Simple method for removal of pollutants from water using freeze-thaw treatment

Abstract

The development of simple and environment-friendly water clean-up techniques would be an important step to achieve sustainable development goals to ensure the access to safe water. In this study, a novel simple method to remove pollutants from water by a freeze-thaw procedure using a syringe, elastic band and cotton wool has been developed. The solution (20 mL) containing an environmental pollutant, Cr(VI), Pb(II), F−, NO3−, NO2−, PO43−, pentachlorophenol, or Congo Red, was added to a syringe separately. The part around the outlet of the syringe was covered with cotton wool and held in place with an elastic band. The syringe was then frozen in a typical freezer. The cotton wool around the syringe plays a role to control the place of the pollutants in the frozen solution. The frozen sample was thawed at room temperature. The pollutant was concentrated in the initial fraction of the thawing solution. The fraction (1 mL) was sampled, and the rest was fully thawed and frozen again. The treatment was repeated 3 times. As a result, the concentration of Cr(VI), Pb(II), F−, NO3−, NO2−, PO43−, pentachlorophenol, or Congo Red, in the final solutions was 0.24, 0.13, 0.20, 0.20, 0.23, 0.25, 0.25 or 0.22 mM, respectively (the initial concentration of the pollutants was 1.0 mM). The removals in percent of the pollutants were over 75%, and the recoveries (%) through the treatment were 100 ± 5% for all conditions. We concluded that the technique is useful for the primary treatment for water clean-up and applicable to improve the water quality during an emergency.