of glyphosate were likewise analyzed in depth.The results showed that the mineralization rate under optimal p H conditions was about 20%higher than under poorer p H conditions.The activation was mainly contributed by UV light at temperatures below,while the reaction rate increased 17-fold when the temperature was raised to 60℃ compared to 40℃.The mineralization of glyphosate could also be improved by 1-fold after doubling the concentration of persulfate concentration from16 mmol/L,but the enhancement of mineralization rate decreased significantly with further increase in concentration.（4）Finally,the feasibility of recovering phosphorus from pesticide wastewater was explored in depth.Various substances such as iron sulfate,manganese sulfate,calcium sulfate,aluminum sulfate,magnesium sulfate,dolomite,mullite,fly ash,zeolite and manganese sand were explored for the recovery of elemental phosphorus from glyphosate wastewater after advanced oxidation.The results showed that the recovery of inorganic phosphorus in the wastewater clear liquor was 85.19%,95.03%,78.91%and 86.53%,respectively,with the addition of iron sulfate,aluminum sulfate,magnesium sulfate or 0.1 g of dolomite in the same amount of substance as inorganic phosphorus under the optimal p H conditions.After increasing the dosage,the phosphorus recovery could all reach more than 90%.The recovered products were characterized by SEM,EDS,XRD and XPS,and it was found that the precipitation generated after the addition of magnesium sulfate was of high purity.At p H=11,the addition of magnesium sulfate resulted in nearly 97%crystallization of potassium magnesium phosphate generated in the oxidation unit.In conclusion,this thesis explored the kinetics of the decomposition process and clarified the factors influencing the mineralization rate and mineralization efficiency during the reaction process using glyphosate,a widely used organophosphorus pesticide,as the target of advanced oxidation of peroxynitrite,and finally recovered the elemental phosphorus from the treated supernatant to achieve the purpose of resourceful treatment.