| Summary: | 碩士 === 國立中山大學 === 環境工程研究所 === 104 === Nitrosamines are of concern because thery are highly carcinogenic and were frequently observed in water and wastewater treatment processes in many countries of the world. In this study, a wastewater treatment technology that reduced the formation potentials (FPs) of nitrosamines by removing potential nitrosamine precursors with high molar conversion rate via adsorption was investigated, with chlorpheniramine being selected as the target pollutants. Graphene oxide (GO), due to its large surface area and strong hydrophilicity, has the potential to remove contaminants by adsorption amongst water and wastewater treatment technoloiges. Considered the nano-size of GO material, the GO-iron oxide (GO/Fe3O4) composite with high adsorption capacity was synthesized by using the method of coprecipitation, as this material possesses the property of being quickly removed from water with magnetic force.
This study is divided into: (1) the batch adsorption experiments that removed chlorpheniramine in deionized water; (2) the batch adsorption experiments that removed chlorphenirame in real wastewater effluents; (3) the adsorption experiments that removed nitrosamine’s FP in wastewater effluents. In the 1st stage of the study, the removal efficiencies of chlorpheniramine by adsorption onto the surface of GO/Fe3O4 composite at pH 6 followed the order of: GO/Fe3O4 powder > GO/Fe3O4 suspension > activated carbon. With the increase of the iron content, the chlorpheniramine concentration onto the surface of GO/Fe3O4 powder was reduced because of limited adsorption sites, whereas the iron content of adsorbent did not significantly affect the removal of chlorpheniramine by the GO/Fe3O4 suspension. The stacking of GO layers became more obvious in the GO/Fe3O4 particle due to drying, forming nano-pore structures braced by Fe3O4 among GO layers to enhance the chlorpheniramine adsorption. The BET surface area, pore volume, pore size distribution measurements of GO/Fe3O4 particle supported the assumption that the enhanced chlorphenirame adsorption was associated with the increasing pore volume (diameter < 2 nm) and specific surface area. The total pore volume was not the critical factor to determine the adsorption capacity of chlorpheniramine onto GO/Fe3O4. By changing the reaction pH, the ionization states of chlorpheniramine and the surface charge of GO/Fe3O4 were both affected, affecting the optimal pH of effective adsorption. The chlorpheniramine adsorption onto the GO/Fe3O4 suspension (in 60 minutes) was overall more efficient than that of the GO/Fe3O4 particle (in 360 minutes), as the effect of changing the iron content of GO/Fe3O4 was negligible.
In the 2nd stage of the study, the chlorpheniramine removal in real effluents by adsorption at pH 6 followed the order of: GO/Fe3O4 suspension > GO/Fe3O4 particle > activated carbon. Compared to the results in the 1st stage of the study using deionized water, the n value in the Freundlich model fittings of both GO/Fe3O4 suspension and particle as well as activated carbon were significantly higher. Natural organic matter (NOM) could be attached onto the surface of GO/Fe3O4, declining the heterogeneity of the adsorbent surface. The rise of n value also represents adsorption process is favorable adsorption, meaning that excess chlorpheniramine adsorbed results in stronger adsorption affinity between chlorpheniramine and the GO/Fe3O4 surface. The chlorpheniramine adsorption by the GO/Fe3O4 particle and activated carbon in wastewater effluents were less efficient when compare to the results using deionized water as the background, atributalbe to the potential competition between dissolved organic matter (DOM) in wastewater and specific functional gourps of chlorpheniramine for adsorption sites on the GO/Fe3O4 surface. A different result was observed for the GO/Fe3O4 suspesion possibly due to the presence of NOM in wastewater decreasing the heterogeneity of the adsorbent sites and increasing the ionic strength.
In the 3rd stage of the experiments, the nitrosamine FPs in wastewater effluents were effectively treated by the GO/Fe3O4 particle at pH 6, as the FPs of N-Nitrosodimethylamine (NDMA), N-Nitrosopiperidine (NPIP), N-Nitrosomorpholine (NMOR) and N-Nitrosodi-n-butylamine (NDBA) were reduced by 29±12, 26±6, 46±1 and 44 %. By adding chlorpheniramine to deionized water in the GO/Fe3O4 particle experiment at pH 6, the nitrosamine FPs were increased suggesting that GO/Fe3O4 could possibly assist in nitrosamine formation. By adding chlorpheniramine to wastewater in the same experiment, the GO/Fe3O4 particle was found to simulataneously treat and result in the formation of nitrosamine. Even at a high chlorpheniramine concentration in wastewater, the nitrosamine FPs could still be efficiently treated by employing the GO/Fe3O4 particle as the adsorbent.
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