Research And Application Of Double Iron Electrode Alternating Current Coagulation Technology In Treatment Of Electroplating Wastewater Containing Heavy Metals

In recent years,the prevention and treatment of heavy metal industrial wastewater have attracted the attention of relevant departments and environmental protection agencies.Electrocoagulation(EC)technology is an environmentally friendly technology,and its application in wastewater treatment has attracted attention of researchers.In this study,we used alternating current coagulation(ACC)technology and Electro-Fenton pulse alternating current coagulation(EF-PACC)coupling technology to remove heavy metal ions and Cu²⁺-organics from electroplating wastewater,respectively.The effects of p H value,current density,initial concentration and reaction time on the removal efficiency of heavy metal ions and chemical oxygen demand(COD)were studied.Response surface methodology(RSM)was used to optimize the process parameters of the experiment to find the optimal process conditions and obtain higher removal efficiency.Compared with direct current coagulation(DCC),ACC can greatly reduce concentration polarization and improve current efficiency,so as to reduce energy consumption.The concentration of heavy metal ions in solution was detected by UV spectrophotometry.The morphology,composition,functional groups and crystal structure of the iron sol were characterized by SEM,EDS,FTIR and XRD.The degradation process of organic compounds in EF-PACC was described by UV,ESR and GC-MS.The adsorption behavior of iron sol on heavy metal ions in wastewater was studied by isothermal adsorption model,adsorption kinetics and adsorption thermodynamics.The main conclusions are as follows:(1)Cr(VI)in wastewater was treated by sinusoidal alternating current coagulation(SACC)with double iron electrodes.The results showed that the removal efficiency of Cr(VI)could reach 99.73%in the simulated wastewater solution containing 33.1 mg·dm^-3Cr(VI)at p H 5.6,the current density of 2.7 A·m^-2and the reaction time of 20.5 min.The flocs produced by SACC have large specific surface area and good adsorption performance.There is a strong interaction between Cr(VI)and ferrosol.Cr(VI)on the electrode can be reduced to insoluble Cr(III)compounds and deposited.Langmuir adsorption isotherm model and Pesudo-second-order kinetic can more accurately describe the adsorption behavior of Cr(VI)on iron sol.(2)The effects of SACC and DCC on Cu²⁺removal from printed circuit board(PCB)wastewater were compared in terms of removal efficiency(Re),energy consumption(EEC),electrode consumption,sludge amount and treatment cost.The results showed that under the optimal process conditions,i.e.c₀=41.99 mg·dm^-3,p H=7.14,j=0.293 A·m^-2,t=16.7 min,the removal efficiency of Cu²⁺by SACC and DCC were 99.86%and 98.21%respectively,and the energy consumption(EEC)were 2.76×10^-2k Wh·m^-3and 4.42×10^-2k Wh·m^-3,respectively.The pilot test results show that the process is feasible in practical industrial application.The mechanism of removing Cu²⁺by SACC mainly includes three aspects:electrodeposition on iron electrode,formation of copper hydroxide precipitation with OH^-and final co-precipitation of Cu²⁺adsorption by iron sol.The adsorption of Cu²⁺by SACC and DCC followed the Langmuir adsorption model and the pseudo-second-order kinetics.The maximum saturated adsorption capacity(q_max)of Cu²⁺by the iron sol generated by SACC was greater than that by DCC.Adsorption thermodynamics studies show that the adsorption process is endothermic and spontaneous.(3)Electro-Fenton(EF)coupled pulse alternating current coagulation(EF-PACC)technology was used to remove Cu²⁺-organic compounds in copper plating wastewater.The effects of various factors on the removal efficiency(Re)of Cu²⁺-organic matter were studied and the optimum operating parameters were determined.The results show that under the optimal conditions of initial p H=2.5,current density(j)=2 A·m^-2,initial c(Cu²⁺)=50mg·dm^-3,c(COD)=500 mg·dm^-3,c[H₂O₂]=10 cm³·dm^-3,frequency(f)=1Hz,t=20 min,the R_e(Cu²⁺)was 99.59%.R_e(COD)was 90.21%.Compared with single EF and PACC process,the order of treatment effect is EF-PACC>EF>PACC.EF-PACC technology has a good application prospect in the treatment of Cu²⁺-organic composite wastewater.The EF-PACC process includes two processes:·OH degradation of organic compounds generated during the EF process,and Fe³⁺generated by EC process further forms nano-iron sol with adsorption capacity.The interaction of these two effects can effectively remove Cu²⁺-organic in wastewater.(4)Based on the process and mechanism of heavy metal wastewater treatment by SACC in laboratory,a wastewater treatment system was independently designed and developed by optimizing and self-made main reactor.Under specific experimental conditions,the main factors affecting the p H value of Fe SACC process are current efficiency?and reaction time?t.Under the optimal test conditions:j=1.3 A·m^-2,initial p H=10,t=85 min,Re(Ni²⁺),Re(Zn²⁺)and Re(Cu²⁺)in SAC mode are slightly higher than those in DC mode.However,compared with the traditional DC mode,using Photovoltaic energy supply sinusoidal AC coagulation(PE-SACC)real-time control strategy can reduce EEC by 37.1%,electrode consumption by 62.2%and sludge yield by 66.6%.The main agglomerate is?-Fe OOH,which is consistent with the laboratory results.Ni²⁺,Zn²⁺and Cu²⁺were successfully adsorbed on the iron sol.The operation cost of pilot scale treatment of wastewater containing Ni²⁺,Zn²⁺and Cu²⁺is 64.86%lower than that of traditional DCC methods.PE-SACC has the advantages of high efficiency,stable effect and lower cost,which provides technical support for the application of PE-SACC in industrial wastewater treatment.