Remediation of Groundwater Contaminated with Cadmium by Nano-Zero Valence Iron (at Batch and Pore Media Scales)

Since a major portion of the food we use is provided by corps irrigated with water that is supplied from groundwater resources, remediation of contaminated groundwater using in-situ methods like permeable reactive barriers (PRBs) seems to be a top priority. Given the need to reduce Cd contamination in southern Tehran, the present study was designed to compare the rate of Cd absorption by nZVI with that by Zeolite and Calcite. The results of the study revealed a higher Cd adsorption by nZVI as compared to that by Calcite and Zeolite. Also, when nZVI concentration was raised from 1 to 2 g/l, enhancements were observed after two hours in Cd adsorption by up to 5.5%, 3.4%, and 11.5% in solutions containing 0.2, 0.5, and 4 ppm of Cd, respectively.Moreover, for a contact time of 24 hours and when the initial concentration of the contaminant was raised from 0.2 to 0.5 ppm, the adsorption rate declined to 5.45% and 7.75% for nZVI injections of 1 and 2 g/l, respectively. In a second part of the study, such environmental conditions as changes in pH and temperature were investigated for their effects on Cd adsorption. Compared to the initial concentration of 4 ppm, Cd adsorption reduced by 37.15% under acidic conditions (pH=3.7) and by 92.75% under alkaline conditions (pH=13.1) after a contact time of 3 hours. Similarly, a reduction equal to 38.5% was observed in Cd adsorption after 6 hours when temperature was raised from 20 °C to 75 °C. In order to explore the bioenvironmental impacts of injecting nanoparticles aimed at adsorption and precipitation of Cd, the concentration of iron nanoparticles present in the environment was measured. As a result of the reaction between the solutions containing 0.5 ppm of Cd with the absorbent solution containing 2 g/l iron, the iron nanoparticle concentration in the solution was observed to decline to 0.0041% of its initial concentration after 24 hours. In the experiments conducted in a vertical saturated porous and homogeneous medium, injection of 3 g/l of nZVI, as the absorbent, into water containing 2.92 ppm of the contaminant reduced the contaminant concentration to levels below the limits recommended for drinking water. The reaction between nZVI and Cd dissolved in the medium revealed that the nanoparticles served as an efficient absorbent as they not only adsorbed Cd over time, but also removed it from the medium through precipitation.