REMOVAL OF HEAVY METALS FROM WASTEWATER USING LIVING PLANTS AND LATERITE SOIL

Abstract

Wastewater generation is a massive problem not only in India but all across the world. Wastewater is generated from industrial and domestic sources. One of the major constituent of the industrial wastewater is heavy metals. Heavy metals are extremely hazardous and pose great threat to the environment. Many of the conventional physico-chemical techniques used for heavy metal removal have their inherent advantages and disadvantages, the cost being a major factor along with the generation and disposal of sludge. The need of the hour is the viable usage of low cost, eco-friendly techniques for the heavy metal removal from wastewater. Two such techniques have been examined in the present study; they are phytoremediation and adsorption by using laterite soil. Phytoremediation is basically a technique that utilizes plants to remediate the contaminated sites. In the present study, a lab scale experiment for the removal of lead and chromium from synthetic wastewater using the plant Vetiver Zizanioides was performed. The experiment was performed in a setup made of Perspex which was specifically designed for this study using the floating platform technique. Since the metal contaminants are generally present in groups and are rarely present as single ions both Pb and Cr were added simultaneously in the water samples in a 1:1 ratio. The metal removal capacity of the plant was studied for a specified time of 15 days. Three studies were carried out, in the first study the initial concentration of the metal ions were varied and their uptake was checked with respect to time, in the second study the concentration of the metal ions was kept constant and the pH was varied thus scrutinizing the effect of pH on metal removal and in the third study the metal uptake in various parts of the plant was investigated. The vetiver grass was able to remove about 98% of Pb and about 84% of Cr. It performed well for the pH range of 6 to 9. iv The laterite soil was chosen for the adsorption study due to its low cost and its wide availability. In the present study the metal uptake ability of laterite soil was tested in batch mode. Surface modification of laterite soil was carried out by treatment with acid, base and iron chloride solution to examine their effect on metal uptake and compare their removal ability to that of natural laterite soil. The Raw laterite soil was chosen as the best adsorbent and was further studied. The various process parameters such as contact time, adsorbent dose, pH and the effect of initial concentration were optimized and examined. The laterite soil showed the best adsorption capabilities at the adsorbent dose 10g/l, at the contact time of 4 hr and at pH 6, the temperature was kept constant at 305K and the rpm at 150. The regenerative and reuse capability of laterite soil was also investigated. The equilibrium and kinetic studies were performed for the better understanding of the various design parameters. The adsorptive study followed a pseudo-second order model and The Freundlich isotherm was found to fit best to the data generated.