Feasibility investigation of adsorptive removal of NH4+ and NO3− species from clayey aquifer using special soils

Abstract

Soil and water contamination due to nitrogen species disseminated from fertigation, landfill leachates and percolating sewages poses considerable health risks. Physicochemical adsorption primarily controls the extent of migration of soluble contaminants, especially ammonium and nitrate ions in the subsurface. On the other hand, there is an increasing need to identify suitable natural material for filtration/adsorption treatment in order to reduce the usage of normal river sand. In this study, detailed batch experiments have been conducted to investigate the feasibility of ammonium and nitrate adsorption onto red soil and manufactured sand (M-sand) in comparison with normal clay and sandy soil. Based on the isotherm analysis, instantaneous adsorption of ammonium ion is higher than the nitrate for all types of soils. The adsorption of ammonium is found to be highest (75%) for bentonite clay and lowest (36%) for sandy soil. Similarly, the average percentage of adsorbed nitrate on red soil, M-sand, bentonite clay and fine sand was 26%, 18%, 13% and 4%, respectively. The contact time is found to be a significant parameter on ammonium and nitrate adsorption in adsorbents. Moreover, the ammonium adsorption rate has doubled from the lower initial concentration (20 ppm) to higher concentration (200 ppm) in clay, red soil and M-sand. On the other hand, the nitrate adsorption percentage for all types of soil is initially very high at low aqueous concentration and reduces drastically during the higher aqueous concentration. Further, the best combination for favorable adsorption was found to be on bentonite clay for ammonium and red soil for nitrate which is revealed by Langmuir isotherm model. It is also observed that the M-sand has been found to be a good replacement for river sand, especially for adsorptive removal of nitrate. The significance of optimum range of concentrations and dosages from the isotherm experimental studies is found to be consistent with the ANOVA analysis.