Electrochemical Treatment Of Wastewater Containing Pesticides Or Cr(Ⅵ)

How to deal with the refractory wastewater at high concentration of is a key issue to be solved urgently in the process of rapid industrialization.A growing number of electrochemical methods for treating waste water for its green and pollution-free characteristics in the treatment of pesticides and heavy metal wastewater have appeared.The pollution and treatment development of pesticides and heavy metal wastewater was briefly described in this paper.Especially,several electrochemical treatment technologies were highlighted,and then the application of electrochemical methods for practical pesticide wastewater and Cr（VI）wastewater were studied.Firstly,the 1-（4-chlorophenyl）-2H-pyrazoline-3-one production wastewater was treated with Fenton method,electro-catalytic oxidation method and Fenton-electrocatalytic oxidation method,respectively.The results showed that when the pH was 3.0 in the Fenton reaction,the molar ratio of Fe²⁺to H₂O₂ was 1:10;the Fe²⁺content was 700 mg·L^-1;the reaction temperature was 40°C,and the reaction time was2.5 h,now the COD_Crr removal rate was 41.7%.In the electrocatalytic oxidation reaction,when the pH was 11.0,the current density was 0.03 A·cm^-2,the reaction time was 24 h,and the COD_Crr removal rate was 72.0%.Based on these results,the removal rate of COD_Crr can reach 98.3%when combining Fenton method and electro-catalytic oxidation.HPLC and GC-MS characterization showed that a large amount of organics in the raw water were completely degraded into CO₂ and H₂O due to Fenton-electrocatalytic oxidation.Secondly,the wastewater of 1-（4-chlorophenyl）-3-pyrazolol was treated with Fenton method,electro-catalytic oxidation method and Fenton-electrocatalytic oxidation method.The results showed that in the Fenton-electrocatalytic oxidation,when the pH was 4.0;the molar ratio of Fe²⁺to H₂O₂ was 1:10;the Fe²⁺content was500 mg·L^-1;and the reaction temperature was 30°C;andthe reaction time was 3 h,the COD_Crr removal rate was 11.2%.When the electrocatalytic oxidation reaction adjusted the pH to 11.0,the current density 0.035 A·cm^-2,the reaction time 20 h,and the COD_Crr removal rate was 23.3%.After the Fenton-electrocatalytic oxidation was cycled for three times under the above conditions,The rate of COD_Crr has increased to55.9%.HPLC and GC-MS characterization showed that some of the organics in the water samples were degraded into CO₂ and H₂O due to Fenton-electrocatalytic oxidation.after three cycles of treatment.Finally,the carbon paste electrodes modified by D-gluconate（DCP）and EDTA（ECP）were prepared by coating method and used for electrochemical treatment of Cr（VI）wastewater.The results showed that the residual rate of Cr（VI）at 50 mg·L^-1was 33.5%（DCP）and 4.8%（ECP）for 3h at pH of 3.0,working voltage of-1.2 V,plate distance of 1.0 cm,temperature of 313 K and NaCl concentration of 3%,respectively.The test data showed that the above process included both electroreduction and electrosorption.The ratio of electroreduction is 60.5%（DCP）and 88.3%（ECP）,and the ratio of electro-adsorption is 6.0%（DCP）and 6.9%（ECP）,respectively.