Study On Degradation Of Nitrosamine In Water By Zero - Valent Iron Composite Membrane

Nowdays, a high security of water quality had been increasingly demanded due to the growing problems such as population explosion and environmental pollution. Studies have demonstrated that N-nitrosodimethylamine (NDMA) is one disinfection by-product of chlorination and chloramination of water and waste water. NDMA is reasonably anticipated to be a human carcinogen so that aroused increasing concern among public health agencies. The U.S. Environmental Protection Agency (EPA) estimated it had a 10"6 carcinogenic risk from 0.7ng/L oral exposure. However, current alternative treatment methods are relatively inefficient. So there is a considerable need for new technologies to rapidly and economically treat water contaminated with NDMA because of its high toxicity. Zero-Valent iron reduction technology has a great value of theory and engineering application since its high yield and simple preparation. In this sutdy, two zero-valent iron composite membranes are prepared to reduce the NDMA in solution, polyacrylonitrile (PAN) flat membrane and hollow-fiber membrane are used as support respectively.In this study, modified PAN flat membranes firmly immobilized with zero-valent iron (ZVI) are successfully prepared via polyelectrolyte layer-by-layer asswmbly technology, Polyethylenimine (PEI) as cationic polyelectrolyte, coordination polymers carried P-CD as anionic polyelectrolyte (Fe/AA-MAH/β-CD). Due to the formation of ladder structure, the ZVI particles with sizes of several hundred nanometers and have well-distrbution. Small molecule NDMA were absorbed based on the inclusion association of β-CD during the process of NDMA penetrate through the membrane, meanwhile, NDMA were reduced by zero-valent iron. The study found that initial concentration of NDMA dose not much affect the reduction, while pH has significantly influenced on the reduction of NDAM by Fe°.Pd/Fe bimetallic were immobilied on PAN hollow-fiber membrane and prepared by a modified liquid reduction method, then the membrane were applied to reduct the NDMA in the water. Fe ions were immbilized on modified hollow-fiber membrane via coordination with carboxyl groups, which were carrid on membrane via NaOH modified. In the experiments, FTIR and SEM, XRD were used to characterize the morphology of Pd/Fe bimetallic membrane. It was found that the removal efficiency of NDMA is markedly increased when Pd was loaded. Menwhile, the effect of initial concentration of NDAM and pH, temperature, common ions on the reduction of NDAM were also inverstgated in the experiments. However, the dissolved oxygen has no effect on the removal of NDAM. Low pH and high temperature may increase the removal efficiency of NDMA.The reduction mechanisms of these two zero-volent iron membranes were speculated. First, Fe° release e- and e- transferred to H to form FeHads.Then, the FeHads reducted the NDMA to kinds of products, UDMH, DMA and NH4+. Meanwhile, there is a mass of carboxyl groups on the surfance of these two composites membranes, this makes it’s possible to immobilized Fe ions by coordinaion with carboxyl groups once again. During the reduction of NDMA, the concentration of iron in the solution is low.