Removal of dissolved organic matter (DOM) from raw water by single-walled carbon nanotubes (SWCNTs)

Dissolved organic matter (DOM) in raw water is a precursor for the formation of disinfection by-products (DBPs) during chlorination at a water treatment plant in southern Taiwan. The presence of DOM also has a large impact on the behavior of nanoparticles. The adsorption kinetics of single-walled carbon nanotubes (SWCNTs) was investigated in the presence of DOM as a possible technique for the pretreatment of DBP precursors. pH, ionic strength and temperature are major factors in adsorption tests. Experimental results indicated that adsorption reached equilibrium after 120 min. Additionally, the adsorption capacity of SWCNTs increased with an increasing DOM concentration and decreased with an increasing ionic strength. The optimum adsorption model out of a selection including the Modified Freundlich equation, the Pseudo-first-order equation and Pesudo-second order equation, was the Modified Freundlich equation model. The intraparticle diffusion equation model was also examined. The adsorption process was controlled by pore diffusion that was confirmed by the fits of intra-particle diffusion model. The maximum adsorption capacity was 26.1-20.8 mg/g at 4°C and 45°C. Isotherm adsorption results demonstrated that the adsorption of DOM onto SWCNTs was favorable at a high initial DOM concentration and at low ionic strength, pH and temperature. These findings highlighted the importance of pretreatments and the presence of DOM on the adsorption behavior of nanomaterials.