Removal of Nitrosodimethylamine (NDMA) from water by Silica and Activated Carbon Adsorbents

Abstract

nanostructured mesoporous MCM-41, diatomite, spherical silica gel, and zeolite were selected for this study. Upon evaluating the efficiency of these adsorbents in batch tests, the most suitable one among them is subjected to operate a continuous up-flow reactor so that ability of the adsorbent in actual systems can be estimated. Along with silica adsorbents, the most popular activated carbon adsorbents are subjected to experimentation as well. Coconut shell powdered activated carbon, wood powdered activated carbon, and wood granular activated carbon were studied in batch tests. Based on the results of batch tests, coconut shell PAC and wood GAC are employed in continuous up-flow reactors and their efficiency to take up NDMA from water was studied. To facilitate the scale-up of continuous reactors, their operation mode (HRT) was set according to slow sand filter which was consistent with the optimum contact time of adsorbent with adsorbate based on the batch test studies. Silica adsorbents showed lower NDMA removal efficiency rather than those of activated carbons in batch tests. In continuous reactors, the best observed silica adsorbent, Spherical Silica gel, showed negligible adsorption. In case of activated carbons using continuous fixed bed reactors, granular activated carbon played better than powdered activated carbon but the performance was not more than 25% as compared to that in batch systems. Considering the results of batch and continuous reactor tests, it was determined that diffusion into micro pores of adsorbents is very important factor of NDMA adsorption. Therefore, the continuous reactors were modified to dispersed beds of activated carbons and then NDMA removal efficiency was obtained similar with the results of batch tests. The saturation time was 3 days and NDMA removal efficiency was decreased from over 90% to less than 10%.; N-Nitrosodimethylamine (NDMA) is an emerging contaminant found in water and wastewater systems. It is highly soluble in water and conventional water treatment processes are unable to remove it. Since its identification, many techniques have been applied to remove it but there is not a single one which is successful in all aspects especially efficiency and economy of the process. In this research, adsorption is employed as a potential treatment for the removal of NDMA in order to avoid formation of by products, which were inevitable in case of chemical treatment. Chemically inert and physically stable silica adsorbents are tested in batch tests for their ability to adsorb NDMA. Four silica adsorbents