Study On Treatment Of Shale Gas Wastewater By Electrolysis And Its Safety Analysis

In view of the advantages of electrolytic process,such as simple preparation process and no secondary pollution,activated persulfate technology has been widely used in wastewater treatment field.In this article,the wastewater from Chongqing Fuling shale gas production base in studied.In order to reduce the harm of pollutants to the ecological environment,the wastewater is treated by electroflocculation and electrocatalysis process.Application of electroflocculation-persulfate synergistic process to the treatment of shale air pressure cracking wastewater.The main contents and results are as follows:（1）Study on the treatment of back row wastewater by electroflocculationpersul fate synergistic.（1）The effects of electrolysis time、current density、electrode spacing、stirring speed、pH of wastewater and the amount of persulfate with the removal of COD were investigated.The optimum conditions of electroflocculation-persulfate synergistic treatment were determined as follows:electrolysis time 25 min,current density 41.7 mA/cm²,electrode spacing 4 cm,stirring speed 100r·min^-1,wastewater pH 7.0,and the amount of persulfate0.006mol/L.Under these conditions,the removal rate of COD in the wastewater is 94.5%,the electrical conductivity is 71mS/m,the salinity is 4065mg/L,the unfiltered residue content is59 mg/L,the effluent COD is 225 mg/L and the BOD₅ is 126 mg/L,which meets the national secondary discharge standard.（2）The CV test on the process of co-flocculation and persulfate synergistic treatment of returned wastewater was performed,and the results of XRD、SEM、EDS and FT-IR characterization of the flocculated product show that the Fe²⁺activated persulfate produced by the electrolysis process produces organic compounds in the waste water of strong oxidizing radical sulfate radical oxidation,at the same time,Fe²⁺was oxidized to Fe³⁺and then hydrolyzed to flocculate.The preliminary kinetics study showed that the reaction was first order kinetics.（3）The water quality safety of the treated wastewater under optimized conditions is analyzed.The results show that four heavy metal ions of manganese,chromium,copper and lead have all reached the standard of safe discharge.（2）Preparation of composite RuO₂-PPy（PPy:Polypyrrole）electrode and treatment of wastewater by electrocatalytic oxidation（1）The SnO₂-Sb₂O₃-Er as the intermediate layer was prepared by the coating thermal decomposition method,and the composite electrode material with RuO₂-PPyas the surface layer was prepared by electrodeposition.Using XRD characterization and LSV testing,it was determined that when Sn:Er=100:4,the stability of the intermediate layer is highest.The effects of PPy concentration,current density,and temperature on RuO₂-PPy in the surface layer were investigated by XRD characterization and LSV measurements.The optimum preparation conditions for the determined surface:the ratio of Ru³⁺:C₄H₅N is 1:2,the current density is 8 mA/cm²,and the temperature is 55°C.The coating prepared under the optimal condition was characterized by FT-IR,SEM and EDS analysis,By the analysis of the functional group,it can be found that the coating has pyrrole ring formation.Through the morphology test,it is known that the surface is flat and dense,and the PPy particles are produced.The stability test shows that the conductivity of the composite electrode is obviously enhanced and the electric life is prolonged.（2）The effects of electrocatalytic oxidation on wastewater treatment were investigated by single factor experiment,the final optimization conditions were as follows:current density30mA/cm²,electrode spacing 1 cm,pH 5.5,electrolyte concentration 1200 mg/L.Under the optimum conditions,the removal rate of COD can reach 96%,the electrical conductivity is 53mS/m,the salinity is 3325 mg/L,the unfiltered residue content is 41 mg/L,the effluent COD is 163mg/L and the BOD₅ is 110 mg/L,which nears the national secondary discharge standard.The kinetics of organic matter degradation by electrocatalytic degradation was investigated by fitting the relation between In（COD₀/COD_t）and time.It was determined that the electrocatalytic reaction of different current densities,electrode spacing,pH and electrolyte concentrations on the returned wastewater was a first-order reaction.Through the detection of heavy metal ions in water quality,Manganese,chromium,copper and lead four kinds of heavy metal ions have reached the national secondary discharge standard or above,and the safety of effluent has been determined.The effect of electric flocculation and persulfate synergistic、electrocatalytic oxidation on wastewater of shale gas is remarkable,which makes the biodegradability of the wastewater improved and the threat to the safety of human body and environment has been greatly reduced.