Efficient Degradation Of Persistent Organic Pollutants In Salinity Refining Wastewater By Electrochemical Advanced Oxidation Processes

High salinity wastewater is diffuclt to treat because it consists of persistent organic pollutants(POPs)and high content of total dissolved solids.Due to high concentration of salt,traditional treatment like biological method can't effectively treat wastewater.Additionally,POPs will be harmful to environment and human if they are not degradated effectively.Thus,it's a huge challenge for chemical engineerer and environment protecter to mineralize high salty refining wastewater effectively and efficiently.In this thesis,using electrochemical advanced oxidation processes(EAOPs),POPs in salinity wastewater were degradated by Boron Doped Diamond(BDD).A common POPs,2,4-dichlorophenol(2,4-DCP)was degradated as specific pollutant and the effects of SO42-and Cl-to EAOPs system were investigated.In order to solve the problem that toxic organic chlorine containing by products produced by anodic oxidation,we designed and prepared nickel hydroxide nanosheet with Pd on nickel foam(Pd/Ni(OH)2/NF)to electrocatalytic hydrodechlorination(ECH).In this study,SO4·-were efficiently produced by electrochemical activation of SO42-at boron doped diamond(BDD)anode.The degradation rate of 2,4-DCP(k=0.828±0.05 h-1)in the presence of Na2SO4 was approximately 4 times than that without Na2SO4(k=0.219 ± 0.01 h-1),indicating that SO4·-exhibited higher reactivity than ·OH at initial pH=9.Moreover,the amount of O2 decreased by 65%after 100 min during electro-oxidation of 2,4-DCP when the concentration of Na2SO4 increased from 0.01 to 0.1 M.The impact of sulfate ions in the electrochemical advanced oxidation were investigated.Electron spin resonance(ESR)measurements were conducted to identify the formation of SO4·-.Electrolysis of 2,4-DCP with specific radical scavengers(ethanol and tert-Butanol)were conducted and the results revealed that SO4·-were mainly produced by one-electron loss of sulfate at basic condition.Electro-generation persulfate was measured and participation of non-radical activation of persulfate was investigated.Taken all findings,a mechanism of electrochemical activation of sulfate at BDD anode was summarized.This technology eliminates the requirement for pH adjustment for wastewater treatment and makes EAOPs more effective and economic as wellBDD anode can active chloride into inorganic radical species such as Cl-,Cl2·-,and accelerate degradation of pollutants.In our experiments,along with concentration of Cl-increase from 0 to 120 mM,degradation rate of 2,4-DCP was improved from 0.36±0.05 h-1 to 18.44±0.35 h-1.However,with increase of Cl-,the mineralization efficiency was decreased.Though analysis of intermediate products,toxic chlorinated organic and inorganic by-products were found.Thus,the formation of toxic chlorinated by-products during electrooxidation was a serious concern when chlorine wastewater was treatedTo solve the toxic by-products' problem,ECH was used to remove chlorinated compounds.We reported a facile synthesis by combining electrodeposition and galvanic replacement reaction to fabricate Ni(OH)2 nanosheet with Pd on nickel foam(e-Pd/Ni(OH)2/NF)through one-step process,which exhibited excellent stability and maintained high electrocatalytic activity at the same time.Anodic oxidation was combined with cathodic reduction for treatment of wastewater contained Cl-.Compared to anodic oxidation,TOC removal rate was improved from 11.25±1.56%to 30.25±2.41%and the specific energy consumption was reduced from 0.68 kWh·(g TOC)-1 to 0.26 kWh(g TOC)-1.