| With the rapid development of industry and agriculture,nitrogen pollution has become increasingly serious.According to the 2015 National Environmental Statistics Communique,the amount of ammonia nitrogen in waste water was up to 2.299 million tons/year,and ammonia nitrogen can be transformed into nitrate nitrogen in the nitrogen cycle.These two kinds of inorganic nitrogen can not only lead to eutrophic lakes,red tides in the waters,and the high nitrogen content in drinking water is harmful to human health,so solving the problem of nitrogen pollution is imminent.In this paper,the degradation of ammonia nitrogen and nitrate nitrogen was removed by chemical removal method,while reducing the content of ammonia nitrogen or nitrate nitrogen in wastewater,they can also be converted into nitrogen-containing precipitate or nitrogen.Thus,ammonia nitrogen or nitrate nitrogen were completely separated from the water system and eventually achieved the goal of reducing the total nitrogen in the wastewater.In the treatment of ammonia nitrogen wastewater,chemical precipitation and sodium hypochlorite oxidation were used.The former can convert ammonia nitrogen into magnesium phosphate(MAP)precipitation,the latter can oxidize ammonia to harmless nitrogen,both can achieve the goal of reducing total nitrogen..For nitrate effluents,nano Fe and nano Fe/Cu were used as reducing agents to achieve efficient removal of nitrate nitrogen.Finally,Fe-loading titanium dioxide(TiO2)was used as photocatalyst to reduce nitrate nitrogen,and promoted more conversion of nitrate to nitrogen,total nitrogen was also significantly reduced.The main contents are generalized as follows:First,precipitation and sodium hypochlorite oxidation were used to remove 100mg/L ammonia nitrogen.For precipitation,NaH2PO4·2H2O and MgSO4·7H2O had greater ammonia nitrogen removal efficiency than other mixtures,and at pH of 10,the three ions was in the ratio n(Mg):n(N):n(P)=1.1:1:1,after 30 min reaction time,the ammonia-nitrogen removal efficiency was 80.60%.As to sodium hypochlorite oxidation,with n(NaClO):n(NH3)=1.7:1 and at pH of 8,the reaction yielded the best ammonia nitrogen removal efficiency,after 20 min reaction time,the ammonia nitrogen removal efficiency was 71.53%,and the product was N2.Second,nano Fe was prepared,these products were characterized by TEM、ICP、XRD,and do nitrate removal experiments,the optimal preparing condition was that in 20℃,c(NaBH4)/c(Fe2+)=3 and c(Fe2+)=0.01 mol/L,when the ionic liquid[Bmim]PF6 was added to the solution,c([Bmim]PF6)/c(Fe2+)=1,i.e.,P-Fe.When applying P-Fe to reduce 100mg/L nitrate,the reaction reached equilibrium after 60 min and the nitrate removal efficiency was 70.82%,which was 11.41%higher than the reaction using N-Fe,i.e.,the process of preparing nano Fe without ionic liquid.In addition,the ammonia nitrogen selectivity was 91.73%while the TN removal efficiency was 5.93%.To improve the nitrate removal efficiency,nano Fe/Cu particles were prepared as reducing agent,and these products were characterized.The nano Fe/Cu with an initial copper-iron mass ratio of 10%by simultaneous reduction method,i.e.,10FeCu,had the highest nitrate removal efficiency.The reaction of 10FeCu with 100 mg/L nitrate approached to equilibrium after 45 min when the nitrate removal efficiency reached 90.14%,which was 19.32%higher than that of P-Fe as reductant.Additionally,the ammonia nitrogen selectivity was 94.31%and the TN removal efficiency was 5.13%.At last,in order to convert more nitrate nitrogen into nitrogen and increase total nitrogen removal efficiency,Fe-loading TiO2 was applied as photocatalyst to reduce nitrate nitrogen,and these products were characterized.0.5Fe/P25,i.e.,initial m(Fe)/m(TiO2)with the mass ratio of 0.5%,was the best.When applying 0.5Fe/P25 to reduce 100mg/L nitrate,in use of 40 mM formic acid as a capture agent,the nitrate removal efficiency of 0.5Fe/P25 was 96.93%while the TN removal efficiency was 72.99%,5.79%higher than P25,moreover,the N2 selectivity was 74.65%,greater than P25 by 5.77%. |
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