Study On The Reduction Of N-nitrosodimethylamine With Zero-valent Zinc In Water In The Presence Of Transition Metal Ions

Metal ions and organic pollutants often appear together in the water,and become the co-contamination.NDMA is the most representative pollutant of nitrosamine pollutions among the emerging nitrogenous disinfection byproducts.Its potential three-cause toxicity is greatly higher than other disinfection by-products,such as trihalomethane.Conventional water treatment process can not effectively eliminated NDMA.During the enhanced treatment,the degradation of NDMA with UV has the best effect.But it needs large energy consumption and is expensive.Thus,it is not suitable for practical application.Due to wide availability of raw materials,convenient operation and good effect on various kinds of pollutants,the reduction technology with zero-valent zinc is widely concerned.The presence of metal ions can affect the rate and product composition of metal reduction organic pollutants during the repair process of the composite polluted the water.The transition metal ions in metal elements have an unfilled d orbital and have catalytic effect,which causes the attention of this subject.In the study of reduction of NDMA with zero-valent iron in water in the presence of transition metal ions.The influences of the initial concentration of transition metal ions,pH,dissolved oxygen,and rotate speed on the reaction were investigated.The morphology and combining state of the metal powder which were got after reaction were analyzed.The differences of electrochemical parameters in different systems during reduction were studied.Basing on the above results,the mechanism was proposed.Besides,the results can provide data support for the practical application.The investigation on the influence factors of the reduction of NDMA with zero-valent iron in water in the presence of transition metal ions showed that transition metal ions could promote the reduction of NDMA with zero-valent iron effectively.When the loading of zinc powder was 10g·L^-1,the initial concentration of transition metal ions was 1 mmol·L^-1,reaction time was 24 h,the removal rate reacheed 78.53%.Cu²⁺showed the best effect,reaction time was 3 h,the removal rate was 99.9%;The rotation speed which was too fast,high dissolved oxygen concentration and alkaline condition restrained the reduction reaction;The removal efficiency is low with low concentration of transition metal ions in the solution.When the concentrations reache a certain value,all the removal effeciencies of NDMA in the different systems are high;the reduction of NDMA has a good effect under the neutral and acidic conditions,and the removal rate and the reaction speed will be higher with lower pH values.The degradation products of NDMA in the differnt systems(Zn?0?,Zn/Mn²⁺,Zn/Co²⁺,Zn/Ni²⁺,Zn/Cu²⁺)are UDMH and DMA.At the initial stage of the reaction,the concentration of UDMH and DMA increased with the degradation of NDMA.As the reaction continues,the concentration of UDMH starts to decline.Catalytic hydrogenation is proposed to be the reductive pathway.Analysis of morphology and junction state of solid products in reaction process showed that the existence of transition metal ions enhanced surface activity to some extent by changing surface morphology of zero-valent zinc which improved reduction reaction.Through the analysis of linear scanning voltammetry and Tafel polarization curves,it is concluded that the transition metal ions affect the rate of the metal corrosion process,and the reduction efficiencies are directly proportional to the corrosion rates.