Experiment And Mechanistic Study On Ammonia-N Removing By Oxidation Of Electro-catalysis And Photo-catalysis

Based on the problem of the main pollutants in the surface water-ammonia and nitrogen exceeding the standard caused by concentrated discharge of large and medium urban sewage,a method of removing ammonia-N by photo-catalytic oxidation and electrochemical oxidation with clean energy such as solar energy as driving source is proposed against many problems of traditional biological methods,such as large land occupation,high investment and operation cost,and many factors that are influenced by external environment.According to the two existing forms of ammonia-N-NH3-N and NH4+-N,considering the different physical and chemical properties and affecting the ionization balance factors,the concept of "photoelectric combination" for remove ammonia-N pollutants was proposed including the photo-catalytic oxidation of the cathode region including "N4+-N cathode adsorption-cathode region NH3-N conversion-photo-catalytic oxidation removal" and electrochemical oxidation of the anode region of "NH4+-N anode direct oxidation+chlorination electrochemical oxidation removal".Based on the theoretical conception,a specific experimental study was carried out around photo-catalytic oxidation and electrochemical oxidation.In the photo-catalytic oxidation removal of ammonia nitrogen,the effective doping modification of Ru3+ and CdS to titanium dioxide was achieved by sol-gel method and electro-deposition method,respectively,which showed good photo-catalytic activity.Comparing the advantages and disadvantages of the two modified photo-catalysts and the applicability in this study,Ru/TiO2 was determined as the photo-catalyst material of this study,and the nano-scale photo-catalyst powder was solidified by using nafion as the carrier,and the photo-catalyst still showed good photo-catalytic activity and removal effect on free ammonia in the ultraviolet-visible region after being supported.By fitting the kinetic equation of ammonia-N photo-catalytic oxidation,the quantitative measurement of the photo-catalytic oxidation removal rate of free ammonia was realized,and the effect of photo-catalytic oxidation to remove ammonia-N was quantitatively evaluated and analyzed.The reaction mechanism of NH3-N to N2-N and NO2--N conversion was presumed by analyzing the production of NO2--N and NO3-N in the photo-catalytic oxidation process under different conditions,and the inference is proposed that the oxidative strength is the important factors to control NO2--N and NO3--N production.In the electrochemical oxidation removal of ammonia-N,aiming at problem that it is hard to remove the ionic ammonia by electrochemical oxidation directly.By comparing with the electrode materials such as graphite and pure titanium,RuO2-IrO2/TiO2 with good anodic chloride characteristics is selected to be an anode material.Based on the existing academic research on the reaction conditions of such as current density and chloride ion concentration,the experimental was studied on the effects of mixing conditions,initial ammonia-N concentration,plate spacing and power supply on ammonia-N removal in the reaction process.The judgment is proposed that the application of stirring during the reaction process can improve the ammonia-N removal effect,the low initial concentration of ammonia-N has a relative high removal rate and high power consumption,the relative small plate spacing has a higher ammonia-N removal efficiency,and the power supply power is related to the ammonia-N removal efficiency.On the basis of above,the comparison test of cathode(Ti)was carried out before and after coating photo-catalyst film.After the film coating,the cathode showed a relatively strong effect on ammonia-N removal in the electrochemical reaction environment and the removal efficiency of ammonia-N is relatively higher under the same current power and illumination conditions comparing with the pure photo-catalytic oxidation and the simple electrochemical oxidation method.Through experimental analysis,the mechanism of electrochemical oxidation and photoelectric combined catalytic oxidation to remove NH3-N and the conversion to N2-N and NO2--N was studied.And,it is suggested that excessive chlorination is the main reason leading to the production of nitrate nitrogen.Meanwhile,in the effective reduction of cathode reduction conditions,the production of NO3--N can be better controlled in the electrochemical reaction system.Based on the conclusions of the technical test,photo-catalytic oxidation,electrochemical oxidation and photoelectric combined catalytic oxidation to remove ammonia-N are conducted to the actual sewage from the typical regional sewage treatment plant.This study proposes that there is a big difference in the removal efficiency of ammonia-N in different types of sewage without adding a chlorine source.After adding chlorine ions to the sewage,the electro-catalytic removal efficiency of ammonia-N can be improved.Even under the condition of lower energy consumption,it can achieve better ammonia-N removal efficiency.Under the same electric energy consumption and illumination conditions,the photoelectric combined catalytic oxidation method shows a relatively good effect on the removal of ammonia-N in sewage.