Photocatalytic Removal Of Pollutants In Initial Rainwater

The initial rainwater runoff has become an important urban non-point source pollution source,which has the characteristics of high pollution level,large instantaneous flow,and intermittent generation.However,the commonly used biological treatment methods are difficult to withstand impact loads in rainy days and maintain microbial systems in sunny days.Therefore,it is of great significance to find a quick and effective method to remove nitrate nitrogen,ammonia nitrogen and organic matter in the initial rainwater.In this study,the photoreduction method was used to prepare different metal-doped TiO₂ photocatalysts.The nitrate nitrogen,ammonia nitrogen and organic matter in the initial rainwater were used as the target pollutants,and the experimental study of photocatalytic degradation was carried out.The experimental research includes three aspects:（1）Photocatalytic reduction of nitrate and simultaneous oxidation of organic compounds;（2）Photocatalytic oxidation performance of ammonia nitrogen;（3）Study on photocatalytic treatment of early rainwater simulation.In the third part of the study,the co-degradation of nitrate nitrogen,ammonia nitrogen and organic matter in the same system was achieved.In the study of photocatalytic reduction of nitrate and simultaneous oxidation of organic compounds,preliminary experiments show that Ag/TiO₂ photocatalyst synergistically degrades nitrate nitrogen and organic compounds,and the product gas selectivity is high.Then the influence of factors such as initial p H value,Ag dosing amount,catalyst dosage,and the amount of organic matter added on the reduction of nitrate（degradation rate,gas selectivity,total nitrogen removal rate）and oxidation of organic matter were studied.The experiment found that when the initial concentration of COD is 100 mg/L,NO₃^--N is 15 mg/L,the actual amount of Ag is 0.53 wt%,the initial p H is 4.5,and the dosage is 1 mg/L,the synergistic degradation efficiency is high.Under this condition,the NO₃^--N degradation rate was 95.3%,the nitrogen selectivity was 76.3%,and the COD removal rate reached 69.5%.In addition,the experiment also shows that the photocatalytic system does not have strict requirements on the reaction conditions.At a p H value of 4-7,the removal rate of nitrate nitrogen,organic matter,and nitrogen selectivity are maintained at a high level.n the research of photocatalytic oxidation of ammonia nitrogen,the oxidation effect of metal Fe,Cu,Ag-doped TiO₂ on the ammonia nitrogen in water under ultraviolet light was investigated.In the research of photocatalytic oxidation of ammonia nitrogen,the oxidation effect of metal Fe,Cu,Ag-doped TiO₂ on the ammonia nitrogen in water under ultraviolet light was investigated.Preliminary experiments show that Ag-modified TiO₂ significantly improves the efficiency of photocatalytic oxidation of ammonia nitrogen and the selectivity of products to nitrogen.When the actual doping amount of Ag is 0.53 wt%,the initial p H is 10,and the catalyst dosage is 1.0 mg/L,the oxidation effect of ammonia nitrogen is the best.The ammonia nitrogen removal rate reached79.8%,the product selectivity for gas was 90.2%,and the total nitrogen removal rate was 72.0%.The characterization results of the photocatalyst showed that Ag was successfully doped on TiO₂ with a doping efficiency of about 50%.The doping modification of the three metals does not affect the crystal structure of TiO₂,but will cause the catalyst particle size to shrink and the arrangement to become tight.XPS characterization results show that the metal Ag is incorporated on the surface of TiO₂at zero valence.In the simulation of the initial rainwater degradation study,the initial conditions of acidic,neutral and alkaline were explored respectively.The first reaction under the three conditions was the photocatalytic reduction of nitrate and simultaneous oxidation of organic compounds.When the reaction reached 120 min,there was a lack of dissolved oxygen in the solution,resulting in a large accumulation of ammonia nitrogen.Taking neutral initial conditions as the research object,aeration at 120 min,the degradation effect of ammonia nitrogen in the photocatalytic system is obvious.Finally,the concentration of nitrate nitrogen in the photocatalytic system was 5.18mg/L,the concentration of ammonia nitrogen was 3.29 mg/L,the concentration of nitrite was 0.03 mg/L,and the concentration of COD was 15.4 mg/L.The total nitrogen removal rate was 75.5%,and the COD degradation rate was 85.4%.Using glass fiber cloth as the catalyst carrier,the supported photocatalyst prepared by the coating method was used instead of the powdered photocatalyst.The final total nitrogen removal rate was 50.9%,and the COD degradation rate was 73.3%.The research results show that the photocatalytic technology can quickly remove nitrate nitrogen,ammonia nitrogen and organic matter in the initial rainwater,can process a large amount of rainwater in a short time,and has certain application prospects.