Experimental Research On Removal Of Nitrogen-containing Wastewater By Three-dimensional Electrode Process

Excessive nitrogenous compounds in industrial sewage have caused harm to the ecological environment and human body,moreover,as the environmental quality of water becomes more and more demanding,the total nitrogen index is also included in the control,therefore,effective technology for wastewater denitrification has become extremely important and has received a lot of attention.With the advantages of simple operation,small size of equipment and short hydraulic residence time,electrochemical technology has been used to remove nitrate in wastewater.However,one of the major limitations of electrochemical technology is the low current efficiency when treating nitrogen wastewater.In this study,we select a strong oxidation anode,a strong denitration cathode and a high catalytic activity particle electrode to develop a high efficiency electrochemical method with small equipment size.The high content of nitrate nitrogen in tailwater cause the exceeding standard of the total nitrogen,therefore,in order to remove the nitrate nitrogen in simulate industrial wastewater,the three-dimensional electrode method was used at first.Electrode material,filling quantity and filling ratio of particle electrode were utilized to characterize the removal efficiency.The experimental results indicate that in the condition of the solution is neutral and free chloride ions,the removal efficiency of three-dimensional titanium mesh,two-dimensional titanium mesh and titanium plate is 60%,57% and 40% respectively when using stainless steel as cathode and titanium based material as anode.The new three-dimensional titanium mesh has high removal efficiency.Using three-dimensional titanium mesh as anode and other cathode materials such as stainless steel,copper,titanium,49% and 33% for stainless steel,copper,titanium and nickel.The above results show that the new three-dimensional titanium mesh anode has better performance and superiority.Besides,activated carbon and zero-valent iron were selected as particle electrode of the three-dimensional system,different filling amount and filling ration of the electrode was determined,at the cast iron/activated carbon filling ratio of 1/15 and the total filling amount of 250 g,the nitrate removal rate was 86%.Secondly,the three-dimensional titanium mesh and stainless steel were used as the cathode and anode,and activated carbon and zero-valent iron were used as the particle electrode to form a three-dimensional electrochemical system.The effect of current intensity,p H value,initial concentration and chloride ion concentration on the removal effect of nitrate nitrogen in simulate industrial sewage was observed through a single factor experiment.The optimal reaction conditions are the initial p H=9.5 and the chloride ion concentration = 30 mg Cl/L in solution.High initial nitrate nitrogen concentration may reduce the overall removal rate.Besides,with the increasing of current intensity,the removal efficiency of nitrate nitrogen increase.After treating high total nitrogen simulate sewage by three-dimensional electrochemical system,the concentration of total nitrogen in simulate sewage reduce from 45.42 mg N/L to 13.15 mg N/L,which conform to national level A standard.According to the results of single factor experiment,the box-benhnken center combination test was used for data analysis,and the removal rate(%)of nitrate nitrogen was taken as the response value,and the three factors of current intensity,iron-carbon ratio and p H value were constructed.The regression equation was obtained by using the software to carry out regression fitting to the data results,and the result of variance analysis showed that the P value was less than 0.05,which proved that the response model was significant.The model can reflect the correlation between the variables and the response value within the response regression region,and has a good ability to reflect the actual value.By taking the first partial derivative equal to zero of the regression equation,the optimal experimental conditions were obtained: the current intensity was 2A,the p H was 9.28,the ratio of activated carbon and cast iron was 23:1,under which the electrochemical system was operated,and the removal rate of nitrate nitrogen and total nitrogen was 88.93% and 78%.Finally,reduction products of nitrate nitrogen in denitrification system was observed through the three-dimensional electrochemical system reaction,which react under the experimental conditions determined by the single factor experiment.The experimental results indicate that the reduction products of the solution are mainly ammonia nitrogen and nitrite nitrogen,nitrite is quickly reacted in the reaction.The properties and morphology of electrode materials were observed and analyzed by cyclic voltammetry and scanning electron microscopy to verify the electrode characteristics of the electrochemical system.Adding p-chlorobenzoic acid(PCBA)to the system to inhibit the direct oxidation efficiency of ammonia nitrogen in the intermediate product.The change of nitrate nitrogen removal rate was observed.The results showed that the removal efficiency of nitrate nitrogen decreased from 81% to 67% after adding PCBA,which indicated that improving the degradation efficiency of ammonia nitrogen in the intermediate product could enhance the removal efficiency of nitrate nitrogen.The introduction of external electric field can strengthen microelectrolysis of iron-carbon particles,and the effect of particle electrode on plate current is verified.