Electrochemical Degradation Of Spent Tributyl Phosphate-Xylene Wastewater By Using Boron-doped Diamond Elecrotrode

The radioactive spent organic solvents have great harm to the environment and the human body.Accordingly,we should pay attention to the storage,treatment and discharge of these waste organic solvents.At present,there are more or less problems existed in the commonly used treatment methods of waste organic solvents.Thus,it is necessary to improve the treatment methods to increase the efficiency of treatment,enhance the effect of treatment,and avoid secondary pollution as much as possible.The electrochemical advanced oxidation method has unique advantages including simple equipment,being easy to realize automatic control,no secondary pollution,and so on,which has been widely used in the treatment of organic wastewater.The electrochemical oxidation degradation technique using boron doped diamond electrode?BDD?has been a research focus in recent years,since the BDD electrode has such advantages as low resistivity,wide electrical potential window and low background current,etc.In this thesis,the electrochemical oxidation degradation of simulated radioactive organic wastewater was studied using BDD electrode,and the main contents are as follows:?1?The simulated tributyl phosphate wastewater was taken as our research object,and the electrochemical oxidation technology using BDD electrode was adopted in this work.The influences of degradation time,initial concentration of tributyl phosphate(1.0-12.0 g L^–1),current density(10-80 mA cm^-2),the pH value of solution?3-11?,the concentration(the concentration of Na₂SO₄ as 0.05-0.75 mol L^–1)and type(0.05 mol L^–1NaCl,NaClO₄ and Na₂SO₄)of the electrolyte on the degradation effect of simulated wastewater are studied systematically,and the optimized degradation conditions were obtained as below:4 g L^–11 as the initial concentration of TBP,0.5 mol L^–1 Na₂SO₄ as the supporting electrolyte,the current density of 40 mA cm^-2,unadjusted pH value of wastewater,and the degradation time of 180 min.Under these conditions,the COD removal ratio of tributyl phosphate simulated wastewater is achieved as the highest as82.3%,and the energy consumption is 26.16 kWh m^–3.Through analysis of the degradation products of simulated tributyl phosphate wastewater:DBP,phosphate,butanol and some short chain aldehydes or carboxylic acids maybe exist in the degradation products.Therefore,it is preliminarily deduced that the degradation process of tributyl phosphate is as below:TBP is degraded to be DBP and butanol firstly,and then DBP is further degraded to be phosphate,while butanol is degraded to be aldehydes or carboxylic acids with short chains.?2?The simulated xylene wastewater was taken as the research object,and the BDD electrochemical oxidation technology was adopted in this work.The influences of degradation time,current density(10-60 mA cm^–2),initial concentration of xylene(1.72-6.88 g L^–1),the pH value of the solution?3,7,11?and the electrolyte concentration(0.05-0.50 mol L^–1Na₂SO₄)on the degradation effect of simulated wastewater are studied systematically,and the optimized degradation conditions were obtained as below:6.88 g L^–1 as the initial concentration of xylene,the supporting electrolyte of 0.5 mol L^–1 Na₂SO₄,the current density of 30 mA cm^-2,the pH value of wastewater of 3,and the degradation time of 180 min.Under these conditions,the COD removal ratio of simulated xylene wastewater is achieved as the highest as 88.6%,and the energy consumption is 26.28 kWh m^–3.In addition,it is preliminarily deduced that the degradation process of simulated xylene wastewater using BDD electrode is as below:Hydroxylation of xylene occurs after being attacked by·OH to produce phenolic compounds firstly;Then they are further oxidized to be quinones and continue to be degraded to be simple organic acids;And eventually they are mineralized to be CO₂ and H₂O.?3?Combining with the optimized degradation conditions in the degradation processes of simulated tributyl phosphate and xylene wastewater,we treated tributyl phosphate-xylene mixed simulated wastewater with the initial COD value of 4979.16mg L^–1 using BDD electrode.The experimental conditions are controlled as below:current density of 30 mA cm^-2,Na₂SO₄ concentration of 0.5 mol L^-1,solution pH value of 3,reaction temperature of 15±5?,and the degradation time of 180 min.The COD removal ratio of mixed simulated wastewater reaches 79.2%,and the energy consumption is 25.44 kWh m^-3.