Study On The Technology And Mechanism Of Electrochemical Treatment Of Manganese Wastewater And Phosphorus-Organic Wastewater

In the field of industrial wastewater,complex wastewater containing heavy metals,inorganic substances and refractory organic substances is difficult to be treated.Several technics have been used to treat such wastewater.Among them,electroflocculation(EC)is widely used to treat wastewater containing heavy metal ions and inorganic pollutants due to its good environmental protection and high removal efficiency.Electro-Fenton(EF)is one of efficient and environmentally friendly methods for treating organic wastewater.However,the severe problems,such as electrode plate passivation,high energy consumption,and large sludge are led in the direct current(DC)electrolysis process,which greatly limit the application of electrochemical technology in wastewater treatment.In our study,the above problems are solved by applying a positive unidirectional pulse or a sinusoidal AC signal.Polyvinyl alcohol in the simulated wastewater was removed by unidirectional pulsed electro-Fenton technique(PACEF).The effects of operating parameters of current density(j),initial pHo and H2O2 addition on COD removal were investigated.The morphology,elemental composition,crystal structure and functional groups of the sludge were characterized by SEM,EDS,XRD,FTIR and XPS.The main conclusions are obtained as follows:(1)The unidirectional pulse electrocoagulation process(PACC)was used to treat manganese-containing wastewater and the optimal operating conditions were determined.The results showed that at j=2.5 A·m-2,pH0=7,c0(Mn2+)=50 mg·dm-3,f=500 Hz,c0(NaCl)=500 mg·dm-3,t=40 min,Re(Mn2+)was 99.09%.The removal mechanism of manganese by PACC process is to produce metal hydroxide precipitation and form manganese oxide.(2)The sinusoidal alternating current fenton-electrocoagulation coupled process was used to treat phosphorus and COD wastewater and the optimal operating conditions were determined.The results showed that Re(TP)and Re(COD)were 97.56%and 87.77%,respectively,under the conditions of pH0=3,j=0.5 A·m-2,c0(TP)=18 mg·dm-3,c0(COD)=300 mg·dm-3,c0[30%H2O2)]=6 cm3·dm-3,t=45 min.EEC was 0.09 kWh·m-3.The sinusoidal alternating current flocculation(SACC),sinusoidal alternating current Fenton(SACEF),and sinusoidal alternating current Fenton oxidation-electrocoagulation coupling(SACEF-SACC)processes were compared.The order of removal efficiency was SACEF-SACC>SACEF>SACC.Compared with DCEF-DCC,SACEF-SACC can reduced 45%energy consumption.However,the COD removal efficiency was not only increased by 37%,but the TP removal rate was also improved by 2%.Organic pollutants are removed by the combined effect of electro-Fenton oxidation and flocculation.Phosphate radicals are mainly removed by electro-flocculation.(3)The adsorption mechanism of manganese on iron hydroxide colloids was studied by using the adsorption kinetic model.The adsorption behavior of manganese on the iron sol prepared under the optimum conditions conformed to the pseudo-second-order kinetic model.(4)The degradation process of polyvinyl alcohol,phosphorus and surfactants was studied by the reaction kinetic model.Under different initial concentrations,the degradation behavior of polyvinyl alcohol during the PACEF process was more consistent with the pseudo-first-order kinetic model.The degradation behavior of total phosphorus and COD by SACEF-SACC processes also follow a pseudo-first-order kinetic model.